The future of canine glaucoma therapy.

Canine glaucoma is a group of disorders that are generally associated with increased intraocular pressure (IOP) resulting in a characteristic optic neuropathy. Glaucoma is a leading cause of irreversible vision loss in dogs and may be either primary or secondary. Despite the growing spectrum of medical and surgical therapies, there is no cure, and many affected dogs go blind. Often eyes are enucleated because of painfully high, uncontrollable IOP. While progressive vision loss due to primary glaucoma is considered preventable in some humans, this is mostly not true for dogs. There is an urgent need for more effective, affordable treatment options. Because newly developed glaucoma medications are emerging at a very slow rate and may not be effective in dogs, work toward improving surgical options may be the most rewarding approach in the near term. This Viewpoint Article summarizes the discussions and recommended research strategies of both a Think Tank and a Consortium focused on the development of more effective therapies for canine glaucoma; both were organized and funded by the American College of Veterinary Ophthalmologists Vision for Animals Foundation (ACVO-VAF). The recommendations consist of (a) better understanding of disease mechanisms, (b) early glaucoma diagnosis and disease staging, (c) optimization of IOP-lowering medical treatment, (d) new surgical therapies to control IOP, and (e) novel treatment strategies, such as gene and stem cell therapies, neuroprotection, and neuroregeneration. In order to address these needs, increases in research funding specifically focused on canine glaucoma are necessary.

APHAKIC PHACOEMULSIFICATION AND AUTOMATED ANTERIOR VITRECTOMY, AND POSTRETURN MONITORING OF A REHABILITATED HARBOR SEAL (PHOCA VITULINA RICHARDSI) PUP.

A female harbor seal pup rescued along the coast of San Diego on 13 June 2012 was diagnosed with bilateral mature cataracts, apparently congenital, in association with vitreal herniation in the anterior chamber of each eye. The cataracts were surgically removed on 1 August 2012 with single-port aphakic phacoemulsification and automated anterior vitrectomy. Postoperative monitoring during the next several weeks indicated that vision had been functionally repaired and that she could visually orient to and capture live fish in three different environments and in the presence of other animals. Consequently, we equipped the seal with a satellite-linked radio transmitter and returned her to the Pacific Ocean on 21 November 2012, and then monitored her movements until radio contact ended on 2 March 2013. She remained along the San Diego coast from 21 November until 5 December 2012 when she relocated to the Coronado Islands and remained there until 26 December. She then traveled directly to San Clemente Island and remained foraging in the near-shore kelp beds there through 2 March 2013, when radio contact ended. To our knowledge, this is the first published report of cataract treatment in a marine mammal using high-frequency ultrasound to emulsify the lenses followed by suction removal of the emulsified microfragments (i.e., phacoemulsification). Moreover, the rapid postoperative recovery of the seal and its quick acclimation, orientation, navigation, and foraging in marine habitats after return to the Pacific Ocean indicates that these surgical procedures can be safe and effective treatments for cataracts in seals, with substantially reduced postsurgical complications relative to other types of lens fragmentation and removal procedures.

Efficacy of prophylactic antiglaucoma and anti-inflammatory medications in canine primary angle-closure glaucoma: a multicenter retrospective study (2004-2012).

