EXCIMER LASER PHOTOREFRACTIVE KERATECTOMY IN HIGH MYOPIA: A MULTICENTER STUDY* BY Richard L. Lindstrom, MD, Neal A. Sher, MD (BY INVITATION), Mark Barak, MD (BY INVITATION),Janet DeMarchi, COT Angela Tucci, BS (BY INVITATION), Sheraz Daya, MD (BY INVITATION), David R. Hardten, MD (BY INVITATION), Jonathan M. Frantz, MD (BY INVITATION), Richard A. Eifermn, MD (BY INVITATION), Paula Parker, COMT (BY INVITATION), William B. Telfair III, PhD (BY INVITATION), AND Stephen S. Lane, MD (BY INVITATION) (BY INVITATION),
INTRODUCTION
THE 193-NM EXCIMER
LASER HAS GENERATED GREAT INTEREST BECAUSE
of its potential to eliminate myopia in a brief surgical procedure under topical anesthetic. Most early published studies of this new technology were limited to eyes with less than 8 D of myopia. 12 It had been thought that the deeper ablations needed for larger corrections would result in increased corneal haze. More recent reports using the Summit UV 200 laser (Summit Technologies, Watertown, MA)3,4 and the VISX Model Twenty/Twenty laser (VISX Co, Sunnyvale, CA) reported unpredictable results in attempted corrections over 7 D. This has led investigators to limit attempted corrections to 8 D, and the newer protocols from the US Food and Drug Administration (FDA) limits the phase III photorefractive keratectomy (PRK) trials to corrections between - 1.0 and -6.0 D. *From the Excimer Research Group, Phillips Eye Institute, Metropolitan Mount Sinai Medical Center, Minneapolis, and the Department of Ophthalmology, University of Minnesota School of Medicine, Minneapolis; The Eve Center of Florida, Fort Myers; the Department of Ophthalmology, University of Louisville, and V7eterans Affairs Medical Center, Louisville; and V'ISX Corporation, Sunnvvale, California. This research was supported in part by a grant from Taunton Technologies Co, Monroe, Connecticut (now VISX Co, Sunnyvale, California); Health One Corporation and the Friends of the Phillips Foundation, Minneapolis; and Humana, Inc. TR. AM. OPHTH. Soc. vol. LXXXX, 1992
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Our early experience with higher myopic corrections has been more favorable. In 1990, we reported our earliest cases with excimer PRK in a phase II study using a 5.0-mm diameter ablation zone and a heavy regimen of topical corticosteroids on seven sighted eyes with myopia ranging from - 5.5 to - 12.0 D.5 We found near-total correction of myopia in these initial patients and minimal regression at 2 years. Our group subsequently performed a phase IIA series of 31 eyes with encouraging results on patients between - 4.5 and - 8.0 D.6 Our experience with phototherapeutic keratectomy (PTK) for scar removal also found that deeper ablations, up to 220 ,Lm, did not induce an unacceptable level of corneal haze.7 This initial success encouraged our groups and the VISX Corp to request from the FDA permission to perform excimer PRK on a small series of patients with very high myopia. We report herein the results of excimer PRK performed on a series of 16 highly myopic eyes ranging from -8.62 to -14.50 D. METHODS PATIENT SELECTION
Patient selection met US FDA8 criteria under an Investigational Device Exemption for this phase IIA study. Patients were at least 18 years old and had myopia between 8.62 and 14.50 D (spherical equivalent) and best corrected visual acuity of 20/60 or better. Because of anisometropia after excimer PRK, the ability to successfully wear a contact lens was a prerequisite. Patients with abnormal corneas, severe dry eyes, blepharitis, or lagophthalmos were excluded. Preoperative and postoperative corneal topography at 1, 3, and 6 months was performed using the Computed Anatomy System (New York) (Minnesota cases), the Eyesys System (Eyesys Labs, Houston) (Kentucky cases), or an integrated digital keratoscope within the laser. If subelinical keratoconus was suggested by corneal topography, the patient was excluded from treatment. Only one eye from each patient was treated. All patients included in the protocol and followed up for at least 6 months were included. There were no cases left to follow up. Patient data are summarized in Table I. INSTRUMENTATION
The laser used in Minneapolis and Fort Myers, FL, was the VISX Model LV 2015 (VISX Co). The laser used in Louisville was a modified VISX Model L 2000, which had laser cavity and output parameters identical to the LV 2015. These lasers were originally manufactured by Taunton Technologies, Monroe, CT, which has merged with VISX Company; the
Photoreactive Keratectomy in High Myopia
279
TABLE I: PATIENT POPULATION DATA
PATIENT NO.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
SITE
