Björn Ekesten

Objective: To determine whether serial evaluation of pectinate ligament morphology could aid in predicting the onset of elevated intraocular pressure (IOP) in eyes predisposed to primary angle closure glaucoma (PACG). Animals Studied: The second eye of dogs affected with PACG (20) that had already developed elevated IOP in the first eye and normal dogs (12) with no history of glaucoma. Procedures: Serial goniophotographs of all quadrants of the iridocorneal angle were obtained every 9 months over approximately 18 months in normal dogs. Images were obtained every 3 months in dogs with PACG until that eye developed elevated IOP. A modified ZibWest score was calculated for each image. The earliest ZibWest score was then compared with the last ZibWest score for each eye. Additionally, matched images from the same quadrant from the first and last time point were presented to masked experienced evaluators to see whether the progression of abnormalities could be detected. Results: A difference in ZibWest scores between the first and the last time point for each eye was not detected across all dogs ( p = 0.3673), within dogs affected with PACG ( p = 0.2665), or normal dogs ( p = 0.3953). Experienced evaluators were unable to detect significant progression of pectinate ligament abnormalities. Conclusions: Serial gonioscopic evaluation of pectinate ligament morphology does not appear to be useful in the prediction of the time of onset of elevated IOP in dogs with PACG.

The most suitable light intensity for cows during nighttime has not been thoroughly investigated. Recommendations on the night-time lighting regimen on dairy farms differ between countries and range from light throughout the night to darkness to allow the animals a rest from artificial light. Commercial actors recommend red light for night-time lighting in cattle barns to facilitate livestock supervision with minimum disturbance for the animals. However, little is known about how light intensity, spectrum, and uniformity affect the ability of cows to navigate their indoor environment. Thus, in a change-over study with 12 pregnant, nonlactating dairy cows, we observed how the cows walked through an obstacle course under different light treatments. Obstacles were positioned differently for every run, to present a novel challenge for each light environment. Fourteen different light treatments were tested, involving intensity ranging from -2 s^-1, high or low uniformity, and white or red color. Light was characterized in terms of illuminance, photon flux density, spectral composition, and uniformity. Additionally, assessment of the environmental light field was used to describe each lighting condition from a bovine and human perspective. Data were analyzed in a generalized mixed model to assess whether lighting conditions affected cow walking speed or stride rate. Pair-wise post hoc comparisons showed that the cows walked at a slower speed in nonuniform red light compared with uniform white light or uniform red light. Interestingly, darkness did not alter walking speed or stride rate. The odds of different behaviors occurring were not affected by lighting conditions. In conclusion, darkness did not affect the ability of cows to navigate through the obstacle course, but medium-intensity, nonuniform red light affected their speed. Hence, cows do not necessarily need night-time lighting to navigate, even in a test arena with obstacles blocking their way, but nonuniform light distribution may have an effect on their movements.

Purpose: To study retinal appearance and morphology in Labrador retrievers (LRs) heterozygous and homozygous for an ABCA4 loss-of-function mutation. Methods: Ophthalmic examination, including ophthalmoscopy and simple testing of vision, was performed in five ABCA4^wt/wt, four ABCA4^wt/InsC, and six ABCA4^InsC/InsC LRs. Retinas were also examined with confocal scanning laser ophthalmoscopy (cSLO) and optical coherence tomography (OCT). Infrared and fundus autofluorescence (FAF) images were studied, and outer nuclear layer (ONL) and neuroretinal thickness were measured in the central and peripheral area centralis. Results: Clinical signs in young ABCA4^InsC/InsC LRs were subtle, whereas ophthalmoscopic findings and signs of visual impairment were obvious in old ABCA4^InsC/InsC LRs. Retinal appearance and vision testing was unremarkable in heterozygous LRs regardless of age. The cSLO/OCT showed abnormal morphology including ONL thinning, abnormal outer retinal layer segmentation, and focal loss of retinal pigment epithelium in the fovea equivalent in juvenile ABCA4^InsC/InsC LRs. The abnormal appearance extended into the area centralis and visual streak in middle-aged ABCA4^InsC/InsC and then spread more peripherally. A mild phenotype was seen on cSLO/OCT and FAF in middle-aged to old ABCA4^wt/InsC LRs. Conclusions: Abnormal appearance and morphology in the fovea equivalent are present in juvenile ABCA4^InsC/InsC. In the older affected LRs, the visual streak and then the peripheral retina also develop an abnormal appearance. Vision deteriorates slowly, but some vision is retained throughout life. Older heterozygotes may show a mild retinal phenotype but no obvious visual impairment. The ABCA4^InsC/InsC LR is a potential model for ABCA4-mediated retinopathies/juvenile-onset Stargardt disease in a species with human-sized eyes. Translational Relevance: The ABCA4^InsC mutation causes juvenile-onset abnormal appearance of the fovea equivalent in affected dogs that slowly spreads in the retina, while only a mild phenotype is seen in older carriers. This is the first non-primate, large-animal model for ABCA4-related/STGD1 retinopathies in a species with a fovea equivalent.

