Retinal Vascular Plexuses Are Unequally Affected in Canine Inherited Retinal Degenerations.

Purpose: To characterize the progression of vascular changes that occur in each retinal plexus, in three canine models of inherited retinal degeneration. Methods: In this retrospective cohort study, we examined the retinal imaging records of 44 dogs from a research colony that had undergone optical coherence tomography angiography (OCTA) imaging. Animals enrolled included crd2/NPHP5 and xlpra2/RPGR mutant dogs imaged at different stages of photoreceptor loss, as well as RHOT4R/+ dogs after acute light-induced rod degeneration. Also included were normal controls imaged at similar ages. OCT angiograms of the superficial vascular plexus combined with the intermediate capillary plexus (SVP + ICP), and the deep capillary plexus (DCP) were analyzed using the AngioTool software to calculate vessel density and other vascular parameters. Results: A reduction in vessel density was seen over time in both the SVP + ICP and DCP in all mutant dogs but was more pronounced in the DCP. Scans were subclassified based on outer nuclear layer (ONL) thinning compared to age-matched normal controls. When ONL loss was 0% to 50%, vessel density in the DCP was significantly lower than in age-matched controls. In all cases, when ONL loss exceeded 87.5%, vessel density in the SVP + ICP was significantly reduced as well. In the acute light-induced rod degeneration model, the vascular regression changes were observed mainly in the DCP. Conclusions: Vessel density reduction in dogs undergoing retinal degeneration is first detected by OCTA in the DCP, and only at later stages in the SVP + ICP.

Targeting ON-bipolar cells by AAV gene therapy stably reverses LRIT3-congenital stationary night blindness.

SignificanceCanine models of inherited retinal diseases have helped advance adeno-associated virus (AAV)-based gene therapies targeting specific cells in the outer retina for treating blinding diseases in patients. However, therapeutic targeting of diseases such as congenital stationary night blindness (CSNB) that exhibit defects in ON-bipolar cells (ON-BCs) of the midretina remains underdeveloped. Using a leucine-rich repeat, immunoglobulin-like and transmembrane domain 3 (LRIT3) mutant canine model of CSNB exhibiting ON-BC dysfunction, we tested the ability of cell-specific AAV capsids and promotors to specifically target ON-BCs for gene delivery. Subretinal injection of one vector demonstrated safety and efficacy with robust and stable rescue of electroretinography signals and night vision up to 1 y, paving the way for clinical trials in patients.

Novel insights into chorioretinal and juxtapapillary colobomas by optical coherence tomography.

PURPOSE: The purpose was to describe the in vivo microanatomy of typical and atypical chorioretinal and juxtapapillary colobomas in the dog. METHODS: Three cross-breed dogs were found to be affected with colobomas. Two of the cases were NEHJ1 homozygous and Collie Eye Anomaly (CEA) affected and had the typical optic nerve head colobomas seen with the disease. The third case had an unexpected atypical coloboma. In vivo retinal photography and non-invasive retinal imaging by confocal scanning laser ophthalmoscope (cSLO) and optical coherence tomography (OCT) were done, and the eye affected with the atypical coloboma was collected and processed for histopathological evaluation. RESULTS: The majority of the defining features within the CEA defects were similar, with the extent of change to the choroid being of note. Similar to the first two cases, the atypical coloboma demonstrated absent normal retina, RPE, and choroid within the coloboma. Prominent intercalary membranes and vitreal strands attached to the depth of the coloboma were also apparent in all affected eyes. However, unlike the CEA-associated colobomas, the atypical coloboma possessed normal choroid surrounding the lesion and the depth of the lesion was apparent throughout. CONCLUSIONS: Advanced retinal imaging enables the appreciation of microanatomical changes that occur in the living eye. The ability of OCT to enhance visualization of abnormal retinal structures and detect subtle neurosensory retinal defects has allowed for the in vivo characterization of features observed in typical and atypical colobomas, as well as the appreciation of some of the resulting structural changes not visible by ophthalmoscopy alone.

Monocular retinopathy of prematurity-like retinal vasculopathy in a dog.

PURPOSE: To describe a case of monocular retinopathy of prematurity (ROP)-like vasculopathy without oxygen supplementation in the dog. METHODS: Fundus photographs (RetCam), spectral-domain optical coherence tomography (sdOCT), confocal scanning laser ophthalmoscopy (cSLO), and fluorescein angiography (FA), as well as postmortem histology and immunohistochemistry (Collagen IV and anti-vWF antibodies), were carried out to characterize the vascular abnormalities. RESULTS: Ophthalmic examination showed peripheral and mid-temporal avascular areas in the tapetal region, neovascularization and abnormally dilated and tortuous retinal vessels in the left eye. sdOCT demonstrated not only cross-sectional views of preretinal fibrovascular proliferation but also extensive proliferation extraretinally into the vitreous. FA emphasized demarcation of vascular and avascular zones with neovascular tufts "popcorns." Histology and immunohistochemistry confirmed presence of abnormally dilated vessels and the intravitreal blood vessels. CONCLUSIONS: ROP is a disease of abnormally developed retinal vascularization associated with oxygen supplementation therapy, potentially causing blindness in premature infants. Although the mechanism of ROP-like vasculopathy in our case is unclear, it is important to appreciate that the abnormal vascular pattern seen in ROP in premature infants can occur in canines without oxygen administration.