Efficacy of the positioning system when measuring canine intraocular pressures with the Reichert® Tono-Vera® Vet rebound tonometer.

OBJECTIVE: To compare intraocular pressure (IOP) measurements in dogs taken with the Reichert® Tono-Vera® Vet rebound tonometer with and without the automatic positioning system. ANIMALS STUDIED: Measurements were taken on 49 eyes from 26 Beagle-derived dogs with variable genetics-four non-glaucomatous and 22 ADAMTS10-mutant dogs affected with different stages of open-angle glaucoma. Seventeen of the 26 dogs were measured 2-4 times on different days with variable intervals since IOP-lowering medications were administered. PROCEDURES: In each dog, tonometry was performed with the Tono-Vera® Vet using three different methods in a randomized order: (Method 1) Average of three readings with an automatic positioning system; (Method 2) one reading with an automatic positioning system; and (Method 3) average of three readings obtained without the automatic positioning system. Statistical analyses included one-way ANOVA, Tukey pairwise comparisons, and Bland-Altman plots (MiniTab®). RESULTS: With each of the three tonometry methods, 116 measurements were taken, resulting in 348 total IOP measurements with a range of 12.8-49.9 mmHg. The means and standard deviations for each method were 25.4 ± 6.9 mmHg (Method 1), 26.0 ± 7.2 mmHg (Method 2), and 26.9 ± 7.7 mmHg (Method 3), with no significant differences (p = .27). Mean IOP variances were also not significantly different between tonometry methods (p = .24 to .78). CONCLUSIONS: Because mean IOPs and their standard deviations were not statistically different between the three tonometry methods, we conclude that Tono-Vera® Vet measurements conducted without the aid of the positioning system still provide reliable results.

Iris angiography in ADAMTS10 mutant dogs with open-angle glaucoma (ADAMTS10-OAG).

OBJECTIVE: To evaluate anterior segment angiographic findings in hypertensive ADAMTS10-open-angle glaucoma (ADAMTS10-OAG) eyes as compared to normotensive control eyes. ANIMALS STUDIED: Nine ADAMTS10-OAG beagles and four wild-type control dogs. PROCEDURES: Anterior segment angiography was performed under general anesthesia following intravenous injection of indocyanine green (ICG; 1 mg/kg) and sodium fluorescein (SF; 20 mg/kg) using a Heidelberg Spectralis® confocal scanning laser ophthalmoscope. Time to onset of iridal angiographic phases and the presence/severity of dye leakage into the iris stromal and/or aqueous humor were recorded. Group findings were compared, and multiple linear regression analysis was performed to identify potential factor associations with disease status. RESULTS: Time to onset of all angiographic phases visualized using ICG was significantly prolonged while time to onset of SF leakage into the aqueous humor was significantly reduced in glaucomatous eyes compared to controls. Only glaucomatous eyes (n = 9) demonstrated evidence of SF stromal leakage. Mean intraocular pressure (IOP) and age were significantly higher, while mean cardiac pulse was significantly lower in glaucomatous eyes compared to controls. Blood pressure and ocular perfusion pressure were not significantly different between groups. Multiple linear regression analysis, controlling for age, IOP, and pulse demonstrated glaucoma, was not predictive of the time to onset of any angiographic phase, stromal, or aqueous humor leakage. However, pulse was a significant factor contributing to the severity of aqueous humor leakage. CONCLUSIONS: A compromised vascular supply to the anterior segment exists in dogs with ADAMTS10-OAG. These observations warrant further exploration of what role altered perfusion and/or disruption to the blood-aqueous barrier may play.

Comparison of three rebound tonometers in normal and glaucomatous dogs.