Minneapolis Minneapolis Minneapolis Minneapolis Minneapolis Minneapolis Minneapolis Minneapolis Louisville Louisville Louisville Louisville Fort Myers Fort Myers Fort Myers Fort Myers
AGE
SEX
SURGERY DATE
ABLATION DEPTH (,um)
TREATMENT DIAMETER (mm)
74 53 34 47 42 34 21 42 34 27 27 37 22 49 31 66
M F F M F M M M M F F F F M F F
7/10/91 6/26/91 7/08/91 7/24/91 7/31/91 7/24/91 7/29/91 8/22/91 9/04/91 9/04/91 9/11/91 9/25/91 6/28/91 6/28/91 7/12/91 8/21/91
137 223 172 223 199 223 223 230 170 153 180 146 149 180 178 164
6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 5.6 5.6 5.6 5.6 5.5 5.5 5.5 5.5
laser has been fully described by L'Esperance and associates9 10 and by our group.5-7 It utilized an argon-fluoride gas mixture to produce a 193nm wavelength at 10 Hz and was adjusted to deliver a fluence of 100 to 120 mJ/cm2. The entire laser system has a computer control module with an interactive menu, real time monitoring of procedure parameters, and an integrated digital keratoscope. The laser was calibrated prior to each treatment session by ablating standardized plastic discs and measuring ablation depths with a special micrometer gauge. The desired dioptric change was entered into the computer control console. The maximum beam diameter was 5.5 mm, 5.6 mm, or 6.0 mm, depending on the site. A suction device placed within 1 cm of the cornea was used to remove particles in the ejection plume. PREOPERATIVE AND POSTOPERATIVE EXAMINATION
All patients received complete ophthalmologic examinations including slit-lamp photography, topographic analysis, and ultrasonic pachometry, the details of which have been fully described elsewhere.5-7 Contrast sensitivity was tested in Minnesota by forced choice testing using the MCT 8000 (Vistech Consultants, Dayton, OH). Standardized lighting under the day vision protocol was used in all testing. Testing was performed at five spatial frequencies from 1.5 cycles per degree to 18 cycles per degree. The paired Student's t-test was used to compare the values at each frequency to determine statistical significance.
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Lindstrom et al
Corneal haze was evaluated subjectively for the epithelium (superficial, deep) and the stroma (anterior, posterior) separately using a qualitative scale (0 to 5). A rating of 0 was a clear cornea, 0.5 was barely detectable haze, and 1.0 was mild haze probably not affecting vision. A rating of 2.0 showed moderate haze, probably affecting vision. Objective documentation of haze was provided by standardized slit-lamp photography, including tangential broad beam, thin slit at 45 degrees, broad beam at 45 degrees, and diffuse views. Testing was repeated at 3, 6, 12, and 24 weeks. All refractions, manifest and cycloplegic, were done by one clinical coordinator at each center at similar levels of illumination with notation of pupil size. SURGICAL PROCEDURE
The same surgical technique was performed at all sites. All surgeons at each site have had extensive experience with PRK and have been involved in the trials since 1989. The visual axis was marked with the patient fixating on an internal fixation target coaxial with the surgeons fixating the eye and marking the patient's cornea over the center of the entrance pupil, as suggested by Uozato and Guyton.11 A 6- or 7-mm corneal marker, premarked with blue dye, was centered on the epithelial impression made by the Sinskey hook and was then used to mark the epithelium, which was then gently removed using a Tooke knife. Visualizing the patient's eye through the microscope and video monitors, the surgeon aligned the corneal apex to the lasing plane by adjusting table travel in the X, Y, and Z directions. The eye was sometimes fixated with a forceps. Laser energy was delivered in a series of pulses, predetermined through a rotating series of 15 apertures of diminishing size. The duration of the actual laser emission was 45 to 90 seconds. POSTOPERATIVE REGIMEN
Following the ablation, tobramycin dexamethasone suspension drops (Tobrex, Alcon, Fort Worth, TX) and 5% homatropine hydrobromide (Alcon) were instilled and the eye was patched overnight, or a disposable soft contact lens Vistakon Acuvue (Johnson & Johnson, Claremont, CA) was placed in addition to the patching. In some cases, the contact lens was continued for the first 3 weeks to promote epithelial growth. On the next day, treatment was started on 0.1% fluorometholone (FML Liquifilm, Allergan, Irvine, CA) every 2 hours for the first week, then four times daily for 1 month, and twice daily for the second month; dosage was gradually tapered over the next 2 to 3 months. A 0.3 solution of tobramycin (Tobrex, Alcon) was administered four times daily until the epithelium was healed.
