A C T A 0 P H T H A L M 0 LOG I C A
70 (1992) 427-433
Contrast visual acuities in cataract patients II. After IOL implantation Hiroko Miyajima’,2, Osamu Katsumi3x4,Tomoko Ogawa’>* and Guang Ji-Wang3 National Saitama Hospital’, Saitama, Japan, Department of Ophthalmology*,Keio University School of Medicine, Tokyo,Japan, Schepens Eye Research Institute3,and Department of Ophthalmology, Harvard Medical School4,Boston, MA, USA
Abstract. Contrast visual acuities were measured in 100 eyes of 75 patients who attained a best-corrected visual acuity of 20.8 (20125) after intraocular lens (IOL) implantation. The variable contrast visual acuity chart (VCVAC), with three contrast levels of 90, 15, and 2.5% and reverse polarity of 90%contrast, was used to measure contrast visual acuities. The follow-up period ranged from 3 to 35 months (mean 7.41). The mean visual acuities measured with the 90, 15, and 2.5% charts were 0.92 (SD = O.ll), 0.59 (SD = 0.13), and 0.33 (SD = 0.14), respectively. The mean visual acuity measured with the 90% reverse polarity chart was 0.97 (SD = 0.11). The decreases in visual acuities compared with the 90% contrast were 0.64 and 1.48 octaves in the 15% and the 2.5% contrast charts, respectively. The pattern of the contrast acuity profile was comparable to normal subjects, but in 28 of 100 (28%) eyes, the visual acuities measured with the reverse polarity chart were slightly better than those measured with the standard 90% contrast chart, suggesting that the glare effect still exists after IOL implantation, though to a lesser degree than in cataractous eyes.
Key words: cataract - contrast sensitivity function - contrast visual acuity - glare - intraocular lens implantation.
Clinically, it is well known that early-cataract patients complain of difEculty seeing objects in the presence of a glare source, such as driving at night or viewing objects in bright daylight.The light rays entering the eyes are dif€racted by small lens opacities, resulting in visual impairment with discrimination of the low- to medium-contrast ob-
jects. However, when these early-cataract patients are evaluated with the high-contrast visual acuity charts, their visual acuities are generally good and do not correlate with their visual disabilities (Neumann et al. 1988). Numerous important studies, both clinical and basic, have been undertaken regarding this subject. In addition to the standard Snellen acuity test, the importance of a contrast sensitivity function test or a contrast visual acuity test with or without the glare source is now being emphasized. We previously analyzed the changes in the contrast acuity profile in both normal subjects and cataract patients with the variable contrast visual acuity chart (VCVAC) (Miyajima et al. 1992) and found that in cataract patients, a significant visual acuity decrease was observed when they were evaluated with the intermediate- and low-contrast optotypes. In the present study, as a’continuation of the previous study, we measured contrast acuity profiles in patients after successful intraocular lens (IOL) implantations and analyzed whether these IOL patients regained the visual function found in normal subjects of corresponding ages.
Subjects and Methods Subjects A total of 75 patients (100 eyes) (33 males, 42 females; aged 40-81 years; mean 65.58) who attained
427
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60
70
80
90
CHART 1 CHART 4 CHART 2 CHART3
AGE (Years)
Fig. 1. Age distribution of study patients. The abscissa shows the age, and the ordinate denotes the number of cases.
a best-corrected visual acuity of 2 0.8 (20/25) after IOL implantation using the Landolt ring were selected for inclusion in this study. The selection of 0.8 as the lower level of visual acuity was made because we were interested in the visual performance of those who attained good visual acuity after IOL implantation. Fig. 1 shows the age distribution at the time of the visual acuity examination. Patients who had either intra- or postoperative complications were excluded. Similar to the selection criteria used in the previous study, subjects with corned, vitreal, and retinal pathologies, especially in the macula, were excluded. Patients with myopia > 5.0 diopters also were excluded. The follow-up period after IOL implantation ranged from 3 to 35 months (mean 7.41; SD = 6.54). Those patients whose follow-up was < 3.0 months were excluded &om this study because of the possible effect of surgical intervention.
Fig. 2. The line graph shows the results of the contrast visual acuity test in 100 eyes. The abscissashows the chartsused, and the ordinate indicates the visual acuity in parentheses and acuity levels expressed in geometric progression (Holladay & Prager 1991). The dashed lines indicate the upper and lower limits of acuity in normal subjects.
