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The objective of the study was to examine whether a nutritional antioxidant supplementation could improve visual function in healthy dogs as measured by electroretinography (ERG) and autorefraction. A total of twelve Beagles, 6 to 8 years of age, with normal eyes upon indirect ophthalmoscopy and slit lamp biomicroscopy, were age and sex matched and randomly assigned to receive a feeding regimen for 6 months with or without a daily antioxidant supplementation. Portable, mini-Ganzfeld ERG and a Welch Allyn hand-held autorefractor were used to test retinal response and refractive error in the dogs at baseline and at the end of the supplementation period. All ERG a-wave amplitudes obtained were increased in the treatment group compared with those of dogs in the control group, with significant improvements in the scotopic high and photopic single flash cone ERG responses (P < 0·05 for both). For the b-wave amplitudes, all responses were similarly increased, with significant improvements in responses for the scotopic high light intensity stimulation (P < 0·05), and for photopic single flash cone and 30 Hz flicker (P < 0·01 for both) recordings. Change in refractive error was significantly less in the treatment group compared with that of the control group during the 6-month study (P < 0·05). Compared with the control group, the antioxidantsupplemented group showed improvement to varying degrees for retinal function and significantly less decline in refractive error. Dogs, like humans, experience retinal and lens functional decline with age. Antioxidant supplementation as demonstrated may be beneficial and effective in the long-term preservation and improvement of various functions of the canine eye. [ABSTRACT FROM AUTHOR]

The article reports on an investigation of the clinical and electroretinographic (ERG) features of the retina in normal and progressive retinal atrophy (PRA) in canines. Topics discussed include the different classifications of PRA, the way animals in the authors' study were prepared for ERG, and the results of the ophthalmoscopic examination. Also mentioned is the methodology used by the authors in their study.

Objective--To develop a method to electrophysiologically differentiate heterozygous-carrier Abyssinian-crossbred cats from homozygous-affected Abyssinian-crossbred cats before clinical onset of inherited rod-cone retinal degeneration. Animals--14 back-crossed Abyssinian-crossbred cats of unknown genotype (homozygous or heterozygous) for inherited rod-cone retinal degeneration, 24 age-matched mixed-breed control cats, 6 age-matched heterozygous Abyssinian-crossbred cats, and 6 homozygous Abyssinian cats. Procedure--Electroretinography (ERG) of heterozygous and homozygous cats revealed differences, especially for scotopic recordings. Frequent ophthalmoscopy and ERG (2 to 5 times; at intervals of 3 to 6 months) of back-crossed cats were performed. Amplitudes and implicit times were analyzed by use of a graphic representation of results. Ratios for amplitudes of the b-waves to amplitudes of the a-waves (b-wave:a-wave) were compared. Results--8 back-crossed cats had decreased a-wave amplitudes, increased b-wave implicit times, and abnormal ERG waveforms. Values for the b-wave:a-wave for the highest scotopic light intensity were significantly higher for those same 8 cats. Conclusions and Clinical Relevance--The 8 back-crossed Abyssinian-crossbred cats with abnormal results developed fundus changes over time consistent with disease. A graphic representation of ERG results can be used to differentiate between genotypes prior to funduscopic changes. Values for the b-wave:a-wave ratio provide confirmation. These ERG analyses may be applied clinically in the diagnosis of retinal degenerations in various species. Impact for Human Medicine--Cats with hereditary rod-cone degeneration may be a useful model for comparative studies in relation to retinitis pigmentosa in humans. Similar evaluations of ERG results could possibly be used for humans with suspected generalized retinal degeneration. [ABSTRACT FROM AUTHOR]

The genome sequence (1.9-fold coverage) of an inbred Abyssinian domestic cat was assembled, mapped, and annotated with a comparative approach that involved cross-reference to annotated genome assemblies of six mammals (human, chimpanzee, mouse, rat, dog, and cow). The results resolved chromosomal positions for 663,480 contigs, 20,285 putative feline gene orthologs, and 133,499 conserved sequence blocks (CSBs). Additional annotated features include repetitive elements, endogenous retroviral sequences, nuclear mitochondrial (numt) sequences, micro-RNAs, and evolutionary breakpoints that suggest historic balancing of translocation and inversion incidences in distinct mammalian lineages. Large numbers of single nucleotide polymorphisms (SNPs), deletion insertion polymorphisms (DIPs), and short tandem repeats (STRs), suitable for linkage or association studies were characterized in the context of long stretches of chromosome homozygosity. In spite of the light coverage capturing ~65% of euchromatin sequence from the cat genome, these comparative insights shed new light on the tempo and mode of gene/genome evolution in mammals, promise several research applications for the cat, and also illustrate that a comparative approach using more deeply covered mammals provides an informative, preliminary annotation of a light (1.9-fold) coverage mammal genome sequence. [ABSTRACT FROM AUTHOR]

