A Comparison of Methods For Tracking Progression in Patients with X-Linked Retinitis Pigmentosa Using Frequency Domain OCT

Abstract

 

Purpose

 

Frequency domain optical coherence tomography (fdOCT) holds promise as a method for following disease progression in clinical studies of retinitis pigmentosa (RP).[1-3] To compare the efficacy of different outer retinal measures, patients with x-linked (xl) RP were followed over time.

 

Methods

 

26 xlRP patients (15±6yrs), with regions of healthy central retina and flicker ERG responses greater than 0.3 μV, were studied with fdOCT (Spectralis, Heidelberg). All patients had 9mm horizontal and vertical line scans, and macular volume scans recorded using automated tracking. By manually correcting an automated segmentation program,[3] outer segment (OS), outer nuclear layer (ONL), retinal pigment epithelium (RPE), and total receptor (TotRec) volumes were determined. The ISe contour (black border in Fig. 1), i.e. the location where OS thickness decreases to zero, was marked on all scans. Three parameters were derived from the ISe contour: its horizontal midline width (HW), its vertical midline width (VW), and the area (A) within the contour. Initial and final values over an approximate 2-year period were compared with paired t-tests.

 

Results

 

OS, ONL and RPE volumes were not significantly different between initial and final visits (Table 1), although TotRec volume did show a marginally significant decrease with time (p = .02). On the other hand, all ISe measures showed changes that were markedly significant (p<0.003). On the cube scan, the ISe HW moved inwards (23/26 patients) by about 10% a year, while the VW moved inwards (25/26 patients) by about 16% a year. The area within the ISe contour was reduced (25/26 patients) on average by 21.7% a year. The horizontal (ISe HW) and vertical (ISe VW) line scan measures had t-scores in the same range as the volume scan measures (Table 1).

 

Conclusions

 

Measures of the ISe contour are more effective in detecting disease progression than are outer retinal volume measures. Given the similar effectiveness of line and volume scans, the ISe width on vertical and/or horizontal line scans provides the quickest and most effective clinical method for tracking progression in xlRP. 1. Hood et al., Biomed Opt Express, 2011; 2. Locke et al., ARVO, 2012; 3. Yang et al., Biomed Opt Exp, 2011.

 

 

Fig.1 OS and ONL volume maps for one patient.

 

 

Table 1. t-statistics for all 9 methods. *p<.03, **p<.003

 

Keywords: 689 retina: distal (photoreceptors, horizontal cells, bipolar cells) • 696 retinal degenerations: hereditary • 550 imaging/image analysis: clinical