Correlation of cone spacing with retinal thickness and microperimetry in patients with inherited retinal degenerations and healthy subjects

Abstract

Purpose : The current study proposes to use high resolution measures of macular structure and function over 36 months in patients with retinal degeneration (RD) and age-similar normal subjects.

Methods : 4 eyes of 4 patients with RD and 10 eyes from 6 healthy subjects were studied at baseline and 36 months later. Adaptive Optics Scanning Laser Ophthalmoscopy (AOSLO) was used to image the central 5 degrees. Regions of interest (ROIs) with unambiguous cones were chosen to measure cone spacing by 1-2 graders in random order using a density recovery profile. AOSLO images were precisely aligned with images acquired with spectral-domain optical coherence tomography (SD-OCT, Spectralis, Heidelberg Engineering, CA, USA) and fundus-guided microperimetry (MP1, Nidek, CA, USA) images to permit correlation between measures of retinal structure and function. SD-OCT images were segmented manually to measure inner and outer segment (IS and OS) length at locations corresponding to ROIs. Fundus guided microperimetry was measured in the central 10 degrees. 8-12 ROIs were used from each montage that corresponded to horizontal and vertical SD-OCT scans acquired through the fovea. Correlations between cone spacing, OS, IS length, and sensitivity were assessed using Huber robust regression.

Results : 41 ROIs from patients and 98 ROIs from healthy eyes were measured. Cone spacing was inversely correlated with IS length (P = 0.0007), and OS length (P=0.0002) when all eyes were analyzed together. Cone-mediated sensitivity was not significantly correlated with cone spacing (P = 0.2). We detected no significant change in cone spacing, IS or OS length or MP1 sensitivity over 36 months in the 4 patients studied.

Conclusions : Cone spacing correlated with IS and OS length in all subjects, but not with cone mediated sensitivity. Cone spacing increases with eccentricity in the macula but sensitivity is stable throughout the central macula in normal eyes due to a ceiling effect, possibly accounting for the lack of correlation between cone spacing and sensitivity. Although we observed no significant change over 36 months in this small study, the correlations observed suggest that high resolution images of cone structure can be used to assess patients with RD over time, proving they may be appropriate outcome measures for clinical trials.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.