Color vision, dark adaptation and retinal structure in Aniridia

Abstract

Purpose : To investigate color vision, dark adaptation and retinal structure in individuals with aniridia

Methods : Twenty-seven males and females, aged 11–67 yrs, with aniridia were included in the study. Color vision was examined with HRR pseudo-isochromatic plates (4^th ed., 2002) and the Color Assessment and Diagnosis (CAD) test. Observers viewed the CAD stimulus binocularly with optimal optical correction from a 1.4 m distance. Stimuli size was 2.2 deg with increased luminance noise and slower speed to mask rod intrusion. Color-vision deficiency (CVD) was defined if CAD thresholds in standard normal units (SNU) > 2.5. Rod and cone mediated dark adaptation (DA) were measured with the Roland Consult DarkAdaptometer after a 5 min photobleach (7000 cd/m²) with fixation target at 20 deg temporal eccentricity. Speed of DA was characterized by the time to the rod-cone break (TRCB). Visual acuity (VA), corneal and lens opacities were assessed. Retinal straylight was measured with the Oculus C-Quant using the compensation comparison method. The central 30 deg of both eyes were imaged with the Heidelberg Spectralis OCT. Foveal, para- and perifoveal retinal layers and severity of foveal hypoplasia (FH) were analyzed by calculating longitudinal reflectivity profiles (LRP) after correction of scaling for individual axial length.

Results : VA ranged from logMAR 0.00–1.76. Two subjects were classified with tritan and three with red-green (RG) CVD on the HRR. Five males and 13 females were classified to have a RG CVD on the CAD (RG threshold 2.6–16.6 [SNU]). Three of these were also classified with tritan CVD (YB threshold 4.5–11.6 [SNU]), including the two HRR-classified tritans. The three with RG CVD on the HRR had CAD RG of 3.1, 4.9 and 8.4. TRCB was normal compared with age-matched controls. Measurements of retinal thickness, relative lengthening of the photoreceptor layer and outer nuclear layer, showed a considerable variation in FH grade. A significant positive correlation was found between FH severity, logMAR VA (p<0.001) and RG threshold (p=0.02). LogMAR VA, RG and YB thresholds increased with keratopathy severity (all p<0.05). No significant correlations were found between RG threshold and age, lens opacities or retinal straylight.

Conclusions : The results suggest that the observed red-green deficiencies may be secondary to foveal hypoplasia as a consequence of a central structural organization that is similar to that in normal perifovea.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.