PURPOSE: To evaluate long-term efficacy of antiglaucoma medications with or without combined topical anti-inflammatory treatment in preventing increased intraocular pressure and clinical signs of glaucoma in eyes considered at risk of the development of the disease. METHODS: Retrospective analysis identified 88 canine patients presenting with unilateral acute congestive primary angle-closure glaucoma (IOP > 25 mm Hg) and gonioscopic findings of pectinate ligament dysplasia and/or narrow or closed iridocorneal angle in the contralateral nonglaucomatous eye. Patients with histopathologic confirmation of pectinate ligament dysplasia or angle closure in the initial glaucomatous eye receiving prophylactic medical therapy in the contralateral eye were included. Time to medical failure for each antiglaucoma medication and efficacy of the combination therapy were evaluated. RESULTS: The most commonly affected pure-breds were the American Cocker Spaniel (20.4%) and Basset Hound (11.36%). The patients receiving demecarium bromide 0.125% had the longest estimated median time to medical failure at 330.0 days, followed by latanoprost 0.005%, dorzolamide hydrochloride 2.0%, and demecarium bromide 0.25% at 284.0 days, 272.5 days, and 143.0 days, respectively. The estimated median time to medical failure for patients receiving topical antiglaucoma and anti-inflammatory medication was 324.0 days versus 195.0 days in patients receiving antiglaucoma medication alone. Survival analysis showed no statistical significance. CONCLUSIONS: None of the four antiglaucoma medications evaluated statistically delayed medical failure when compared to each other. Although significance was not achieved, our data suggest that adjunctive use of topical anti-inflammatory medications may be beneficial in these cases.

Evaluation of intraorbital prosthetic pigmentation using 0.3 and 1.5 Tesla magnetic resonance imaging and computed tomography.

PURPOSE: To investigate the magnetic susceptibility artifact associated with pigmented intraorbital prosthetics when performing magnetic resonance imaging (MRI) and computed tomography (CT). Potential artifact reduction techniques were also investigated. STUDY DESIGN: Prospective study. METHODS: Five different-colored 20-millimeter small animal silicone intraorbital prosthetics and two equine prosthetics were evaluated using 0.3 and 1.5 Tesla (T) MRI and CT. MRI sequences included T1- (T1WI) and T2-weighted spin echo (T2WI), T2 gradient echo (T2*), short tau inversion recovery (STIR), and fluid-attenuated inversion recovery (FLAIR). When present, artifact size was measured using computerized software by three separate observers. Artifact reduction techniques included alterations in receiver bandwidth, field of view, slice thickness, and matrix size. RESULTS: The ferrous brown-pigmented prosthetic resulted in a magnetic susceptibility artifact with MRI. No artifact was observed on CT images. Interobserver variability was not statistically significant. For both the 0.3T and 1.5T MRI, the T2* sequence exhibited the largest artifact surface area followed by T2WI, T1WI, STIR, and FLAIR. Decreasing slice thickness showed a decrease in artifact size; however, this difference was not statistically significant. CONCLUSIONS: The ferrous substances in the brown intraorbital prosthetic resulted in a significant magnetic susceptibility artifact when performing MRI. Artifact reduction techniques did not significantly decrease artifact surface area. The use of ferrous brown-pigmented prosthetics and their potential to affect future MR imaging studies should be adequately discussed with pet owners.

Major breed distribution of canine patients enucleated or eviscerated due to glaucoma following routine cataract surgery as well as common histopathologic findings within enucleated globes.

PURPOSE: To identify the most significantly represented breeds that were enucleated or eviscerated due to intractable glaucoma following elective cataract surgery and to describe the major histopathologic features of enucleated globes. METHODS: A retrospective review of the Comparative Ocular Pathology Laboratory of Wisconsin database revealed 153 canine evisceration or enucleation submissions that met inclusion criteria. The most commonly represented breeds were identified, and enucleated globes of these breeds were further evaluated histologically (n = 69). Following standard hematoxylin & eosin staining, globes were evaluated for the presence of; corneal pathology, goniodysgenesis, pigment dispersion, pre-iridal fibrovascular membranes (PIFVMs), peripheral anterior, and/or posterior synechiation, inflammatory infiltrates, lens pathology, retinal pathology, and/or endophthalmitis. RESULTS: The most significantly represented breeds were the Cocker Spaniel (11.7%), Boston Terrier (10.5%), Labrador Retriever (6.5%), Bichon Frise (6.5%), Shih Tzu (5.8%), and Jack Russell Terrier (5.8%). Common histopathologic findings included inflammatory keratitis, the presence of PIFVMs, and lymphoplasmacytic uveal infiltrates. CONCLUSIONS: The Cocker Spaniel, Boston Terrier, Labrador Retriever, Bichon Frise, Shih Tzu, and Jack Russell Terrier may be at increased risk of the development of glaucoma following elective cataract surgery. These findings have potential clinical implications.

