The earliest histopathological change in retinitis pigmentosa (RP) is a shortening of the photoreceptor outer segments.1 Therefore, morphological assessments of the photoreceptors can be useful in estimating the disease progression in RP patients. In the optical coherence tomography (OCT) images, the photoreceptor inner/outer segment junction (IS/OS) is observed as a distinct, highly reflective line just vitread of the retinal pigment epithelium. A continuous IS/OS line has been shown to indicate a normal alignment of the membranous discs in the photoreceptor outer segments.2 Because the alignment of the discs is necessary for the normal functioning of the photoreceptors, the continuous IS/OS line would strongly suggest that the photoreceptors would function normally.

Several OCT studies have been conducted on RP patients to determine whether a significant correlation exists between the IS/OS line and the visual acuity.3^–5 Sandberg et al3 graded the IS/OS into three groups; …