Development of Keratoconus After Contact Lens Wear Patient Characteristics Marian S. Macsai, MD; Gary A.
Varley, MD; Jay
\s=b\ A retrospective review of 398 eyes of 199 patients with keratoconus revealed 106 eyes of 53 patients with an association between contact lens wear and the development of keratoconus. The absence of keratoconus at the time of contact lens fitting was confirmed by slit-lamp examination, keratometry readings, and manifest refraction. Keratoconus was diagnosed after a mean of 12.2 years of contact lens wear. This group was compared with patients with sporadic keratoconus with either no history of contact lens wear or a history of contact lens wear after the diagnosis. They were older at the time of diagnosis, had central vs decentered cones, and had a tendency toward flatter corneal curvatures. We believe that these patients suggest that long-term contact lens wear is a factor that can lead to keratoconus.
(Arch Ophthalmol. 1990;108:534-538)
/" eratoconus (KCN) is a noninflammatory disorder of the cornea characterized by progressive conical ectasia with protrusion of the thinned area.1 It results in
increasing myopia irregular astigmatism. Inferior steepening, corneal thinning, and ir¬ regular astigmatism may be the ear¬ liest signs of KCN. Other clinical signs include an epithelial iron ring, ante¬ rior stromal scarring, and striae ante¬ rior to Descemet's membrane (Vogt's striae). Early in its course, optical cor¬ rection is achieved through spectacles. As the irregular astigmatism pro¬ gresses, rigid contact lenses can be quite successful in restoring vision. When patients either have poor vision with
with a contact lens or cannot wear one, surgery is performed. The cause of KCN remains unclear. Proposed causes include biochemical alterations in collagen or proteoglycan physiologic activity.2'8 Many condi¬ tions in which KCN occurs have com¬ mon causative factors. One group is Accepted for publication October 11,
1989. From the Iowa Lions Cornea Center, Department of Ophthalmology, University of Iowa Hospital, Iowa City. Dr. Macsai is now with the Department of Ophthalmology, West Virginia University, Morganstown. Dr Varley is now with the Department of Ophthalmology, the Cleveland (Ohio) Clinic Foundation. Reprint requests to Iowa Lions Cornea Center, Department of Ophthalmology, University of Iowa Hospitals, Iowa City, IA 52242 (Dr Krach-
mer).
H.
Krachmer, MD
patients in whom an abnormality in collagen physiologic activity is an un¬ derlying theme. This includes EhlersDanlos syndrome, osteogenesis imper¬ fecta, Marfan's syndrome, mitral valve prolapse, and other connective-tissue diseases.9 Familial cases, suggesting an inherited origin, have also been reported.1015 Another group indicates
ocular trauma as a common causative factor. This includes Down's syn¬ drome, atopy, Leber's congenital amaurosis, and a history of mechani¬ cal eye rubbing.1626 Long-term contact lens wear may represent another source of ocular trauma. We define sporadic KCN as existing in a patient who does not have Down's syndrome, atopic disease, systemic collagen dis¬ a tapetoretinal degeneration, a history of eye rubbing, or a family his¬
ease,
tory of KCN.
The relationship between contact lens wear and KCN has been contro¬ versial. In 1965 Hartstein27 reported 12 cases of corneal warpage due to con¬ tact lenses. In 4 of these patients, the induced astigmatism was permanent, and 1 patient developed KCN. In 1968 Hartstein28 described an additional 4 patients in whom KCN developed while wearing hard contact lenses. Three of these were patients with prefitting corneal astigmatism of less than 0.50 diopter (D). Two additional cases of hard contact lens wearers who developed KCN were reported by Nauheim29 in 1969. Gasset et al30 pro¬ posed a circumstantial causal relation¬ ship between hard contact lens wear and the development of KCN. Despite isolated reports of KCN developing in hard contact lens wearers, this associ¬ ation has been difficult to clarify. Many patients with myopia and high astig¬ matism receive contact lenses for cor¬ rection, and in these cases, it is not surprising that KCN was diagnosed during contact lens wear. The numerous reports in the litera¬ ture of patients with minimal myopia in whom KCN was diagnosed while wearing contact lenses certainly sug¬ gest a relationship.28·29·31 We have un¬ dertaken this study to answer two questions: Is there a group of patients in whom long-term contact lens wear was the probable cause of the develop¬ ment of KCN? If so, is KCN in contact lens wearers historically and clinically different from sporadic KCN?
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MATERIALS AND METHODS
We retrospectively reviewed 386 charts of patients seen in the Iowa Lions Cornea Center, Iowa City, from 1984 through 1989 with the diagnosis of KCN. Patients were removed from the study if they had any of the following exclusion criteria: previous penetrating keratoplasty (35 patients); un¬
obtainable pre-contact lens fit data (19 pa¬ tients); Marian's syndrome (2 patients); Down's syndrome (37 patients); Leber's congenital amaurosis (3 patients); previous ocular surgery (2 patients); KCN with pel¬ lucid marginal degeneration (12 patients); eczema, asthma, or hay fever (55 patients); amblyopia (6 patients); family history of KCN (10 patients); or a history of habitual eye rubbing (6 patients). Therefore, this study group consists of 199 patients with sporadic KCN. Historical data reviewed included age at the time of examination, age at the time of diagnosis of KCN, sex, the history of con¬ tact lens wear before the diagnosis of KCN, and the history of contact lens wear after the diagnosis of KCN. Additional data col¬ lected on patients with a history of contact lens wear before the diagnosis of KCN included slit-lamp examination findings, manifest refraction, keratometry readings prior to the fit of contact lenses, the reason for the contact lens fitting, the type of con¬ tact lenses worn, and the wear time includ¬ ing hours per day and number of years. All patients received a complete eye ex¬ amination in the Iowa Lions Cornea Center. For this study, ocular data included Snellen visual acuity with best manifest refraction, Snellen visual acuity with contact lenses, keratometry readings, the presence of infe¬ rior steepening, the amount of inferior steepening, cone location, and the presence of an iron ring, anterior stromal scarring, or Vogt's striae. In addition, pachymetry was performed on some of the patients cen¬ trally and equal distances above and below the center of the cornea using a Haag-Streit
(Haag-Streit Ag, Berne, Switzerland) opti¬ pachymeter or ultrasonic pachymetry (Pachysonic II, Teknar, Ine, St Louis, Mo) depending on the date of examination. All patients were seen by one of us ( J.H.K.). The amount of inferior steepening was deter¬ mined using the Soper Topogometer (Topogometer Co, Houston, Tex) on a Bausch & Lomb Keratometer (Bausch & Lomb Ine, Rochester, NY). Cone location was deter¬ mined by using both a Keeler-Kline Keratoscope (Keeler Instruments Ine, Broomall, Pa) and slit-lamp examination. If the apex of the cone was in the central portion of the cornea, as defined by the vertical level of a constricted pupil, it was determined to be central (Figs 1 through 3). cal
The minimal criteria used to define KCN central or paracentral area of corneal thinning and protrusion that is detectable are a
Fig 1.—Low-magnification lateral view of a central cone in a patient with a long-term ( 11.5 years) history of contact lens wear before the diagnosis of keratoconus.
—
Sex,
No.
(%) M
Contact lens before
Total
use
keratoconus
24
(45.3)
29
(54.7)
53
34
(43.6)
44
(56.4)
78
Keratoconus before contact lens
use
Keratoconus with no contact
lens Total
use
in
a
Slit-lamp photograph of a central cone patient with a long-term (13.0 years) his¬
2.