the system consists of charts 1-4: a standard, highcontrast chart (go%), an intermediate-contrast chart (15%), a low-contrast chart (2.50/0),and a reverse polarity chart (90%).In the last, the contrast is the same as the standard 90% contrast chart, but instead of black optotypes on a white background, the reverse is printed. Two E optotypes on 13 different visual acuity levels ranging from 2.0 to 0.12 are used at a 366 cm testing distance. The visual acuity levels are arranged in geometric progression so that three acuity levels are equivalent to 1.0 octave. Acuity level 13 corresponds to 2.0, and acuity level 10 to 1.0. Acuity levels 7,4, and 1 correspond to the visual acuities of 0.48, 0.24, and 0.12, respectively. Surgical procedure
Methods Visual acuity testing was performed to obtain the best distant visual acuity with optical correction when required. The amount of optical correction (spherical equivalence: diopter of spherical lens plus half of the cylindrical lens) required to attain the best distant vision ranged from -4.00 to +3.50 diopters (mean +0.5; SD = 1.44). Contrast visual acuity was measured with the VCVAC. The technical details have been described previously p a n g & Pomerantzeff 1991). Briefly, 428
In all cases, the cataract operation was performed under local anesthesia by one surgeon (HM).After a fornix-based conjunctival flap was made, a scleral lamellar dissection was performed, starting 2 mm behind the limbus. Continuous circular capsulorhexis followed by hydrodissection was performed and then phacoemulsification (Alcon 10 000 Master, Alcon Inc, Forth Worth, TX,USA). The cortex was removed by irrigationlaspiration, and HealonTM(sodium hyaluronate, Kabi Pharmacia AB, Uppsala, Sweden) was injected into the anterior chamber. A posterior chamber lens was inserted in
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Fig 3A-D. The bar histograms show the distributionof visual acuity levels in study eyes from charts 1,4,2,and 3, respectively.The abscissa shows the visual acuity levels expressedin geometric progressionand the ordinate denotes the number of cases.
the bag, and the Healon was aspirated. The wound was closed with a 10-0 nylon suture. Determination of IOL power
To determine the IOL power, the biometry was performed with the A-scan ultrasonographic analyzer (Model Alpha 20/20, Storz Inc, St. Louis, Mo, USA). To calculate the IOL power, the SRK formula developed by Retzlaff et al. (1981) was used. The types of IOLs implanted were plano or planoconvex (n = 65) and bi-convex (n = 35). Analysis of visual results
The results of the visual acuity examination were analyzed with the one-way analysis of variance test (ANOVA).The statistical treatment of visual acuity was based on the geometric measure (Holladay & Prager 1991). When the overall F-test was signifi-
cant, Scheffe's method of multiple comparison was used to compare the visual acuity between the charts. A p value of < 0.05 was considered statistically significant.
Results Visual acuity
Fig. 2 shows the results of contrast visual acuity testing in each of the 100 patients after posterior chamber IOL implantation. The visual acuities, measured with charts 1-4, respectively, were as follows: 0.92 (SD = O.ll), 90% high-contrast chart; 0.59 (SD = 0.12), 15%intermediate-contrast chart; 0.33 (SD = 0.14), 2.5% low-contrast chart; and 0.97 ( ~ ~ = 0 . 1 190% ) , reverse polarity chart. The distribution of the visual acuities 429
Chart 1 VS. Chart 4
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CHANGEOFACUITY LEVELS
measured with these four charts is comparable to that of the normals, but there were differences in acuities, especially those measured with intermediate- and low-contrast optotypes. Visual acuity distribution
Fig. 3A-D shows the distribution of visual acuity levels measured with charts 1-4. In chart 1 the visual acuities ranged from levels 8 (0.60) to 12 (1.5), with a peak level 10 (1.0). In chart 4, the visual acuities ranging from levels 8 (0.60) to 13 (2.0) also peaked at level 10. In chart 2, the visual acuity ranged from levels 5 (0.30) to 11 (1.2), and levels 1 (0.12) to 9 (0.75) in chart 3. The range of visual acuity (poorest vs. best) increased from four acuity levels (1.33 octaves) in chart 1 and five acuity levels in chart 4 (1.67 octaves) to six acuity levels (2.0 octaves) in chart 2 and eight acuity levels (2.67 octaves) in chart 3, showing a wider range of acuity differences with the low-contrast optotypes. 430
Fig. 4A-C. The bar histograms show the decline of visual acuity measured with charts 4,2, and 3, respectively, compared with the 90%high-contrast chart (chart 1). The abscissa shows the changes of visual acuity levels compared with the high-contrastchart. Acuity level changes were calculated based on geometric measures (Holladay & Prager 1991).The positive values indicate the decrease of visual acuity compared with the high-contrast chart, and the negative values denote the increase of visual acuity compared with the high-contrast chart.
Reduction of visual acuity in lower contrast optotypes
Fig. 4A-C show the reduction of visual acuity compared with the 90% high-contrast chart. Fig. 4A shows the results between charts 1 and 4 (90% reverse polarity). In this comparison, the visual acuities measured with chart 4 were either equal to (n = 72) or better than (n = 28) those measured with chart 1. The change of visual acuity was between 0 to -1 acuity level (mean -0.2; SD = 0.36), which is equivalent to 0.067 octave. The difference in visual acuities between these two charts was not statistically significant (Scheffe’s F-test = 1.135). Fig. 4B shows the results of a comparison between the visual acuities measured with charts 1 and 2 (15% intermediate-contrast chart). The visual acuities measured with chart 2 were either equal to (n=13) or lower (n=87) than those measured with chart 1. The reduction of visual acuity ranged &om 0 to 5 acuity levels (mean 1.93;
0
Normal Subjects
Lens type and visual acuity difference
Cataract (Pre-Op)
W
Cataract (IOL)
The reduction of the visual acuity level was analyzed by subdividing the 100 eyes into two groups, those receiving bi-convex IOLs (n = 35) and those receiving the plano or plano-convex IOLs (n = 65). When comparing the visual acuity results between charts 1 and 4,3 of 35 patients (8.57%)with bi-convex IOLs showed better visual acuities when measured with chart 4; 22 of 65 patients (33.8%) with the plano or plano-convex lens showed better visual acuities when measured with chart 4 compared with chart 1 (Chi square = 7.75; p < 0.05).
