Jason S. Ng

OCT reveals regional differences in macular thickness with age.

Purpose. To assist identification of macular thickness abnormalities by optical coherence tomography (OCT), we use techniques that improve spatial localization across the retina to establish any age-related retinal thickness changes in healthy eyes. Methods. Retinal thickness was measured in 30 eyes of 30 healthy subjects aged 13 to 69 years. Using Stratus OCT 3, 12 radial scans centered at the foveola were acquired and points between scans were interpolated to create a topographic map of the central 20°. The thickness map was divided into 37 hexagonal regions. A mean retinal thickness for each hexagon was computed. Retinal thickness vs. age was evaluated for the entire scanned area, five anatomical regions, and within individual hexagons. The retinal nerve fiber layer (RNFL) contribution to total retinal thinning was analyzed in the papillomacular region. Results. There was a small but significant thinning of the overall macular area with increasing age (2.7 &mgr;m/decade; p = 0.027). Comparing the 10 youngest subjects (age 13 to 27 years) with the 10 oldest (age 51 to 68 years), retinal thicknesses in the temporal, superior, inferior, and foveal regions were not significantly different. However, the two age groups differed significantly in retinal thickness in the nasal region (p < 0.008). Across all subjects, retinal thickness in this region was linearly correlated with age, decreasing by 4.1 &mgr;m/decade (p < 0.002). Approximately 43% of the retinal thinning in the nasal region was attributed to RNFL loss. Conclusions. The method of OCT acquisition and analysis used in this study allows for greater spatial localization of change in retinal thickness associated with aging or pathological processes. Based on the results of this study, the macula thins with increasing age but does so nonuniformly. The greatest amount of thinning occurs nasal to the fovea. RNFL loss accounts for much, but not all the thinning in this area.

Determinants and standardization of mesopic visual acuity.

Purpose It is well established that visual acuity (VA) decreases with luminance but the specific factors that are responsible remain unclear. The purpose of this study was to quantify the contributions of accommodative error, pupil size, and higher-order aberrations to the decrease in VA when transitioning from photopic to mesopic light levels. Additionally, repeatability of VA at photopic and mesopic levels was measured to derive a luminance recommendation for mesopic VA testing, which can provide the standardization needed for future translational clinical studies and the widespread adoption of mesopic VA testing. Methods Monocular VAs were assessed at one photopic and three mesopic light levels: 94, 3, 0.75, and 0.38 cd/m2, with an E-ETDRS testing system in 43 normal subjects. Accommodative error, pupil size, and higher-order aberrations were obtained. Twenty subjects were retested at another visit to assess VA repeatability. Results The mean (±SD) logMAR (logarithm of the minimum angle of resolution) VA was −0.08 (±0.06) at 94 cd/m2, 0.05 (±0.07) at 3 cd/m2, 0.16 (±0.06) at 0.75 cd/m2, and 0.27 (±0.09) at 0.38 cd/m2. Light level and accommodative error were significantly associated with VA, and light level explained 75% of the variance. The mean differences in VAs between two visits were not significantly different from zero (p > 0.05). The coefficients of repeatability for 94, 3, 0.75, and 0.38 cd/m2 were 0.08, 0.11, 0.14, and 0.14 logMAR, respectively. Conclusions Light level, among all other factors studied, contributes the most to the reduction in VA tested under mesopic conditions. Testing mesopic VA at 0.75 cd/m2, or about 2.0 log units less than photopic testing, provides a significant and repeatable decrease in VA similar to standardized low-contrast VA testing, and therefore this level is recommended.

Specific medical intervention for diabetic retinopathy

Diabetes is a global epidemic and the major complication of diabetes in the eye, diabetic retinopathy, is a leading cause of blindness in several countries. Medical and surgical interventions have been formally investigated for over half a century, but currently only surgical interventions are the standard of care and these treatments are not without significant side effects. Several clinical trials have investigated a protein kinase C (PKC) beta inhibitor as a possible medical intervention for diabetic retinopathy. Though successful in animal studies and smaller clinical studies, the drug showed only marginal success in clinical trials. It is likely that the clinical trials failed for two reasons: (1) enrolling patients with too severe a disease state at baseline and (2) utilizing conventional outcome measures that essentially require severe disease states at baseline for evaluation after a standard follow-up time. Additional clinical trials that enroll patients with earlier stages of diabetic retinopathy and/or utilizing more sensitive surrogate outcomes over a longer follow-up would likely show clinical success of PKC-beta inhibition for the treatment of the diabetic retinopathy.