—
39 (57.4) 68 29 (42.6) 87(43.7)112(56.3) 199
slit-lamp examination in a patient with irregular keratometric mires and no signs of previous corneal inflammation. To mea¬ sure inferior steepening, patients were on
seated at a Bausch & Lomb Keratometer. The keratometry mires were aligned in the vertical axis while the patient fixated cen¬ trally on the Soper Topogometer. The fixa¬ tion light on the topogometer was moved superiorly and the keratometer mires were observed as the patient looked up. If the mires separated, then the presence of infe¬ rior steepening was confirmed. The amount of inferior steepening was quantitated by realigning the keratometry mires while the patient looked up, and the change in diop¬ ters was recorded. To establish whether inferior steepening or a thin central cornea was present in nor¬ mal patients with or without a history of contact lens wear, 100 eyes of 50 normal controls of similar age and sex distribution were examined. Twenty-five controls from the University of Iowa contact lens clinic who had a history of contact lens wear were examined. In addition, 25 University of Iowa employees who had no history of con¬ tact lens wear served as controls. Controls
Fig 3. cone
in
Slit-lamp photograph of an inferior sporadic keratoconus in a patient with¬
—
tory of
contact lens wear before the diagnosis of keratoconus. Note the presence of an iron ring (arrows) and anterior stromal scarring.
out a
examined 20 minutes after lenses were removed. Keratometry readings and the presence and amount of inferior steepening were recorded after slit-lamp examination. Corneal thickness was determined cen¬ trally and at two points peripherally in the 3-, 6-, 9-, and 12-o'clock meridians using ul¬ trasonic pachymetry. A thin central cornea was defined as either a central reading of less than 0.490 mm or a paracentral pachymetry reading that was less than the central reading. The central cornea thick¬ ness criteria were selected based on the Prospective Evaluation of Radial Keratotomy (PERK) Study, in which 90% of the patients had a central corneal thickness greater than 0.490 mm," and all paracen¬ tral readings were greater than the central
spectacles was 20/40 or worse and visual acuity with best contact lens fit was better
were
Sex Distribution
Table 1.
Fig
history of contact lens wear. Note the presence of an iron ring (arrow) and anterior stromal scarring.
than 20/80. Severe KCN was defined as vi¬ sual acuity with best contact lens fit equal to or worse than 20/80. The eyes within each of the three patient groups were compared such that eyes of equal severity were ana¬ lyzed using an overall t test evaluating age at the time of diagnosis, age at the time of examination, manifest refraction, kera¬ tometry, amount of inferior steepening, and 2 pachymetry at the apex of the cone. analysis was used to compare the cone location, iron ring, presence of anterior stromal scarring, and Vogt's striae. RESULTS
Similarly, keratometry readings were analyzed with a paired t test. In addition to these three patient groups defined by a history of contact lens wear, three KCN severity categories were defined
A retrospective review was done on 386 patients. We excluded 187 patients for reasons previously stated. A total of 199 patients were included, 87 (43.7% ) of whom were women and 112 (56.3% ) of whom were men. Sex distri¬ bution was similar within each group of patients (Table 1). No patients had unilateral KCN. The average age at the time of diagnosis in patients with a history of contact lens wear before the diagnosis of KCN was 32.0 years (range, 26.5 to 53 years) in female pa¬ tients and 31.3 years (range, 25 to 48 years) in male patients. They were fit with lenses at a mean age of 20 years (range, 13 to 36 years). Nine (17%) were fit at age 25 years or older. Pa¬ tients with KCN who had not worn contact lenses and those in whom KCN was diagnosed before contact lens fit¬
defined as mild KCN. Moderate KCN in¬ cluded eyes in which the visual acuity with
diagnosed
readings.33
Three groups of patients were estab¬ lished. The first group was defined as pa¬ tients with a history of contact lens wear before the diagnosis of KCN. The absence of KCN at the time of contact lens fitting was confirmed by slit-lamp examination, kera¬ tometry readings, and manifest refraction. The second group included patients with KCN and no history of contact lens wear prior to or after the diagnosis of KCN. The third group included patients with diagno¬ sis of KCN before wearing contact lenses. In the group of patients with a history of contact lens wear before the diagnosis of
KCN, a paired t test was performed to com¬ pare the manifest refraction prior to con¬ tact lens fit with that at the time of
exam¬
ination.
based on Snellen visual acuity. Visual acu¬ ity better than 20/40 with spectacles was
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ting were significantly younger (P < .0001) at the time of diagnosis (Table 2). Ninety-seven percent were at 25 years old
or
younger.
Table 2.—Patient Age at the Time of Diagnosis Mean
Age,
y
(Range) [SD] by Sex
-1 Table 4.—Categorization of Keratoconus by Severity at the Time of Examination
M
[4.35] [2.57] (13.5-29) [3.51]
No.
keratoconus_32.0 (26.5-53) [3.95]_31.3 (25-48) Keratoconus before contact lens use_19.6 (13.5-25.5) [2.81]_18.0 (13-24)
Contact lens
use
Keratoconus with
before no
contact lens
18.0
use
Table 3.—Patient
Age
(14-28) [2.65]
19.3
at the Time of Examination Mean age, y
(Range)
[SD] by Sex
(%) of Eyes by Severity
Mild
Moderate Severe
Contact lens use before keratoconus 44 (42.0) 59 (56.0) Keratoconus before contact lens use 97(63.0) 51(32.0)
3
(3)
8(5)
Keratoconus with no contact
M
Contact lens use before keratoconus Keratoconus before contact lens use Keratoconus with no contact lens use
(27-56) [4.75] 30.6 (15-43) [5.28] 31.8 (14.5-48) [3.85] 33.4
(26-53.5) [4.21] 29.0 (16-46) [5.10] 29.3 (15.5-51) [4.45]
lens
use
79
(58.0) 52 (38.0)
5
(4)
32.5
analysis. All patients with a history of wear before the diagnosis of KCN had less than 1.25 D of cylinder by manifest refraction and keratome¬ try readings before they were fit. An overall t test was performed comparing the keratometry readings, manifest refraction, amount of infe¬ rior steepening, and pachymetry read¬ ings in the mild, moderate, and severe KCN groups with a history of contact lens wear before the diagnosis of KCN with eyes of equal severity in patient contact lens
There was no statistically significant difference in patient age at the time of examination (Table 3). Of the 199 patients, 53 (27% ) had a history of contact lens wear before KCN, 68 (34% ) had no history of con¬ tact lens wear before or after the diag¬ nosis of KCN, and 78 (39% ) had a his¬ tory of KCN before wearing contact lenses. These three patient groups were classified by KCN severity (de¬ fined in the "Materials and Methods" section) according to Table 4. The 53 patients with a history of contact lens wear before the diagnosis of KCN had been wearing contact lenses for an average of 12.2 years (range, 5.5 to 22 years) for 15.2 hours per day. All 53 patients had an area of central or paracentral corneal thin¬ ning and irregular keratometric astig¬ matism or inferior steepening. In ad¬ dition, 98 (92.5%) of 106 eyes had either Vogt's striae, an iron ring, or anterior stromal scarring. The 8 eyes that had only the minimal criteria used to define KCN were in patients whose other eye had more advanced KCN. Of these 53 patients, 47 (89.0% ) wore hard polymethylmethacrylate lenses, 3 (5.5%) wore soft contact lenses, and 3 (5.5%) wore gas-perme¬ able contact lenses. Five (9.5% ) of the 53 patients in this group were exam¬ ined in our department prior to fit. The remaining 48 (90.5%) were examined by referring ophthalmologists and op¬ tometrists. Cosmesis was the reason for the contact lens fitting in 48 pa¬ tients (90.5% ), while 2 (3.8% ) were fit for anisometropia and 3 (5.7%) were fit for high axial myopia. Fifty eyes of 25 control patients (av¬ erage age, 28.5 years; 48% women, 52% men), with a history of contact lens wear for an average of 9.3 years (range, 4.5 to 15.0 years) for 12.4 hours per day, were examined for inferior steepening and a thin central cornea. Fifteen con¬ trol group patients wore hard poly-