Discussion Cataract is the most frequently occurring eye disorder encountered by ophthalmologists.The treatment has been documented historically. However, compared with the numerous reports on its mode of treatment, until recently, relatively little attention had been paid to the visual disabilities resulting from cataract, especially in the early stages of the disease. The cataract examination previously was limited to the visual acuity examination using the high-contrast optotypes. In the early stages of the disease, the visual acuity results and patients’ vis~ ~ = 0 . 9 9which ), is equivalent to 0.64 octave. The visual acuities measured with chart 1 were signifi- ual complaints often do not agree. Hess & Woo cantly higher than those measured with the 15% (1978)issued the first report on the loss of contrast intermediate-contrast chart (chart 2) (Scheffe’s sensitivity function in cataract patients. Since then, studies on the visual disabilities of cataract paF-test = 116.934; p < 0.05). Fig. 4C shows the results of the comparison be- tients using the contrast sensitivity function with a tween charts 1 and 3 (the 2.5% low-contrast chart), glare source have followed (Paulsson & Sjostrand in which the visual acuities measured with chart 1 1980; Abrahamsson & Sjostrand 1984; Hirsch et al. 1984; Koch 1989; Elliott et al. 1989).Their common were better than those measured with chart 3 in frndings are that cataract patients, even during the all 100 eyes. The visual acuity dif€erences ranged from 2 to 8 acuity levels (mean 4.44; ~ ~ = 1 . 3 1 ) ,early stage of the disease, have difficulty detecting which is equivalent to 1.48 octaves. The visual acui- intermediate- to low-contrast objects, especially in ties measured with the high-contrast chart were the presence of a glare source. We previously compared the visual perforsignificantly higher than those measured with the low-contrast chart (Scheffe’s F-test = 671.448; mances of normal subjects and cataract patients in detecting the intermediate- and low-contrast optop < 0.05). types (Miyajima et al. 1992). We found that the reFig. 5 summarizes the visual acuity changes in normal, cataractous, and IOL eyes. In eyes with duction of visual acuity with the intermediate- and IOLs, the visual acuity measured with the inter- low-contrast optotypes is sigmficantly greater in cataract patients than normal subjects. In the presmediate- and low-contrast charts resulted in a value that fell between those of the normal and ent study, the reduction of visual acuity with the intermediate- and low-contrast charts compared cataractous eyes. An increase of visual acuity with chart 4 also was observed, though to a lesser de- with the high-contrast chart was 0.64 and 1.48 octaves, respectively, in the IOL patients. When comgree than with the cataractous eyes. CHART 2
CHART 3 CHART 4 Fig. 5. The bar histogram shows the changes of visual acuities measured with the intermediate (15%), low (2.5O/o), and reverse polarity charts. The negative values indicate that the visual acuity decreased when compared with the 90% high-contrastchart. Acuity level changes were calculated based on geometric measures.
