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Objectives: This study aimed to describe the epidemiology and clinical presentation of presumed hereditary or presumed breed-related ocular diseases in a population of cats in France., Methods: Medical records from between September 2013 and August 2017 were reviewed to identify cats with at least one presumed hereditary or breed-related ocular disease. Cats with concurrent, or a history of, ocular or systemic infectious diseases were excluded. Signalment, history and clinical findings were recorded., Results: Of the 1161 cats that presented to our institution during the study period, 129 were diagnosed with at least one presumed hereditary or presumed breed-related ocular disease (11.1%, 95% confidence interval [CI] 9.3-12.9). Five ocular abnormalities had a prevalence of >1%: entropion, corneal sequestration, persistent pupillary membrane, cataract and retinal dysplasia. The prevalence of entropion was 2.2% (95% CI 1.3-3.0), with Persians ( P  = 0.03), Maine Coons ( P <0.01) and male cats ( P <0.01) being over-represented. The prevalence of corneal sequestration was 2.4% (95% CI 1.5-3.3), with Persians ( P <0.01) and Exotic Shorthairs ( P  = 0.02) being over-represented. Persistent pupillary membranes and cataracts had the same prevalence of 2.3% (95% CI 1.5-3.2), with no particular sex or breed significantly over-represented. Retinal dysplasia had a prevalence of 1.6% (95% CI 0.8-2.3) and Persian cats were over-represented ( P  = 0.04). Anterior segment dysgenesis had a low prevalence (0.9%, 95% CI 0.4-1.5), with all affected cats being domestic shorthairs and this breed therefore was over-represented ( P  = 0.04)., Conclusions and Relevance: In a French population of cats, presumed hereditary or breed-related ocular diseases accounted for 11.1% of all ocular diseases. Cataracts, corneal sequestration, persistent pupillary membrane, entropion and retinal dysplasia were the most common conditions. Statistical breed over-representation was observed for entropion, corneal sequestration and retinal dysplasia. We recommend that more systematic screening of feline species is conducted.

Objective: To describe the in vivo structural characteristics of multifocal and geographic retinal dysplasia visualized with advanced retinal imaging including confocal scanning laser ophthalmoscopy (cSLO), optical coherence tomography (OCT), en face OCT, and the novel vascular imaging technique OCT angiography (OCTA)., Dogs Studied and Procedures: Two dogs were diagnosed with unilateral multifocal or geographic retinal dysplasia and underwent advanced retinal imaging under general anesthesia at the Retinal Disease Studies Facility of the University of Pennsylvania., Results: In both cases, the morphological pattern of the lesions was similar including outer retinal folds that invaginated and formed tubular retinal rosettes, surrounding a central inner retinal thickening (multifocal) or plaque (geographic). The two dogs had multiple vascular anomalies in the lesions such as increased tortuosity, abnormal change of vessel diameter including aneurysms and capillary network disruption. We also identified increased autofluorescence by AF cSLO with short wavelength light source (488 nm and barrier filter at 500 nm), and several areas of photoreceptor loss associated with the lesions., Conclusion: The use of OCTA allowed the identification of microvascular abnormalities associated with multifocal and geographic retinal dysplasia in two dogs. To our knowledge, this is the first report where the dye-free OCTA technique is used to study vascular lesions in canine retinas., (© 2021 American College of Veterinary Ophthalmologists.)

