Evaluation of Inner Retinal Layers in Patients with Retinitis Pigmentosa Using Optical Coherence Tomography

Abstract

 

Purpose

 

Preservation of the inner retina in patients with retinitis pigmentosa (RP) is an important prerequisite for restoration therapy. However, the degree of preservation is not fully understood. Using frequency-domain optical coherence tomography (fdOCT), we evaluated changes of the thickness of the inner retinal layers in patients with x-linked (xl) RP and tracked the thickness over a 2-year period

 

Methods

 

FdOCT 9mm X 6mm (30°X20°) volume scans (Spectralis, Heidelberg) were obtained from one eye of 26 patients with xlRP (15.0 ±7.0 yrs) and compared with those of 41 controls (22.0 ±7 yrs). Three layers, the retinal nerve fiber layer (RNFL), the combined retinal ganglion cell and inner plexiform layers (RGCL+), and the inner nuclear layer (INL), were segmented using an automated algorithm[1] and then manually hand-corrected[2]. Average thickness values were obtained for 3 areas centered on the fovea: 2X2 mm, 4X4 mm, and 6X6 mm of the scan. The measurements were evaluated and compared at the initial point and final time points spaced by approximately 2 years

 

Results

 

For all 3 areas analyzed, RNFL thickness was greater than controls and the average RNFL thickness for the entire (6X6mm) scan showed the largest absolute (30.1um) and relative (1.67) increase (table 1). The increased thickness of the other 2 layers (INL & RGCL+) was smaller and reached statistically significant in the center of the macula (2x2 and 4x4mm; table 1), but not for the entire scan. For all layers and areas, the change in thickness over the 2 year period was extremely small (<3 um) and not statistically significant (p>0.39 to p>0.95)

 

Conclusions

 

There is disagreement over which inner retinal layers in RP are increased in thickness.[2-6] Here patients with xlRP showed increased thickness of all 3 inner retinal layers compared to controls, although the major thickening was observed for the RNFL. This thickening did not appear to change over the 2-year period studied. 1. Yang et al. Biomed Opt Exp. 2011; 2. Hood et al. IOVS, 2009; 3. Walia et al. IOVS, 2007; 4. Walia et al. IOVS, 2008; 5. Jacobson et al. BJO, 2007; 6. Aleman et al. IOVS, 2007

 

 

Table 1. Average thickness in um for 3 retinal layers and 3 areas of analysis. * p < 0.05, ** p <0.01

 

Keywords: 688 retina • 691 retina: proximal (bipolar, amacrine, and ganglion cells)