Abstract
Purpose: The P23H rhodopsin mutation is an autosomal dominant cause of retinitis pigmentosa (RP). The degeneration can be tracked using different anatomical and functional methods. In our case, we evaluated the anatomical changes using Spectral-Domain Optical Coherence Tomography (SD-OCT) and correlated the findings with retinal thickness values determined by immunocytochemistry.Methods: Pigmented rats heterozygous for the P23H mutation, with ages between P18 and P180 were studied. Function was assessed by means of optomotor testing and ERGs. Retinal thicknesses measurements, autofluorescence and fluorescein angiography were performed using Spectralis OCT. Retinas were studied by means of immunohistochemistry. Results: Between P30 and P180, visual acuity decreased from 0.500 to 0.182 cycles per degree (cyc/deg) and contrast sensitivity decreased from 54.56 to 2.98 for a spatial frequency of 0.089 cyc/deg. Only cone-driven b-wave responses reached developmental maturity. Flicker fusions were also comparable at P29 (42 Hz). Double flash-isolated rod-driven responses were already affected at P29. Photopic responses revealed deterioration after P29.A reduction in retinal thicknesses and morphological modifications were seen in OCT sections. Statistically significant differences were found in all evaluated thicknesses. Autofluorescence was seen in P23H rats as sparse dots. Immunocytochemistry showed a progressive decrease in the outer nuclear layer (ONL), and morphological changes. Although anatomical thickness measures were significantly lower than OCT values, there was a very strong correlation between the values measured by both techniques.Conclusions: In pigmented P23H rats, a progressive deterioration occurs in both retinal function and anatomy. Anatomical changes can be effectively evaluated using SD-OCT and immunocytochemistry, with a good correlation between their values, thus making SD-OCT an important tool for research in retinal degeneration.
Highlights
Mutations in the rhodopsin gene are a common cause of retinitis pigmentosa (RP),1 with P23H being one of the most common autosomal mutations of this gene (Dryja et al, 1990), and accounting for approximately one third of RP cases in the USA (Dryja et al, 2000)
Pigmented rats are easier to use for visual acuity evaluation with the optomotor system and to define the lines of the Optical coherence tomography (OCT) exploration
Their visual acuity resolution is higher than that of albino rats, which helps to distinguish the effect of the degeneration from the result of any therapeutic approach that we use on them
Summary
Mutations in the rhodopsin gene are a common cause of retinitis pigmentosa (RP), with P23H being one of the most common autosomal mutations of this gene (Dryja et al, 1990), and accounting for approximately one third of RP cases in the USA (Dryja et al, 2000). 1www.sph.uth.tmc.edu/RetNet/disease.htm have been examined, at both anatomical and electrophysiological level (Machida et al, 2000; Cuenca et al, 2004; Pinilla et al, 2005), using the P23H transgenic rat (Lewin et al, 1998). These studies have relied on animals bred with an albino background, which is likely to increase the complexity of the retinal degenerative process. The pigmented background makes it easier to use functional evaluation tests for visual features such as visual acuity and contrast sensitivity
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