Purpose: To compare the scanning laser ophthalmoscopy (SLO), optical coherence tomography (OCT), and fluorescein angiography (FA) findings in retrievers with a single unilateral circular retinal plaque to those of an English springer spaniel with bilateral retinal dysplasia., Procedures: A retrospective record review identified three dogs with circular retinal plaques that underwent SLO and OCT; in two of the three dogs, FA was also completed. Morphologic changes, lesion measurements, and angiogram characteristics were documented. An English springer spaniel with bilateral retinal dysplasia that had undergone SLO, OCT, and FA was used for comparison., Results: Scanning laser ophthalmoscopy of the retriever dogs revealed circular retinal plaques with a dark periphery located in the tapetal retina. OCT revealed a thickening of the nerve fiber layer corresponding to the circular pattern observed on SLO. Within the circular plaque, the retina was predominantly of normal architecture. FA revealed variable hypofluorescence of both the rim and the center of the circular lesion throughout the early angiogram phases. In the late recirculation phase, small multifocal areas of hyperfluorescence were observed. OCT of geographic retinal dysplasia in the English springer spaniel revealed disorganization of both inner and outer retinal layers, and retinal detachment., Conclusions: Circular plaques observed in the tapetal retina are predominantly formed by a thickening of inner retina, while retinal dysplasia has disorganization of both inner and outer retinal layers. Further etiologic research is needed, including pedigree mapping to determine whether retinal plaques are an acquired or inherited condition., (© 2020 American College of Veterinary Ophthalmologists.)

Purpose: To examine the in vivo microanatomy of retinal folds and geographic lesions in dogs with acquired or inherited retinal dysplasia., Material and Methods: Thirteen dogs had retinal microanatomy evaluation under general anesthesia using cSLO/sdOCT; two eyes had noninherited multifocal retinal folds, five had inherited multifocal retinal folds (drd1 or drd2), and 10 geographic retinal dysplasia. Retinas from two drd2 carrier dogs were examined by histology and immunohistochemistry (IHC) after in vivo imaging., Results: Retinal folds are the common feature of acquired focal/multifocal or geographic retinal dysplasia, are indistinguishable structurally from those associated with syndromic oculoskeletal dysplasia, and represent outer nuclear layer invaginations and rosettes visible by sdOCT. In dogs heterozygous for oculoskeletal dysplasia, the folds form clusters in a perivascular distribution along superior central vessels. IHC confirmed photoreceptor identity in the retinal folds. The geographic dysplasia plaques are not focally detached, but have inner retinal disorganization and intense autofluorescence in cSLO autofluorescence mode that is mainly limited to the geographic lesion, but is not uniform and in some extends beyond the plaques., Conclusion: We propose that the autofluorescent characteristic of the geographic lesions is associated with an inner retinal disruption associated with perivascular or infiltrating macrophages and phagocytosis of cellular debris. As well, we suggest restructuring the examination forms to distinguish the folds that are sporadically distributed from those that have a perivascular distribution as the latter likely represent carriers for drd. In this latter group, DNA testing would be a helpful tool to provide specific breeding advice., (© 2019 American College of Veterinary Ophthalmologists.)

Microphthalmia is characterized by abnormally small eyes and usually retinal dysplasia, accounting for up to 11% of the blindness in children. Right now there is no effective treatment for the disease, and the underlying mechanisms, especially how retinal dysplasia develops from microphthalmia and whether it depends on the signals from lens ectoderm are still unclear. Mutations in genes of the TGF-β superfamily have been noted in patients with microphthalmia. Using conditional knockout mice, here we address the question that whether ocular surface ectoderm-derived Smad4 modulates retinal development. We found that loss of Smad4 specifically on surface lens ectoderm leads to microphthalmia and dysplasia of retina. Retinal dysplasia in the knockout mice is caused by the delayed or failed differentiation and apoptosis of retinal cells. Microarray analyses revealed that members of Hedgehog and Wnt signaling pathways are affected in the knockout retinas, suggesting that ocular surface ectoderm-derived Smad4 can regulate Hedgehog and Wnt signaling in the retina. Our studies suggest that defective of ocular surface ectoderm may affect retinal development.