OBJECTIVE: The objectives of the study were to compare intraocular pressure (IOP) readings across a wide range and obtained via three rebound tonometers in ADAMTS10-mutant Beagle-derived dogs with different stages of open-angle glaucoma (OAG) and normal control dogs and to investigate the effect of central corneal thickness (CCT). ANIMALS STUDIED: Measurements were performed on 99 eyes from 50 Beagle-derived dogs with variable genetics-16 non-glaucomatous and 34 with ADAMTS10-OAG. Seventeen OAG eyes were measured twice-with and without the use of IOP-lowering medications. PROCEDURES: IOP was measured in each eye using three tonometers with their "dog" setting-ICare® Tonovet (TV), ICare® Tonovet Plus® (TVP), and the novel Reichert® Tono-Vera® Vet (TVA)-in randomized order. CCT was measured with the Accutome® PachPen. Statistical analyses included one-way ANOVA, Tukey pairwise comparisons, and regression analyses of tonometer readings and pairwise IOP-CCT Pearson correlations (MiniTab®). RESULTS: A total of 116 IOP measurements were taken with each of the three tonometers. When comparing readings over a range of ~7-77 mmHg, mean IOPs from the TV were significantly lower compared with TVP (-4.6 mmHg, p < .001) and TVA (-3.7 mmHg, p = .001). We found no significant differences between TVA and TVP measurements (p = .695). There was a moderate positive correlation between CCT and IOP for TVA (r = 0.53, p < .001), TVP (r = 0.48, p < .001), and TV (r = 0.47, p < .001). CONCLUSIONS: Our data demonstrate strong agreement between TVP and TVA, suggesting that the TVA may similarly reflect true IOP values in canines. CCT influenced IOP measurements of all three tonometers.

A genome-wide association study to investigate genetic loci associated with primary glaucoma in American Cocker Spaniels.

OBJECTIVE: To identify genetic associations with primary glaucoma (PG) in American Cocker Spaniels using a genome-wide association study (GWAS). ANIMALS: A nationwide ambidirectional case-control cohort study was performed in American Cocker Spaniels that had an ophthalmic examination performed by a veterinarian. Ninety-four dogs with PG (cases) and 111 dogs without glaucoma (controls) met phenotypic criteria and had a blood sample collected after receiving informed owner consent. PROCEDURES: Genomic DNA was extracted from whole blood samples and genotyped (CanineHD BeadChip, Illumina Inc). A case-control GWAS using a linear mixed model was performed, and 3 significance thresholds were calculated (1) using a Bonferroni correction on all single nucleotide polymorphisms (SNPs) included in the GWAS, (2) using a Bonferroni correction on only the unlinked SNPs from a pruned data set, and (3) using 10,000 random phenotype permutations. RESULTS: Following genotype data quality control, 89 cases and 93 controls were included in the GWAS. We identified an association on canine chromosome (CFA10); however, it did not reach statistical significance. Potential candidate genes within the surrounding linkage disequilibrium interval include coiled-coil domain containing 85A (CCDC85A) and extracellular growth factor containing fibulin extracellular matrix protein 1 (EFEMP1). CLINICAL RELEVANCE: Primary glaucoma in the American Cocker Spaniel is a complex heterogeneous disease that may be influenced by a locus on CFA10. The candidate genes CCDC85A and EFEMP1 within the identified linkage disequilibrium interval have been shown to be involved in human open-angle glaucoma.

Comparative effects of latanoprost and latanoprostene bunod on intraocular pressure and pupil size in ophthalmologically normal Beagle dogs.

OBJECTIVE: To compare effects of latanoprost, a topical prostaglandin analogue (PGA) commonly used to treat glaucoma and lens instability in dogs, and latanoprostene bunod, a novel PGA with a nitric oxide-donating moiety, on intraocular pressure (IOP) and pupil diameter (PD). ANIMALS STUDIED: Ten ophthalmologically normal Beagle dogs. PROCEDURES: Dogs were treated twice a day for 5 days in a randomly selected eye with either latanoprost or latanoprostene bunod. After a 6-week washout period, dogs were treated with the opposite drug. IOP and PD were measured at treatment times, at midday on days 1 and 5, and for 6 days post-treatment. RESULTS: Both drugs significantly decreased IOP and PD. At midday on day 5 of treatment, mean IOP in eyes treated with latanoprost was 4.5 mmHg lower than the fellow eye and 3.0 mmHg lower than the same eye at baseline, while mean IOP in eyes treated with latanoprostene bunod was 5.5 mmHg lower than the fellow eye and 3.6 mmHg lower than baseline. Mean PD was 0.94 mm in eyes treated with latanoprost and 0.76 mmHg in eyes treated with latanoprostene bunod. There was no significant difference between the two drugs for either parameter at that time point (p = .372 and .619, respectively, for IOP relative to control and to baseline; p = .076 for PD) or when analyzed longitudinally. Significant diurnal variation in PD was noted and may have implications for treatment of lens' instability. CONCLUSIONS: Latanoprost and latanoprostene bunod produce similar IOP reduction and miosis in normal canine eyes.