431
pared with the reduction in normal and cataractous eyes reported previously, the reductions were 0.52 and 0.71 octaves with the intermediate-contrast charts and 1.21 and 1.75 octaves with the lowcontrast charts. The reduction of visual acuity levels in the IOL patients fell between the values of the normal and cataract patients with the intermediate- and low-contrast charts. Regarding recovery of the visual function after IOL implantation, the improvement of mesopic vision and the lessening of glare after cataract surgery have been reported by Masket (1989)and Weiss (1990). Other important findings relate to the results obtained with the reverse polarity chart. Twentytwo of 40 eyes (55%)of cataract patients showed better visual acuities when measured with the reverse polarity chart; in normal subjects, no differences were observed (Miyajima et al. 1992). In the present study, even though the acuity level difference was limited to one level, 28 of 100 eyes (2800)showed better acuity when measured with the reverse polarity chart, a finding similar to that of the cataractous eyes. However, the dif€erence of visual acuity was 0.07 octave, which is considerably smaller than the 0.22 octave of the cataractous eyes. We also found that the range of visual acuity (poorest vs. best) was wider in the IOL eyes (5-8 acuity levels) than the normal subjects reported previously (3-5 acuity levels).Despite the recovery of visual acuity, these results suggest that patient detection of intermediate- to low-contrast optotypes still is slightly lower than in normal subjects. With the reverse polarity chart, the glare effect still seems to be a factor in the IOL patients, although to a lesser degree when compared with the cataractous eyes. When comparing visual function between the normal subjects and IOL patients, after testing 110 pseudophakic patients, LeClaire et al. (1982) found significantly more glare in the pseudophakic patients compared with the normal subjects. Van der Heijde et al. (1985)reported that the IOLs scatter light about 2.3 times more than healthy human lenses. Our results, that 28 of 100 (28%)eyes with successful posterior chamber IOL implantation still showed better acuity with the reverse polarity chart, may suggest the residual effect of optical glare. Tagami et al. (1986) reported the increased glare sensitivity in posterior chamber IOL cases, and Nakaizumi et al. (1989)reported a loss of high-frequency contrast sensitivity in certain posterior chamber IOL cases. 432
The reason for the slightly lower contrast discrimination in patients with IOLs compared with the normal subjects may be multifactorial, as already mentioned by Howe et al. (1986)and Tagami et al. (1986). Factors to be considered are, among others, the effect of corneal endothelium, minute deposits on the lens surface, opacities in the posterior capsule, and pupil size. Understanding the effects of these factors requires future clinical and basic research. One interesting finding in this study was that less glare effect was observed with patients who had bi-convex IOLs. Wang & Pomerantzeff (1982) reported that the bi-convex IOL is superior to the plan0 or plano-convex designs. Since the shape of the lens is convex, the light intensity within the eye is less, resulting in less glare effect and better contrast discrimination. Hammer et al. (1986) reported better spectral sensitivity in patients who had IOLs with an ultraviolet absorbing filter than those without it. They reported that the toxic effect of short wavelength light rays is a causative factor, but we speculate that less intraocular light scatter due to the elimination of the short wavelength may be another contributing factor as reported by Zigman (1989).Analysis of this factor was beyond the scope of this study, but it is an important area that needs consideration. Another limitation of this study is that we did not monitor the changes of contrast visual acuities in the same subject. Analyzing the pre- and postoperative changes in the contrast acuity profiles would provide information to enable us to predict the postoperative visual improvement. In conclusion, we found that the contrast acuity profile of the IOL eyes was comparable to that of the normal eyes. However, the residual effect of glare still was observed. Analysis of this small difference in visual performance, which we consider to be multifactorial, requires further clinical and basic research.
Acknowledgments We are deeply indebted to Charles L. Schepens, MD, of the Schepens Eye Research Institute for his support in this investigation. We appreciate the constructive criticism provided by Tatsuo Hirose, MD. Lynda Charters edited the manuscript. This study was supported by a grant from the Kimmelman Foundation (New York, NY) and the Nihon Tenganyaku Institute (Nagoya,Japan).
This study was presented in part at the Annual Association for Research in Vision and Ophthalmology meeting in Sarasota, FL, May 1991.
References Abrahamsson M & Sjostrand J (1984): Impairment of contrast sensitivity function (CSF) as a measure of disability glare. Invest Ophthalmol Vis Sci 2 7 11311136. Elliott D B, Gilchrist J & Whitaker D (1989):Contrast sensitivity and glare sensitivity changes with three types of cataract morphology: are these techniques necessary in a clinical evaluation of cataract? Ophthalmic Physiol Opt 9: 25-30. Hammer H M, Yap M & Wetherhill J R (1986):Visual performances in pseudophakia with standard and ultraviolet-absorbing intraocular lenses: a preliminary report. Trans Ophthalmol Soc UK 105: 441-446. Hess R F & Woo G (1978):Vision through cataracts. Invest Ophthalmol Vis Sci 17: 428-435. Hirsch R P, Nadler M P & Miller D (1984):Clinical performance of a disability glare tester. Arch Ophthalmol 102: 1633-1636. HolladayJ T & Prager T C (1991): Mean visual acuity. Am J Ophthalmol 111: 372-374. Howe J W, Mitchell K W, Mahabaleswara M & Abdel-Khalek M N (1986): Visual evoked potential latency and contrast sensitivity in patients with posterior chamber intraocular lens implants. Br J Ophthalmol 70: 890894. Koch D D (1989):Glare and contrast sensitivity testing in cataract patients. J Cataract Refract Surg 15: 158-164. LeClaire J, Nadler M P, Weiss S & Miller D (1982):A new glare tester for clinical testing. Results comparing normal subjects and variously corrected aphakic patients. Arch Ophthalmol 100: 153-158. Masket S (1989):Reversal of glare disability after cataract surgery.J Cataract Refract Surg 15: 165-168. Miller D, Jernigan M E, Molnar S, Wolf E & Newman J (1972):Laboratory evaluation of a clinical glare tester. Arch Ophthalmol87 324-332. Miyajima H, Katsumi 0 & Wang G J (1992):Contrast visual acuities in cataract patients. I. Comparison with normal subjects. Acta Ophthalmol (Copenh) 70: 44-52.