Evidence from other species justifies the hypotheses that useful hybrid vigour occurs in dogs and that it can be exploited for improved health, welfare and fitness for purpose. Unfortunately, most of the relevant published canine studies do not provide estimates of actual hybrid vigour because of inadequate specification of the parentage of mixed-bred dogs. To our knowledge, only three published studies have shed any light on actual hybrid vigour in dogs. There are two reports of actual hybrid vigour between Labrador and Golden retrievers, the first ranging from +2.5% to -6.0% for components of a standardised applied-stimulus behavioural test, and the second being at least +12.4% for chance of graduating as a guide dog. The third study provides a minimum estimate of negative actual hybrid vigour: crossbreds between Labrador retrievers and poodles had a higher prevalence of multifocal retinal dysplasia than the average prevalence in their purebred parent breeds. The lack of estimates of actual hybrid vigour can be overcome by including the exact nature of the cross (e.g. F1, F2 or backcross) and their purebred parental breeds in the specification of mixed-bred dogs. Even if only F1 crossbreds can be categorised, this change would enable researchers to conduct substantial investigations to determine whether hybrid vigour has any utility for dog breeding., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Sudden loss of vision is an ophthalmic emergency with numerous possible causes. Abnormalities may occur at any point within the complex vision pathway, from retina to optic nerve to the visual center in the occipital lobe. This article reviews specific prechiasm (retina and optic nerve) and cerebral cortical diseases that lead to acute blindness. Information regarding specific etiologies, pathophysiology, diagnosis, treatment, and prognosis for vision is discussed., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Objective: To investigate qualitative and quantitative differences in the structure of the posterior segment of the eye in 1-day post-hatch and 12-month-old retinal dysplasia and degeneration (rdd) and wild-type chickens., Animal Studied: Retinal dysplasia and degeneration and wild-type chickens., Procedure: Using a commercially available spectral domain optical coherence tomography (OCT) system, 15° horizontal line scans were performed in both eyes of 24 live birds. Qualitative differences in retinal lamination and choroidal structure were investigated, and retinal and choroidal thickness were measured., Results: Progressive retinal thinning with loss of outer retinal lamination and changes in the appearance of the choroid were seen in the rdd birds. Mean total retinal thickness was 202 μm (SD 7.8) and 251 μm (SD 8.8) in the rdd and wild-type chicks and 154 μm (SD 18) and 280 μm (SD 10.8) in the adult birds. Much of the difference was the result of loss of outer retinal lamination and thickness in the rdd birds. Mean choroidal thickness was 76 μm (SD 19.6) and 112 μm (SD 36.9) in the rdd and wild-type chicks and 85 μm (SD 23.7) and 228 μm (SD 44.1) in the rdd and wild-type adult birds, respectively., Conclusions: Differences in retinal and choroidal structure and thickness between rdd and wild-type birds were evident on spectral domain OCT imaging at 1-day post-hatch and more marked at 1 year. Spectral domain OCT may provide a reliable end point for therapeutic intervention in this animal model of inherited retinal degeneration., (© 2013 American College of Veterinary Ophthalmologists.)

One-hundred and seventy-five labradoodles underwent slit-lamp biomicroscopy and direct and indirect ophthalmoscopy between January 2008 and December 2009. These examinations were performed at shows by the first author. In addition, labradoodle eye certificates from the 2008 and 2009 British Veterinary Association/Kennel Club/International Sheep Dog Society (BVA/KC/ISDS) Eye Scheme were analysed (n=260). The results of the examinations were reviewed, and all ophthalmic abnormalities were recorded. The prevalence of any abnormality was compared with that reported by the Eye Scheme and the KC during 2009 for the labrador retriever, miniature, toy and standard poodles. Multifocal retinal dysplasia (MRD) was identified in 20 labradoodles (4.6 per cent), and cataracts were identified in 16 labradoodles (3.7 per cent). The prevalence of MRD in labradoodles was significantly greater than in labrador retrievers (P<0.0001). There was no difference in the prevalence of cataract between labradoodles and labrador retrievers (P=0.4866). The results of this study suggest that MRD is a relatively common finding in the labradoodle population in the UK. Given such an apparent high prevalence of MRD, routine screening for hereditary eye disease before breeding is advised for this increasingly popular new crossbreed.