Photoreactive Keratectomy in High Myopia
281
Statistical comparisons utilized a Student's t-test. All mean values are presented with standard deviations. The results will be presented according to guidelines for presenting refractive surgical data as suggested by Waring. 12 RESULTS PATIENT DATA
All cases performed at the three sites with a 6-month follow-up are included. Patient 1 was also included, but PTK protocol for anisometropia was followed. This 74-year-old man had had previous extracapsular cataract surgery and intraocular lens (IOL) implantation and approximately 9 D of anisometropia. He was unable to wear a contact lens due to arthritis. The remainder of the patients had not undergone previous corneal or intraocular surgery. Sixteen eyes in seven male and nine female patients ranging in age from 21 to 74 years were treated. The location, age, date- of treatment, ablation depth, and maximum ablation diameter are listed in Table I. All patients had epithelialized by 4 days postoperatively. It was our clinical impression that the newly healed corneal surface took longer to become smooth than in ablations of lower dioptic corrections. There were no instances of recurrent corneal erosions. REFRACTIVE DATA
Table II lists the manifest refraction, average keratometry, central pachometry, corneal haze scale values, and corrected and uncorrected visions for each patient at 6 weeks, 12 weeks, and 6 months postoperatively. The mean sphere equivalent preoperatively was - 11.59 ± 1.62 D; postoperatively it was + 1.04 + 1. 71 at 6 weeks, - 0.55 ± 2.37 at 12 weeks, and - 0.90 ± 2.13 at 12 months. Fig 1A shows the individual refractive change over time at Minnesota, and Fig 1B shows the changes over time at Kentucky and Florida. Fig 2 shows the attempted versus achieved refraction at 6 months for all three sites. At Minnesota, all eight eyes achieved correction within 2 D of attempted refraction, at Florida three of four cases achieved similar results, and at Kentucky one of four eyes had similar success. Overall, at the 6-month visit, 11 of 16 (69%) were corrected within 2 D of attempted refraction. All cases except two achieved their best corrected preoperative vision within one Snellen line. Patient 14 experienced a loss of vision to 20/50 best corrected. Patient 9 had undercorrection and significant epithelial hyperplasia.
Lindstrom et al
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TABLE II: REFRACTIV'E DATA
V'ISUAL ACUITY PATIENT NO.
I
2
3
4
5
6
7
8
9
10
11
12
'MANIFEST REFRACTION
AV'ERAGE KERATOMETRY
CORNEAL HAZE
BEST CORRECTED
-9.25+ 1.25x 165 + 1.50+ 1.25 x 95 +2.00+0.75x 155 0.00+0.50x 80 - 16.50+3.00x 15 -2.25+ 1.00x 170 -0.75+ 1.25x 145 + 1.25 sph - 10.75+0.75x70 -2.25+ 1.00x 170 -0.75+ 1.50x95 -0.50+ 1.50x95 - 12.00+ 1.25x 80 + 0.25+ 1.25x80 + 0.25+ 1.25x80 0.00+ 1.25x75 - 12.00+0.75x85 + 1.25+0.75x 80 +0.50+0.25x 85 -1.00+1.25x75 - 14.50+ 1.00x 165 +0.75+2.25x 110 +0.50+2.50x 110 0.00+ 1.50x 115 - 13.25+ 1.25x 125 +0.25+3.50x 10 -0.50+2.00x 165 + 1.00+ 1.00x 180 - 14.50+0.50x90 +0.25+ 1.50x70 - 1.00+ 1.75x 75 - 1.50+0.75x65 -12.25+ 1.50x 105 -2.00+ 1.00x 135 -3.50+ 1.75x90 -4.25+ 1.75x 105 -10.25 sph -2.25 sph -5.00 sph -4.50 sph - 12.25+ 1.00x55 0.00+0.50x95 -3.00+0.75x90 -4.00+0.50x 100 10.50+ 1.00x60 -2.25+0.25x 105 1.00+0.75x 105 -3.75+ 1.00x65
43.37 36.25 37.00 35.75 45.25 37.87 37.12 37.00 45.25 36.75 37.50 38.75 46.63 37.00 37.00 38.12 47.50 39.50 39.43 40.43 45.50 35.87 36.38 36.63 47.12 40.50 40.75 36.75 45.75 37.87 38.37 37.87 44.00 40.12 40.50 40.75 42.50
0.0 0.5 0.5 0.5 0.0 1.0 1.0 0.5 0.0 0.5 0.0 0.0 0.0 1.0 1.0 1.0 0.0 1.5 0.5 0.5 0.0 0.5 0.5 0.0 0.0 1.5 1.0 1.0 0.0 1.5 0.5 1.0 0.0 1.0 1.0 2.0 0.0 1.0 1.5 1.5 0.0 1.0 2.0 2.0 0.0 1.0 1.5 2.0
20/30 20/25 20/40 20/25 20/40 20/40 20/40 20/30 20/30 20/25 20/25 20/25 20/40 20/20 20/20 20/20 20/20
V'ISIT
Preop 6 wk 12 wk 6 mo Preop 6 wk 12 wk 6 mo Preop 6 wk 12 wk 6 mo Preop 6 wk 12 wk 6 mo Preop 6 wk 12 wk 6 mo Preop 6 wk 12 wk 6 mo Preop 6 wk 12 wk 6 mo Preop 6 wk 12 wk 6 mo Preop 6 wk 12 wk 6 mo Preop 6 wk 12 wk 6 mo Preop 6 wk 12 wk 6 mo Preop 6 wk 12 wk 6 mo
-
-
42.62 42.62 47.00 40.00 42.68 42.25
48.37 42.25 42.87 45.00
20/25 20/20 20/25 20/20 20/20 20/20 20/25 20/50 20/30 20/30 20/20 20/25 20/25 20/20 20/20 20/25 20/25 20/20 20/20 20/20 20/20 20/20 20/20 20/25 20/25 20/25 20/20 20/30 20/20 20/20
UNCORB,ECTED C]F 20/]'100 20/'40 20/] 30 C]F 20/W30 20/'50 20/'40 C]F 20/] 30 to 20/] 30 20/ C. F 20/'40 20/'40 20/.20 CF 20/'50 20/b 40 20/,25 CF 20/'40 20/] 30 20/'40 CF
20/4 '0 20/P30 20/] 30 CF
20/'40 20/'40 20/] 30 CF 20/'50
20/4 '0 20/ 200 CF 20/l50 20/'400 CF CF 20/,25 20/ 50 20/'200 CF 20/, 40 20/'50 20/ so
Photoreactive Keratectomy in High Myopia
283
TABLE II: REFRACTIVE DATA CONT'D
V'ISUAL ACUITY PATIENT NO.