Screening ADAMTS10 in dog populations supports Gly661Arg as the glaucoma-causing variant in beagles.

PURPOSE: Previously, we mapped the disease locus in the beagle model of autosomal recessive primary open angle glaucoma (POAG) to a 4-Mb interval on chromosome 20, and identified a Gly661Arg variant in ADAMTS10 as the candidate disease-causing variant. The purpose of this study was to test the hypothesis that the Gly661Arg variant of ADAMTS10 causes glaucoma by genotyping dogs of various breeds affected and unaffected by primary glaucoma. METHODS: Dogs of various breeds, affected or unaffected with primary glaucoma, were genotyped for the Gly661Arg variant of ADAMTS10, as well as 7 other nonsynonymous single nucleotide polymorphisms (SNPs) in other genes in the beagle POAG locus that segregate with disease. Alternate allele frequencies were calculated with 95% confidence intervals and comparisons made to expected allele frequency relative to disease prevalence or between cases and controls. RESULTS: For the nonsynonymous SNPs other than the ADAMTS10 variant, control dogs were identified that were homozygous for the alternative alleles, ruling out those variants as causative. None of the nonsynonymous SNPs were found associated with primary glaucoma in American cocker spaniels. The Gly661Arg variant of ADAMTS10 was the only variant with minor allele frequency consistent with the prevalence of primary glaucoma in the general beagle population. The only dog found homozygous for the Gly661Arg variant of ADAMTS10 was an affected beagle, unrelated to the POAG colony. CONCLUSIONS: These findings support the Gly661Arg mutation of ADAMTS10 as the likely cause of POAG in beagles.

Postoperative glaucoma in the Labrador Retriever: incidence, risk factors, and visual outcome following routine phacoemulsification.

OBJECTIVE: To evaluate the incidence and risk factors associated with development of postoperative glaucoma in the Labrador Retriever following routine phacoemulsification. METHODS: Medical records from Labradors and a randomly selected population of non-Labradors were retrospectively evaluated. Signalment, diabetic status, cataract stage, gonioscopic findings, presence of preoperative lens-induced uveitis, development of postoperative hypertension (POH), postoperative glaucoma and postoperative visual status were recorded for each patient. Survival curves were developed using the Cox proportional hazards model. RESULTS: Forty-two Labradors (66 eyes) and 199 non-Labradors (314 eyes) were included. The incidence of POH was significantly higher in Labradors (33%) than non-Labradors (18%). Labradors were at significantly increased risk of postoperative glaucoma and blindness compared to non-Labradors. Estimated probabilities of postoperative glaucoma in Labradors were 23%, 25%, 30% and 35% at weeks 4, 26, 52 and 104, respectively, compared with 5%, 6%, 7% and 9% at weeks 4, 26, 52 and 104, respectively, in non-Labradors. Estimated probabilities of postoperative blindness in Labradors were 5%, 9%, 15% and 27% at weeks 4, 26, 52 and 104, respectively, compared with 2%, 3%, 5% and 10% at weeks 4, 26, 52 and 104, respectively, in non-Labradors. Risk factors for the development of glaucoma in Labradors included increasing age and development of POH. No statistically significant risk factors for the development of glaucoma were identified in non-Labradors. CONCLUSIONS: Labradors are at increased risk of glaucoma and blindness following phacoemulsification compared with non-Labradors. POH and increasing age represent risk factors for the development of postoperative glaucoma in Labradors.

A review of orbital and intracranial magnetic resonance imaging in 79 canine and 13 feline patients (2004-2010).