Mitochondrial transcription factor A (Tfam) has been implicated in the pathogenesis of retinal dysplasia in miniature schnauzer dogs and it has been proposed that affected dogs have altered mitochondrial numbers, size, and morphology. To test these hypotheses the Tfam gene of affected and normal miniature schnauzer dogs with retinal dysplasia was sequenced and lymphocyte mitochondria were quantified, measured, and the morphology was compared in normal and affected dogs using transmission electron microscopy. For Tfam sequencing, retina, retinal pigment epithelium (RPE), and whole blood samples were collected. Total RNA was isolated from the retina and RPE and reverse transcribed to make cDNA. Genomic DNA was extracted from white blood cell pellets obtained from the whole blood samples. The Tfam coding sequence, 5' promoter region, intron1 and the 3' non-coding sequence of normal and affected dogs were amplified using polymerase chain reaction (PCR), cloned and sequenced. For electron microscopy, lymphocytes from affected and normal dogs were photographed and the mitochondria within each cross-section were identified, quantified, and the mitochondrial area (μm²) per lymphocyte cross-section was calculated. Lastly, using a masked technique, mitochondrial morphology was compared between the 2 groups. Sequencing of the miniature schnauzer Tfam gene revealed no functional sequence variation between affected and normal dogs. Lymphocyte and mitochondrial area, mitochondrial quantification, and morphology assessment also revealed no significant difference between the 2 groups. Further investigation into other candidate genes or factors causing retinal dysplasia in the miniature schnauzer is warranted.

Purpose: To elucidate the gene defect in a pedigree of cats segregating for autosomal dominant rod-cone dysplasia (Rdy), a retinopathy characterized extensively from a clinical perspective. Disease expression in Rdy cats is comparable to that in young patients with congenital blindness (Leber congenital amaurosis [LCA] or retinitis pigmentosa [RP])., Methods: A pedigree segregating for Rdy was generated and phenotyped by clinical ophthalmic examination methods including ophthalmoscopy and full-field flash electroretinography. Short tandem repeat loci tightly linked to candidate genes for autosomal dominant retinitis pigmentosa in humans were genotyped in the pedigree., Results: Significant linkage was established to the candidate gene CRX (LOD = 5.56, = 0) on cat chromosome E2. A single base pair deletion was identified in exon 4 (n.546delC) in affected individuals but not in unaffected littermates. This mutation generates a frame shift in the transcript, introducing a premature stop codon truncating the putative CRX peptide, which would eliminate the critical transcriptional activation region. Clinical observations corroborate previously reported clinical reports about Rdy. Results show that the cone photoreceptor system was more severely affected than the rods in the early disease process., Conclusions: A putative mutation causative of the Rdy phenotype has been described as a single base pair deletion in exon 4 of the CRX gene, thus identifying the first animal model for CRX-linked disease that closely resembles the human disease. As such, it will provide valuable insights into the mechanisms underlying these diseases and their variable presentation, as well as providing a suitable model for testing therapies for these diseases.

Objective: To compare relative amounts of WBC mitochondrial DNA (mtDNA; assessed via real-time PCR assay) and morphology of lymphocyte mitochondria (assessed via transmission electron microscopy [TEM]) in blood samples collected from English Springer Spaniels with and without retinal dysplasia., Animals: 7 and 5 client-owned English Springer Spaniels (1 to 11 years old) with and without retinal dysplasia, respectively., Procedures: Blood samples were obtained from affected and unaffected dogs via venipuncture. Genomic DNA was extracted from WBCs of the 7 affected and 5 unaffected dogs, and relative quantification of the cytochrome c oxidase subunit 1 gene (COX1) was determined via analysis of real-time PCR results. White blood cells from 3 affected and 4 unaffected dogs were embedded in epoxide resin for TEM; cross sections were examined for lymphocytes, which were measured. The mitochondria within lymphocytes were quantified, and the mitochondrial surface area per lymphocyte cross section was calculated. A masked technique was used to compare mitochondrial morphology between the 2 groups., Results: Compared with the smallest measured quantity of mtDNA among unaffected dogs, mtDNA amounts varied among unaffected (1.08- to 4.76-fold differences) and affected dogs (1- to 2.68-fold differences). Analysis of lymphocyte measurements and mitochondrial surface area, morphology, and quantity revealed no significant differences between affected and unaffected dogs., Conclusions and Clinical Relevance: No significant differences were detected in relative amounts of WBC mtDNA or the size, number, or morphology of lymphocyte mitochondria in English Springer Spaniels affected with retinal dysplasia, compared with results for unaffected control dogs.

