Phantom Cones: Visual function in photoreceptors with abnormal scattering properties

Abstract

Purpose : Confocal adaptive optics scanning laser ophthalmoscope (AOSLO) images provide sensitive measures of cone structure, but the relationship between structural findings and visual function is unclear. We evaluated visual function in regions of apparent cone loss using fundus-referenced visual testing.

Methods : Patients with foveal lesions and spectral-domain optical coherence tomography (SDOCT) images indicating focal loss of the inner segment-outer segment (IS/OS) junction band with intact overlying external limiting membranes (ELMs) were selected. We performed fundus-referenced vision tests to assess function in the region of apparent cone loss, including microperimetry with tracking SLO (TSLO), AOSLO acuity, and analysis of preferred retinal locations (PRLs). Regular-appearing retina outside of the lesion was used as internal control for TSLO microperimetry. Complete eye exam, including best-corrected visual acuity (BCVA), visual field tests, color fundus photos, and fundus auto-fluorescence were also performed.

Results : Three patients, ages 27, 45 and 65 (BCVA 20/25, 20/32 and 20/40-2, respectively), had lesions at or near the fovea with SDOCT images demonstrating intact ELMs but central outer nuclear layer thinning and disrupted IS/OS junction layers, suggesting loss of cones. Despite lack of visible cone profiles in the foveal lesion, fundus-referenced vision testing demonstrated measurable visual thresholds within the lesion, and AOSLO visual acuity tests were abnormal but measurable in the 27 year old. In 2 of the patients, PRLs were within the lesion. The 27 year old had additional testing with TSLO; microperimetry threshold values were greatest at the center of the lesion compared to at the margins, which were greater than areas of normal-appearing retina at 1 degree eccentricity. Visual sensitivity outside the lesion was within normal limits.

Conclusions : Three patients with foveal lesions caused by distinct maculopathies presented with apparent cone loss but preserved ELMs on OCT and measurable but reduced visual function within the lesion using fundus-referenced vision testing. These findings characterize a common structural and functional phenotype that may be discovered in other maculopathies, where fundus-referenced vision testing may indicate the presence of cones that may be amenable to recovery or response to experimental therapies despite not being directly visible on confocal or OCT images.

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