13
14
15
16
REFRACTION
AVERAGE KERATOMETRY
CORNEAL HAZE
BEST CORRECTED
UNCORRECTED
-10.25 sph +1.00+2.50x20 - 6.00 + 0.50 x 30 -4.25+0.75x 15 -12.00 sph +3.75+2.25x68 +1.00+2.00x70 + 0.50+2.50x 150 -12.75+ 1.50x 106 + 1.00 sph -0.25+0.50x 126 -1.00+0.50x 105 -11.00 sph -0.50+1.75x88 -0.75+2.00x76 -1.00+2.25x76
44.87 40.12 42.50 41.94 43.87 36.00 42.31 38.25 44.12 37.75 38.75 38.25 45.12 37.00 38.37 37.62
0.0 1.0 0.5 1.0 0.0 1.0 2.0 2.0 0.0 1.0 1.0 1.0 0.0 0.5 0.0 0.0
20/15 20/30 20/20 20/20 20/20 20/25 20/50 20/50 20/25 20/30 20/30 20/30 20/20 20/30 20/30 20/30
CF 20/30 20/400 20/200 CF 20/200 20/100 20/70 CF 20/30 20/30 20/30 CF 20/70 20/70 20/80
MANIFEST
V'ISIT
Preop 6 wk 12 wk 6 mo Preop 6 wk 12 wk 6 mo Preop 6 wk 12 wk 6 mo Preop 6 wk 12 wk 6 mo
CF, count fingers. ASTIGMATISM
There was no significant change in preoperative and postoperative refractive cylinder at 6 months (2-sided t-test). MEAN KERATOMETRY VALUES
Mean keratometry values measured before surgery and at various postoperative intervals are shown in Fig 3. The preoperative mean keratometry was 45.39 + 1.61 and the mean postoperative value at 6 months was 39.25 + 2.61 D, indicating considerable corneal flattening. PACHOMETRY VALUES
Pachometry values at these intervals are plotted in Fig 4. NMean preopera+ 39, and mean postoperative value at 24 weeks was
tive value was 542 450 + 48. CORNEAL HAZE
Corneal haze readings are listed in Table II and summarized in Fig 5. The mean haze scores for the epithelium and stroma are shown over time. The highest scores observed in the epithelium or stroma for an individual patient are presented in Table II and were used to compute the mean values. Corneal clarity readings at 6 months of 1.5 or less were seen in all but
284
Lindstrom et al PT 1 MN PT 2 MN PT 3 MN PT 4 MN PT 5 MN PT 6 MN PT 7 MN PT 8 MN
a
0 a
z x: 0 C-) CL
CZ:
0
3
6
9
12 15 18 21
24 27 30
WEEKS AFTER PRK 6Ci
.--
4-
CL
PT 9 KY PT 10 KY PT 11 KY PT 12 KY
2:
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w
-1
IS
-1
2 -1 4 A_W
3
6
9
12 15 18 21 24 27 30
WEEKS AFTER PRK PT PT PT PT
0
a
13 FL 14 FL
15 FL 16 FL
C,, 0
C-) z
0
3
6
9
12 15 18 21
24 27 30
WEEKS AFTER PRK FIGURE
1
Change in refraction (spherical equivalent) after excimer PRK for each patient at 6, 12, and 24 weeks at each site. A, NMinnesota; B, Kentucky; C, Florida. Dotted lines represent + 2 D from emmetropia.
Photoreactive Keratectomy in High Myopia
285
* ACH6MMN
A ACH6MFL 0
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'a
0 CR = 0
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0
0 0
wi C.J
2
0
4
8
6
10
12
14
16
ATTEMPTED CORRECTION, SPH EQUIV, D FIGURE 2
Attempted refraction (sphere equivalent) versus achieved refraction at 6 months for three sites. MN, Minnesota; FL, Florida; KY, Kentucky.
C
c-
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o 47
o 45
C,)
43
.