Rod-cone dysplasia type 2 (rcd2) is an autosomal recessive disorder that segregates in collie dogs. Linkage disequilibrium and meiotic linkage mapping were combined to take advantage of population structure within this breed and to fine map rcd2 to a 230-kb candidate region that included the gene C1orf36 responsible for human and murine rd3, and within which all affected dogs were homozygous for one haplotype. In one of three identified canine retinal RD3 splice variants, an insertion was found that cosegregates with rcd2 and is predicted to alter the last 61 codons of the normal open reading frame and further extend the open reading frame. Thus, combined meiotic linkage and LD mapping within a single canine breed can yield critical reduction of the disease interval when appropriate advantage is taken of within-breed population structure. This should permit a similar approach to tackle other hereditary traits that segregate in single closed populations.

Purpose: To describe electroretinographic (ERG) findings in a strain of Standard Wire Haired Dachshund (SWHD)-derived dogs at the ages of approximately 5, 8 and 52 weeks selected for inherited early onset cone-rod dystrophy., Methods: Nineteen affected and 13 age-matched control SWHDs were included in the study. All dogs were subjected to standardized bilateral Ganzfeld ERGs and ophthalmoscopic examinations at regular intervals., Results: Photopic cone-derived ERG amplitudes were significantly lower and never reached similar levels as those recorded in control dogs. In affected dogs there was no increase with age in amplitudes recorded using 30.1 and 50.1 Hz flicker stimuli. In contrast, in the control groups the photopic b-wave amplitude recorded at 50.1 Hz increased significantly from age 5 to 8 and from 5 to 52 weeks. In affected animals, scotopic rod-derived amplitudes were significantly lower for most recordings compared to those of control dogs, although they increased significantly from age 5 to 8 weeks in both affected and controls. Both a- and b-wave implicit times were significantly longer in the youngest affected group when compared to the age-matched control group at 0.6 log cd s/m(2) and 5.1 Hz single flash light stimuli. In the control dogs, however, there was a significant shortening in a-wave implicit times from age 5 to 8 weeks, and in a- and b-wave implicit times recorded at 5.1 Hz single flash stimuli from age 5 to 52 weeks., Conclusions: The described retinal degeneration in the SWHD is an early onset cone-rod dystrophy, initially affecting the cone system most severely. Early functional changes are seen in the rod system as well. Inner retina also appears affected already at a young age with findings indicating postsynaptic functional changes already at the earliest time point studied, at age 5 weeks. The present study further indicates that the canine retina reaches maturity later than previously reported, or that there exist major breed differences.

Purpose: To investigate the molecular basis of inherited retinal dysplasia in miniature Schnauzers., Methods: Retina and retinal pigment epithelial tissues were collected from canine subjects at the age of 3 weeks. Total RNA isolated from these tissues was reverse transcribed to make representative cDNA pools that were compared for differences in gene expression by using a subtractive hybridization technique referred to as representational difference analysis (RDA). Expression differences identified by RDA were confirmed and quantified by real-time reverse-transcription PCR. Mitochondrial morphology from leukocytes and skeletal muscle of normal and affected miniature Schnauzers was examined by transmission electron microscopy., Results: RDA screening of retinal pigment epithelial cDNA identified differences in mRNA transcript coding for two mitochondrial (mt) proteins--cytochrome oxidase subunit 1 and NADH dehydrogenase subunit 6--in affected dogs. Contrary to expectations, these identified sequences did not contain mutations. Based on the implication of mt-DNA-encoded proteins by the RDA experiments we used real-time PCR to compare the relative amounts of mt-DNA template in white blood cells from normal and affected dogs. White blood cells of affected dogs contained less than 30% of the normal amount of two specific mtDNA sequences, compared with the content of the nuclear-encoded glyceraldehyde-3-phosphate dehydrogenase (GA-3-PDH) reference gene. Retina and RPE tissue from affected dogs had reduced mRNA transcript levels for the two mitochondrial genes detected in the RDA experiment. Transcript levels for another mtDNA-encoded gene as well as the nuclear-encoded mitochondrial Tfam transcription factor were reduced in these tissues in affected dogs. Mitochondria from affected dogs were reduced in number and size and were unusually electron dense., Conclusions: Reduced levels of nuclear and mitochondrial transcripts in the retina and RPE of miniature Schnauzers affected with retinal dysplasia suggest that the pathogenesis of the disorder may arise from a lowered energy supply to the retina and RPE.