Evaluation of the Waggoner Computerized Color Vision Test

Purpose Clinical color vision evaluation has been based primarily on the same set of tests for the past several decades. Recently, computer-based color vision tests have been devised, and these have several advantages but are still not widely used. In this study, we evaluated the Waggoner Computerized Color Vision Test (CCVT), which was developed for widespread use with common computer systems. Methods A sample of subjects with (n = 59) and without (n = 361) color vision deficiency (CVD) were tested on the CCVT, the anomaloscope, the Richmond HRR (Hardy-Rand-Rittler) (4th edition), and the Ishihara test. The CCVT was administered in two ways: (1) on a computer monitor using its default settings and (2) on one standardized to a correlated color temperature (CCT) of 6500 K. Twenty-four subjects with CVD performed the CCVT both ways. Sensitivity, specificity, and correct classification rates were determined. Results The screening performance of the CCVT was good (95% sensitivity, 100% specificity). The CCVT classified subjects as deutan or protan in agreement with anomaloscopy 89% of the time. It generally classified subjects as having a more severe defect compared with other tests. Results from 18 of the 24 subjects with CVD tested under both default and calibrated CCT conditions were the same, whereas the results from 6 subjects had better agreement with other test results when the CCT was set. Conclusions The Waggoner CCVT is an adequate color vision screening test with several advantages and appears to provide a fairly accurate diagnosis of deficiency type. Used in conjunction with other color vision tests, it may be a useful addition to a color vision test battery.

Color Vision Deficiency in Zahedan, Iran: Lower than Expected

Purpose To estimate the prevalence of congenital red-green color vision defects in the elementary school students of Zahedan in 2012. Methods In this cross-sectional study, 1000 students with a mean (±SD) age of 9.0 (±1.4) years were selected randomly from a large primary school population. Color vision was evaluated using the Ishihara pseudoisochromatic color plates (38-plate edition). A daylight fluorescent tube was used as an illuminant C equivalent (i.e., 860 lux, color rendering index greater than 92, and color temperature = 6500 K). Having more than three misreadings on the test was considered a failing criterion. Data were analyzed in SPSS version 17 software using &khgr;2 tests. Results Nine students (0.9%) made more than three errors on the Ishihara test. Based on this criterion, the prevalence of red-green color vision deficiency in girls and boys was 0.2 and 1.6% (p = 0.02), respectively. Conclusions The prevalence of red-green color vision deficiency was found to be significantly lower in Zahedan than comparable reports in the literature.

Accommodative amplitude using the minus lens at different near distances

Purpose: The purpose of this study was to compare the mean findings and the repeatability of the minus lens (ML) amplitude of accommodation (AA) at 33 cm and 40 cm. Materials and Methods: AA was measured from the dominant eye of 120 fully corrected subjects using the ML procedure when viewing the target at both 33 and 40 cm. Each measurement was repeated between 24 and 48 hours after the first trial. Results: Mean AA when tested at 33 cm and 40 cm was 10.20 diopter (D) (standard deviation [SD] =1.24) and 8.85 D (SD = 1.23), respectively (P < 0.001). The limits of agreement of the measured amplitude calculated with taking into account of the replicates at 33 and 40 cm were − 0.19 (95% confidence interval [CI]: −0.34 to −0.04) and 2.53 (95% CI: 2.38 to 2.68), respectively. The repeatability of testing at the two distances 33 and 40 cm was ± 1.24 and ± 0.99, respectively. In addition, the retest reliability of measured amplitude using the intraclass correlation coefficient was 0.87 (95% CI: 0.789–0.920) at 33 cm and 0.91 (95% CI: 0.872–0.945) at 40 cm. Conclusion: There is no agreement in the obtained amplitude at the two measurement distances. Testing the ML AA at 40 cm may be superior given that a lower repeatability coefficient was observed. However, it is unclear whether the larger amplitude measured at 33 cm reflects a larger increase in accommodation (greater proximity effect) or a decrease in the ability to perceive the first slight sustained blur.