Safety and efficacy of topically administered netarsudil-latanoprost fixed dose combination (FDC; Rocklatan™) in normal and glaucomatous dogs with ADAMTS10-open-angle glaucoma (ADAMTS10-OAG).

OBJECTIVE: The aim of the study was to evaluate safety and efficacy of topically administered 0.02% netarsudil-0.005% latanoprost fixed-dose combination (FDC) (Rocklatan™; Aerie Pharmaceutical) in normal and glaucomatous dogs with ADAMTS10-open-angle glaucoma (ADAMTS10-OAG). ANIMALS STUDIED: Five normal and five glaucomatous beagle dogs with ADAMTS10-OAG were the study animals. PROCEDURES: In each dog, left (OS) or right eye (OD) was randomly selected for netarsudil-latanoprost FDC treatment. Contralateral eyes served as latanoprost-treated controls. The study was divided into four consecutive study periods: following a 4-day baseline period, two sequential 8-day study periods followed with once daily (q24h) and twice daily (q12h) treatments and ending with a washout period. Efficacy was measured by diurnal intraocular pressure (IOP) and pupil diameter. Safety was assessed by routine ophthalmic examination, gonioscopy, and pachymetry. Differences in least square means of quantitative outcome measures were compared between FDC and latanoprost treatments by using the linear Gaussian model. RESULTS: Baseline IOPs were 13.6 ± 0.7 mmHg (mean ± SEM) in normal and 28.3 ± 1.4 mmHg in OAG-affected dogs. There was a significant decrease in mean diurnal IOP following FDC administration in both normal (q24h: -2.1 mmHg; q12h: -4.1 mmHg) and glaucomatous dogs (q24h: -14.2 mmHg; q12h: -17.7 mmHg; p < .0001). There was no significant difference in the treatment effect when comparing FDC to latanoprost. Both FDC and latanoprost administration resulted in similarly significant pupil constriction (p < .0001). The FDC administration was well-tolerated but resulted in conjunctival hyperemia. CONCLUSIONS: Once or twice daily administration of netarsudil-latanoprost FDC (Rocklatan™) and latanoprost was equally effective in lowering IOP in normal and OAG-affected dogs. There was no netarsudil-related added treatment effect.

Safety and efficacy of topically administered netarsudil (Rhopressa™) in normal and glaucomatous dogs with ADAMTS10-open-angle glaucoma (ADAMTS10-OAG).

OBJECTIVE: To evaluate safety and efficacy of topically administered 0.02% netarsudil ophthalmic solution (Rhopressa™; Aerie Pharmaceutical) in normal and glaucomatous dogs with ADAMTS10-open-angle glaucoma (ADAMTS10-OAG). ANIMALS STUDIED: Five normal and 5 glaucomatous Beagle dogs with ADAMTS10-OAG. PROCEDURES: In each dog, left or right eye was randomly selected for netarsudil treatment. Contralateral eyes were sham-treated with balanced salt solution (BSS). Following a 1-week baseline period, dogs were treated once daily (q24h) during week 2, and twice daily (q12h) during week 3; week 4 served as washout period. Efficacy was measured by diurnal intraocular pressure (IOP) and pupil diameter. Safety was assessed by routine ophthalmic examination, gonioscopy, and pachymetry. Differences in least square means of quantitative outcome measures were compared between netarsudil and BSS sham-treated eyes by linear Gaussian model. RESULTS: Baseline IOPs were 18.5 ± 0.5 mm Hg (mean ± SEM) in normal and 27.8 ± 1.0 mm Hg in OAG dogs. Even though mean IOPs were lower in netarsudil- vs sham-treated eyes, the overall differences were neither significant nor clinically relevant, regardless of treatment frequency (q24h-normal: sham 16.4 ± 1.1 mm Hg vs treatment 15.6 ± 1.0 mm Hg; q24hr-OAG: sham 25.8 ± 2.3 mm Hg vs. treatment 25.7 ± 2.4 mm Hg; q12hr-normal: sham 15.4 ± 0.8 mm Hg vs. treatment 14.4 ± 0.8 mm Hg; q12hr-OAG: sham 26.3 ± 1.7 mm Hg vs. treatment 25.4 ± 1.8 mm Hg). Netarsudil administration was well tolerated but resulted in significant, moderate-to-severe conjunctival hyperemia (P < .001). CONCLUSIONS: Once or twice daily administration of netarsudil resulted in marginal and clinically irrelevant IOP decreases in normal and OAG-affected dogs. Except for conjunctival hyperemia, the drug was well tolerated.