Eyes from 88 otters found dead in south-west England between 1990 and 2000, were collected as part of a larger pathological study. Histopathological examination of 131 eyes revealed dysplastic changes such as rosetting and folding in the retinas of 26 of the otters. In the eyes of 42 of the otters there were postmortem and fixation-induced retinal detachment which complicated the differentiation of dysplastic from normal retina, but 11 eyes had folds which probably indicated a dysplastic pathology. The eyes of 18 of the otters had inflammatory or autolytic changes which precluded a definitive evaluation of their dysplastic status. Liver samples from 55 of the otters were analysed for a range of polychlorinated hydrocarbons and for vitamin A. The otters with dysplastic retinas had significantly lower concentrations of vitamin A and higher concentrations of dieldrin than the otters with normal retinas.

The objectives of this study were to define the clinical syndrome of retinal dysplasia and persistent primary vitreous in Miniature Schnauzer dogs and determine the etiology. We examined 106 Miniature Schnauzers using a biomicroscope and indirect ophthalmoscope. The anterior and posterior segments of affected dogs were photographed. Four enucleated eyes were examined using routine light microscopy and scanning electron microscopy. A pedigree was constructed and related dogs were test-bred to define the mode of inheritance of this syndrome. Congenital retinal dysplasia was confirmed in 24 of 106 related Miniature Schnauzer dogs. Physical and postmortem examinations revealed that congenital abnormalities were limited to the eyes. Biomicroscopic, indirect ophthalmoscopic, and neuro-ophthalmic examinations confirmed that some of these dogs were blind secondary to bilateral retinal dysplasia and detachment (nonattachment) (n = 13), and the remainder had generalized retinal dysplasia (n = 11). Fifteen of these dogs were also diagnosed with unilateral (n = 9) or bilateral (n = 6) persistent hyperplastic primary vitreous. Nutritional, infectious, or toxic etiologies were not evident on physical, postmortem, light microscopic, or transmitting and scanning electron microscopic examination of four affected Miniature Schnauzers. We examined the pedigree and determined that an autosomal recessive mode of inheritance was most likely. Three test-bred litters including those from affected parents, carrier and affected parents, and carrier parents confirmed this mode of inheritance. This study confirms that retinal dysplasia and persistent hyperplastic primary vitreous is a congenital abnormality that is inherited as an autosomal recessive condition in Miniature Schnauzers.

Thirty-three live 9-day-old broiler chicks were submitted for laboratory evaluation because of blindness. Blindness was observed in up to 1% of 25,000 birds from four different houses. All the chicks were from the same breeder source. Blindness was apparent when the chicks were 2-3 days old. Clinically, the blind chicks were smaller than their counterparts, were unable to find feed and water, and wandered aimlessly. Necropsy did not reveal any lesions. Two chicks examined clinically at 14 days of age lacked pupillary reflexes after light stimulation, and the anterior and posterior segments of the eye were normal. Microscopically, degeneration of photoreceptor cells characterized by vacuoles was evident at 9 days of age, and rosette formation of the retina, disorganization of retinal layers, synechia of the retina with mild inflammation in the choroid, and proliferation of the retinal pigment epithelial cells were evident by 15 days of age. Because the chicks came from the same breeder source and the incidence of blindness was low, a probable genetic etiology is suspected as the cause of blindness in this flock.

A unilateral scleral staphyloma in an 18-month-old, female spayed Domestic Short-haired cat was treated with excision, primary closure and fascial graft. Other ocular abnormalities noted on examination included iris coloboma, anterior cortical cataract, focal lens equator flattening and retinal dysplasia. The staphyloma was presumed to be congenital in origin.