methylmethacrylate lenses, 5 wore gaspermeable lenses, and 5 wore soft con¬ tact lenses. No controls with a history
of contact lens wear demonstrated in¬ ferior steepening. Two control eyes of different patients had central corneal pachymetry readings of less than 0.490 mm (0.479 mm and 0.483 mm), neither of which demonstrated inferior steep¬
ening or irregular astigmatism. No peripheral corneal pachymetry read¬ ings were less than the central read¬ ing. Fifty eyes of 25 controls (average age, 27 years; 52% men, 48% women) with no history of contact lens wear
examined. One control demon¬ strated 0.75 D OD of inferior steepen¬ ing and 1.0 D OS. The other 48 eyes demonstrated no inferior steepening. Three eyes had central pachymetry readings of less than 0.49 mm (0.475 mm, 0.479 mm, and 0.481 mm). No in¬ ferior steepening or irregular astigma¬ tism was found in these eyes. No pe¬ ripheral corneal pachymetry readings were less than the central reading. Paired t test analysis of the patients with a history of contact lens wear be¬ fore the diagnosis of KCN, comparing manifest refractions prior to fit with manifest refractions at the time of di¬ agnosis of KCN, revealed a statisti¬ cally significant increase in myopia and astigmatism in the mild and mod¬ erate groups (P < .0001) and in the se¬ vere group (P < .02). However, the number of patients in the severe group was too small to rely on the results of the paired t test. The paired t test for the same group, comparing the kera¬ tometry readings prior to contact lens fit with keratometry readings at the time of diagnosis of KCN, revealed a statistically significant increase in astigmatism in the mild and moderate groups (P < .0001) and in the severe group (P < .02). However, again, the number of patients in the severe group was too small to rely on this test of were
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groups where either contact lenses were never worn or were
fitted after
diagnosis. The overall t test of keratometry readings showed that these patients had significantly flatter readings when compared with both of the other mild groups (P < .001) and the
the moderate group in which lenses fit after the diagnosis (P < .005). Differences in the other groups were
were
not
statistically significant, but there
was a
trend toward flatter curvatures
(Table 5). No statistically significant
difference was found in manifest re¬ fraction, the amount of inferior steep¬ ening, pachymetry readings, or the presence of an iron ring, anterior stro¬ mal scarring, or Vogt's striae in these groups. Iron lines were not seen in 12 eyes (11.5% ) of patients with a history of contact lens wear before the diag¬ nosis of KCN, 13 eyes (8.3% ) diagnosed with KCN before contact lens wear, and 16 eyes (11.7% ) with no history of contact lens wear. X2 Analysis compared the cone loca¬ tion in the mild, moderate, and severe categories of patients with a history of contact lens wear before the diagnosis of KCN with patients in the other groups (Table 6). There was a statisti¬ cally significant difference (P < .0001) in every category, demonstrating a central cone in patients with a history of contact lens wear prior to the diag¬ nosis of KCN. No eyes in any categories were noted to have superior cones. In each category, cone location was not recorded in less than 15% of the pa¬ tient charts.
Table 5.—Average Keratometry
Readings*
Table 7.—Keratoconus after Contact Lens Wear: Patient Characteristics
Keratometry Readings by Severity Group, Diopters
Mean ± SD
Contact lens
use
before keratoconus
Keratoconus before contact lens Keratoconus with
no
Mild
Moderate
44.34 ± 2.00 45.11 ± 2.86
46.82 ± 4.00
4.93t 5.81t 6.55t 8.10t
48.20 ± 5.32 49.47 ± 5.50 50.32 ± 5.58 53.83 ± 7.12
46.45 47.55
use
contact lens use
50.49
52.67
Flat and steep keratometry readings
were
\P < .001 compared with the contact lens %P < .005 compared with the contact lens
48.80 ± 4.56
Normal examination findings before long-term
Severe
contact lens wear
Older at the time of diagnosis of keratoconus
54.12 58.37
1.24 3.36
(P< .0001) History of contact lens
57.50 61.50
6.73 4.20
sis of keratoconus
57.00 64.67
2.83 4.53
Central
use
before keratoconus group.
use
before keratoconus group.
No.
ings
Patients
(%) by Severity Group for Keratoconus
Mild
Moderate
*
Severe
35 5
NR indicates not recorded.
COMMENT
We realize that we cannot prove that contact lens wear has caused the de¬ velopment of KCN in all of these pa¬ tients. It is possible that KCN would have developed regardless of contact lens wear or that extremely subtle signs of KCN may have been missed on initial examination. In each of these patients, pre-contact lenses fit kera¬ tometry readings and manifest refrac¬ tions demonstrated less than 1.25 D of regular keratometric cylinder, and paired t test evaluation demonstrated a significant change in manifest re¬ fraction and keratometry readings (P < .0001). In 48 patients (90.5%) the reason for contact lens fitting was cosmesis, according to the patients' charts. It is possible that the need for contact lens fitting could have arisen due to an early undetected central cone; however, review of these pa¬ tients' charts reveals that only 5 pa¬ tients (9.5%) were fit for anisometropia. All eyes of these 53 patients had clinically detectable corneal thinning and protrusion with irregular astig¬ matism. We define a cornea with con¬ tact lens warpage syndrome as that having irregular astigmatism without other features of KCN such as thin¬ ning, protrusion, or an iron ring. All 106 eyes of patients who wore contact lenses before the diagnosis of KCN had corneal thinning and protrusion and therefore fall under our definition of KCN and not corneal warpage syn-
were
divided into
severity
groups to examine whether differences
45 (76.2) central 3 (100) central (79.6) central 8 (13.5) inferior 0 inferior (11.4) inferior _4 (9.0) NR_6 (10.2) NR_NR_ Keratoconus before contact lens use 3 (3.2) central 3 (5.2) central 0 central 6 (100) inferior 71 (81.6) inferior 49 (86.0) Inferior _13 (14.9) NR_5 (8.8) NR_0 NR_ Keratoconus with no contact lens use 2 (5.1) central 0 central 5 (5.2) central 82 (85.4) inferior 35 (89.7) inferior 7 (100) inferior 9 (9.4) NR 0 NR 2(5.1)NR before keratoconus
location (P < .0001) toward flatter keratometry read¬
compared separately.
Table 6.—Cone Location*
use
prior to diagno¬
cone
Tendency
were
Contact lens
wear
drome. No patients underwent contact lens withdrawal to see if these changes reversed. It is our practice to withdraw contact lenses in patients with contact lens warpage syndrome to see if there is a resolution of irregular astigma¬ tism. However, we do not withdraw contact lenses in patients who have corneal thinning and protrusion and therefore KCN by our definition. The patients with a history of con¬ tact lens wear before the diagnosis of KCN were significantly older at the time of diagnosis than the other pa¬ tients (P < .0001). The patients' ages at the time of diagnosis of KCN were obtained from patient charts (either at the University of Iowa or at the refer¬ ring physician's office). However, it is impossible to know when KCN devel¬ oped. Despite the fact that the age at the time of diagnosis is not the same as the age of onset, the difference in age between these groups is significant. We believe that the most likely reason for the age difference is that it takes years for contact lenses to induce KCN. It is possible that the contact lens masked the visual disturbance of early KCN, although it is difficult to imagine the existence of KCN for so many years without the diagnosis being made. The three patient groups had comparable disease stages of KCN at the time of examination, thereby countering the possibility that increased age at the time of diagnosis was due to delayed
recognition (Table 4).