Effectiveness of MB-102, a novel fluorescent tracer agent, for conducting ocular angiography in dogs.

OBJECTIVE: To evaluate the effectiveness of a novel fluorescence tracer agent, MB-102, for conducting ocular angiography in dogs. ANIMALS: 10 ophthalmologically normal dogs (2 to 4 years old) and 10 dogs with retinal degeneration or primary open-angle glaucoma (< 6 years old). PROCEDURES: While anesthetized, all dogs received sodium fluorescein (20 mg/kg, IV) or MB-102 (20 or 40 mg/kg, IV) first and then the other dye in a second treatment session 2 days later in a randomized crossover design. Anterior fluorescence angiography was performed on one eye and posterior fluorescence angiography on the other. Imaging was performed with a full-spectrum camera and camera adaptor system. Filter sets that were tailored to match the excitation and emission characteristics of each angiographic fluorescent agent were used. RESULTS: All phases and phase intervals during anterior and posterior segment angiography were identified, regardless of the dye used. However, agent fluorescence and visualization of the iridal blood vessels were hindered in some dogs, irrespective of agent, owing to the degree of iridal pigmentation present. No significant difference was noted between the 2 dyes in any phase or phase interval, and slight improvement in image contrast was observed with MB-102 during the venous phases owing to a reduction of vessel wall staining in both normal and diseased eyes. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that MB-102 would be useful for conducting ocular angiography in dogs.

Evaluation of ADAMTS17 in Chinese Shar-Pei with primary open-angle glaucoma, primary lens luxation, or both.

OBJECTIVE To evaluate the coding regions of ADAMTS17 for potential mutations in Chinese Shar-Pei with a diagnosis of primary open-angle glaucoma (POAG), primary lens luxation (PLL), or both. ANIMALS 63 Shar-Pei and 96 dogs of other breeds. PROCEDURES ADAMTS17 exon resequencing was performed on buccal mucosal DNA from 10 Shar-Pei with a diagnosis of POAG, PLL, or both (affected dogs). A candidate causal variant sequence was identified, and additional dogs (53 Shar-Pei [11 affected and 42 unaffected] and 95 dogs of other breeds) were genotyped for the variant sequence by amplified fragment length polymorphism analysis. Total RNA was extracted from ocular tissues of 1 affected Shar-Pei and 1 ophthalmologically normal Golden Retriever; ADAMTS17 cDNA was reverse transcribed and sequenced, and ADAMTS17 expression was evaluated by quantitative reverse-transcription PCR assay. RESULTS All affected Shar-Pei were homozygous for a 6-bp deletion in exon 22 of ADAMTS17 predicted to affect the resultant protein. All unaffected Shar-Pei were heterozygous or homozygous for the wild-type allele. The variant sequence was significantly associated with affected status (diagnosis of POAG, PLL, or both). All dogs of other breeds were homozygous for the wild-type allele. The cDNA sequencing confirmed presence of the expected variant mRNA sequence in ocular tissue from the affected dog only. Gene expression analysis revealed a 4.24-fold decrease in the expression of ADAMTS17 in ocular tissue from the affected dog. CONCLUSIONS AND CLINICAL RELEVANCE Results supported that the phenotype (diagnosis of POAG, PLL, or both) is an autosomal recessive trait in Shar-Pei significantly associated with the identified mutation in ADAMTS17.