OBJECTIVE: To review the distribution of orbital and intracranial disease in canine and feline patients undergoing magnetic resonance imaging (MRI) following referral to a veterinary ophthalmologist and to correlate results of MRI with pathologic conditions including neoplasia, suspected optic neuritis (ON) and orbital cellulitis. Recognized and emerging imaging techniques are reviewed. PROCEDURE: Medical records of 79 canine and 13 feline patients were reviewed. RESULTS: Neoplasia was diagnosed in 53/92 (57.6%) of patients. The most prevalent types of neoplasia were carcinoma (16/53, 30.1%), sarcoma (11/53, 20.8%), lymphoma (8/53, 15.1%) and presumptive meningioma (9/53, 17.0%). Carcinomas and sarcomas were characterized by bony lysis and intracranial/sinonasal extension. Lymphoma was generally unilateral, less invasive and originated from the ventromedial orbit. Intracranial masses representing presumptive meningiomas frequently exhibited a 'dural tail' sign. Diagnosis of suspected ON was made in 13 of 92 (14.1%) patients. Results of MRI in patients with suspected ON included unilateral optic nerve hyperintensity (3/13, 23.0%), bilateral optic nerve hyperintensity (1/13, 7.7%) and optic chiasmal hyperintensity (3/13, 23.0%). Seven suspected ON patients demonstrated intracranial multifocal patchy contrast enhancement (7/13, 53.8%). Diagnosis of orbital cellulitis was made in 12/92 (13.0%) patients. CONCLUSIONS: Orbital neoplasia was the most common pathologic condition detected. Essential Roentgen characteristics are helpful when diagnosing pathologic processes and providing prognoses in cases of orbital or intracranial disease. Magnetic resonance imaging comprises an important diagnostic component in cases of suspected ON. Emerging contrast and functional MRI techniques as well as SI data may increase our ability to characterize disease processes.

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.

Suspected uveal metastasis of a nail bed melanoma in a dog.

A 13-year-old Golden Retriever was referred for evaluation of generalized corneal edema, dyscoria, and suspected glaucoma affecting the right eye. The dog exhibited no signs of systemic illness, but had a history of a melanoma of the nail bed of the first digit of the right hind limb, excised 1 year previously. Ophthalmologic examination revealed diffuse corneal edema, mild anterior uveitis, glaucoma and a mass within the right iris. Enucleation was performed and histopathologic evaluation of the globe revealed the iris to be infiltrated with an anaplastic melanoma, suspected to represent a metastasis of the original nail bed tumor.

Development of a microarray chip for gene expression in rabbit ocular research.

PURPOSE: To develop a microarray for the rabbit that can be used for ocular gene expression research. METHODS: Messenger RNA was isolated from anterior segment tissues (cornea, conjunctiva, and iris) and posterior segment tissues (lens, retina, and sclera) of rabbit eyes and used to create two independent cDNA libraries through the NEIBank project. Clones from each of these libraries were sequenced from both the 5' and 3' ends. These sequences and those from the National Center for Biotechnology Information (NCBI) taxonomy database for rabbit were combined and electronically assembled into a set of unique nonoverlapping continuous sequences (contigs). For each contig, a homology search was performed using BLASTX and BLASTN against both the NCBI NR and NT databases to provide gene annotation. Unique contigs were sent to Agilent Technologies, where 60 base oligonucleotide probes were designed and synthesized, in situ, on two different arrays in an 8 array x 1900 element format. Glaucoma filtration surgery was performed on one eye of six rabbits. After 14 days, tissue was harvested from the conjunctiva and Tenon's capsule of both the surgically treated and untreated control eyes. Total RNA from each sample was labeled with cyanine dyes and hybridized to our custom microarrays. RESULTS: Of the 3,154 total probes present on the two arrays, 2,522 had a signal value above the background. The expression of 315 genes was significantly altered by glaucoma filtration surgery. Genes whose expression was altered included proteins associated with inflammatory response, defense response, and proteins involved in synthesis of the extracellular matrix. CONCLUSIONS: The results of this rabbit microarray study are consistent with those from other wound healing studies, indicating that this array can provide valid information on broad patterns of gene expression. This is the first microarray available for rabbit studies and is a valuable tool that can be used to study molecular events in the eye.