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dependent on severity, 2 Analy¬
sis demonstrated a statistically signif¬ icant (P < .0001) difference in cone lo¬ cation in mild, moderate, and severe categories. Patients fit before the diagnosis of KCN typically demon¬ strated a central cone while an inferior cone was observed in patients with KCN with no history of contact lens wear and in patients who had worn contact lenses after the diagnosis of KCN. We assume that the presence of the contact lens influenced the location of the cone. It is tempting to speculate that contact lens rigidity may have an effect on cone location" and keratome¬ try readings in these patients, result¬ ing in central cones and flatter kera¬ tometry readings. Corneal hypoxia due to decreased oxygen permeability may also be a contributing factor, espe¬ cially in those patients wearing hard polymethylmethacrylate lenses. How¬ ever, as yet we do not have an animal model for the development of KCN af¬ ter contact lens wear, and the role of contact lens rigidity and oxygen per¬ meability is unclear. It is interesting that of these 53 pa¬ tients fit with contact lenses before the diagnosis of KCN, 3 patients had worn only soft contact lenses and 3 patients had worn only gas-permeable contact lenses. After completing this study, we examined an additional patient in whom soft contact lenses were worn for 10 years who developed features of contact-lens induced KCN. In reviewing the charts, two patients were found in whom KCN developed in the only eye fit with a contact lens. One of these patients was a 45-year-old man diagnosed with unilateral aphakia and who was postoperatively fit with a hard contact lens. There was no history of previous trauma. Ten years after wearing the lens for an average of 16 hours per day, the patient devel¬ oped KCN in his aphakic eye; his other eye was normal. The other patient was a 31-year-old man who had undergone bilateral strabismus surgery for exo¬ tropia. His left eye remained amblyopic and his right eye was fit with a hard contact lens for cosmesis. After 13.6 years of wearing the lens for an
average of 14 hours per day, he devel¬ oped KCN in the right eye; his left cor¬ nea was normal. These patients fur¬ ther support our theory that KCN can develop in contact lens wearers, but due to the history of ocular surgery, both patients were excluded from this study.
We did not set out to determine the
frequency with which contact lens wearers might develop KCN. The prev¬ alence of patients fit before the diag¬ nosis of KCN in our population was 13.7% (53/386). However, ours is a re¬ ferral-based practice and we cannot infer th; ,t this is the prevalence in the general population of patients with
KCN. As a result of the bias introduced by our referral-based practice, it is not possible to determine the incidence of KCN in the general population of con¬ tact lens wearers. In addition, 60 pa¬ tients were excluded from this study due to unavailable data, amblyopia, or previous surgery. It is possible that the inclusion of these patients could have altered our results considerably. It would be interesting to compare the overall incidence of KCN before the development of contact lenses with the overall incidence today. An increase may further support that contact lens role in the develop¬ wear may play ment of KCN. Unfortunately, these data are not available. To exclude the existence of inferior steepening or a thin central cornea in people without KCN, we examined 100 control eyes. Fifty eyes with a compa¬ rable long-term history of contact lens wear were examined to test the possi¬ bility that inferior steepening or a thin central cornea can be found as a typi¬ cal finding in contact lens wearers. Five of our control eyes (2 with a his¬ tory of contact lens wear) demon¬ strated a central corneal thickness of less than 0.49 mm, and 1 control who did not have a history of contact lens wear did have inferior steepening but did not have a thin central cornea. As of this writing, this patient has not developed KCN, though we will con¬ tinue to observe her. We believe that the wearing of con¬ tact lenses involves trauma to the cor¬ nea that in most cases either is not se¬ vere enough or the patient is not sus¬ ceptible to the development of KCN over a long wearing time. However, in some patients, wearing contact lenses along with other probable traumatic causes of KCN, such as Down's syn¬ drome, Leber's congenital amaurosis, atopy, and significant history of eye rubbing, may cause KCN. Despite the presence of an adequate tear film be¬ tween the contact lens and cornea, it is easy to recognize that long-term con¬ tact lens wear may be a source of ocu¬ lar trauma. We cannot say with abso-
lute
certainty that these 53 patients developed KCN because of the contact
c\l=o^\ne: il-etude
lenses and would not have done so without the contact lenses. It is clear, at the very least, that contact lenses have influenced the corneal topogra¬
6:203-218. 8. Waardenburg
phy (central
location, tendency toward flatter curvature). Nine (17% ) of the 53 patients were fit at the age of 25 years or older, at which time they cone
did not have KCN. In the two other groups, 97% of the patients were diag¬ nosed with KCN by the age of 25 years. On the basis of age alone, it is unlikely
that these 9 patients would have de¬ veloped KCN without the contact lenses. The mean age of diagnosis in the group of 53 patients was also dis¬ tinctly higher than that for the other two groups. The previously mentioned unilateral cases further substantiate the association between contact lenses and KCN. The question is whether contact lenses caused the disorder in all or just some of the group of 53 pa¬ tients (Table 7). As a result of our findings, we rec¬ ommend that contact lens wearers be followed up closely. Follow-up exami¬ nations should include monitoring for the earliest signs of KCN, including
irregular astigmatism, increasing my¬ opia, and inferior steepening. Further considerations for early detection
would include serial measurements of corneal thickness. If any of the above signs were to develop, we would rec¬ ommend discontinuation of contact lens use. However, we cannot be sure these signs will not progress regard¬ less of discontinuing contact lens wear. This project was supported in part by an unrestricted grant from Research to Prevent Blindness Inc, New York, NY. This project was awarded the P. J. Leinfelder Award for the Outstanding Fellow Research Project at the University of Iowa (Iowa City) in 1989. The authors gratefully acknowledge the contributions of Jill A. Fishbaugh, RN, BSN, for data collation; James Hulbert, PhD, for statistical analysis; Cathi Miller, FCLSA; and Colleen A. Howe, OD, all of Iowa City, for providing control patients for this study; and Michael Lynn, PhD, Atlanta, Ga, for providing us with data from the PERK Study. References
RS, Belin MW. Keratoand related noninflammatory corneal thinning disorders. Surv Ophthalmol. 1984;28:293-322. 2. Maumenee IH. Hereditary connective tissue diseases involving the eye. Trans Ophthalmol Soc UK. 1974;94:753-763. 3. Kao WWY, Vergnes J-P, Ebert J, et al. Increased collagenase and gelatinase activities in keratoconus. Biochem Biophys Res Commun. 1. Krachmer JH, Feder
conus
1982;107:929-936. 4. Rehany U, Lahav M, Shoshan S. Collagenolytic activity in keratoconus. Ann Ophthalmol. 1982;14:751-754. 5. Yue BY JT, Sugar J, Benveniste K. Heterogeneity in keratoconus: possible biochemical basis. Proc Soc Exp Biol Med. 1984;517:336-341. 6. Robert L, Schillinger G, Moczar M, et al.
\l=E'\tudemorphologique
et
biochemique
du
k\l=e'\rato-
Downloaded From: http://archopht.jamanetwork.com/ by a University of Michigan User on 06/16/2015
biochemique. Arch Ophthalmol (Paris). 1970;30:589-608. 7. Meek KM, Elliot GF, Nave C. A synchroton x-ray difraction study of bovine cornea stained with cupromeronic blue. Coll Relat Res. 1986;
PJ, Francischetti A, Klein D. Genetics and Ophthalmology. Springfield, Ill: Charles C Thomas Publisher; 1961:452-456. 9. Shapiro MB, France TD. The ocular features of Down's syndrome. Am J Ophthalmol. 1985; 99:659-663. 10. Redmond KB. The role of heredity in keratoconus. Trans Ophthalmol Soc Austr. 1968;27:52\x=req-\ 54. 11. Falls
HF, Allen AW. Dominantly inherited keratoconus: report of a family. J Genet Hum. 1969;17:317-324.
12. Hammerstein W. Die Bedeutund des Geschlechtsverhaltnisses fur die Ermittlung des x-Chromosomalen erbganges, dar gestellt am Krankheitsbild des Keratokonus. Klin Monatsbl
Augenheilkd. 1971;159:602-608.