Open-angle glaucoma in the Petit Basset Griffon Vendeen.

OBJECTIVES: To report the prevalence and clinical characteristics of an open-angle glaucoma in Petit Basset Griffon Vendeen (PBGV) dogs in the United Kingdom (UK). ANIMALS STUDIED AND METHODS: At breed society clinics extending over a 6-year period, 366 dogs of varying ages and both sexes were clinically examined for signs of glaucoma using slit-lamp biomicroscopy, indirect and direct ophthalmoscopy, tonometry, and gonioscopy. RESULTS: The prevalence of glaucoma was 10.4% (38 dogs). Clinical signs of the disease presented from 3 years of age onwards, the commonest initial feature being the elevation of intraocular pressure (IOP) in 15 dogs (39.4%). In addition to elevated IOP, another 13 dogs (34.2%) presented with other features of glaucoma, some with lens subluxation and globe enlargement and all with possible or known vision defects. In the remaining 10 dogs (26.3%), phacodonesis or lens subluxation was observed before subsequent elevation of IOP. CONCLUSIONS: High prevalence and similarity to the primary open-angle glaucoma (POAG) seen in the Beagle and Elkhound breeds indicate that an open-angle glaucoma is present in the PBGV in the UK and that this disease may be genetically determined in this breed. Although increased IOP is the commonest early diagnostic feature, lens instability prior to an increase in IOP may be part of the clinical picture.

Changes in posterior scleral collagen microstructure in canine eyes with an ADAMTS10 mutation.

PURPOSE: We aimed to characterize alterations in the posterior scleral collagen microstructure before detectable disease onset in a canine model of open-angle glaucoma caused by an ADAMTS10 mutation. METHODS: Collagen orientation, anisotropy degree (proportion of preferentially aligned collagen), and relative density were measured at 0.4 mm spatial resolution using synchrotron wide-angle X-ray scattering. For statistical evaluation of structure parameters, regional averages of the peripapillary and mid-posterior sclera were compared between ADAMTS10 mutant (affected) dogs (n = 3) and age-matched (carrier) controls (n = 3). RESULTS: No marked differences in the general pattern of preferential collagen fibril orientation were noted between the control and affected dogs. The peripapillary sclera of all specimens featured strongly aligned circumferential collagen ringing the optic nerve head. Collagen anisotropy was significantly reduced in the mid-posterior sclera of the affected dogs (carrier: 0.27±0.11; affected: 0.24±0.10; p = 0.032) but was not statistically significantly different in the peripapillary sclera (carrier: 0.46±0.15; affected: 0.45±0.17; p = 0.68). Collagen density was statistically significantly reduced in the affected dogs for the mid-posterior sclera (carrier: 28.1±9.14; affected: 18.3±5.12; p<0.0001) and the peripapillary sclera (carrier: 34.6±9.34; affected: 21.1±6.97; p = 0.0002). CONCLUSIONS: Significant alterations in the posterior scleral collagen microstructure are present before the onset of clinical glaucoma in ADAMTS10 mutant dogs. A reduction in fibrous collagen density is likely an important contributory factor in the previously reported mechanical weakening of the sclera in this model. Baseline scleral abnormalities have the potential to interact with intraocular pressure (IOP) elevations in determining the course of glaucoma progression in animal models of the disease, and potentially in human glaucoma.

Golden retriever cystic uveal disease: a longitudinal study of iridociliary cysts, pigmentary uveitis, and pigmentary/cystic glaucoma over a decade in western Canada.