41
ui 39 id
37-
35 0
6
12
18
24
30
WEEKS AFTER EXCIMER PRK FIGURE 3
Mean keratometry (+ SD) values preoperatively and at 3, 6, 12, and 24 weeks.
four cases (9, 11, 12, and 14). Patients 9, 11, and 12 had a haze rating of 2, and all experienced some undercorrection. None of these three patients experienced a significant loss of best corrected vision. Patient 14 also had a stromal haze rating of 2 and an initial overcorrection that regressed. This patient sustained a loss of best corrected vision to 20/50 + 2. In most cases, the haze peaked at 6 to 12 weeks and then diminished slightly. A fine reticulation noted at the stromal interface was seen in all patients. Some
Lindstrom et al
286
ci CO cr_
z
0
cr I
0
WEEKS AFTER PRK FIGURE 4
Mean central ultrasonic pachometry (+ SD) values preoperatively and at 6, 12, and 24 weeks. WJ
4.5-
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3.0
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INTRODUCTION
THE 193-NM EXCIMER
LASER HAS GENERATED GREAT INTEREST BECAUSE
of its potential to eliminate myopia in a brief surgical procedure under topical anesthetic. Most early published studies of this new technology were limited to eyes with less than 8 D of myopia. 12 It had been thought that the deeper ablations needed for larger corrections would result in increased corneal haze. More recent reports using the Summit UV 200 laser (Summit Technologies, Watertown, MA)3,4 and the VISX Model Twenty/Twenty laser (VISX Co, Sunnyvale, CA) reported unpredictable results in attempted corrections over 7 D. This has led investigators to limit attempted corrections to 8 D, and the newer protocols from the US Food and Drug Administration (FDA) limits the phase III photorefractive keratectomy (PRK) trials to corrections between - 1.0 and -6.0 D. *From the Excimer Research Group, Phillips Eye Institute, Metropolitan Mount Sinai Medical Center, Minneapolis, and the Department of Ophthalmology, University of Minnesota School of Medicine, Minneapolis; The Eve Center of Florida, Fort Myers; the Department of Ophthalmology, University of Louisville, and V7eterans Affairs Medical Center, Louisville; and V'ISX Corporation, Sunnvvale, California. This research was supported in part by a grant from Taunton Technologies Co, Monroe, Connecticut (now VISX Co, Sunnyvale, California); Health One Corporation and the Friends of the Phillips Foundation, Minneapolis; and Humana, Inc. TR. AM. OPHTH. Soc. vol. LXXXX, 1992
278
Lindstrom et al
Our early experience with higher myopic corrections has been more favorable. In 1990, we reported our earliest cases with excimer PRK in a phase II study using a 5.0-mm diameter ablation zone and a heavy regimen of topical corticosteroids on seven sighted eyes with myopia ranging from - 5.5 to - 12.0 D.5 We found near-total correction of myopia in these initial patients and minimal regression at 2 years. Our group subsequently performed a phase IIA series of 31 eyes with encouraging results on patients between - 4.5 and - 8.0 D.6 Our experience with phototherapeutic keratectomy (PTK) for scar removal also found that deeper ablations, up to 220 ,Lm, did not induce an unacceptable level of corneal haze.7 This initial success encouraged our groups and the VISX Corp to request from the FDA permission to perform excimer PRK on a small series of patients with very high myopia. We report herein the results of excimer PRK performed on a series of 16 highly myopic eyes ranging from -8.62 to -14.50 D. METHODS PATIENT SELECTION
Patient selection met US FDA8 criteria under an Investigational Device Exemption for this phase IIA study. Patients were at least 18 years old and had myopia between 8.62 and 14.50 D (spherical equivalent) and best corrected visual acuity of 20/60 or better. Because of anisometropia after excimer PRK, the ability to successfully wear a contact lens was a prerequisite. Patients with abnormal corneas, severe dry eyes, blepharitis, or lagophthalmos were excluded. Preoperative and postoperative corneal topography at 1, 3, and 6 months was performed using the Computed Anatomy System (New York) (Minnesota cases), the Eyesys System (Eyesys Labs, Houston) (Kentucky cases), or an integrated digital keratoscope within the laser. If subelinical keratoconus was suggested by corneal topography, the patient was excluded from treatment. Only one eye from each patient was treated. All patients included in the protocol and followed up for at least 6 months were included. There were no cases left to follow up. Patient data are summarized in Table I. INSTRUMENTATION
The laser used in Minneapolis and Fort Myers, FL, was the VISX Model LV 2015 (VISX Co). The laser used in Louisville was a modified VISX Model L 2000, which had laser cavity and output parameters identical to the LV 2015. These lasers were originally manufactured by Taunton Technologies, Monroe, CT, which has merged with VISX Company; the