Four Irish setters were diagnosed with bilateral retinal degeneration and cataracts at an age ranging from six to 11 years. In three of these dogs, progressive night blindness was reported from an age of eight to 11 years. In the fourth dog, aged six, no signs of visual impairment had been noticed. In all four dogs, the rod-cone dysplasia type 1 (rcd1) mutation was excluded as a cause, using an allele-specific PCR. From their three-generation pedigrees, a familial relationship was detected in three out of four dogs, which were also related to four additional Irish setter dogs with a history and clinical signs suggestive of late-onset progressive retinal degeneration. These results suggest the existence of a possibly hereditary, late-onset, progressive retinal atrophy in the Irish setter breed, that is distinct from rcd1.

Between 1989 and 1997, 8204 rough collies were examined for collie eye anomaly (CEA) at up to 10 weeks of age. All dogs were positively identified and the results were registered under the Swedish Kennel Club genetic health programme. A significant decrease in litter size occurred if one of two affected parents had coloboma (3.8 pups) compared with litters from two chorioretinal dysplasia- (CRD-) affected collies (5.2 pups) or litters by two normal collies (5.0 pups), indicating an influence of the coloboma genotype on offspring vitality. The prevalence of CRD in pups from normal x normal matings and CRD x CRD matings was significantly different from that expected under simple autosomal recessive inheritance (43 per cent versus 25 per cent and 85 per cent versus 100 per cent). The results are compatible with polygenic inheritance but not with simple autosomal recessive inheritance. CRD prevalence in offspring of CRD x coloboma matings was significantly lower than in pups of CRD x CRD matings, reflecting effects of the coloboma genotype on vitality. These results have important implications for breeding programmes and the genetic control of CEA.

A total of 8204 rough collies, representing 76 per cent of all collies registered by the Swedish Kennel Club between 1989 and 1997, were examined before 10 weeks of age for collie eye anomaly (CEA). All dogs were permanently identified and examination results were registered and computerised. The policy of breeders during the study period was to select against coloboma in breeding stock, but to allow breeding of chorioretinal dysplasia (CRD) affected animals. The prevalence of CRD increased significantly from 54.2 per cent to 68.1 per cent (P < 0.001) from 1989 to 1997, while the prevalence of coloboma did not (8.3 per cent to 8.5 per cent, P = 0.4). These results are not compatible with a simple, recessive, autosomal inheritance for the entire CEA complex.

A 5-wk-old female dromedary camel (Camelus dromedarius) was clinically diagnosed with bilateral corneal dermoids, incomplete congenital cataracts, a left persistent hyaloid artery (PHA), and a ventricular septal defect (VSD). The corneal dermoids were removed by lamellar keratectomy, and vision improved in the left eye. Thirteen months after dermoid surgery, the calf was presented for enlargement of the right eye. Glaucoma was confirmed in the right eye, and corneal fibrosis and cataract were noted in the left eye. Persistence of the VSD was confirmed by cardiac ultrasonography. The calf was euthanized, and necropsy findings confirmed VSD. Histopathologic examination revealed bilateral corneal thinning and fibrosis, cataracts with retrolental fibroplasia, and retinal dysplasia. Additional changes in the right globe were anterior segment dysgenesis, ruptured lens capsule, chronic phacoclastic uveitis, and retinal separation. The PHA was confirmed in the left eye.

Mother and son of a Yorkshire Terrier family showed excessive multifocal retinal dysplasia (RD1) and geographical retinal dysplasia (RD2), intra- and preretinal hemorrhages partial and total retinal detachment (total RD/RD3), residues of the pupillary membrane and as a newness in this combination a geographical, subepithelial corneal opacity, composed of small dots. One, not examined son of the same litter was congenitally blind. Similar corneal opacities were also found in two Rough Collies affected with CEA, RD, and microphthalmia, a young German Wirehair Pointer with primary absolute glaucoma in conjunction with goniodysplasia and RD in the healthy seeming fellow eye as well as in a poodle puppy affected with bilateral posterior suture-line cataract in connection with persistent primary hyperplastic vitreous (PHPV) in one and a globe-shaped deformed retina in connection with a persistent, blood conducting hyaloid artery in the other eye. The latter finally resulted in intraocular hemorrhage and secondary glaucoma. A pathogenetic connection between ocular malformations and subepithelial corneal opacity seems to be likely.

