Evaluation of visual function following neodymium:YAG laser posterior capsulotomy.

PURPOSE: Improvement in visual acuity is the primary endpoint for successful neodymium:YAG (Nd:YAG) laser posterior capsulotomy for posterior capsule opacification. There is limited information on related parameters of visual function that may also improve after laser treatment. The authors evaluate changes in contrast sensitivity and glare disability, aside from visual acuity, following Nd:YAG laser posterior capsulotomy. METHODS: Measurements of visual acuity, contrast sensitivity (using the Pelli-Robson chart), and glare disability (using the Brightness Acuity Tester [Mentor O & O, Inc., Norwell, MA]) were obtained from 24 consecutive patients before and after Nd:YAG laser posterior capsulotomy. Glare testing was done with both the Pelli-Robson and Early Treatment Diabetic Retinopathy Study (ETDRS) charts. The degree of glare disability was indicated by the difference between visual function with glare (at medium and high settings) and without glare. Prelaser measurements were taken within 2 weeks prior to treatment, and postlaser measurements were obtained within 3 months after treatment. Only one eye per patient was evaluated. RESULTS: Mean differences between prelaser and postlaser measurements were significantly different from zero: (1) Contrast sensitivity, mean difference = 0.24 log units (P < 0.0001); (2) High glare disability using Pelli-Robson chart, mean difference = 0.15 log units (P = 0.004); (3) Visual acuity using ETDRS chart, mean difference = 11 letters (P < 0.0001); 4) High glare disability using ETDRS chart, mean difference = 7 letters (P = 0.005). CONCLUSIONS: Using the above methods for visual function testing, Nd:YAG laser capsulotomy is shown to significantly improve visual acuity, contrast sensitivity, and glare disability measurements as compared with prelaser values. The ophthalmologist may find it helpful to document the last two measurements prior to Nd:YAG laser capsulotomy, especially in patients who have good visual acuity but complain of glare sensitivity.

A longitudinal study of cortical cataracts using retroillumination photographs.

The National Eye Institute (NEI) computer planimetry system has been shown to have good reproducibility in assessing the size of cortical cataracts from retroilluminatin photographs. In this study, we determined the usefulness of this system in monitoring cortical cataract changes over time. Using the Neitz Kawara retroillumination camera, retroillumination photographs of cortical cataracts in 81 eyes were obtained every six months for an average of 31 months. As previously described, the cortical cataract outlines were traced in a masked fashion onto transparent plastic overlays, and the tracings then digitized into a Macintosh Quadra computer using a computer scanner. Cortical cataract area was then determined using a specially developed software program. For each eye, the rate of cortical area change was determined by the slope of the regression line fitted to the follow-up measurements. Cataract progression was classified to be significant if the slope exceeded a critical value. Of the 81 eyes, 24 (30%) had significant cataract progression, while 57 (70%) did not progress. This study presents data on progression of the area of cortical cataracts and suggests the usefulness of the NEI computer planimetry system for monitoring such changes from retroillumination photographs. The slope-based test can also play a useful part in longitudinal studies with irregular time intervals and variable number of visits.

Potential vision tests in patients with cataracts.

PURPOSE: To determine the limits of usefulness of the potential acuity meter (PAM) and the laser interferometer (LI) in determining potential visual acuity in various severities and types of cataracts. METHODS: The study included 48 patients (67 eyes) who were undergoing cataract surgery and who had PAM and LI tests. The 67 eyes were grouped into (1) eyes with cataracts only (45 eyes) and (2) eyes with cataracts and other ocular diseases (22 eyes). Group 1 eyes were subdivided into two groups according to their Lens Opacities Classification System II (LOCS II) grading: 1a eyes (moderate cataracts) had an LOCS II grade of nuclear opalescence (NO) < 4 and cortical opacity (C) < 5 and posterior sub-capsularcataract (P) < 4, and group 1b eyes (severe cataracts) had an LOCS II grade of NO = 4 or C = 5 or P = 4. The accuracy of the PAM and LI was estimated separately for each group. RESULTS: For moderate cataracts, the accuracy of the PAM was 100% and of the LI was 92%. For severe cataracts, the accuracy of the PAM was 52% and of the LI was 79%. Both instruments tended to underestimate visual outcome more in eyes with posterior subcapsular cataracts. For eyes with other ocular diseases, the LI tends to overestimate the probable visual outcome more than the PAM, especially in patients with poor retinal function. CONCLUSIONS: Several factors such as preoperative visual acuity of 20/200 or worse, the type and severity of the cataract, and coexisting retinal disorders may affect the accuracy of the PAM and LI tests, and these should be considered when interpreting predicted vision, especially in preoperative counseling of patients.

Scheimpflug photography and postcataract surgery posterior capsule opacification.

We describe a method to objectively document postcataract surgery posterior capsule opacification using Zeiss Scheimpflug photography and computerized image analysis. We examined 42 eyes with clear capsules (group A) and 27 with posterior capsule opacities (group B). The group A eyes had significantly better visual acuity (P < .05), lower mean capsular densitometry readings (0.03 +/- 0.03 optical density units versus 0.15 +/- 0.11 optical density units; P < .0001), and thinner capsules (0.03 +/- 0.4 mm versus 0.10 +/- 0.05 mm) than the group B eyes. This new objective method of documenting postoperative capsular haze may be useful for clinical studies such as clinical trials of drugs or surgical techniques being developed to prevent or minimize capsule opacification.