Photoreactive Keratectomy in High Myopia
279
TABLE I: PATIENT POPULATION DATA
PATIENT NO.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
SITE
Minneapolis Minneapolis Minneapolis Minneapolis Minneapolis Minneapolis Minneapolis Minneapolis Louisville Louisville Louisville Louisville Fort Myers Fort Myers Fort Myers Fort Myers
AGE
SEX
SURGERY DATE
ABLATION DEPTH (,um)
TREATMENT DIAMETER (mm)
74 53 34 47 42 34 21 42 34 27 27 37 22 49 31 66
M F F M F M M M M F F F F M F F
7/10/91 6/26/91 7/08/91 7/24/91 7/31/91 7/24/91 7/29/91 8/22/91 9/04/91 9/04/91 9/11/91 9/25/91 6/28/91 6/28/91 7/12/91 8/21/91
137 223 172 223 199 223 223 230 170 153 180 146 149 180 178 164
6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 5.6 5.6 5.6 5.6 5.5 5.5 5.5 5.5
laser has been fully described by L'Esperance and associates9 10 and by our group.5-7 It utilized an argon-fluoride gas mixture to produce a 193nm wavelength at 10 Hz and was adjusted to deliver a fluence of 100 to 120 mJ/cm2. The entire laser system has a computer control module with an interactive menu, real time monitoring of procedure parameters, and an integrated digital keratoscope. The laser was calibrated prior to each treatment session by ablating standardized plastic discs and measuring ablation depths with a special micrometer gauge. The desired dioptric change was entered into the computer control console. The maximum beam diameter was 5.5 mm, 5.6 mm, or 6.0 mm, depending on the site. A suction device placed within 1 cm of the cornea was used to remove particles in the ejection plume. PREOPERATIVE AND POSTOPERATIVE EXAMINATION
All patients received complete ophthalmologic examinations including slit-lamp photography, topographic analysis, and ultrasonic pachometry, the details of which have been fully described elsewhere.5-7 Contrast sensitivity was tested in Minnesota by forced choice testing using the MCT 8000 (Vistech Consultants, Dayton, OH). Standardized lighting under the day vision protocol was used in all testing. Testing was performed at five spatial frequencies from 1.5 cycles per degree to 18 cycles per degree. The paired Student's t-test was used to compare the values at each frequency to determine statistical significance.
280
Lindstrom et al
Corneal haze was evaluated subjectively for the epithelium (superficial, deep) and the stroma (anterior, posterior) separately using a qualitative scale (0 to 5). A rating of 0 was a clear cornea, 0.5 was barely detectable haze, and 1.0 was mild haze probably not affecting vision. A rating of 2.0 showed moderate haze, probably affecting vision. Objective documentation of haze was provided by standardized slit-lamp photography, including tangential broad beam, thin slit at 45 degrees, broad beam at 45 degrees, and diffuse views. Testing was repeated at 3, 6, 12, and 24 weeks. All refractions, manifest and cycloplegic, were done by one clinical coordinator at each center at similar levels of illumination with notation of pupil size. SURGICAL PROCEDURE
The same surgical technique was performed at all sites. All surgeons at each site have had extensive experience with PRK and have been involved in the trials since 1989. The visual axis was marked with the patient fixating on an internal fixation target coaxial with the surgeons fixating the eye and marking the patient's cornea over the center of the entrance pupil, as suggested by Uozato and Guyton.11 A 6- or 7-mm corneal marker, premarked with blue dye, was centered on the epithelial impression made by the Sinskey hook and was then used to mark the epithelium, which was then gently removed using a Tooke knife. Visualizing the patient's eye through the microscope and video monitors, the surgeon aligned the corneal apex to the lasing plane by adjusting table travel in the X, Y, and Z directions. The eye was sometimes fixated with a forceps. Laser energy was delivered in a series of pulses, predetermined through a rotating series of 15 apertures of diminishing size. The duration of the actual laser emission was 45 to 90 seconds. POSTOPERATIVE REGIMEN
Following the ablation, tobramycin dexamethasone suspension drops (Tobrex, Alcon, Fort Worth, TX) and 5% homatropine hydrobromide (Alcon) were instilled and the eye was patched overnight, or a disposable soft contact lens Vistakon Acuvue (Johnson & Johnson, Claremont, CA) was placed in addition to the patching. In some cases, the contact lens was continued for the first 3 weeks to promote epithelial growth. On the next day, treatment was started on 0.1% fluorometholone (FML Liquifilm, Allergan, Irvine, CA) every 2 hours for the first week, then four times daily for 1 month, and twice daily for the second month; dosage was gradually tapered over the next 2 to 3 months. A 0.3 solution of tobramycin (Tobrex, Alcon) was administered four times daily until the epithelium was healed.