OBJECTIVES: To determine the incidence of iridociliary cysts, pigmentary uveitis (PU)/pigmentary cystic glaucoma (PCG) in golden retriever dogs in western Canada, the progression of iridociliary cysts to PU/PCG, and a mode of inheritance for this disorder. ANIMAL STUDIED: A total of 830 golden retriever dogs from Alberta, Saskatchewan, and Manitoba from 2004 to 2014 were studied. PROCEDURE: Data were compiled from Canine Eye Registry Foundation (CERF) or Orthopedic Foundation for Animals (OFA) records (n = 630) and clinical consultations (n = 200) for a retrospective assessment of iridociliary cysts, PU, and PCG. RESULTS: Total incidence of iridociliary cysts and PU from CERF/OFA data were 4.8% (n = 30/630) and 5.9% (n = 37/630), respectively. Incidence of PU increased with ages >4 years (12.7%, n = 32/251). Dogs diagnosed with thin-walled, attached iridociliary cysts had a high risk of being diagnosed with PU or PCG upon re-examination (56.5%, n = 13/23). No dogs diagnosed with thick-walled, anterior chamber cysts (n = 7) developed PU or PCG within the time frame of the study. Data from clinical consultations confirmed that PU carried a poor prognosis for the affected eyes as 44.9% (n = 22/49) of dogs progressed to PCG. PU- and PCG-affected dogs followed a familial pattern and there was an association with thin-walled iridociliary cysts. Pedigree analysis suggested an autosomal dominant mode of inheritance with partial penetrance. CONCLUSIONS: Thin-walled iridociliary cysts are associated with PU and PCG. All breeding golden retriever dogs should be examined annually by an ophthalmologist. The incidence of this disorder is higher in western Canada than previous reports in North America.

A Novel Genome-Wide Association Study Approach Using Genotyping by Exome Sequencing Leads to the Identification of a Primary Open Angle Glaucoma Associated Inversion Disrupting ADAMTS17.

Closed breeding populations in the dog in conjunction with advances in gene mapping and sequencing techniques facilitate mapping of autosomal recessive diseases and identification of novel disease-causing variants, often using unorthodox experimental designs. In our investigation we demonstrate successful mapping of the locus for primary open angle glaucoma in the Petit Basset Griffon Vendéen dog breed with 12 cases and 12 controls, using a novel genotyping by exome sequencing approach. The resulting genome-wide association signal was followed up by genome sequencing of an individual case, leading to the identification of an inversion with a breakpoint disrupting the ADAMTS17 gene. Genotyping of additional controls and expression analysis provide strong evidence that the inversion is disease causing. Evidence of cryptic splicing resulting in novel exon transcription as a consequence of the inversion in ADAMTS17 is identified through RNAseq experiments. This investigation demonstrates how a novel genotyping by exome sequencing approach can be used to map an autosomal recessive disorder in the dog, with the use of genome sequencing to facilitate identification of a disease-associated variant.

Two Independent Mutations in ADAMTS17 Are Associated with Primary Open Angle Glaucoma in the Basset Hound and Basset Fauve de Bretagne Breeds of Dog.

PURPOSE: Mutations in ADAMTS10 (CFA20) have previously been associated with primary open angle glaucoma (POAG) in the Beagle and Norwegian Elkhound. The closely related gene, ADAMTS17, has also been associated with several different ocular phenotypes in multiple breeds of dog, including primary lens luxation and POAG. We investigated ADAMTS17 as a candidate gene for POAG in the Basset Hound and Basset Fauve de Bretagne dog breeds. METHODS: We performed ADAMTS17 exon resequencing in three Basset Hounds and three Basset Fauve de Bretagne dogs with POAG. Identified variants were genotyped in additional sample cohorts of both breeds and dogs of other breeds to confirm their association with disease. RESULTS: All affected Basset Hounds were homozygous for a 19 bp deletion in exon 2 that alters the reading frame and is predicted to lead to a truncated protein. Fifty clinically unaffected Basset Hounds were genotyped for this mutation and all were either heterozygous or homozygous for the wild type allele. Genotyping of 223 Basset Hounds recruited for a different study revealed a mutation frequency of 0.081 and predicted frequency of affected dogs in the population to be 0.007. Based on the entire genotyping dataset the association statistic for the POAG-associated deletion was p = 1.26 x 10-10. All affected Basset Fauve de Bretagne dogs were homozygous for a missense mutation in exon 11 causing a glycine to serine amino acid substitution (G519S) in the disintegrin-like domain of ADAMTS17 which is predicted to alter protein function. Unaffected Basset Fauve de Bretagne dogs were either heterozygous for the mutation (5/24) or homozygous for the wild type allele (19/24). Based on the entire genotyping dataset the association statistic for the POAG-associated deletion was p = 2.80 x 10-7. Genotyping of 85 dogs of unrelated breeds and 90 dogs of related breeds for this variant was negative. CONCLUSION: This report documents strong associations between two independent ADAMTS17 mutations and POAG in two different dog breeds.