28 Acta Ophthal. 70.4
Nakaizumi Y, Kojima A & Ichikawa N (1989): Contrast sensitivity measured with intraocular lens implantation. IOL (Japanese) 3: 133-137. Neumann A C, McCarty G R, Steedle T 0,Sanders D R & Raanan M G (1988):The relationship between indoor and outdoor Snellen visual acuity in cataract patients. J Cataract Refract Surg 14: 35-39. Paulsson L E & Sjostrand J (1980):Contrast sensitivity in the presence of a glare light. Theoretical concepts and preliminary studies. Invest Ophthalmol Vis Sci 19: 401406. Retzlaff J, Sanders D & Kraff M (1981): A manual of implant power calculation. SRK'" formula. Retzlaff, Sanders, and Kraff, Medford, Oregon. Tagami Y, Okazaki S, Kitagaki K, Matsumi J, Yamanaka A, Ikeuchi T & Murai M (1986):Measurement of glare sensitivity in pseudophakic eyes via Arden's Grating Chart. Folia Ophthalmol Jpn 37: 693-697. Van der Heijde G L, Weber J & Boukes R (1985):Effect of stray light on visual acuity in pseudophakia. Doc Ophthalmol59: 81-84. Wang G-J & Pomerantzeff 0 (1991): A new set of variablecontrast visual acuity charts. Optom Vis Sci 68: 34-40. Wang G-J & Pomerantzeff 0 (1982): Obtaining a highquality retinal image with a biconvex intraocular lens. Am J Ophthalmol 94: 87-90. Weiss J F (1990): Glare and mesopic vision before and after cataract surgery. J Cataract Refract Surg 16: 88-91. Zigman S (1989): Vision enhancement using a short wavelength-light absorbing fiter. Optom Vis Sci 67: 100104.
~
~
Received on December llth, 1991. Author's address: Hiroko Miyajima, MD, Department of Ophthalmology, Keio University School of Medicine, 35 Shinanomachi, Shinjuku-ku, Tokyo 160 Japan.
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70 (1992) 427-433
Contrast visual acuities in cataract patients II. After IOL implantation Hiroko Miyajima’,2, Osamu Katsumi3x4,Tomoko Ogawa’>* and Guang Ji-Wang3 National Saitama Hospital’, Saitama, Japan, Department of Ophthalmology*,Keio University School of Medicine, Tokyo,Japan, Schepens Eye Research Institute3,and Department of Ophthalmology, Harvard Medical School4,Boston, MA, USA
Abstract. Contrast visual acuities were measured in 100 eyes of 75 patients who attained a best-corrected visual acuity of 20.8 (20125) after intraocular lens (IOL) implantation. The variable contrast visual acuity chart (VCVAC), with three contrast levels of 90, 15, and 2.5% and reverse polarity of 90%contrast, was used to measure contrast visual acuities. The follow-up period ranged from 3 to 35 months (mean 7.41). The mean visual acuities measured with the 90, 15, and 2.5% charts were 0.92 (SD = O.ll), 0.59 (SD = 0.13), and 0.33 (SD = 0.14), respectively. The mean visual acuity measured with the 90% reverse polarity chart was 0.97 (SD = 0.11). The decreases in visual acuities compared with the 90% contrast were 0.64 and 1.48 octaves in the 15% and the 2.5% contrast charts, respectively. The pattern of the contrast acuity profile was comparable to normal subjects, but in 28 of 100 (28%) eyes, the visual acuities measured with the reverse polarity chart were slightly better than those measured with the standard 90% contrast chart, suggesting that the glare effect still exists after IOL implantation, though to a lesser degree than in cataractous eyes.
Key words: cataract - contrast sensitivity function - contrast visual acuity - glare - intraocular lens implantation.
Clinically, it is well known that early-cataract patients complain of difEculty seeing objects in the presence of a glare source, such as driving at night or viewing objects in bright daylight.The light rays entering the eyes are dif€racted by small lens opacities, resulting in visual impairment with discrimination of the low- to medium-contrast ob-
jects. However, when these early-cataract patients are evaluated with the high-contrast visual acuity charts, their visual acuities are generally good and do not correlate with their visual disabilities (Neumann et al. 1988). Numerous important studies, both clinical and basic, have been undertaken regarding this subject. In addition to the standard Snellen acuity test, the importance of a contrast sensitivity function test or a contrast visual acuity test with or without the glare source is now being emphasized. We previously analyzed the changes in the contrast acuity profile in both normal subjects and cataract patients with the variable contrast visual acuity chart (VCVAC) (Miyajima et al. 1992) and found that in cataract patients, a significant visual acuity decrease was observed when they were evaluated with the intermediate- and low-contrast optotypes. In the present study, as a’continuation of the previous study, we measured contrast acuity profiles in patients after successful intraocular lens (IOL) implantations and analyzed whether these IOL patients regained the visual function found in normal subjects of corresponding ages.