Photoreactive Keratectomy in High Myopia
281
Statistical comparisons utilized a Student's t-test. All mean values are presented with standard deviations. The results will be presented according to guidelines for presenting refractive surgical data as suggested by Waring. 12 RESULTS PATIENT DATA
All cases performed at the three sites with a 6-month follow-up are included. Patient 1 was also included, but PTK protocol for anisometropia was followed. This 74-year-old man had had previous extracapsular cataract surgery and intraocular lens (IOL) implantation and approximately 9 D of anisometropia. He was unable to wear a contact lens due to arthritis. The remainder of the patients had not undergone previous corneal or intraocular surgery. Sixteen eyes in seven male and nine female patients ranging in age from 21 to 74 years were treated. The location, age, date- of treatment, ablation depth, and maximum ablation diameter are listed in Table I. All patients had epithelialized by 4 days postoperatively. It was our clinical impression that the newly healed corneal surface took longer to become smooth than in ablations of lower dioptic corrections. There were no instances of recurrent corneal erosions. REFRACTIVE DATA
Table II lists the manifest refraction, average keratometry, central pachometry, corneal haze scale values, and corrected and uncorrected visions for each patient at 6 weeks, 12 weeks, and 6 months postoperatively. The mean sphere equivalent preoperatively was - 11.59 ± 1.62 D; postoperatively it was + 1.04 + 1. 71 at 6 weeks, - 0.55 ± 2.37 at 12 weeks, and - 0.90 ± 2.13 at 12 months. Fig 1A shows the individual refractive change over time at Minnesota, and Fig 1B shows the changes over time at Kentucky and Florida. Fig 2 shows the attempted versus achieved refraction at 6 months for all three sites. At Minnesota, all eight eyes achieved correction within 2 D of attempted refraction, at Florida three of four cases achieved similar results, and at Kentucky one of four eyes had similar success. Overall, at the 6-month visit, 11 of 16 (69%) were corrected within 2 D of attempted refraction. All cases except two achieved their best corrected preoperative vision within one Snellen line. Patient 14 experienced a loss of vision to 20/50 best corrected. Patient 9 had undercorrection and significant epithelial hyperplasia.
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TABLE II: REFRACTIV'E DATA
V'ISUAL ACUITY PATIENT NO.
I
2
3
4
5
6
7
8
9
10
11
12
'MANIFEST REFRACTION
AV'ERAGE KERATOMETRY
CORNEAL HAZE
BEST CORRECTED
-9.25+ 1.25x 165 + 1.50+ 1.25 x 95 +2.00+0.75x 155 0.00+0.50x 80 - 16.50+3.00x 15 -2.25+ 1.00x 170 -0.75+ 1.25x 145 + 1.25 sph - 10.75+0.75x70 -2.25+ 1.00x 170 -0.75+ 1.50x95 -0.50+ 1.50x95 - 12.00+ 1.25x 80 + 0.25+ 1.25x80 + 0.25+ 1.25x80 0.00+ 1.25x75 - 12.00+0.75x85 + 1.25+0.75x 80 +0.50+0.25x 85 -1.00+1.25x75 - 14.50+ 1.00x 165 +0.75+2.25x 110 +0.50+2.50x 110 0.00+ 1.50x 115 - 13.25+ 1.25x 125 +0.25+3.50x 10 -0.50+2.00x 165 + 1.00+ 1.00x 180 - 14.50+0.50x90 +0.25+ 1.50x70 - 1.00+ 1.75x 75 - 1.50+0.75x65 -12.25+ 1.50x 105 -2.00+ 1.00x 135 -3.50+ 1.75x90 -4.25+ 1.75x 105 -10.25 sph -2.25 sph -5.00 sph -4.50 sph - 12.25+ 1.00x55 0.00+0.50x95 -3.00+0.75x90 -4.00+0.50x 100 10.50+ 1.00x60 -2.25+0.25x 105 1.00+0.75x 105 -3.75+ 1.00x65
43.37 36.25 37.00 35.75 45.25 37.87 37.12 37.00 45.25 36.75 37.50 38.75 46.63 37.00 37.00 38.12 47.50 39.50 39.43 40.43 45.50 35.87 36.38 36.63 47.12 40.50 40.75 36.75 45.75 37.87 38.37 37.87 44.00 40.12 40.50 40.75 42.50
0.0 0.5 0.5 0.5 0.0 1.0 1.0 0.5 0.0 0.5 0.0 0.0 0.0 1.0 1.0 1.0 0.0 1.5 0.5 0.5 0.0 0.5 0.5 0.0 0.0 1.5 1.0 1.0 0.0 1.5 0.5 1.0 0.0 1.0 1.0 2.0 0.0 1.0 1.5 1.5 0.0 1.0 2.0 2.0 0.0 1.0 1.5 2.0
20/30 20/25 20/40 20/25 20/40 20/40 20/40 20/30 20/30 20/25 20/25 20/25 20/40 20/20 20/20 20/20 20/20
V'ISIT
Preop 6 wk 12 wk 6 mo Preop 6 wk 12 wk 6 mo Preop 6 wk 12 wk 6 mo Preop 6 wk 12 wk 6 mo Preop 6 wk 12 wk 6 mo Preop 6 wk 12 wk 6 mo Preop 6 wk 12 wk 6 mo Preop 6 wk 12 wk 6 mo Preop 6 wk 12 wk 6 mo Preop 6 wk 12 wk 6 mo Preop 6 wk 12 wk 6 mo Preop 6 wk 12 wk 6 mo
-
-
42.62 42.62 47.00 40.00 42.68 42.25
48.37 42.25 42.87 45.00
20/25 20/20 20/25 20/20 20/20 20/20 20/25 20/50 20/30 20/30 20/20 20/25 20/25 20/20 20/20 20/25 20/25 20/20 20/20 20/20 20/20 20/20 20/20 20/25 20/25 20/25 20/20 20/30 20/20 20/20
UNCORB,ECTED C]F 20/]'100 20/'40 20/] 30 C]F 20/W30 20/'50 20/'40 C]F 20/] 30 to 20/] 30 20/ C. F 20/'40 20/'40 20/.20 CF 20/'50 20/b 40 20/,25 CF 20/'40 20/] 30 20/'40 CF
20/4 '0 20/P30 20/] 30 CF
20/'40 20/'40 20/] 30 CF 20/'50
20/4 '0 20/ 200 CF 20/l50 20/'400 CF CF 20/,25 20/ 50 20/'200 CF 20/, 40 20/'50 20/ so
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TABLE II: REFRACTIVE DATA CONT'D
V'ISUAL ACUITY PATIENT NO.