Canine generalised progressive retinal atrophy (gPRA) is a large and ever-increasing collection of naturally occurring, heterogeneous, progressive disorders. Most are inherited in an autosomal recessive manner and new, breed-specific forms continue to be described. The gPRAs cause photoreceptor cell death and subsequent retinal degeneration, culminating in blindness. In humans, similar inherited retinal dystrophies are recognised as retinitis pigmentosa and macular dystrophy. Molecular biological studies have revealed disease-causing mutations in several genes in humans and also in mice with retinal dystrophies. Recently, molecular genetic techniques have identified the cause of one form of gPRA in Irish setters while important candidate genes have been investigated in other breeds. Identification of mutations responsible for different forms of gPRA allows carrier and predegenerate animals to be detected using DNA-based tests. Such genetic tests will greatly facilitate the eradication of these diseases in different breeds.

A survey to establish the UK prevalence of the gene mutation causing the rod-cone dysplasia type one (rcd1) form of generalised progressive retinal atrophy (gPRA) in Irish setters was carried out. The dogs were selected by members of two Irish setter breed societies to provide examples from most of the main breeding lines in the UK. A total of 210 Irish setters were tested and one bitch was found to be a carrier of the rcd1 mutation. These results show that although a confirmed case of rcd1 has not been reported in Irish setters in the UK for over a decade the gene is still present in the gene pool.

We have found four mutations in the human gene encoding the beta-subunit of rod cGMP phosphodiesterase (PDE beta) that cosegregate with autosomal recessive retinitis pigmentosa, a degenerative disease of photoreceptors. In one family two affected siblings both carry allelic nonsense mutations at codons 298 and 531. Affected individuals have abnormal rod and cone electroretinograms. PDE beta is the second member of the phototransduction cascade besides rhodopsin that is absent or altered as a cause of retinitis pigmentosa, suggesting that other members of this pathway may be defective in other forms of this disease.

Eight hereditary eye diseases are discussed. These eight abnormalities follow the main possible patterns of inheritance. The clinical aspects and the prevention of these illnesses are discussed.

Detailed morphological analyses, including retinal layer thickness studies, were performed on heterozygous affected cats with autosomal dominant rod-cone dysplasia (gene symbol Rdy). Abnormalities were evident in retinas from the earliest age examined (2 weeks). Both rod and cone photoreceptors were affected equally by the dystrophy which was characterized by retarded and abnormal development of the visual cells. Photoreceptor inner segments remained rudimentary and outer segments did not elongate normally. Outer segment material was sparse and consisted mostly of whorls of disorganized and disoriented disc lamellae. Photoreceptor cell synaptic terminals showed delayed and incomplete synaptogenesis. Degenerative changes were first observed at 4.5 weeks of age and were characterized by the appearance of pyknotic nuclei in the outer nuclear layer and displacement of photoreceptor cells into the subretinal space. Degeneration began in central retinal regions and proceeded towards the periphery, resulting in progressive loss of the photoreceptor cell layers. By 30 weeks of age only two to five rows of nuclei remained in the outer nuclear layer. Area centralis degenerative lesions in advanced affected eyes were characterized by focal absence of the retinal pigment epithelium and choriocapillaris and thinning of the underlying tapetum. Retinal autoradiography showed that in normal kittens aged between 4.5 and 11 weeks of age rod outer segment renewal rates varied between 2.49 and 2.79 microns per 24 hr. The failure to form a labelled band in retinal autoradiograms from Rdy-affected kittens most probably indicates defective rod disc morphogenesis. It appears that the genetic defect in Rdy cats permits retarded development of the photoreceptor cells, but becomes lethal when these cells begin functional differentiation.