Comparison Of Outer Retinal Structure And Serial Retinal Sensitivity Measurements With Rings Of High Density Fundus Autofluorescence In 12 Patients With Retinitis Pigmentosa

Abstract

Purpose: : To assess structural and functional changes across parafoveal rings of high density fundus autofluorescence (AF) in 12 patients with retinitis pigmentosa (RP) monitored over periods of up to 8.7 years.

Methods: : Twelve patients with autosomal recessive RP or Usher syndrome type 2 (USH2A confirmed in 5) were ascertained who had a parafoveal ring of high density AF and a visual acuity (VA) of 20/30 or better at baseline. The lateral dimensions of the ring at follow-up were compared with those of the photoreceptor IS/OS band, external limiting membrane (ELM) and outer nuclear layer (ONL), measured using spectral-domain optical coherence tomography (OCT) along each of 6 radial axes intersecting the fovea. Photopic and scotopic sensitivity measurements were made at 100 macular locations using fine matrix mapping (FMM) and were compared with those obtained previously (N=1600 measurements; median follow-up period 8.0 years).

Results: : The mean diameters for the internal and external edges of the ring were 6.6 (range 3.4-13.8) and 12.6 (range 6.2 to 21.0) degrees. Ring constriction was seen in 11 of 12 subjects at follow-up; the ring dispersed in 1. The mean reductions in diameter for the internal and external edges of the ring were 3.2 degrees (mean rate of constriction 7.1% per year) and 4.2 degrees (mean rate of constriction 2.4% per year) respectively. Correlations between the internal ring diameter and the lateral extent of the IS/OS band (r2= 0.97; slope =1.00, N=11) and ELM (r2=0.95, slope = 0.92) were stronger than for the external ring diameter. The ONL tapered beyond the ring in 11 of 11 cases. Photopic thresholds were normal over the central macula. Mean thresholds were elevated by 0.6 log units over the ring and by 1.2 log units external to the ring at baseline and differed by less than 0.1 log units at follow-up. Mean scotopic thresholds over parafoveal areas within the ring were elevated in 8 of 10 at baseline and were severely elevated in 9 of 11 at follow-up.

Conclusions: : These findings confirm and extend a previous study showing that the internal edge of the ring of increased AF demarcates central areas of preserved outer retinal structure and preserved photopic function. Ring constriction mirrors progressive photopic sensitivity loss. Progressive parafoveal rod dysfunction within the ring occurs before there is detectable disruption of outer retinal structure and accumulation of lipofuscin.

Keywords: retinal degenerations: hereditary • clinical (human) or epidemiologic studies: natural history • imaging/image analysis: clinical