Microanatomy of the anterior uveoscleral outflow pathway in normal and primary open-angle glaucomatous dogs.

OBJECTIVE: To compare the morphology of the uveoscleral (US) outflow pathway in normal and glaucomatous canines. ANIMALS STUDIED: 10 normal beagles, 10 beagles with inherited primary open-angle glaucoma, 4 cocker spaniels with spontaneous glaucoma. PROCEDURES: Formalin-preserved globes were sectioned tangentially and sagittally and treated with H&E, Masson's trichrome, or elastin stains or analyzed by immunohistochemistry to visualize smooth muscle actin. Tissues associated with the US pathway were observed and compared using light microscopy. RESULTS: Tangentially oriented sections clearly revealed spaces for the transport of aqueous humor at the junction of the posterior iridocorneal angle (ICA) and anterior ciliary body musculature (CBM). Within the external anterior-most of the US pathway, the supraciliary space, distinct connective tissue cords and smooth muscle pegs fastened the ciliary body to the adjacent sclera. Compared to normal controls, glaucomatous eyes developed a robust scleral elastic sheath at the junction between the posterior ICA and the anterior CBM. In advanced glaucomatous beagles and cocker spaniels, a large amount of melanophores were seen in the US pathway and surrounding vasculature. Within the C8M of glaucomatous specimens, the smooth muscle bundles appeared fewer and separated by elastic-rich ECM. Structures of the US pathway changed little with age. CONCLUSIONS: The anterior portion of the canine US pathway is well defined and appears to be altered little with age. However with glaucoma, changes of the US pathway were associated with its the elastic components, as well as the accumulation of melanophores. Collectively, these changes may have an effect on US outflow and, subsequently, aqueous humor dynamics.

Evaluation of the CYP1B1 gene as a candidate gene in beagles with primary open-angle glaucoma (POAG).

PURPOSE: In humans, primary open-angle glaucoma (POAG) is a complex genetic disorder and is the leading cause of visual impairment. Although all relevant genes were not identified, a small subset of the condition is found to be caused by mutations in the MYOC and CYP1B1 genes. Inherited glaucoma also occurs in several breeds of dogs including beagles. Primary glaucoma in beagles is inherited as an autosomal recessive trait. The purpose of this study is to investigate the role of the CYP1B1 gene in beagles with POAG. METHODS: For the purpose of genetic analysis, total RNAs from the spleen of the canines were isolated and CYP1B1 cDNA was prepared. Genomic DNA from five affected, two carriers, and 13 randomly selected normal beagles with no sign of glaucoma was amplified by the polymerase chain reaction (PCR) using four pairs of primers. The amplified products were directly sequenced using BigDye terminator cycle sequencing. RESULTS: Genomic DNA analyses have identified a substitution polymorphism (109A-->C) in the 5'-untranslated region (UTR) as well as a missense mutation (P93R) in exon 2 of the gene. Three affected, two carriers, and nine normal dogs are heterozygous while two affected and three normal dogs are homozygous for the missense mutation. One normal dog did not show this alteration. Normal dogs also contain the substitution polymorphism in the 5'-UTR. Similar experiments with exon 3 did not identify any additional mutation in the gene. CONCLUSIONS: The above results suggest that CYP1B1 alterations in the coding and UTR are not the primary cause of glaucoma in beagles by possible monogenic association. They may be classified as polymorphisms or they may modify glaucoma phenotype.

The histopathological and immunohistochemical characteristics of pigmentary and cystic glaucoma in the Golden Retriever.