Subjects and Methods Subjects A total of 75 patients (100 eyes) (33 males, 42 females; aged 40-81 years; mean 65.58) who attained
427
20
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60
70
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90
CHART 1 CHART 4 CHART 2 CHART3
AGE (Years)
Fig. 1. Age distribution of study patients. The abscissa shows the age, and the ordinate denotes the number of cases.
a best-corrected visual acuity of 2 0.8 (20/25) after IOL implantation using the Landolt ring were selected for inclusion in this study. The selection of 0.8 as the lower level of visual acuity was made because we were interested in the visual performance of those who attained good visual acuity after IOL implantation. Fig. 1 shows the age distribution at the time of the visual acuity examination. Patients who had either intra- or postoperative complications were excluded. Similar to the selection criteria used in the previous study, subjects with corned, vitreal, and retinal pathologies, especially in the macula, were excluded. Patients with myopia > 5.0 diopters also were excluded. The follow-up period after IOL implantation ranged from 3 to 35 months (mean 7.41; SD = 6.54). Those patients whose follow-up was < 3.0 months were excluded &om this study because of the possible effect of surgical intervention.
Fig. 2. The line graph shows the results of the contrast visual acuity test in 100 eyes. The abscissashows the chartsused, and the ordinate indicates the visual acuity in parentheses and acuity levels expressed in geometric progression (Holladay & Prager 1991). The dashed lines indicate the upper and lower limits of acuity in normal subjects.
the system consists of charts 1-4: a standard, highcontrast chart (go%), an intermediate-contrast chart (15%), a low-contrast chart (2.50/0),and a reverse polarity chart (90%).In the last, the contrast is the same as the standard 90% contrast chart, but instead of black optotypes on a white background, the reverse is printed. Two E optotypes on 13 different visual acuity levels ranging from 2.0 to 0.12 are used at a 366 cm testing distance. The visual acuity levels are arranged in geometric progression so that three acuity levels are equivalent to 1.0 octave. Acuity level 13 corresponds to 2.0, and acuity level 10 to 1.0. Acuity levels 7,4, and 1 correspond to the visual acuities of 0.48, 0.24, and 0.12, respectively. Surgical procedure
Methods Visual acuity testing was performed to obtain the best distant visual acuity with optical correction when required. The amount of optical correction (spherical equivalence: diopter of spherical lens plus half of the cylindrical lens) required to attain the best distant vision ranged from -4.00 to +3.50 diopters (mean +0.5; SD = 1.44). Contrast visual acuity was measured with the VCVAC. The technical details have been described previously p a n g & Pomerantzeff 1991). Briefly, 428
In all cases, the cataract operation was performed under local anesthesia by one surgeon (HM).After a fornix-based conjunctival flap was made, a scleral lamellar dissection was performed, starting 2 mm behind the limbus. Continuous circular capsulorhexis followed by hydrodissection was performed and then phacoemulsification (Alcon 10 000 Master, Alcon Inc, Forth Worth, TX,USA). The cortex was removed by irrigationlaspiration, and HealonTM(sodium hyaluronate, Kabi Pharmacia AB, Uppsala, Sweden) was injected into the anterior chamber. A posterior chamber lens was inserted in
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Fig 3A-D. The bar histograms show the distributionof visual acuity levels in study eyes from charts 1,4,2,and 3, respectively.The abscissa shows the visual acuity levels expressedin geometric progressionand the ordinate denotes the number of cases.
the bag, and the Healon was aspirated. The wound was closed with a 10-0 nylon suture. Determination of IOL power
To determine the IOL power, the biometry was performed with the A-scan ultrasonographic analyzer (Model Alpha 20/20, Storz Inc, St. Louis, Mo, USA). To calculate the IOL power, the SRK formula developed by Retzlaff et al. (1981) was used. The types of IOLs implanted were plano or planoconvex (n = 65) and bi-convex (n = 35). Analysis of visual results
The results of the visual acuity examination were analyzed with the one-way analysis of variance test (ANOVA).The statistical treatment of visual acuity was based on the geometric measure (Holladay & Prager 1991). When the overall F-test was signifi-
cant, Scheffe's method of multiple comparison was used to compare the visual acuity between the charts. A p value of < 0.05 was considered statistically significant.
Results Visual acuity
Fig. 2 shows the results of contrast visual acuity testing in each of the 100 patients after posterior chamber IOL implantation. The visual acuities, measured with charts 1-4, respectively, were as follows: 0.92 (SD = O.ll), 90% high-contrast chart; 0.59 (SD = 0.12), 15%intermediate-contrast chart; 0.33 (SD = 0.14), 2.5% low-contrast chart; and 0.97 ( ~ ~ = 0 . 1 190% ) , reverse polarity chart. The distribution of the visual acuities 429
Chart 1 VS. Chart 4
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Chart 1 VS. Chart 2
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. .