13. Hammerstein W. Zur Genetik des KeratoAlbrecht von Graefes Arch Klin Exp Ophthalmol. 1974;190:293-308. 14. Ihalainen A. Clinical and epidemiological features of keratoconus: genetic and external factors in the pathogenesis of the disease. Acta Ophthalmol Suppl (Copenh). 1986;178:1-64. 15. Robertson I. Keratoconus and the Ehlers\x=req-\ Danlos syndrome: a new aspect of keratoconus. Med J Aust. 1975;1:571-573. 16. Pierse D, Eustace P. Acute keratoconus in mongols. Br J Ophthalmol. 1971;55:50-54. 17. Boger WP III, Peterson RA, Robb RM. Keratoconus and acute hydrops in mentally retarded patients with congenital rubella syndrome. Am J Ophthalmol. 1981;91:231-233. 18. Karseras AG, Ruben M. Aetiology of keratoconus. Br J Ophthalmol. 1976;60:522-525. 19. Tabbara KF, Butrus SI. Vernal keratoconjunctivitis and keratoconus. Am J Ophthalmol. conus.
1983;95:704-705.
20. Alstrom CH, Olson O. Heredo-retinopathia congenitalis: monohybrida recessiva autosomalis. Hereditas. 1957;43:1-177. 21. Karel I. Keratoconus in congenital diffuse tapetoretinal degeneration. Ophthalmologica. 1968;155:8-15. 22. Merin S, Auerbach E. Retinitis pigmentosa. Surv Ophthalmol. 1976;20:303-346. 23. Coyle JT. Keratoconus and eye rubbing. Am J Ophthalmol. 1984:527-528. 24. Ridley F. Contact lenses in the treatment of keratoconus. Br J Ophthalmol. 1956;40:295-304. 25. Ridley F. Eye rubbing and contact lenses. Br J Ophthalmol. 1961;45:631. 26. Gritz DC, McDonnell PJ. Keratoconus and ocular massage. Am J Ophthalmol. 1988;106:757\x=req-\
758. 27. Hartstein J. Corneal warping due to wearing of corneal contact lenses: a report of 12 cases. Am J Ophthalmol. 1965;60:1103-1104. 28. Hartstein J. Keratoconus that developed in patients wearing corneal contact lenses. Arch
Ophthalmol. 1968;80:345-346. 29. Nauheim JS. Corneal curvature changes simulating keratoconus occurring in patients wearing contact lenses. Contact Lens Med Bull. 1969;2:7-9.
30. Gassett AR, Houde WL, Garcia-Bengochea M. Hard contact lens wear as an environmental risk of keratoconus. Am J Ophthalmol. 1978; 5:339-341. 31. Nauheim JS, Perry HD. A clinicopathological study of contact-lens-related keratoconus. Am J Ophthalmol. 1985;100:543-546. 32. Lynn MJ, Waring GO, Sperduto RD, PERK Study Group. Factors affecting outcome and predictability of radial keratotomy in the PERK study. Arch Ophthalmol. 1987;105:42-51. 33. Steinberg EB, Waring GO, Lynn MJ. Measurement of corneal thickness in the central, paracentral and peripheral zones with ultrasonic
pachymetry. Invest Ophthalmol Vis Sci. 1986; 27:63.
Varley, MD; Jay
\s=b\ A retrospective review of 398 eyes of 199 patients with keratoconus revealed 106 eyes of 53 patients with an association between contact lens wear and the development of keratoconus. The absence of keratoconus at the time of contact lens fitting was confirmed by slit-lamp examination, keratometry readings, and manifest refraction. Keratoconus was diagnosed after a mean of 12.2 years of contact lens wear. This group was compared with patients with sporadic keratoconus with either no history of contact lens wear or a history of contact lens wear after the diagnosis. They were older at the time of diagnosis, had central vs decentered cones, and had a tendency toward flatter corneal curvatures. We believe that these patients suggest that long-term contact lens wear is a factor that can lead to keratoconus.
(Arch Ophthalmol. 1990;108:534-538)
/" eratoconus (KCN) is a noninflammatory disorder of the cornea characterized by progressive conical ectasia with protrusion of the thinned area.1 It results in
increasing myopia irregular astigmatism. Inferior steepening, corneal thinning, and ir¬ regular astigmatism may be the ear¬ liest signs of KCN. Other clinical signs include an epithelial iron ring, ante¬ rior stromal scarring, and striae ante¬ rior to Descemet's membrane (Vogt's striae). Early in its course, optical cor¬ rection is achieved through spectacles. As the irregular astigmatism pro¬ gresses, rigid contact lenses can be quite successful in restoring vision. When patients either have poor vision with
with a contact lens or cannot wear one, surgery is performed. The cause of KCN remains unclear. Proposed causes include biochemical alterations in collagen or proteoglycan physiologic activity.2'8 Many condi¬ tions in which KCN occurs have com¬ mon causative factors. One group is Accepted for publication October 11,
1989. From the Iowa Lions Cornea Center, Department of Ophthalmology, University of Iowa Hospital, Iowa City. Dr. Macsai is now with the Department of Ophthalmology, West Virginia University, Morganstown. Dr Varley is now with the Department of Ophthalmology, the Cleveland (Ohio) Clinic Foundation. Reprint requests to Iowa Lions Cornea Center, Department of Ophthalmology, University of Iowa Hospitals, Iowa City, IA 52242 (Dr Krach-
mer).
H.
Krachmer, MD
patients in whom an abnormality in collagen physiologic activity is an un¬ derlying theme. This includes EhlersDanlos syndrome, osteogenesis imper¬ fecta, Marfan's syndrome, mitral valve prolapse, and other connective-tissue diseases.9 Familial cases, suggesting an inherited origin, have also been reported.1015 Another group indicates
ocular trauma as a common causative factor. This includes Down's syn¬ drome, atopy, Leber's congenital amaurosis, and a history of mechani¬ cal eye rubbing.1626 Long-term contact lens wear may represent another source of ocular trauma. We define sporadic KCN as existing in a patient who does not have Down's syndrome, atopic disease, systemic collagen dis¬ a tapetoretinal degeneration, a history of eye rubbing, or a family his¬
ease,
tory of KCN.
The relationship between contact lens wear and KCN has been contro¬ versial. In 1965 Hartstein27 reported 12 cases of corneal warpage due to con¬ tact lenses. In 4 of these patients, the induced astigmatism was permanent, and 1 patient developed KCN. In 1968 Hartstein28 described an additional 4 patients in whom KCN developed while wearing hard contact lenses. Three of these were patients with prefitting corneal astigmatism of less than 0.50 diopter (D). Two additional cases of hard contact lens wearers who developed KCN were reported by Nauheim29 in 1969. Gasset et al30 pro¬ posed a circumstantial causal relation¬ ship between hard contact lens wear and the development of KCN. Despite isolated reports of KCN developing in hard contact lens wearers, this associ¬ ation has been difficult to clarify. Many patients with myopia and high astig¬ matism receive contact lenses for cor¬ rection, and in these cases, it is not surprising that KCN was diagnosed during contact lens wear. The numerous reports in the litera¬ ture of patients with minimal myopia in whom KCN was diagnosed while wearing contact lenses certainly sug¬ gest a relationship.28·29·31 We have un¬ dertaken this study to answer two questions: Is there a group of patients in whom long-term contact lens wear was the probable cause of the develop¬ ment of KCN? If so, is KCN in contact lens wearers historically and clinically different from sporadic KCN?