In golden retriever dogs, a 1 bp deletion in the canine TTC8 gene has been shown to cause progressive retinal atrophy (PRA), the canine equivalent of retinitis pigmentosa. In humans, TTC8 is also implicated in Bardet–Biedl syndrome (BBS). To investigate if the affected dogs only exhibit a non-syndromic PRA or develop a syndromic ciliopathy similar to human BBS, we recruited 10 affected dogs to the study. The progression of PRA for two of the dogs was followed for 2 years, and a rigorous clinical characterization allowed a careful comparison with primary and secondary characteristics of human BBS. In addition to PRA, the dogs showed a spectrum of clinical and morphological signs similar to primary and secondary characteristics of human BBS patients, such as obesity, renal anomalies, sperm defects, and anosmia. We used Oxford Nanopore long-read cDNA sequencing to characterize retinal full-length TTC8 transcripts in affected and non-affected dogs, the results of which suggest that three isoforms are transcribed in the retina, and the 1 bp deletion is a loss-of-function mutation, resulting in a canine form of Bardet–Biedl syndrome with heterogeneous clinical signs.

In golden retriever dogs, a 1 bp deletion in the canine TTC8 gene has been shown to cause progressive retinal atrophy (PRA), the canine equivalent of retinitis pigmentosa. In humans, TTC8 is also implicated in Bardet-Biedl syndrome (BBS). To investigate if the affected dogs only exhibit a non-syndromic PRA or develop a syndromic ciliopathy similar to human BBS, we recruited ten affected dogs to the study. The progression of PRA for two of the dogs was followed for two years, and a rigorous clinical characterization allowed a careful comparison with primary and secondary characteristics of human BBS. In addition to PRA, the dogs showed a spectrum of clinical and morphological signs similar to primary and secondary characteristics of human BBS patients, such as obesity, renal anomalies, sperm defects, and anosmia. We used Oxford Nanopore long-read cDNA sequencing to characterize retinal full-length TTC8 transcripts in affected and non-affected dogs, the results of which suggest that three isoforms are transcribed in the retina, and the 1 bp deletion is a loss-of-function mutation, resulting in a canine form of Bardet-Biedl syndrome with heterogeneous clinical signs.

Background: Visual evoked potentials (VEPs) are electrical potentials generated by neurons in the central nervous system in response to visual stimuli. A series of positive and negative wavelets in response to flash-stimuli (flash-VEP; FVEP) or reversing, iso-luminant patterns (pattern-VEP; PVEP) are recorded. Pathological conditions affecting the post-retinal pathways can alter overall waveform morphology, and also affect wavelet peak times and amplitudes. FVEPs have recently been described in horses, but more data on the variability within and between subjects is required, to adequately interpret results from clinical equine patients. Therefore, the purpose of this study was to describe the variability, repeatability and test-retest reliability of equine FVEPs in normal, adult horses.Results: Equine FVEPs were recorded from one randomly selected eye in 17 horses, from both eyes in eight of these horses, and also at two separate recording sessions in six horses. N1, P2, N2 and P4 wavelets were present in 100% of the recordings in all horses, while P1, N2a, P3 and P5 were only present in some recordings. Coefficients of variation (CVs) were low for P2, N2 and P4 peak times, but higher for all amplitudes. There were no statistically significant differences comparing peak times and amplitudes between eyes or between sessions. Coefficients of repeatability (CRs) are reported for P2, N2 and P4 peak times between eyes (P2; 5 ms, N2; 18 ms, P4; 18 ms) and also between sessions (P2; 5 ms, N2; 16 ms, P4; 39 ms). Intraclass correlation coefficients (ICCs), as an estimate of test-retest reliability, was assessed to be fair to excellent for most parameters.Conclusions: This study provides important data on variability, repeatability and test-retest reliability of FVEPs in normal, adult horses. We conclude that P2, N2 and P4 peak times should be included in the evaluation of equine FVEPs. The large inherent variability of FVEP amplitudes is likely to make them less suitable and useful for establishing a diagnosis on their own in most clinical patients, but they may occasionally provide support to a clinical diagnosis.