13
14
15
16
REFRACTION
AVERAGE KERATOMETRY
CORNEAL HAZE
BEST CORRECTED
UNCORRECTED
-10.25 sph +1.00+2.50x20 - 6.00 + 0.50 x 30 -4.25+0.75x 15 -12.00 sph +3.75+2.25x68 +1.00+2.00x70 + 0.50+2.50x 150 -12.75+ 1.50x 106 + 1.00 sph -0.25+0.50x 126 -1.00+0.50x 105 -11.00 sph -0.50+1.75x88 -0.75+2.00x76 -1.00+2.25x76
44.87 40.12 42.50 41.94 43.87 36.00 42.31 38.25 44.12 37.75 38.75 38.25 45.12 37.00 38.37 37.62
0.0 1.0 0.5 1.0 0.0 1.0 2.0 2.0 0.0 1.0 1.0 1.0 0.0 0.5 0.0 0.0
20/15 20/30 20/20 20/20 20/20 20/25 20/50 20/50 20/25 20/30 20/30 20/30 20/20 20/30 20/30 20/30
CF 20/30 20/400 20/200 CF 20/200 20/100 20/70 CF 20/30 20/30 20/30 CF 20/70 20/70 20/80
MANIFEST
V'ISIT
Preop 6 wk 12 wk 6 mo Preop 6 wk 12 wk 6 mo Preop 6 wk 12 wk 6 mo Preop 6 wk 12 wk 6 mo
CF, count fingers. ASTIGMATISM
There was no significant change in preoperative and postoperative refractive cylinder at 6 months (2-sided t-test). MEAN KERATOMETRY VALUES
Mean keratometry values measured before surgery and at various postoperative intervals are shown in Fig 3. The preoperative mean keratometry was 45.39 + 1.61 and the mean postoperative value at 6 months was 39.25 + 2.61 D, indicating considerable corneal flattening. PACHOMETRY VALUES
Pachometry values at these intervals are plotted in Fig 4. NMean preopera+ 39, and mean postoperative value at 24 weeks was
tive value was 542 450 + 48. CORNEAL HAZE
Corneal haze readings are listed in Table II and summarized in Fig 5. The mean haze scores for the epithelium and stroma are shown over time. The highest scores observed in the epithelium or stroma for an individual patient are presented in Table II and were used to compute the mean values. Corneal clarity readings at 6 months of 1.5 or less were seen in all but
284
Lindstrom et al PT 1 MN PT 2 MN PT 3 MN PT 4 MN PT 5 MN PT 6 MN PT 7 MN PT 8 MN
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Change in refraction (spherical equivalent) after excimer PRK for each patient at 6, 12, and 24 weeks at each site. A, NMinnesota; B, Kentucky; C, Florida. Dotted lines represent + 2 D from emmetropia.
Photoreactive Keratectomy in High Myopia
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ATTEMPTED CORRECTION, SPH EQUIV, D FIGURE 2
Attempted refraction (sphere equivalent) versus achieved refraction at 6 months for three sites. MN, Minnesota; FL, Florida; KY, Kentucky.
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Mean keratometry (+ SD) values preoperatively and at 3, 6, 12, and 24 weeks.
four cases (9, 11, 12, and 14). Patients 9, 11, and 12 had a haze rating of 2, and all experienced some undercorrection. None of these three patients experienced a significant loss of best corrected vision. Patient 14 also had a stromal haze rating of 2 and an initial overcorrection that regressed. This patient sustained a loss of best corrected vision to 20/50 + 2. In most cases, the haze peaked at 6 to 12 weeks and then diminished slightly. A fine reticulation noted at the stromal interface was seen in all patients. Some
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Mean central ultrasonic pachometry (+ SD) values preoperatively and at 6, 12, and 24 weeks. WJ
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