David A. Wilkie

Surgery of the Cornea

Corneal surgery is a common and essential part of veterinary ophthalmology and ranges from simple linear keratotomy for indolent ulcers to penetrating keratoplasty for restoration of optical clarity. Success in corneal surgery relies on an understanding of corneal anatomy, physiology and wound healing, meticulous attention to detail, microsurgical equipment and techniques, and use of appropriate preoperative, intraoperative, and postoperative medications. Surgical management of corneal disease is indicated for corneal ulceration, excision of a mass lesion, reconstructive procedures, therapeutic indications, optical restoration, and cosmetic purposes.

Application of In Vivo Confocal Microscopy to the Understanding of Surfactant-Induced Ocular Irritation*

The purpose of this study was to assess the ability of in vivo confocal microscopy (CM) to provide noninvasively derived histopathologic correlates of surfactant-induced eye irritation from which specific pathologic mechanisms can be identified and later evaluated in alternative in vitro models. Rats and rabbits, divided into groups of 5, received 10 μl of an anionic or cationic surfactant in one eye with the other eye used as a control. At specified times, eyes were examined and scored for ocular irritancy using a penlight and slit-lamp. Subsequently, corneas were evaluated by in vivo CM to evaluate epithelial layer thickness and surface epithelial cell area, corneal thickness, depth of necrosis, inflammation, fibrosis, and endothelial injury. At 3 hr, the anionic surfactant produced slight irritation with peak scores of 12.4 and 8.0 out of a possible 110 in the rats and rabbits, respectively. In vivo CM revealed changes limited to the corneal epithelium that decreased in thickness to 78% in rats and 81% in rabbits at 3 hr. This decrease in the thickness correlated with a significant decrease in surface epithelial cell area from 2,061 ± 395 μm2 to 567 ± 330 μm2 in the rats and 1,523 ± 185 μm2 to 934 ± 71 μm2 in the rabbits (p < 0.005 and 0.005, respectively). The cationic surfactant produced severe irritation in both the rats and rabbits with peak scores of 85.4 and 80.2 occurring at day 2, respectively. In vivo CM in the rats showed complete loss of corneal epithelium, lysis of keratocytes, and loss of corneal endothelium. In the rabbits, injury appeared limited to the anterior cornea with complete loss of epithelium and loss of keratocytes extending to 52% of the corneal thickness. These findings establish the application of noninvasive, in vivo CM to qualitatively and quantitatively characterize the pathobiology of ocular irritation in situ. This information will be important in the development and evaluation of mechanistically based in vitro alternatives for ocular irritancy testing.

Long-term outcome after implantation of a suprachoroidal cyclosporine drug delivery device in horses with recurrent uveitis.

OBJECTIVE To determine the long-term efficacy, complications, and duration of effect of a cyclosporine (CsA) suprachoroidal implant (CSI) in horses with equine recurrent uveitis (ERU). METHODS Horses with ERU were treated with a 6-mm diameter, 25 mg, reservoir matrix CsA implant in the deep sclera adjacent to the suprachoroidal space. Horses with follow-up >1 year were examined for frequency of uveitis episodes, complications, and vision at last recheck. RESULTS Data from 151 eyes of 133 horses from the USA and Europe that had CsA devices implanted for ERU were reviewed. Follow-up time ranged from 13 to 85 months after surgery, with a mean and median follow-up time of 28.9 and 26.3 months, respectively. Overall, at last follow-up 78.8% of eyes were considered visual and the overall mean frequency of uveitis episodes after CSI was 0.09 ± SD 0.08 episodes per month. The most common complications leading to vision loss at last follow-up were persistent uveitis episodes (54%), glaucoma (22%), mature cataracts (16%), and retinal detachment (6%). Persistent uveitis episodes tended to be the highest cause of vision loss in horses with <24 months and >48 months of follow-up. CONCLUSIONS This study demonstrated the long-term maintenance of vision of horses with ERU implanted with a CSI. The increased vision loss related to uveitis episode of inflammation in eyes after the likely depletion of CsA from the CSI suggests that a repeat CSI may be required at or before 48 months after surgery.

