Quantifying microstructural changes in retinitis pigmentosa using spectral domain - optical coherence tomography

Background: Most patients of established retinitis pigmentosa (RP) have subnormal peripheral vision and heavily rely on central vision for their daily activities. Central visual acuity is dependent on photoreceptor survival at the macula. Identification of structural changes that precede visual loss is essential. The aim of this study was to correlate the Spectral Domain-Optical Coherence Tomography (SD-OCT) characteristics with visual acuity in patients with typical RP. Methods: This was a retrospective, observational case series of 224 eyes of 113 RP patients conducted a tertiary eye care center. SD-OCT imaging was done for all eyes. Central retinal thickness (CRT), photoreceptor outer segment length (PROS), foveal outer segment pigment epithelial thickness (FOSPET) and ellipsoid zone (EZ) extent were measured. A new variable, FOSPET-PROS ratio (FPR), obtained by dividing FOSPET by PROS is defined and correlated to corrected distance visual acuity (CDVA) in IogMAR using linear regression. Results: Out of 113 patients, 71 were males and 42 females. Mean age of the patients was 35.4 +/- 15.1 years. Mean CDVA was 0.33 +/- 0.25 IogMAR with no difference between the genders. Mean CRT (218.74 +/- 83.5 mu m) and FPR (1.63 +/- 0.22) significantly correlated to CDVA with a correlation coefficient of r = - 0.139 (p = 0.048) and r = 0.842 (p = 0.0001), respectively. FOSPET (mean = 71.15 +/- 13.8 mu m) and PROS (mean = 44.85 +/- 12.5 mu m) did not show a significant correlation to CDVA, independent of FPR. Conclusions: Retinal microstructural changes on SD-OCT, especially the FPR, can be used as a surrogate marker to monitor disease progression in the central retina in degenerative diseases like RP.