Changes in retinal layer thickness with maturation in the dog: an in vivo spectral domain - optical coherence tomography imaging study

Abstract

Background Retinal diseases are common in dogs. Some hereditary retinal dystrophies in dogs are important not only because they lead to vision loss but also because they show strong similarities to the orthologous human conditions. Advances in in vivo non-invasive retinal imaging allow the capture of retinal cross-section images that parallel low power microscopic examination of histological sections. Spectral domain - optical coherence tomography (SD-OCT) allows the measurement of retinal layer thicknesses and gives the opportunity for repeat examination to investigate changes in thicknesses in health (such as changes with maturation and age) and disease (following the course of retinal degenerative conditions). The purpose of this study was to use SD-OCT to measure retinal layer thicknesses in the dog during retinal maturation and over the first year of life. SD-OCT was performed on normal beagle cross dogs from 4 weeks of age to 52 weeks of age. To assess changes in layer thickness with age, measurements were taken from fixed regions in each of the 4 quadrants and the area centralis (the region important for most detailed vision). Additionally, changes in retinal layer thickness along vertical and horizontal planes passing through the optic nerve head were assessed. Results In the four quadrants an initial thinning of retinal layers occurred over the first 12 to 15 weeks of life after which there was little change in thickness. However, in the area centralis there was a thickening of the photoreceptor layer over this time period which was mostly due to a lengthening of the photoreceptor inner/outer segment layer. The retina thinned with greater distances from the optic nerve head in both vertical and horizontal planes with the dorsal retina being thicker than the ventral retina. Most of the change in thickness with distance from the optic nerve head was due to difference in thickness of the inner retinal layers. The outer retinal layers remained more constant in thickness, particularly in the horizontal plane and dorsal to the optic nerve head. Conclusions These measurements will provide normative data for future studies.

Outer retinal thickness and visibility of the choriocapillaris in four distinct retinal regions imaged with spectral domain optical coherence tomography in dogs and cats

“…A fovea‐like region was visually identified in a subset of dogs (five eyes, four dogs) and cats (five eyes, four cats; Figure ). This finding is in accordance with the description of a canine fovea‐like region by Beltran et al 31 and the indication of the same by Occelli et al, 10 and suggests the potential existence of a similar fovea‐like region in the AC in cats.…”

“…These measurements therefore qualify as potential objective markers for the identification of the AC and fovea‐like region, in addition to ONL thickness. This conclusion is supported by a recent publication which reported a demonstrable lengthening of photoreceptor inner/outer segments on SD‐OCT scan images from the AC of dogs between 4 and 52 weeks of age, with an apparent peak inner/outer segment length in the very center of the AC demonstrated in 12‐week‐old dogs 10 . These OCT‐based observations are supported by the increased thickness of the photoreceptor outer segment layer that was previously demonstrated histologically by Mowat et al 39 in the AC, and by Beltran et al 31 in the fovea‐like region.…”

“…This conclusion is supported by a recent publication which reported a demonstrable lengthening of photoreceptor inner/outer segments on SD-OCT scan images from the AC of dogs between 4 and 52 weeks of age, with an apparent peak inner/outer segment length in the very center of the AC demonstrated in 12-week-old dogs. 10 These OCT-based observations are supported by the increased thickness of the photoreceptor outer segment layer that was previously demonstrated histologically by Mowat et al 39 in the AC, and by Beltran et al 31 in the fovea-like region. There are no published or unpublished data from extensive studies in these research colonies, to date, that suggest any ocular pathology in either cats that are heterozygous for the LTBP2 mutation or dogs that are heterozygous for the G661R ADAMTS10 mutation.…”

“…The validation of markers used to identify retinal and choroidal structures on SD‐OCT scans in different species is necessary. In the field of veterinary medicine, there are only relatively few and incomplete published datasets of normative SD‐OCT‐values for the different retinal and choroidal layers 1,10,12,17,21,22,33,47 …”

“…SD-OCT is especially useful for in vivo imaging of the retina and optic nerve head (ONH) in research and clinical settings. [1][2][3][4][5][6][7][8][9][10] The use and utility of SD-OCT have been advocated for primary glaucoma, sudden acquired retinal degeneration syndrome (SARDS), retinal dysplasia (RD), and progressive retinal atrophy (PRA) in veterinary patients. [11][12][13][14][15][16][17][18][19][20][21] Evaluation of retinal layer integrity and accurate measurement of thicknesses of and distances between anatomic layers require consistent and reliable identification of these anatomic layers on SD-OCT scans.…”