’
’
.I
CHANGEOFACUITY LEVELS
measured with these four charts is comparable to that of the normals, but there were differences in acuities, especially those measured with intermediate- and low-contrast optotypes. Visual acuity distribution
Fig. 3A-D shows the distribution of visual acuity levels measured with charts 1-4. In chart 1 the visual acuities ranged from levels 8 (0.60) to 12 (1.5), with a peak level 10 (1.0). In chart 4, the visual acuities ranging from levels 8 (0.60) to 13 (2.0) also peaked at level 10. In chart 2, the visual acuity ranged from levels 5 (0.30) to 11 (1.2), and levels 1 (0.12) to 9 (0.75) in chart 3. The range of visual acuity (poorest vs. best) increased from four acuity levels (1.33 octaves) in chart 1 and five acuity levels in chart 4 (1.67 octaves) to six acuity levels (2.0 octaves) in chart 2 and eight acuity levels (2.67 octaves) in chart 3, showing a wider range of acuity differences with the low-contrast optotypes. 430
Fig. 4A-C. The bar histograms show the decline of visual acuity measured with charts 4,2, and 3, respectively, compared with the 90%high-contrast chart (chart 1). The abscissa shows the changes of visual acuity levels compared with the high-contrastchart. Acuity level changes were calculated based on geometric measures (Holladay & Prager 1991).The positive values indicate the decrease of visual acuity compared with the high-contrast chart, and the negative values denote the increase of visual acuity compared with the high-contrast chart.
Reduction of visual acuity in lower contrast optotypes
Fig. 4A-C show the reduction of visual acuity compared with the 90% high-contrast chart. Fig. 4A shows the results between charts 1 and 4 (90% reverse polarity). In this comparison, the visual acuities measured with chart 4 were either equal to (n = 72) or better than (n = 28) those measured with chart 1. The change of visual acuity was between 0 to -1 acuity level (mean -0.2; SD = 0.36), which is equivalent to 0.067 octave. The difference in visual acuities between these two charts was not statistically significant (Scheffe’s F-test = 1.135). Fig. 4B shows the results of a comparison between the visual acuities measured with charts 1 and 2 (15% intermediate-contrast chart). The visual acuities measured with chart 2 were either equal to (n=13) or lower (n=87) than those measured with chart 1. The reduction of visual acuity ranged &om 0 to 5 acuity levels (mean 1.93;
0
Normal Subjects
Lens type and visual acuity difference
Cataract (Pre-Op)
W
Cataract (IOL)
The reduction of the visual acuity level was analyzed by subdividing the 100 eyes into two groups, those receiving bi-convex IOLs (n = 35) and those receiving the plano or plano-convex IOLs (n = 65). When comparing the visual acuity results between charts 1 and 4,3 of 35 patients (8.57%)with bi-convex IOLs showed better visual acuities when measured with chart 4; 22 of 65 patients (33.8%) with the plano or plano-convex lens showed better visual acuities when measured with chart 4 compared with chart 1 (Chi square = 7.75; p < 0.05).
Discussion Cataract is the most frequently occurring eye disorder encountered by ophthalmologists.The treatment has been documented historically. However, compared with the numerous reports on its mode of treatment, until recently, relatively little attention had been paid to the visual disabilities resulting from cataract, especially in the early stages of the disease. The cataract examination previously was limited to the visual acuity examination using the high-contrast optotypes. In the early stages of the disease, the visual acuity results and patients’ vis~ ~ = 0 . 9 9which ), is equivalent to 0.64 octave. The visual acuities measured with chart 1 were signifi- ual complaints often do not agree. Hess & Woo cantly higher than those measured with the 15% (1978)issued the first report on the loss of contrast intermediate-contrast chart (chart 2) (Scheffe’s sensitivity function in cataract patients. Since then, studies on the visual disabilities of cataract paF-test = 116.934; p < 0.05). Fig. 4C shows the results of the comparison be- tients using the contrast sensitivity function with a tween charts 1 and 3 (the 2.5% low-contrast chart), glare source have followed (Paulsson & Sjostrand in which the visual acuities measured with chart 1 1980; Abrahamsson & Sjostrand 1984; Hirsch et al. 1984; Koch 1989; Elliott et al. 1989).Their common were better than those measured with chart 3 in frndings are that cataract patients, even during the all 100 eyes. The visual acuity dif€erences ranged from 2 to 8 acuity levels (mean 4.44; ~ ~ = 1 . 3 1 ) ,early stage of the disease, have difficulty detecting which is equivalent to 1.48 octaves. The visual acui- intermediate- to low-contrast objects, especially in ties measured with the high-contrast chart were the presence of a glare source. We previously compared the visual perforsignificantly higher than those measured with the low-contrast chart (Scheffe’s F-test = 671.448; mances of normal subjects and cataract patients in detecting the intermediate- and low-contrast optop < 0.05). types (Miyajima et al. 1992). We found that the reFig. 5 summarizes the visual acuity changes in normal, cataractous, and IOL eyes. In eyes with duction of visual acuity with the intermediate- and IOLs, the visual acuity measured with the inter- low-contrast optotypes is sigmficantly greater in cataract patients than normal subjects. In the presmediate- and low-contrast charts resulted in a value that fell between those of the normal and ent study, the reduction of visual acuity with the intermediate- and low-contrast charts compared cataractous eyes. An increase of visual acuity with chart 4 also was observed, though to a lesser de- with the high-contrast chart was 0.64 and 1.48 octaves, respectively, in the IOL patients. When comgree than with the cataractous eyes. CHART 2
CHART 3 CHART 4 Fig. 5. The bar histogram shows the changes of visual acuities measured with the intermediate (15%), low (2.5O/o), and reverse polarity charts. The negative values indicate that the visual acuity decreased when compared with the 90% high-contrastchart. Acuity level changes were calculated based on geometric measures.