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MATERIALS AND METHODS
We retrospectively reviewed 386 charts of patients seen in the Iowa Lions Cornea Center, Iowa City, from 1984 through 1989 with the diagnosis of KCN. Patients were removed from the study if they had any of the following exclusion criteria: previous penetrating keratoplasty (35 patients); un¬
obtainable pre-contact lens fit data (19 pa¬ tients); Marian's syndrome (2 patients); Down's syndrome (37 patients); Leber's congenital amaurosis (3 patients); previous ocular surgery (2 patients); KCN with pel¬ lucid marginal degeneration (12 patients); eczema, asthma, or hay fever (55 patients); amblyopia (6 patients); family history of KCN (10 patients); or a history of habitual eye rubbing (6 patients). Therefore, this study group consists of 199 patients with sporadic KCN. Historical data reviewed included age at the time of examination, age at the time of diagnosis of KCN, sex, the history of con¬ tact lens wear before the diagnosis of KCN, and the history of contact lens wear after the diagnosis of KCN. Additional data col¬ lected on patients with a history of contact lens wear before the diagnosis of KCN included slit-lamp examination findings, manifest refraction, keratometry readings prior to the fit of contact lenses, the reason for the contact lens fitting, the type of con¬ tact lenses worn, and the wear time includ¬ ing hours per day and number of years. All patients received a complete eye ex¬ amination in the Iowa Lions Cornea Center. For this study, ocular data included Snellen visual acuity with best manifest refraction, Snellen visual acuity with contact lenses, keratometry readings, the presence of infe¬ rior steepening, the amount of inferior steepening, cone location, and the presence of an iron ring, anterior stromal scarring, or Vogt's striae. In addition, pachymetry was performed on some of the patients cen¬ trally and equal distances above and below the center of the cornea using a Haag-Streit
(Haag-Streit Ag, Berne, Switzerland) opti¬ pachymeter or ultrasonic pachymetry (Pachysonic II, Teknar, Ine, St Louis, Mo) depending on the date of examination. All patients were seen by one of us ( J.H.K.). The amount of inferior steepening was deter¬ mined using the Soper Topogometer (Topogometer Co, Houston, Tex) on a Bausch & Lomb Keratometer (Bausch & Lomb Ine, Rochester, NY). Cone location was deter¬ mined by using both a Keeler-Kline Keratoscope (Keeler Instruments Ine, Broomall, Pa) and slit-lamp examination. If the apex of the cone was in the central portion of the cornea, as defined by the vertical level of a constricted pupil, it was determined to be central (Figs 1 through 3). cal
The minimal criteria used to define KCN central or paracentral area of corneal thinning and protrusion that is detectable are a
Fig 1.—Low-magnification lateral view of a central cone in a patient with a long-term ( 11.5 years) history of contact lens wear before the diagnosis of keratoconus.
—
Sex,
No.
(%) M
Contact lens before
Total
use
keratoconus
24
(45.3)
29
(54.7)
53
34
(43.6)
44
(56.4)
78
Keratoconus before contact lens
use
Keratoconus with no contact
lens Total
use
in
a
Slit-lamp photograph of a central cone patient with a long-term (13.0 years) his¬
2.
—
39 (57.4) 68 29 (42.6) 87(43.7)112(56.3) 199
slit-lamp examination in a patient with irregular keratometric mires and no signs of previous corneal inflammation. To mea¬ sure inferior steepening, patients were on
seated at a Bausch & Lomb Keratometer. The keratometry mires were aligned in the vertical axis while the patient fixated cen¬ trally on the Soper Topogometer. The fixa¬ tion light on the topogometer was moved superiorly and the keratometer mires were observed as the patient looked up. If the mires separated, then the presence of infe¬ rior steepening was confirmed. The amount of inferior steepening was quantitated by realigning the keratometry mires while the patient looked up, and the change in diop¬ ters was recorded. To establish whether inferior steepening or a thin central cornea was present in nor¬ mal patients with or without a history of contact lens wear, 100 eyes of 50 normal controls of similar age and sex distribution were examined. Twenty-five controls from the University of Iowa contact lens clinic who had a history of contact lens wear were examined. In addition, 25 University of Iowa employees who had no history of con¬ tact lens wear served as controls. Controls
Fig 3. cone
in
Slit-lamp photograph of an inferior sporadic keratoconus in a patient with¬
—
tory of
contact lens wear before the diagnosis of keratoconus. Note the presence of an iron ring (arrows) and anterior stromal scarring.
out a
examined 20 minutes after lenses were removed. Keratometry readings and the presence and amount of inferior steepening were recorded after slit-lamp examination. Corneal thickness was determined cen¬ trally and at two points peripherally in the 3-, 6-, 9-, and 12-o'clock meridians using ul¬ trasonic pachymetry. A thin central cornea was defined as either a central reading of less than 0.490 mm or a paracentral pachymetry reading that was less than the central reading. The central cornea thick¬ ness criteria were selected based on the Prospective Evaluation of Radial Keratotomy (PERK) Study, in which 90% of the patients had a central corneal thickness greater than 0.490 mm," and all paracen¬ tral readings were greater than the central
spectacles was 20/40 or worse and visual acuity with best contact lens fit was better
were
Sex Distribution
Table 1.
Fig
history of contact lens wear. Note the presence of an iron ring (arrow) and anterior stromal scarring.
than 20/80. Severe KCN was defined as vi¬ sual acuity with best contact lens fit equal to or worse than 20/80. The eyes within each of the three patient groups were compared such that eyes of equal severity were ana¬ lyzed using an overall t test evaluating age at the time of diagnosis, age at the time of examination, manifest refraction, kera¬ tometry, amount of inferior steepening, and 2 pachymetry at the apex of the cone. analysis was used to compare the cone location, iron ring, presence of anterior stromal scarring, and Vogt's striae. RESULTS
Similarly, keratometry readings were analyzed with a paired t test. In addition to these three patient groups defined by a history of contact lens wear, three KCN severity categories were defined
A retrospective review was done on 386 patients. We excluded 187 patients for reasons previously stated. A total of 199 patients were included, 87 (43.7% ) of whom were women and 112 (56.3% ) of whom were men. Sex distri¬ bution was similar within each group of patients (Table 1). No patients had unilateral KCN. The average age at the time of diagnosis in patients with a history of contact lens wear before the diagnosis of KCN was 32.0 years (range, 26.5 to 53 years) in female pa¬ tients and 31.3 years (range, 25 to 48 years) in male patients. They were fit with lenses at a mean age of 20 years (range, 13 to 36 years). Nine (17%) were fit at age 25 years or older. Pa¬ tients with KCN who had not worn contact lenses and those in whom KCN was diagnosed before contact lens fit¬
defined as mild KCN. Moderate KCN in¬ cluded eyes in which the visual acuity with
diagnosed
readings.33
Three groups of patients were estab¬ lished. The first group was defined as pa¬ tients with a history of contact lens wear before the diagnosis of KCN. The absence of KCN at the time of contact lens fitting was confirmed by slit-lamp examination, kera¬ tometry readings, and manifest refraction. The second group included patients with KCN and no history of contact lens wear prior to or after the diagnosis of KCN. The third group included patients with diagno¬ sis of KCN before wearing contact lenses. In the group of patients with a history of contact lens wear before the diagnosis of
KCN, a paired t test was performed to com¬ pare the manifest refraction prior to con¬ tact lens fit with that at the time of
exam¬
ination.
based on Snellen visual acuity. Visual acu¬ ity better than 20/40 with spectacles was
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ting were significantly younger (P < .0001) at the time of diagnosis (Table 2). Ninety-seven percent were at 25 years old
or
younger.
Table 2.—Patient Age at the Time of Diagnosis Mean
Age,
y
(Range) [SD] by Sex
-1 Table 4.—Categorization of Keratoconus by Severity at the Time of Examination
M
[4.35] [2.57] (13.5-29) [3.51]
No.