Progression of lens opacities in cataract patients after one year.

We used the Lens Opacities Classification System II to clinically grade the lenses of 57 patients with age-related cataracts in at least one eye. Progression or regression in each lens region was defined as a one or more step change in the Lens Opacities Classification System II grading noted at 1 year and maintained at the 1 1/2 to 2 year visit (the validation visit). A validated change in a lens region in one eye of a patient was considered a change in that region for that patient. Person-specific rates of cataract progression at 1 year were 42% for nuclear, 32% for cortical and 10% for posterior subcapsular opacities. Corresponding regression rates were 5%, 4%, and 2% for nuclear, cortical and posterior subcapsular opacities, respectively. Progression rates were significantly greater than the regression rates only for nuclear and cortical opacities (p < 0.0005). These findings show the applicability of the clinical Lens Opacities Classification System II method in documenting and monitoring lens changes over time. The usefulness of person-specific analysis was also shown.

Measurement error in assessing the size of cortical cataracts from retroillumination photographs.

This study describes a new method of quantifying anteriorly located cortical cataracts using retroillumination photographs and computer planimetry. Cortical cataracts were graded clinically and then photographed using the Neitz retroillumination camera twice by each of 2 photographers. The cataract outlines were traced onto a transparent overlay, and computer planimetry was performed using a Scan Maker 600ZS, a MAC II Computer and specially developed software. We estimated the measurement error of the method and its associated effect on sample size estimates for clinical studies. We calculated that the variability in this technique would contribute about 21 additional subjects to overall sample size estimates in studies comparing the mean areas of cortical opacities. In many studies this would be a small addition to total sample size requirements. This technique provides clinically useful measurements of the size of a cortical opacity as seen on a retroillumination photograph. This may be useful for future clinical studies on natural progression of cortical cataracts as well as for clinical trials of anticataract drugs.

Comparison of linear, multilinear and mask microdensitometric analyses of Scheimpflug images of the lens nucleus.

We wanted to determine the agreement among three methods currently used to measure the average density of the nucleus from a Scheimpflug video image of the lens, namely, the multilinear, linear and mask techniques. Using the NEI Scheimpflug Cataract Imaging System, video images of the lens were obtained from 49 eyes of 31 consecutive patients with predominantly nuclear opacities of varying severities. For each image, 3 separate determinations of the average nuclear density [in optical density units (odu)] were obtained by one analyst sequentially applying each of the three methods. Repeat measurements were obtained by the same analyst one week apart to evaluate reproducibility (using 95% error range), of each of the methods. Pairwise comparisons of the 3 methods were also done. Only the error due to outlining of the nucleus was assessed. Reproducibility of each method was excellent. The 95% error ranges were +/- 0.015 odu for the linear, +/- 0.013 odu for the multilinear, and +/- 0.017 odu for the mask methods. Very strong linear relationships were observed between the linear and multilinear methods (R2 = 0.99), between the linear and mask methods (R2 = 0.97), and between the multilinear and mask methods (R2 = 0.98). Simple linear regressions calibrating these three methods against each other would facilitate comparison of density measurements using any of these methods for analysis of Scheimpflug images of the lens nucleus.

Glare sensitivity in early cataracts.

In a previous study significant glare sensitivity (using Vistech MCT8000) was found only in patients with posterior subcapsular cataracts (PSC) beyond the very early (LOCS II grade 1) stage. The aim of the present study was to evaluate glare sensitivity in patients with early cataracts. The brightness acuity tester (BAT) was used with the Pelli-Robson chart on 50 patients with early cataracts (LOCS II grade 1 or 2) and on 14 normal volunteers. Only age and PSC were found to be associated with change in contrast sensitivity at high glare. Eyes with grade 1 PSC were not significantly different from eyes with grade 0 PSC after adjusting for age. Eyes with grade 2 PSC had significant glare effect compared with eyes having grade 0 PSC. Thus, glare sensitivity is associated only with early (grade 2) PSC. Other tests still need to be developed to assess visual function changes in patients with early cortical and nuclear cataracts.

Contrast and glare sensitivity. Association with the type and severity of the cataract.

PURPOSE: Contrast and glare sensitivity tests are now being used as adjuncts to visual acuity in the assessment of visual function. Limited data are available on the associations of the former tests with cataract type and severity. The aim of the study is to assess these associations using standardized techniques. METHODS: Contrast sensitivity tests (using the Pelli-Robson chart) and glare sensitivity tests (using the Vistech MCT 8000) were done on 128 patients with cataracts and no other ocular disease and on 29 control volunteers. The cataracts were graded using the Lens Opacities Classification System II (LOCS II). Data from the left eyes were analyzed using logistic regression models. RESULTS: Contrast sensitivity loss was associated with cataract severity for cortical (P less than 0.0001) and posterior subcapsular (P = 0.0001) cataracts and with decreased visual acuity (P = 0.0001). Night and day glare sensitivity were each associated only with increased severity of posterior subcapsular cataracts (P less than or equal to 0.003) and with decreased visual acuity (P less than 0.001). Additional analyses showed that contrast and glare sensitivity were similar in eyes with no cataracts and early cataracts. CONCLUSION: These results suggest that the Pelli-Robson Chart and the Vistech MCT 8000 are good techniques for evaluating visual function in moderate to advanced cataracts. However, for early cataracts, other techniques need to be explored to assess visual function loss.