Purpose: Mutations in the retinal transcription factor cone-rod homeobox (CRX) gene result in severe dominant retinopathies. A large animal model, the Rdy cat, carrying a spontaneous frameshift mutation in Crx, was reported previously. The present study aimed to further understand pathogenesis in this model by thoroughly characterizing the Rdy retina., Methods: Structural and functional changes were found in a comparison between the retinas of CrxRdy/+ kittens and those of wild-type littermates and were determined at various ages by fundus examination, electroretinography (ERG), optical coherence tomography, and histologic analyses. RNA and protein expression changes of Crx and key target genes were analyzed using quantitative reverse-transcribed PCR, Western blot analysis, and immunohistochemistry. Transcription activity of the mutant Crx was measured by a dual-luciferase transactivation assay., Results: CrxRdy/+ kittens had no recordable cone ERGs. Rod responses were delayed in development and markedly reduced at young ages and lost by 20 weeks. Photoreceptor outer segment development was incomplete and was followed by progressive outer retinal thinning starting in the cone-rich area centralis. Expression of cone and rod Crx target genes was significantly down-regulated. The mutant Crx allele was overexpressed, leading to high levels of the mutant protein lacking transactivation activity., Conclusions: The CrxRdy mutation exerts a dominant negative effect on wild-type Crx by overexpressing mutant protein. These findings, consistent with those of studies in a mouse model, support a conserved pathogenic mechanism for CRX frameshift mutations. The similarities between the feline eye and the human eye with the presence of a central region of high cone density makes the CrxRdy/+ cat a valuable model for preclinical testing of therapies for dominant CRX diseases.

Purpose: Late infantile neuronal ceroid lipofuscinosis (NCL) is an inherited disorder characterized by progressive vision loss. The disease results from mutations in the TPP1 (CLN2) gene. Studies were undertaken to characterize the effects of a TPP1 frameshift mutation on the retina in Dachshunds., Methods: A litter of four puppies consisting of one homozygous affected dog, two heterozygotes, and one homozygous normal dog were monitored for neurologic and retinal changes through 10 months of age. The affected and homozygous normal dogs, as well as one of the heterozygotes, were then euthanatized, and the retinas were examined morphologically., Results: The affected dog exhibited normal visual behavior and retinal function at 3 months of age, but vision was clearly impaired by 7 months, with markedly reduced ERG b-wave amplitudes. Beyond 7 months of age, the affected dog was functionally blind, and pupillary light reflexes and ERG response amplitudes continued to decline through 10 months of age. Both rod and cone system functions were severely impaired. The retina exhibited accumulation of autofluorescent storage bodies with distinctive curvilinear contents. Substantial cell loss occurred in the inner nuclear layer, with a smaller reduction in photoreceptor cell density., Conclusions: The canine TPP1 mutation results in progressive vision loss and retinal degeneration similar to that which occurs in human late infantile NCL. With the canine model, the natural history of disease progression in the retina provides a better understanding of the pathologic course of the disease and provides objective markers that can be used to assess the efficacy of therapeutic interventions.

Purpose: To describe and classify the morphologic changes in a naturally occurring dog model of early-onset cone-rod dystrophy (CRD) and to correlate these with earlier described clinical characteristics of the disease in dogs., Methods: Purpose-bred Standard Wire-Haired Dachshunds (SWHDs) derived from a large pedigree of dogs with early-onset CRD were euthanatized at defined ages to characterize morphologic changes in the disease process. Specimens were examined by light microscopy, including morphometric studies, electron microscopy, and immunohistochemistry. Peanut agglutinin (PNA), protein kinase C (PKC), synaptophysin (Syn), rhodopsin (Rho)-63, glial fibrillary acidic protein (GFAP), and short-wavelength cone opsin (OS) were used for immunohistochemical characterization., Results: The photopic cone-system-derived ERG amplitudes were already significantly reduced or nonrecordable in CRD-affected dogs at 5 weeks, the earliest age studied. The outer retina was morphologically most severely affected initially, with a subsequent degeneration of the inner retina. Cone degeneration was more pronounced than rod degeneration in young CRD-affected dogs. There was a marked phenotypic variation based on morphologic findings in the affected dogs. At the earliest time point studied (5-8 weeks) cone photoreceptor and glial cell abnormalities were observed, in accordance with earlier studies based on electrophysiological and clinical findings in which day blindness and abnormal cone ERGs were observed in young affected SWHD puppies. Preliminary genetic studies have indicated an autosomal recessive mode of inheritance for the defect., Conclusions: Through functional and structural characterization, early-onset cone abnormalities were found, consistent with a cone dysplasia at an age when rod structure was normal. Further studies are in progress to identify the gene(s) involved in this retinal disease process. The presently described natural animal model of primary cone dysplasia followed by rod degeneration may provide further insight into the human counterpart. Further studies are needed to ascertain an autosomal recessive mode of inheritance for CRD in the SWHD.

