Luminance Thresholds and Their Correlation With Retinal Structure in X-Linked Retinoschisis

Abstract

Purpose To provide a comprehensive analysis of light- and dark-adapted luminance thresholds and their associations with retinal structure in X-linked retinoschisis (XLRS). Methods Nine subjects with XLRS and 10 visually-normal individuals participated. Threshold was measured at 15 locations along the horizontal meridian of the visual field at several adaptation levels (5 × 10 − 5 to 50 cd/m 2 ) after dark-adaptation. The relationship between threshold and adaptation level across the field was described using a standard “threshold-versus-illuminance” model. Optical coherence tomography images were obtained and segmented to quantify outer nuclear layer (ONL + ) and outer segment (OS + ) thickness. A linear structure-function model was used to describe the relationship between threshold and the product of ONL + and OS + thickness. Results For peripheral field measurements, thresholds were generally normal for most subjects with XLRS. All subjects had perifoveal and parafoveal threshold elevations under dark-adapted and high illuminance conditions, with thresholds at moderate illuminances being closer to normal. For foveal measurements, seven of nine subjects with XLRS had normal dark-adapted thresholds, and all had abnormally elevated high illuminance thresholds. Threshold-versus-illuminance curves in the fovea, parafovea, and perifovea were abnormally steep for subjects with XLRS, appearing similar to the normal peripheral field shape. Under both dark- and light-adapted conditions, threshold was predicted by ONL + × OS + thickness at nearly all field locations. Conclusions Threshold elevation in XLRS is complex, depending on both the adaptation level and the visual field location. The pattern of threshold-versus-illuminance suggests that macular function in XLRS is similar to the periphery of controls.

Spatial and Temporal Integration Abnormalities in X-Linked Retinoschisis

“…A recent perimetry study examined luminance thresholds across the visual field under a broad range of adaptation levels (dark-adapted scotopic conditions to 50 cd/m 2 photopic conditions) in a group of subjects who had XLRS. 6 This study found that the pattern of threshold elevation in XLRS was complex, with the extent of abnormality depending on both the adaptation level and the visual field location tested. Interestingly, thresholds measured in the macula of the XLRS subjects were similar to thresholds measured in the peripheral field of control subjects.…”

“…This finding supports previous data suggesting that macular function in subjects with XLRS is functionally similar to the peripheral field function of visually normal individuals. 6 , 19 Specifically, Alexander et al 19 reported contrast sensitivity and contrast discrimination abnormalities in subjects with XLRS and that the pattern of abnormality in these subjects could be simulated in control observers by testing at a parafoveal locus. The eye tracking data presented in Supplemental Figure S1 that show stable foveal fixation indicate that eccentric viewing does not explain the threshold elevations in the present sample of XLRS subjects.…”

“…Recently, we reported thresholds across a broad range of adapting levels (scotopic to photopic) in the present group of XLRS subjects. 6 Thresholds were assessed across the visual field and compared to visually normal subjects. The results showed that threshold elevations in XLRS depended on both the adaptation level and the visual field location where the measurement was made.…”

“…The present study reports the spatial and temporal integration data; the adaptation and luminance noise data are presented elsewhere. 6 , 33 Two subjects (both controls) had prior experience with psychophysical testing.…”

“…3 The bilateral foveal schisis that is apparent in young individuals typically collapses with advancing age, proceeding to an atrophic stage. Although foveal thinning and macular atrophy are apparent in older individuals, younger patients can have thinning of the photoreceptor layer, 5 , 6 suggesting that outer retinal abnormalities may be an early characteristic of the disease in some individuals.…”