The findings of optical coherence tomography of retinal degeneration in relation to the morphological and electroretinographic features in RPE65−/− mice

Abstract

PurposeMutations of the gene encoding RPE65 cause Leber congenital amaurosis (LCA) retinitis pigmentosa (RP). The optical coherence tomography (OCT) is increasingly utilized to noninvasively evaluate various types of retinal diseases, including RP. The present study was conducted to characterize the OCT findings of the RPE65−/− mice—an animal model of LCA and RP—in relation to the morphological features based on histological and electron microscopic findings as well as electroretinography (ERG) features.Materials and methodsRPE65−/− mice were employed as a model of retinal degeneration. C57BL/6J mice were used as a wild-type control. OCT was performed on the RPE65−/− mice from postnatal day (P) 22 to 170. The longitudinal changes in the OCT images and fundus pictures were analyzed both qualitatively and quantitatively in comparison to those of C57BL/6J mice. The OCT images were also compared to the histological and electron microscopic findings. Full field combined rod and cone ERG was performed to analyze the relationship between morphology based on OCT and the amplitudes of the a- and b-waves.ResultsIn the RPE65−/− mice, the photoreceptor rod and cone layer appeared as a diffuse hyperreflective zone contiguous with the inner segment ellipsoid zone (IS-EZ) on OCT, even on P22, whereas the IS-EZ and interdigitation zone were clearly identified in the age-matched C57BL/6J mice. The histological analyses revealed that the regular arrangement of the photoreceptor inner and outer segments was gradually lost in the RPE65-/- mice. On electron microscopy, most of the rod outer segments were degenerated from P21 to P35, whereas outer segments became variably shorter after P49 although ultrastructure appeared to normalize. The thickness of the outer nuclear layer of RPE65−/− mice was slowly and progressively reduced in comparison to C57BL/6J mice. Although the thickness of the inner and outer segment layer of RPE65−/− mice was significantly decreased in comparison to C57BL/6J mice, the change was not progressive, at least until P170. Even at P35, the amplitudes of both a- and b-waves on ERG were severely deteriorated in comparison to those of C57BL/6J mice. Mottled depigmented spots appeared throughout the fundus in RPE65−/− mice after P72, and were detected as hyperreflective deposits under the retinal pigment epithelium on OCT.DiscussionThe pathological changes in the inner and outer segments layer of RPE65−/− mice were identified as diffuse hyperreflective changes on OCT. The rod outer segments showed degeneration in the early postnatal periods but became morphologically normalized in the disc structure after P49, although the sizes of the length of the rod outer segments were variable. OCT could not qualitatively differentiate the early degeneration of rods from the late variability in size of rods. Although the morphology of the photoreceptor outer segments was relatively preserved in the RPE65−/− mice, the amplitudes of ERG were severely disturbed. These structural and functional deficits may be derived from the defe...

Mouse Models of Inherited Retinal Degeneration with Photoreceptor Cell Loss

“…Mutation of genes involved in the visual cycle pathway cause PR degeneration, in most instances with a moderate to slow progression depending on the allele and the genetic background. Most Rpe65 mutant alleles show moderately slow PR cell loss (D 50 = 7-11 months) [284][285][286][287][288]. Allelic effects are observed in models bearing missense mutations, Rpe65 tm1Lrcb [289] or Rpe65 tm1.1Kpal [290], which cause slower progression than observed in Rpe65 tm1Tmr knockout mice [285][286][287][288].…”

“…Most Rpe65 mutant alleles show moderately slow PR cell loss (D 50 = 7-11 months) [284][285][286][287][288]. Allelic effects are observed in models bearing missense mutations, Rpe65 tm1Lrcb [289] or Rpe65 tm1.1Kpal [290], which cause slower progression than observed in Rpe65 tm1Tmr knockout mice [285][286][287][288]. Abca4 tm1Ght on the BALB/c strain, which also carries a homozygous Rpe65 Leu450Met mutation, show a late-onset PR degeneration with 40% loss by 11 months of age [291].…”

A spectral-domain optical coherence tomographic analysis of Rdh5-/- mice retina

“…SD-OCT and fundus photography were performed by the methods as described in detail previously, using a Micron 1 IV, Image-Guided 830 nm OCT (Phoenix Retinal Imaging System, Phoenix Research Labs, Pleasanton, CA, USA) [22,23,25,27]. In brief, SD-OCT and fundus photography were carried out at 6 points of time from postnatal-month (PM) 1 to PM6 for both Rdh5 -/and C57BL/6J mice.…”

“…The pupils were dilated with the instillation of eye drops containing a mixture of 0.5% tropicamide and 0.5% phenylephrine hydrochloride. The mouse ocular fundus was simultaneously monitored by a fundus camera equipped to the Micron 1 IV, and the position of the retinal SD-OCT image was set circumferentially around the optic disc (360˚; diameter, 500 μm; 140 μm away from the optic disc margin, Fig 1) [22]. To analyze the structure of a certain fundus change of interest, the position of the SD-OCT image was set vertically or horizontally, depending on the finding.…”

“…Although SD-OCT is a noninvasive technology that allows us to investigate the morphological characteristics of various retinal diseases [20,21], it is impossible to directly evaluate the pathological features. In contrast, animal models associated with known gene mutations provide strong evidence that facilitate our understanding of the relationship between the SD-OCT findings and the pathological background [22][23][24][25][26][27][28][29][30][31][32]. However, to our knowledge, no study has assessed the relationship between SD-OCT findings and the origin of the structural changes in Rdh5 -/mice.…”