Ultra-high resolution optical coherence tomography assessment of photoreceptors in retinitis pigmentosa and related diseases

Abstract

Purpose: To assess photoreceptor integrity in patients with retinitis pigmentosa (RP) and related diseases using ultra-high resolution optical coherence tomography (UHR-OCT) and to correlate foveal photoreceptor loss with visual acuity.

Design: Observational case series.

Methods: Nine eyes of nine patients with RP and related diseases were imaged with UHR-OCT at the ophthalmology clinic. Patients were diagnosed based on history, examination, fluorescein angiography, and electroretinography. Concurrently, 36 eyes of 36 normal subjects were imaged with UHR-OCT. Central foveal thickness (CFT) and foveal outer segment/pigment epithelium thickness (FOSPET) were defined and measured on UHR-OCT images in all subjects and were compared between the two groups using unpaired t tests. The two thickness measurements in RP patients were correlated with visual acuity using Pearson correlation and linear regression.

Results: UHR-OCT demonstrated macular photoreceptor thinning in all RP patients. The difference in CFT between RP patients and normal subjects was not statistically significant (P = .103), but the difference in FOSPET between the two groups was significant (P = .003). Visual acuity showed a fair correlation with CFT (Pearson r = -0.43, r(2) = 0.187, P = .245) and an excellent correlation with FOSPET (Pearson r = -0.942, r(2) = 0.887, P < .0001).

Conclusions: In the current study using UHR-OCT, a new thickness measurement termed FOSPET is demonstrated to quantify photoreceptor loss. FOSPET was statistically thinner in patients with RP and related diseases than in normal eyes and showed correlation with logMAR visual acuity. FOSPET appears to be a probable predictor of visual acuity in RP.

FIGURE 1

Ultra-high resolution optical coherence tomography (UHR-OCT) of normal eye macular images from the left eye of a normal subject. (Top) A 6-mm vertical scan. (Bottom left) 2× magnification of the extrafoveal macula. Retinal layers are labeled: RNFL = retinal nerve fiber layer; GCL = ganglion cell layer; IPL = inner plexiform layer; INL = inner nuclear layer; OPL = outer plexiform layer; ONL = outer nuclear layer; ELM = external limiting membrane; IS/OS = photoreceptor inner/outer segment junction; RPE/OS = retinal pigment epithelium/outer segment complex. (Bottom right) 2× magnification of the fovea, showing central foveal thickness (CFT) measurement (white line) and foveal outer segment/pigment epithelium thickness (FOSPET) measurement (blue line).

FIGURE 2

Ultra-high resolution optical coherence tomography (UHR-OCT) of eye with retinitis pigmentosa (RP) and normal visual acuity. UHR-OCT macular images from the left eye of case 6. Visual acuity is 20/20. (Top) A 6-mm vertical scan. (Bottom right) 2× magnification of the extrafoveal macula. Note thinning of the outer nuclear layer and disappearance of the external limiting membrane and photoreceptor inner/outer segment junction. Retinal layers are labeled. (Bottom left) 2× magnification of the fovea, showing central foveal thickness (CFT) (white) and foveal outer segment/pigment epithelium thickness (FOSPET) (blue) measurements. Both thickness measurements are within the normal range.

FIGURE 3

Ultra-high resolution optical coherence tomography (UHR-OCT) of eye with retinitis pigmentosa (RP) and decreased visual acuity. UHR-OCT macular images from the left eye of case 2. Visual acuity is 20/70. (Top) A 6-mm vertical scan. (Bottom left) 2× magnification of the extrafoveal macula. Note thinning of the outer nuclear layer and absence of the external limiting membrane and photoreceptor inner/outer segment junction. Retinal layers are labeled. (Bottom right) 2× magnification of the fovea, showing central foveal thickness (CFT) (white) and foveal outer segment/pigment epithelium thickness (FOSPET) (blue) measurements. Both measurements are significantly less than normal.

FIGURE 4

Data plots of thickness measurements of ultra-high resolution optical coherence tomography (UHR-OCT). All graphs were created using SPSS version 11.0.1 for Windows. (Top left) Bar graph of mean central foveal thickness (CFT) in normal (Nl) and patients with retinitis pigmentosa (RP) and related illnesses. Difference between groups was not statistically significant (P = .135). Error bars represent 95% confidence interval (CI). (Top right) Bar graph of mean foveal outer segment/pigment epithelium thickness (FOSPET) in normal eyes and in patients with RP and related illnesses. Difference between groups was statistically significant (P = .004). Error bars represent 95% CI. (Bottom left) Distribution of best-corrected visual acuity (BCVA) and mean CFT in RP patients. There was fair correlation, not statistically significant (r = −0.43, P = .245). A linear regression showed that CFT was a poor predictor of BCVA. 95% CIs are indicated. (Bottom right) Distribution of BCVA and mean FOSPET in RP patients. There was excellent correlation (r = −0.942, P < .0001). A linear regression showed that FOSPET was an excellent predictor of BCVA. 95% CIs are indicated.