Contrast Sensitivity and Equivalent Intrinsic Noise in X-Linked Retinoschisis

To define relationships among contrast sensitivity (CS), equivalent intrinsic noise (Neq; a measure of noise within the visual pathway), and retinal thickness in X-linked retinoschisis (XLRS).

Nine XLRS and 10 visually-normal subjects participated. CS was measured in the presence and absence of luminance noise. These data were fit with a standard model to estimate Neq and sampling efficiency (an estimate of the ability to use stimulus information). Optical coherence tomography images were obtained to quantify outer nuclear layer (ONL+) and outer segment (OS+) thickness. A linear structure-function model was used to describe the relationship between CS and the product of ONL+ and OS+ thickness.

CS in the absence of noise (CS0) for the XLRS subjects ranged from normal to as much as 1.5× below the lower limit of normal. Four of the nine subjects with XLRS had abnormally high Neq, whereas two others had sampling efficiency that was borderline abnormal. Log CS0 for the subjects with XLRS was correlated significantly with log Neq (r = -0.78, P = 0.01), but not with log efficiency (r = 0.19, P = 0.63). CS0 and Neq, but not efficiency, conformed to the linear ONL+ × OS+ structure-function model.

The XLRS subjects in this study who had elevated internal noise had abnormally low CS; both internal noise and CS fell within the predicted limits of a structure-function model.

Internal noise measurements can provide insight into a source of CS loss in some individuals with XLRS.