Purpose: To investigate the effects of a hereditary retinal degeneration on retinal oxygenation and determine whether it is responsible for the severe attenuation of retinal circulation in hereditary photoreceptor degenerations., Methods: Seven adult Abyssinian cats affected by hereditary retinal degeneration were studied. Oxygen microelectrodes were used to collect spatial profiles of retinal oxygenation in anesthetized animals. A one-dimensional model of oxygen diffusion was fitted to the data to quantify photoreceptor oxygen utilization (Qo(2))., Results: Photoreceptor Qo(2) progressively decreased until it reached zero in the end stage of the disease. Average inner retinal oxygen tension remained within normal limits at all disease stages, despite the observed progressive retinal vessel attenuation. Light affected photoreceptors normally, decreasing Qo(2) by approximately 50% at all stages of the disease., Conclusions: Loss of photoreceptor metabolism allows choroidal oxygen to reach the inner retina, attenuating the retinal circulation in this animal model of retinitis pigmentosa (RP) and probably also in human RP. As the degeneration progresses, there is a strong relationship between changes in the a-wave of the ERG and changes in rod oxidative metabolism, indicating that these two functional measures change together.

Purpose: To examine phototransduction using the a-wave and other aspects of retinal function with the intraretinal b- and c-waves at different stages of an inherited photoreceptor degeneration in Abyssinian cats., Methods: Vitreal and intraretinal ERGs were recorded from eight dark-adapted, anesthetized Abyssinian cats. Brief bright flashes were used to elicit vitreal a- and b-waves. Longer, weaker flashes were used to elicit intraretinal b- and c-waves. Stages 1 through 4 of the disease were characterized ophthalmoscopically. Parameters of the Lamb and Pugh a-wave model (a(max), A, and t(eff)) for the Abyssinian cats were compared with those for normal cats. Light microscopy was used to count photoreceptor nuclei., Results: The maximum a-wave amplitude, a(max), was significantly smaller in stage 1, and continued to decrease (stage 1: 50% of normal, stage 2: 28%, stage 3: 27%; and stage 4: unrecordable). There was a small, but not significant, decrease in the amplification constant A from 0.24 +/- 0.11 s(-2) in normal cats to 0.16 +/- 0.08 s(-2) in Abyssinian cats. The intraretinal b- and c-wave amplitudes decreased most dramatically during the early stage of the disease. Affected animals had fewer photoreceptors than unaffected Abyssinians or control animals. The number of photoreceptors declined most rapidly in the inferior periphery., Conclusions: The amplitudes of all ERG components were already reduced significantly by stage 1 and progressively declined. The lack of major changes in a-wave model parameters indicates that the degeneration is probably not due to a mutation in transduction proteins. Losses of photoreceptor function were larger than losses of photoreceptor nuclei.

Purpose: To assess the efficacy of AAV-mediated gene therapy to restore vision in a large number of RPE65(-/-) dogs and to determine whether systemic and local side effects are caused by the treatment., Methods: Normal RPE65 dog cDNA was subcloned into an rAAV vector under control of a cytomegalovirus promoter, and an AAV.GFP control vector was also produced with the titers 2 x 10(12) particles/mL and 2 x 10(10) transducing U/mL, respectively. RPE65(-/-) dogs, aged 4 to 30 months were treated with subretinal injections of the AAV.RPE65 and control vectors, respectively, in each eye, and three 24- to 30-month-old normal control dogs with the latter. Baseline and postoperative systemic and ophthalmic examinations, blood screenings, vision testing, and electroretinography (ERG) were performed. Two RPE65(-/-) dogs were killed at 3 and 6 months after treatment for morphologic examination of the retinas., Results: RPE65(-/-) dogs were practically blind from birth with nonrecordable or low-amplitude ERGs. Construct injections or sham surgeries were performed in 28 eyes; 11 were injected subretinally with the AAV.RPE65 construct. ERGs at 3 months after surgery showed that in the latter eyes, dark-adapted b-wave amplitudes recovered to an average of 28% of normal, and light adapted b-wave amplitudes to 32% of normal. ERG amplitudes were not reduced during a 6- to 9-month follow-up. No systemic side effects were observed, but uveitis developed in nine AAV.RPE65-treated eyes. No uveitis was observed in the eyes treated with the control vector. Immunocytochemistry showed expression of RPE65 in the retinal pigment epithelium (RPE) of AAV.RPE65-treated eyes. Fluorescence microscopy showed expression of green fluorescent protein (GFP) in the RPE and, to a lesser extent, in the neural retinas of AAV.GFP-treated eyes. Ultrastructurally, a reversal of RPE lipid droplet accumulation was observed at the AAV.RPE65 transgene injection site, but not at the site of injection of the control vector., Conclusions: In 10 of 11 treated RPE65(-/-) eyes, gene transfer resulted in development of vision, both subjectively apparent by loss of nystagmus, and objectively recorded by ERG. Structurally, there was reversal of lipid droplet accumulation in the RPE. Uveitis developed in 75% of the transgene-treated eyes, a complication possibly due to an immunopathogenic response to the RPE65 molecule.