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/m2) 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.