keratoconus_32.0 (26.5-53) [3.95]_31.3 (25-48) Keratoconus before contact lens use_19.6 (13.5-25.5) [2.81]_18.0 (13-24)
Contact lens
use
Keratoconus with
before no
contact lens
18.0
use
Table 3.—Patient
Age
(14-28) [2.65]
19.3
at the Time of Examination Mean age, y
(Range)
[SD] by Sex
(%) of Eyes by Severity
Mild
Moderate Severe
Contact lens use before keratoconus 44 (42.0) 59 (56.0) Keratoconus before contact lens use 97(63.0) 51(32.0)
3
(3)
8(5)
Keratoconus with no contact
M
Contact lens use before keratoconus Keratoconus before contact lens use Keratoconus with no contact lens use
(27-56) [4.75] 30.6 (15-43) [5.28] 31.8 (14.5-48) [3.85] 33.4
(26-53.5) [4.21] 29.0 (16-46) [5.10] 29.3 (15.5-51) [4.45]
lens
use
79
(58.0) 52 (38.0)
5
(4)
32.5
analysis. All patients with a history of wear before the diagnosis of KCN had less than 1.25 D of cylinder by manifest refraction and keratome¬ try readings before they were fit. An overall t test was performed comparing the keratometry readings, manifest refraction, amount of infe¬ rior steepening, and pachymetry read¬ ings in the mild, moderate, and severe KCN groups with a history of contact lens wear before the diagnosis of KCN with eyes of equal severity in patient contact lens
There was no statistically significant difference in patient age at the time of examination (Table 3). Of the 199 patients, 53 (27% ) had a history of contact lens wear before KCN, 68 (34% ) had no history of con¬ tact lens wear before or after the diag¬ nosis of KCN, and 78 (39% ) had a his¬ tory of KCN before wearing contact lenses. These three patient groups were classified by KCN severity (de¬ fined in the "Materials and Methods" section) according to Table 4. The 53 patients with a history of contact lens wear before the diagnosis of KCN had been wearing contact lenses for an average of 12.2 years (range, 5.5 to 22 years) for 15.2 hours per day. All 53 patients had an area of central or paracentral corneal thin¬ ning and irregular keratometric astig¬ matism or inferior steepening. In ad¬ dition, 98 (92.5%) of 106 eyes had either Vogt's striae, an iron ring, or anterior stromal scarring. The 8 eyes that had only the minimal criteria used to define KCN were in patients whose other eye had more advanced KCN. Of these 53 patients, 47 (89.0% ) wore hard polymethylmethacrylate lenses, 3 (5.5%) wore soft contact lenses, and 3 (5.5%) wore gas-perme¬ able contact lenses. Five (9.5% ) of the 53 patients in this group were exam¬ ined in our department prior to fit. The remaining 48 (90.5%) were examined by referring ophthalmologists and op¬ tometrists. Cosmesis was the reason for the contact lens fitting in 48 pa¬ tients (90.5% ), while 2 (3.8% ) were fit for anisometropia and 3 (5.7%) were fit for high axial myopia. Fifty eyes of 25 control patients (av¬ erage age, 28.5 years; 48% women, 52% men), with a history of contact lens wear for an average of 9.3 years (range, 4.5 to 15.0 years) for 12.4 hours per day, were examined for inferior steepening and a thin central cornea. Fifteen con¬ trol group patients wore hard poly-
methylmethacrylate lenses, 5 wore gaspermeable lenses, and 5 wore soft con¬ tact lenses. No controls with a history
of contact lens wear demonstrated in¬ ferior steepening. Two control eyes of different patients had central corneal pachymetry readings of less than 0.490 mm (0.479 mm and 0.483 mm), neither of which demonstrated inferior steep¬
ening or irregular astigmatism. No peripheral corneal pachymetry read¬ ings were less than the central read¬ ing. Fifty eyes of 25 controls (average age, 27 years; 52% men, 48% women) with no history of contact lens wear
examined. One control demon¬ strated 0.75 D OD of inferior steepen¬ ing and 1.0 D OS. The other 48 eyes demonstrated no inferior steepening. Three eyes had central pachymetry readings of less than 0.49 mm (0.475 mm, 0.479 mm, and 0.481 mm). No in¬ ferior steepening or irregular astigma¬ tism was found in these eyes. No pe¬ ripheral corneal pachymetry readings were less than the central reading. Paired t test analysis of the patients with a history of contact lens wear be¬ fore the diagnosis of KCN, comparing manifest refractions prior to fit with manifest refractions at the time of di¬ agnosis of KCN, revealed a statisti¬ cally significant increase in myopia and astigmatism in the mild and mod¬ erate groups (P < .0001) and in the se¬ vere group (P < .02). However, the number of patients in the severe group was too small to rely on the results of the paired t test. The paired t test for the same group, comparing the kera¬ tometry readings prior to contact lens fit with keratometry readings at the time of diagnosis of KCN, revealed a statistically significant increase in astigmatism in the mild and moderate groups (P < .0001) and in the severe group (P < .02). However, again, the number of patients in the severe group was too small to rely on this test of were
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groups where either contact lenses were never worn or were
fitted after
diagnosis. The overall t test of keratometry readings showed that these patients had significantly flatter readings when compared with both of the other mild groups (P < .001) and the
the moderate group in which lenses fit after the diagnosis (P < .005). Differences in the other groups were
were
not
statistically significant, but there
was a
trend toward flatter curvatures
(Table 5). No statistically significant
difference was found in manifest re¬ fraction, the amount of inferior steep¬ ening, pachymetry readings, or the presence of an iron ring, anterior stro¬ mal scarring, or Vogt's striae in these groups. Iron lines were not seen in 12 eyes (11.5% ) of patients with a history of contact lens wear before the diag¬ nosis of KCN, 13 eyes (8.3% ) diagnosed with KCN before contact lens wear, and 16 eyes (11.7% ) with no history of contact lens wear. X2 Analysis compared the cone loca¬ tion in the mild, moderate, and severe categories of patients with a history of contact lens wear before the diagnosis of KCN with patients in the other groups (Table 6). There was a statisti¬ cally significant difference (P < .0001) in every category, demonstrating a central cone in patients with a history of contact lens wear prior to the diag¬ nosis of KCN. No eyes in any categories were noted to have superior cones. In each category, cone location was not recorded in less than 15% of the pa¬ tient charts.
Table 5.—Average Keratometry
Readings*
Table 7.—Keratoconus after Contact Lens Wear: Patient Characteristics
Keratometry Readings by Severity Group, Diopters
Mean ± SD
Contact lens
use
before keratoconus
Keratoconus before contact lens Keratoconus with
no
Mild
Moderate
44.34 ± 2.00 45.11 ± 2.86
46.82 ± 4.00
4.93t 5.81t 6.55t 8.10t
48.20 ± 5.32 49.47 ± 5.50 50.32 ± 5.58 53.83 ± 7.12
46.45 47.55
use
contact lens use
50.49
52.67
Flat and steep keratometry readings
were
\P < .001 compared with the contact lens %P < .005 compared with the contact lens
48.80 ± 4.56
Normal examination findings before long-term
Severe
contact lens wear
Older at the time of diagnosis of keratoconus
54.12 58.37
1.24 3.36
(P< .0001) History of contact lens
57.50 61.50
6.73 4.20
sis of keratoconus
57.00 64.67
2.83 4.53
Central
use
before keratoconus group.
use
before keratoconus group.
No.
ings
Patients
(%) by Severity Group for Keratoconus
Mild
Moderate
*
Severe
35 5
NR indicates not recorded.
COMMENT
We realize that we cannot prove that contact lens wear has caused the de¬ velopment of KCN in all of these pa¬ tients. It is possible that KCN would have developed regardless of contact lens wear or that extremely subtle signs of KCN may have been missed on initial examination. In each of these patients, pre-contact lenses fit kera¬ tometry readings and manifest refrac¬ tions demonstrated less than 1.25 D of regular keratometric cylinder, and paired t test evaluation demonstrated a significant change in manifest re¬ fraction and keratometry readings (P < .0001). In 48 patients (90.5%) the reason for contact lens fitting was cosmesis, according to the patients' charts. It is possible that the need for contact lens fitting could have arisen due to an early undetected central cone; however, review of these pa¬ tients' charts reveals that only 5 pa¬ tients (9.5%) were fit for anisometropia. All eyes of these 53 patients had clinically detectable corneal thinning and protrusion with irregular astig¬ matism. We define a cornea with con¬ tact lens warpage syndrome as that having irregular astigmatism without other features of KCN such as thin¬ ning, protrusion, or an iron ring. All 106 eyes of patients who wore contact lenses before the diagnosis of KCN had corneal thinning and protrusion and therefore fall under our definition of KCN and not corneal warpage syn-
were
divided into
severity
groups to examine whether differences
45 (76.2) central 3 (100) central (79.6) central 8 (13.5) inferior 0 inferior (11.4) inferior _4 (9.0) NR_6 (10.2) NR_NR_ Keratoconus before contact lens use 3 (3.2) central 3 (5.2) central 0 central 6 (100) inferior 71 (81.6) inferior 49 (86.0) Inferior _13 (14.9) NR_5 (8.8) NR_0 NR_ Keratoconus with no contact lens use 2 (5.1) central 0 central 5 (5.2) central 82 (85.4) inferior 35 (89.7) inferior 7 (100) inferior 9 (9.4) NR 0 NR 2(5.1)NR before keratoconus
location (P < .0001) toward flatter keratometry read¬
compared separately.