A clinical syndrome comprising the formation of thin-walled cysts within the posterior chamber, proteinaceous exudation, and pigment dispersion, which typically culminates in glaucoma is recognized in the Golden Retriever breed. Although not uncommon, this syndrome has been relatively infrequently documented in the literature, particularly from a histological standpoint. Fifteen globes from Golden Retrievers presented to Eye Care for Animals between 2003 and 2009 were evaluated by routine hematoxylin and eosin (H&E) as well as immunohistochemical staining. Alcian blue, periodic acid Schiff (PAS), Masson's trichrome, Cytokeratin, Vimentin, Neuron Specific Enolase (NSE), S-100, and smooth muscle actin staining were performed. The thin-walled cysts stained positive with Vimentin, NSE, and S-100 in 15/15 globes, consistent with a ciliary body epithelial cellular origin. No globes demonstrated goniodysgenesis. All 15 globes exhibited free pigment within the trabecular meshwork. Little to no inflammatory infiltrate was noted in 15/15 eyes. These findings suggest that the term 'uveitis' may be an inappropriate description of this syndrome.

Myocilin protein levels in the aqueous humor of the glaucomas in selected canine breeds.

OBJECTIVE: To compare aqueous humor myocilin protein levels in dogs with the primary glaucomas to those with the secondary glaucomas, primary cataracts, and diabetic cataracts. MATERIALS AND METHODS: Four groups were selected, based on diagnosis by the attending veterinary ophthalmologists and included: primary glaucoma (primary open-angle glaucoma (POAG) and primary closed angle glaucoma (PCAG); n = 155); secondary glaucoma (n = 94); primary (presumed inherited) cataract (n = 142), and diabetic cataract (n = 83). A total of 474 samples (187 males, 263 females, 24 unreported) with average ages of 117 months for the males and 101 months for the females were analyzed. Myocilin protein was measured using the Coomassie staining and Western blot methods relative to a myocilin control. RESULTS: Differences were seen between nonglaucomatous (cataractous) and glaucomatous dogs with myocilin levels in glaucomatous eyes being many times higher than those in the cataractous dogs. Primary glaucomatous dogs were found to have an aqueous humor myocilin protein level of 17.30 +/- 1.03 units. Secondary glaucomas had the highest level of myocilin in the aqueous humor with 19.27 +/- 1.41 units. Diabetic cataractous dogs had the lowest levels of myocilin reported with 6.60 +/- 0.88 (mean +/- SEM) units. Normal (cataractous) dogs had a myocilin level in the aqueous humor of 8.05 +/- 0.86 units. CONCLUSION: Aqueous humor protein levels were elevated, relative to the myocilin control, in both the primary and secondary glaucoma groups compared to the cataract and diabetic cataract groups. Like in the Beagle POAG, aqueous humor myocilin protein levels are increased. Further studies are indicated to investigate the exact role of the aqueous humor myocilin protein in the genesis in increased IOP in these primary glaucomatous breeds.

Feline primary open angle glaucoma.

OBJECTIVES: We have documented the histomorphological features of feline primary open angle glaucoma. DESIGN: A retrospective morphologic study of eight affected eyes from eight cats, from 1992 to 2006 extracted from a pathology collection, which includes 4000 feline submissions and 1100 cases of feline glaucoma. PROCEDURE: Sections of affected globes, stained with H&E or with alcian blue were examined with a light microscope. Eyes that did not fulfill the criteria for primary open angle glaucoma were excluded from the study. RESULTS: The mean age was 9.1 years. Five cats were female and three cats were male. The breeds included five DSH, two Burmese, and one DLH cat. Significant histomorphological findings included an open irido-corneal angle with an open ciliary cleft in all cases, loss of ganglion cells in eight of eight cases, cupping and gliosis of the optic nerve head in four of four cases in which the optic nerve was adequately sampled, and myxomatous changes of the stroma surrounding the vortex veins in seven of eight cases. CONCLUSIONS: Primary open angle glaucoma in cats is a rare disease that should be taken into consideration when investigating cases of feline glaucoma. The pathogenesis of aqueous outflow obstruction in these cases is not known. This study describes eight additional cases of feline primary open angle glaucoma in cats without an identified cause.