Objective: Our aim was to generate baseline optical coherence tomography (OCT) measurements of retinal thickness in female Beagles and to determine how these are affected by meridian, eccentricity, and age.Methods: Twenty‐three female Beagles, including six puppies (11 years old) were studied. Both retinas of each dog were scanned (in 4 principal meridians) using the Heidelberg Spectralis following ophthalmic examination, refraction, and sedation. In each eye and each meridian, total retinal, outer retinal, and nerve fiber layer (NFL) thickness were measured from the disc rim up to 6 mm peripherally.Results: The canine retina is thickest dorsally and thinnest ventrally. Total retinal, outer retinal, and NFL thickness decrease progressively and significantly as a function of eccentricity. The greatest eccentricity‐dependent thinning occurs dorsally. This thinning is due mostly to NFL tapering, while the eccentricity‐dependent change in outer retinal thickness is more moderate, especially in the lateral meridian, possibly due to the presence of the visual streak. The retina is thickest in puppies, but there were no significant differences between mature and elderly dogs.Conclusions: Our results provide normative values for total, outer, and inner retinal thickness in female dogs and may facilitate OCT use in the diagnosis of canine glaucoma and inherited retinopathies.

Objective: CompareCXLtreatment with medical treatment alone in horses with stromal, ulcerative keratitis. Animals studied: 24 horses (24 eyes) with stromal, ulcerative keratitis were included.Procedure: 12 horses were initially treated withCXL, and 12 horses were given conventional medical treatment. Topical medical treatment was added to horses in theCXLgroup if necessary. Parameters including cytology, microbial growth, time to fluorescein negativity, and time to inhibition of stromal melting were evaluated.Results: After the first day of treatments, a decrease in inflammatory signs and pain from the eye was observed in both groups. Stromal melting ceased within 24 hours regardless of treatment.CXLtreatment alone was sufficient in 3 horses with noninfectious, superficial stromal ulcerations. Clinical signs of impaired wound healing were seen after 3‐14 days in corneas with suspected or proven bacterial infection treated withCXLonly, most likely because of insufficient elimination of bacteria deeper in the corneal stroma or because of re‐infection from bacteria in the conjunctiva. The average decrease in stromal ulcer area per day after onset of treatment was almost identical between the groups, and no significant difference in time to fluorescein negativity was found.Conclusions: We considerCXLa possible useful adjunct treatment of corneal stromal ulcers in horses, especially for melting ulcers and as a potential alternative to prophylactic antibiotic treatment for noninfected stromal ulcers. However,CXLshould not be used alone for infected or suspected infected stromal ulcers, because topical antibiotics were required in all horses with proven infectious keratitis.

Autosomal recessive retinal degenerative diseases cause visual impairment and blindness in both humans and dogs. Currently, no standard treatment is available, but pioneering gene therapy-based canine models have been instrumental for clinical trials in humans. To study a novel form of retinal degeneration in Labrador retriever dogs with clinical signs indicating cone and rod degeneration, we used whole-genome sequencing of an affected sib-pair and their unaffected parents. A frameshift insertion in the ATP binding cassette subfamily A member 4 (ABCA4) gene (c.4176insC), leading to a premature stop codon in exon 28 (p.F1393Lfs*1395), was identified. In contrast to unaffected dogs, no full-length ABCA4 protein was detected in the retina of an affected dog. The ABCA4 gene encodes a membrane transporter protein localized in the outer segments of rod and cone photoreceptors. In humans, the ABCA4 gene is associated with Stargardt disease (STGD), an autosomal recessive retinal degeneration leading to central visual impairment. A hallmark of STGD is the accumulation of lipofuscin deposits in the retinal pigment epithelium (RPE). The discovery of a canine homozygous ABCA4 loss-of-function mutation may advance the development of dog as a large animal model for human STGD. Stargardt disease (STGD) is the most common inherited retinal disease causing visual impairment and blindness in children and young adults, affecting 1 in 8–10 thousand people. For other inherited retinal diseases, the dog has become an established comparative animal model, both for identifying the underlying genetic causes and for developing new treatment methods. To date, there is no standard treatment for STGD and the only available animal model to study the disease is the mouse. As a nocturnal animal, the morphology of the mouse eye differs from humans and therefore the mouse model is not ideal for developing methods for treatment. We have studied a novel form of retinal degeneration in Labrador retriever dogs showing clinical signs similar to human STGD. To investigate the genetic cause of the disease, we used whole-genome sequencing of a family quartet including two affected offspring and their unaffected parents. This led to the identification of a loss-of-function mutation in the ABCA4 gene. The findings of this study may enable the development of a canine model for human STGD.