Table 6.—Cone Location*
use
prior to diagno¬
cone
Tendency
were
Contact lens
wear
drome. No patients underwent contact lens withdrawal to see if these changes reversed. It is our practice to withdraw contact lenses in patients with contact lens warpage syndrome to see if there is a resolution of irregular astigma¬ tism. However, we do not withdraw contact lenses in patients who have corneal thinning and protrusion and therefore KCN by our definition. The patients with a history of con¬ tact lens wear before the diagnosis of KCN were significantly older at the time of diagnosis than the other pa¬ tients (P < .0001). The patients' ages at the time of diagnosis of KCN were obtained from patient charts (either at the University of Iowa or at the refer¬ ring physician's office). However, it is impossible to know when KCN devel¬ oped. Despite the fact that the age at the time of diagnosis is not the same as the age of onset, the difference in age between these groups is significant. We believe that the most likely reason for the age difference is that it takes years for contact lenses to induce KCN. It is possible that the contact lens masked the visual disturbance of early KCN, although it is difficult to imagine the existence of KCN for so many years without the diagnosis being made. The three patient groups had comparable disease stages of KCN at the time of examination, thereby countering the possibility that increased age at the time of diagnosis was due to delayed
recognition (Table 4).
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dependent on severity, 2 Analy¬
sis demonstrated a statistically signif¬ icant (P < .0001) difference in cone lo¬ cation in mild, moderate, and severe categories. Patients fit before the diagnosis of KCN typically demon¬ strated a central cone while an inferior cone was observed in patients with KCN with no history of contact lens wear and in patients who had worn contact lenses after the diagnosis of KCN. We assume that the presence of the contact lens influenced the location of the cone. It is tempting to speculate that contact lens rigidity may have an effect on cone location" and keratome¬ try readings in these patients, result¬ ing in central cones and flatter kera¬ tometry readings. Corneal hypoxia due to decreased oxygen permeability may also be a contributing factor, espe¬ cially in those patients wearing hard polymethylmethacrylate lenses. How¬ ever, as yet we do not have an animal model for the development of KCN af¬ ter contact lens wear, and the role of contact lens rigidity and oxygen per¬ meability is unclear. It is interesting that of these 53 pa¬ tients fit with contact lenses before the diagnosis of KCN, 3 patients had worn only soft contact lenses and 3 patients had worn only gas-permeable contact lenses. After completing this study, we examined an additional patient in whom soft contact lenses were worn for 10 years who developed features of contact-lens induced KCN. In reviewing the charts, two patients were found in whom KCN developed in the only eye fit with a contact lens. One of these patients was a 45-year-old man diagnosed with unilateral aphakia and who was postoperatively fit with a hard contact lens. There was no history of previous trauma. Ten years after wearing the lens for an average of 16 hours per day, the patient devel¬ oped KCN in his aphakic eye; his other eye was normal. The other patient was a 31-year-old man who had undergone bilateral strabismus surgery for exo¬ tropia. His left eye remained amblyopic and his right eye was fit with a hard contact lens for cosmesis. After 13.6 years of wearing the lens for an
average of 14 hours per day, he devel¬ oped KCN in the right eye; his left cor¬ nea was normal. These patients fur¬ ther support our theory that KCN can develop in contact lens wearers, but due to the history of ocular surgery, both patients were excluded from this study.
We did not set out to determine the
frequency with which contact lens wearers might develop KCN. The prev¬ alence of patients fit before the diag¬ nosis of KCN in our population was 13.7% (53/386). However, ours is a re¬ ferral-based practice and we cannot infer th; ,t this is the prevalence in the general population of patients with
KCN. As a result of the bias introduced by our referral-based practice, it is not possible to determine the incidence of KCN in the general population of con¬ tact lens wearers. In addition, 60 pa¬ tients were excluded from this study due to unavailable data, amblyopia, or previous surgery. It is possible that the inclusion of these patients could have altered our results considerably. It would be interesting to compare the overall incidence of KCN before the development of contact lenses with the overall incidence today. An increase may further support that contact lens role in the develop¬ wear may play ment of KCN. Unfortunately, these data are not available. To exclude the existence of inferior steepening or a thin central cornea in people without KCN, we examined 100 control eyes. Fifty eyes with a compa¬ rable long-term history of contact lens wear were examined to test the possi¬ bility that inferior steepening or a thin central cornea can be found as a typi¬ cal finding in contact lens wearers. Five of our control eyes (2 with a his¬ tory of contact lens wear) demon¬ strated a central corneal thickness of less than 0.49 mm, and 1 control who did not have a history of contact lens wear did have inferior steepening but did not have a thin central cornea. As of this writing, this patient has not developed KCN, though we will con¬ tinue to observe her. We believe that the wearing of con¬ tact lenses involves trauma to the cor¬ nea that in most cases either is not se¬ vere enough or the patient is not sus¬ ceptible to the development of KCN over a long wearing time. However, in some patients, wearing contact lenses along with other probable traumatic causes of KCN, such as Down's syn¬ drome, Leber's congenital amaurosis, atopy, and significant history of eye rubbing, may cause KCN. Despite the presence of an adequate tear film be¬ tween the contact lens and cornea, it is easy to recognize that long-term con¬ tact lens wear may be a source of ocu¬ lar trauma. We cannot say with abso-
lute
certainty that these 53 patients developed KCN because of the contact
c\l=o^\ne: il-etude
lenses and would not have done so without the contact lenses. It is clear, at the very least, that contact lenses have influenced the corneal topogra¬
6:203-218. 8. Waardenburg
phy (central
location, tendency toward flatter curvature). Nine (17% ) of the 53 patients were fit at the age of 25 years or older, at which time they cone
did not have KCN. In the two other groups, 97% of the patients were diag¬ nosed with KCN by the age of 25 years. On the basis of age alone, it is unlikely
that these 9 patients would have de¬ veloped KCN without the contact lenses. The mean age of diagnosis in the group of 53 patients was also dis¬ tinctly higher than that for the other two groups. The previously mentioned unilateral cases further substantiate the association between contact lenses and KCN. The question is whether contact lenses caused the disorder in all or just some of the group of 53 pa¬ tients (Table 7). As a result of our findings, we rec¬ ommend that contact lens wearers be followed up closely. Follow-up exami¬ nations should include monitoring for the earliest signs of KCN, including
irregular astigmatism, increasing my¬ opia, and inferior steepening. Further considerations for early detection
would include serial measurements of corneal thickness. If any of the above signs were to develop, we would rec¬ ommend discontinuation of contact lens use. However, we cannot be sure these signs will not progress regard¬ less of discontinuing contact lens wear. This project was supported in part by an unrestricted grant from Research to Prevent Blindness Inc, New York, NY. This project was awarded the P. J. Leinfelder Award for the Outstanding Fellow Research Project at the University of Iowa (Iowa City) in 1989. The authors gratefully acknowledge the contributions of Jill A. Fishbaugh, RN, BSN, for data collation; James Hulbert, PhD, for statistical analysis; Cathi Miller, FCLSA; and Colleen A. Howe, OD, all of Iowa City, for providing control patients for this study; and Michael Lynn, PhD, Atlanta, Ga, for providing us with data from the PERK Study. References
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\l=E'\tudemorphologique
et
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du
k\l=e'\rato-
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