431
pared with the reduction in normal and cataractous eyes reported previously, the reductions were 0.52 and 0.71 octaves with the intermediate-contrast charts and 1.21 and 1.75 octaves with the lowcontrast charts. The reduction of visual acuity levels in the IOL patients fell between the values of the normal and cataract patients with the intermediate- and low-contrast charts. Regarding recovery of the visual function after IOL implantation, the improvement of mesopic vision and the lessening of glare after cataract surgery have been reported by Masket (1989)and Weiss (1990). Other important findings relate to the results obtained with the reverse polarity chart. Twentytwo of 40 eyes (55%)of cataract patients showed better visual acuities when measured with the reverse polarity chart; in normal subjects, no differences were observed (Miyajima et al. 1992). In the present study, even though the acuity level difference was limited to one level, 28 of 100 eyes (2800)showed better acuity when measured with the reverse polarity chart, a finding similar to that of the cataractous eyes. However, the dif€erence of visual acuity was 0.07 octave, which is considerably smaller than the 0.22 octave of the cataractous eyes. We also found that the range of visual acuity (poorest vs. best) was wider in the IOL eyes (5-8 acuity levels) than the normal subjects reported previously (3-5 acuity levels).Despite the recovery of visual acuity, these results suggest that patient detection of intermediate- to low-contrast optotypes still is slightly lower than in normal subjects. With the reverse polarity chart, the glare effect still seems to be a factor in the IOL patients, although to a lesser degree when compared with the cataractous eyes. When comparing visual function between the normal subjects and IOL patients, after testing 110 pseudophakic patients, LeClaire et al. (1982) found significantly more glare in the pseudophakic patients compared with the normal subjects. Van der Heijde et al. (1985)reported that the IOLs scatter light about 2.3 times more than healthy human lenses. Our results, that 28 of 100 (28%)eyes with successful posterior chamber IOL implantation still showed better acuity with the reverse polarity chart, may suggest the residual effect of optical glare. Tagami et al. (1986) reported the increased glare sensitivity in posterior chamber IOL cases, and Nakaizumi et al. (1989)reported a loss of high-frequency contrast sensitivity in certain posterior chamber IOL cases. 432
The reason for the slightly lower contrast discrimination in patients with IOLs compared with the normal subjects may be multifactorial, as already mentioned by Howe et al. (1986)and Tagami et al. (1986). Factors to be considered are, among others, the effect of corneal endothelium, minute deposits on the lens surface, opacities in the posterior capsule, and pupil size. Understanding the effects of these factors requires future clinical and basic research. One interesting finding in this study was that less glare effect was observed with patients who had bi-convex IOLs. Wang & Pomerantzeff (1982) reported that the bi-convex IOL is superior to the plan0 or plano-convex designs. Since the shape of the lens is convex, the light intensity within the eye is less, resulting in less glare effect and better contrast discrimination. Hammer et al. (1986) reported better spectral sensitivity in patients who had IOLs with an ultraviolet absorbing filter than those without it. They reported that the toxic effect of short wavelength light rays is a causative factor, but we speculate that less intraocular light scatter due to the elimination of the short wavelength may be another contributing factor as reported by Zigman (1989).Analysis of this factor was beyond the scope of this study, but it is an important area that needs consideration. Another limitation of this study is that we did not monitor the changes of contrast visual acuities in the same subject. Analyzing the pre- and postoperative changes in the contrast acuity profiles would provide information to enable us to predict the postoperative visual improvement. In conclusion, we found that the contrast acuity profile of the IOL eyes was comparable to that of the normal eyes. However, the residual effect of glare still was observed. Analysis of this small difference in visual performance, which we consider to be multifactorial, requires further clinical and basic research.
Acknowledgments We are deeply indebted to Charles L. Schepens, MD, of the Schepens Eye Research Institute for his support in this investigation. We appreciate the constructive criticism provided by Tatsuo Hirose, MD. Lynda Charters edited the manuscript. This study was supported by a grant from the Kimmelman Foundation (New York, NY) and the Nihon Tenganyaku Institute (Nagoya,Japan).
This study was presented in part at the Annual Association for Research in Vision and Ophthalmology meeting in Sarasota, FL, May 1991.
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28 Acta Ophthal. 70.4
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Received on December llth, 1991. Author's address: Hiroko Miyajima, MD, Department of Ophthalmology, Keio University School of Medicine, 35 Shinanomachi, Shinjuku-ku, Tokyo 160 Japan.
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