Abstract
Purpose :
The slow course and diffuse nature of retinal degenerations (RDs) make the assessment of disease progression difficult. Commonly used measures of progression - visual acuity and foveal sensitivity - remain within normal limits even as foveal cone density decreases by 55%. This study tested the hypothesis that measures of cone structure obtained using spectral-domain optical coherence tomography (SD-OCT) and adaptive optics scanning laser ophthalmoscopy (AOSLO) correlate with measures of visual function at identical parafoveal locations in eyes with and without RDs and across a spectrum of disease severity.
Methods :
We enrolled 9 patients with RDs (retinitis pigmentosa or Usher syndrome type 3) and 9 controls. SD-OCT horizontal and vertical scans through the fovea were obtained from 32 eyes (17 RD, 15 controls), segmented using custom software, and used to calculate photoreceptor inner (IS) and outer segment (OS) length. High-resolution AOSLO images were obtained from each eye and aligned with the OCT scans using retinal landmarks. 8-12 regions of interest (ROIs) in each AOSLO image were selected to overlap with the OCT scans. Cone spacing measures were performed at each ROI using custom software. Fundus-guided microperimetery was used to measure cone-mediated sensitivity at each ROI using a red stimulus under photopic conditions in 8 of the eyes with RDs. Correlations between cone spacing, OS and IS length, and sensitivity were assessed using the Spearman rank correlation r while controlling for eccentricity.
Results :
Cone spacing inversely correlated with IS length (P<0.05; 95% CI, -0.50 to -0.13), OS length (P<0.05; 95% CI, -0.72 to -0.33), and cone-mediated sensitivity (P<0.05; 95% CI, -0.77 to -0.32). The correlation between cone spacing and IS length was similar in the control (r= -0.41) and in the RD group (r=-0.40). A significant inverse correlation between cone spacing and OS length was found, both in the control (r=-0.55) and in the RD group (r=-0.71). Cone-mediated sensitivity significantly correlated with OS length (P<0.01; 95% CI, 0.20 to 0.63), but not with IS length (P=0.91).
Conclusions :
Cone spacing correlated with IS and OS length, and with cone-mediated sensitivity, indicating that high resolution measures of cone structure may be sensitive indicators of cone survival in patients with RDs.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.