Surgical management of a malacic corneal ulcer in a greater one-horned Asian rhinoceros (Rhinoceros unicornis) using a free island tarsoconjunctival graft.

A greater one-horned Asian rhinoceros (Rhinoceros unicornis) presented for presumed ocular trauma to the left eye, with secondary bacterial infection, resulting in severe and progressive corneal ulceration. Following a poor response to medical therapy, the animal was anesthetized for further examination, and a bulbar conjunctival pedicle graft performed. This graft failed by 48-h postsurgery as a result of self-trauma. The animal was re-anesthetized, and a free island tarsoconjunctival graft performed. This second procedure was successful, resulting in globe preservation, cosmesis, and functional vision in the affected eye.

Microarray analysis of the failure of filtering blebs in a rat model of glaucoma filtering surgery.

PURPOSE: To generate data concerning changes in levels of protein expression associated with wound healing and bleb failure in a rat model of glaucoma filtration surgery (GFS), and to identify factors that may play a role in this process. METHODS: Of 36 Sprague-Dawley rats, GFS was performed on 27 by introducing a silicone cannula through a scleral tunnel under a conjunctival flap, resulting in aqueous-filtering blebs that failed over 8 to 13 days. The additional nine rats were used as the nonsurgical control. Nine blebs were harvested at each of days 0, 2, 5, and 12 and pooled, yielding three replicates of three blebs per time point. RNA was extracted, labeled, and hybridized to 230A rat GeneChip arrays (Affymetrix, Santa Clara, CA). RESULTS: Of the 15,924 probe sets/genes present on the array, 923 genes were indicated to have a significant treatment effect at P < 0.005. Eight gene expression clusters were identified that could be broadly classified into three basic patterns. These were an increase on day 2, a decrease on day 2, or an increase on either day 5 or 12. The greatest change occurred between days 0 and 2. The most heavily populated functional categories included growth factors, structural proteins, and matrix metalloproteinases. CONCLUSIONS: This study represents the first large-scale gene expression analysis after GFS. Expression patterns for known mediators of the bleb scarring process, including transforming growth factor-beta, connective tissue growth factor, and matrix metalloproteinases, were confirmed, and a number of mediators not previously associated with this process were identified.

Expression of connective tissue growth factor after glaucoma filtration surgery in a rabbit model.

PURPOSE: Connective tissue growth factor (CTGF) appears to play a significant role in mediating fibrosis in several tissues. To gain further understanding of the role of CTGF in the scar formation that occurs after glaucoma filtering surgery (GFS), experiments were performed in a rabbit model. METHODS: . Three experiments were performed: (1) CTGF and transforming growth factor (TGF)-beta expression were measured quantitatively after GFS, using ELISA. (2) After GFS conjunctival bleb tissues were immunostained for the presence of CTGF and TGF-beta. (3) Exogenous CTGF was injected into mitomycin-C (MMC)-treated filtering blebs and the scaring response compared to TGF-beta and physiological saline-injected blebs. RESULTS: CTGF and TGF-beta were expressed maximally by day 5 after surgery and were both shown to be present in the bleb tissues after GFS. The addition of exogenous CTGF and TGF-beta increased the rate of failure of GFS blebs. CONCLUSIONS: These data support the hypothesis that CTGF plays an important role in scarring and wound contracture after GFS. Inhibition of CTGF synthesis or its action may help prevent bleb failure and improve long-term GFS outcomes.

A muscleblind knockout model for myotonic dystrophy.

The neuromuscular disease myotonic dystrophy (DM) is caused by microsatellite repeat expansions at two different genomic loci. Mutant DM transcripts are retained in the nucleus together with the muscleblind (Mbnl) proteins, and these abnormal RNAs somehow interfere with pre-mRNA splicing regulation. Here, we show that disruption of the mouse Mbnl1 gene leads to muscle, eye, and RNA splicing abnormalities that are characteristic of DM disease. Our results support the hypothesis that manifestations of DM can result from sequestration of specific RNA binding proteins by a repetitive element expansion in a mutant RNA.