Purpose: To assess changes of the light increment sensitivity (LIS) of the macular area in patients with type 2 idiopathic macular telangiectasia (IMT).
Methods: Fifty-eight eyes of 30 patients were examined in a cross-sectional study. All eyes were assigned to group A (early disease stages) or group B (late disease stages with retinal pigment clumping or vascular membranes). Investigation of visual function included visual acuity and fundus-related microperimetry.
Results: Thirty-seven and 16 eyes were assigned to group A and group B, respectively. Temporal to the fovea, each eye of group B had an absolute scotoma. Topographically, the areas with reduced LIS correlated well with the angiographically hyperfluorescent areas or retinal pigmentations and showed a sharp demarcation from areas with normal LIS. However, within areas with angiographic alterations, at least some test locations exhibited preserved LIS in group B eyes; in 51% of group A eyes, none of those test locations showed abnormal LIS. Group A eyes that showed marked LIS reduction revealed common abnormalities: either hyporeflective spaces between the neurosensory retina and the retinal pigment epithelium in OCT imaging or atrophic areas, both topographically related to the scotoma. Visual acuity was correlated with foveal LIS but not with the LIS temporal to the fovea.
Conclusions: Long-standing morphologic macular alterations from type 2 IMT are associated with topographically related functional impairment. Eyes with profound parafoveal scotomas can exhibit relatively preserved visual acuity. Therefore, testing for retinal light sensitivity should be included as an additional outcome measure for future interventional studies.