Abstract
Purpose :
To assess foveal cone structure and function using AOSLO in patients with inherited retinal degenerations (IRD) and normal subjects. AO correction can minimize aberrations that influence visual acuity and resolution of retinal images, permitting evaluation of foveal cone structure with single cell resolution.
Methods :
High-resolution images of the cone mosaic were obtained with AOSLO from 7 eyes of 4 normal subjects and 23 eyes of 14 patients with IRD in whom AOSLO images showed resolved cones within 0.5 degrees of the preferred retinal location (PRL). AOSLO visual acuity threshold measurements modulated the scanning laser to directly project letters onto the retina and subjects reported the orientation of the tumbling E. The average threshold was converted into logMAR acuity. Cone spacing was measured close to or at the PRL center (mean eccentricity, 0.16 degree; maximum eccentricity, 0.24 degree) by 2 independent graders within a standardized 0.1 degree2 box. Cone spacing measures were correlated with best-corrected (ETDRS) visual acuity, foveal threshold, outer segment (OS) thickness and AOSLO visual acuity, correcting for eccentricity. Relationships were assessed with Spearman rho using clustered bootstrap for 95% confidence interval (CI) values.
Results :
Cone spacing was significantly correlated with ETDRS acuity (rho = -0.66, 95% CI -0.85 to -0.26, P < 0.01); the correlation was significant for IRD patients (P = 0.026, clustered bootstrap), but not normal subjects (P = 0.33, mixed model). Cone spacing showed a significant, negative correlation with foveal threshold (rho = -0.70, 95% CI: -0.82 to -0.34) and OS thickness (rho=-0.73, 95% CI: -0.89 to -0.39). Cone spacing was significantly correlated with visual acuity measured using AOSLO in all subjects combined (P = 0.028) and in IRD patients (P = 0.045), but not in normal subjects alone (P = 0.48, mixed model). AOSLO acuity was strongly correlated with ETDRS visual acuity (rho = -0.73, 95% CI = -0.88 to -0.36, P < 0.01).
Conclusions :
Measures of visual acuity using ETDRS and AOSLO correction showed a linear correlation with cone spacing in patients with IRD, but not normal subjects, perhaps due to variability in foveal cone density in normal eyes. AOSLO cone measures and visual acuity may provide more sensitive measures of foveal function than standard measures.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.