Ultraviolet Radiation-Induced Corneal Degeneration in 129 Mice

Ultraviolet radiation (UVR) is a risk factor for the development of ocular disease in humans, including acute photokeratitis, chronic corneal spheroidal degeneration, and cataract formation. This report describes the ocular lesions seen in 21 mice chronically exposed to UVR as part of a skin carcinogenicity study. All globes were affected to varying degrees. The primary lesion, not previously reported in UVR-exposed mice, was marked loss of keratocytes relative to age-matched controls. Secondary lesions included corneal stromal thinning, keratoconus, corneal vascularization and fibrosis, keratitis, globe rupture, and phthisis bulbi. In addition, more than 90% of UVR-exposed and unexposed lenses had evidence of cataract formation; this is the first report of the occurrence of spontaneous cataracts in 129 mice. In a subsequent study, apoptotic cells were identified histologically and by cleaved caspase 3 immunoreactivity in the corneal epithelium and, less commonly, in the corneal stroma after acute UVR exposure. Based on this finding, we propose that the loss of keratocytes observed in the chronic study was due to UVR-induced apoptosis.

Semiconductor diode laser transscleral cyclophotocoagulation for the treatment of glaucoma in horses: a retrospective study of 42 eyes.

OBJECTIVE To evaluate the outcome of diode laser transscleral cyclophotocoagulation (TSCP) for the treatment of glaucoma in horses. PROCEDURE Medical records at The Ohio State University were reviewed. All horses that underwent diode laser TSCP between the years of 1995 and 2007 were included. Preoperative, procedural and clinical follow-up data were collected, and telephone follow-up was performed. RESULTS Forty-two eyes of 36 horses were included. Twenty-four hours prior to surgery mean intraocular pressure (IOP) was 37.17 + or - 13.48 mmHg (42 eyes). Forty-one of 42 eyes (98%) were sighted and 39 of 39 (100%) of eyes were receiving topical glaucoma medication. At 3-5 weeks postoperatively the average IOP was 19.36 + or - 12.04 mmHg (22 eyes). IOP remained significantly lower than pretreatment values at all periods of clinical follow-up (P < 0.05). There was no significant difference in vision outcome, or the requirement for topical glaucoma medication relative to pretreatment values at any follow-up period. Hyphema in 5 of 42 eyes was the only complication noted. Of the 27 eyes seen for clinical follow-up, 2 were enucleated because of refractory elevation of IOP. Mean telephone follow-up was 49 months. Twenty-one of 22 owners contacted (95%) reported that the treatment had been of value, 14 of 22 eyes (64%) were receiving topical glaucoma medication, and 13 of 22 eyes (59%) were considered sighted. CONCLUSIONS Diode laser TSCP aided in the control of IOP and maintenance of vision but did not eliminate the need for topical glaucoma medication during the period of clinical follow-up.

Extraocular lymphoma in the horse

OBJECTIVE To describe the clinical findings and prognosis for extraocular lymphoma in the horse. PROCEDURES   Retrospective medical records study of horses diagnosed with third eyelid, corneoscleral, conjunctival, and/or eyelid lymphoma from multiple academic and private veterinary institutions. Data collected from the medical records included signalment, clinical descriptions of the extraocular lesions, treatment, and treatment outcomes. Nonparametric statistical analysis was performed with Fischers exact tests. RESULTS   Extraocular lymphoma involving the eyelid, third eyelid, cornea, sclera, and/or conjunctiva was diagnosed in 26 horses. Differences in signalment, unilateral vs. bilateral extraocular involvement, and single vs. multiple extraocular lesion locations held no significance in terms of outcome. ANIMALS STUDIED   Horses with lesions localized to the eyelid or other nonextraocular cutaneous locations had a significantly higher chance of negative outcome when compared to the horses with no eyelid or cutaneous involvement (P = 0.019). Lesions to the third eyelid, corneosclera, and conjunctiva were either nodular or diffuse in nature. Nodular lesions when compared to diffuse lesions were associated with a higher chance of a positive outcome (P = 0.007). Surgical resection of the extraocular lesions as part of the treatment produced a statistically higher chance of a positive outcome when compared to horses where resection was not performed (P = 0.03). CONCLUSIONS   The prognosis for clinical remission in horses with extraocular lymphoma is generally fair to good, as long as the affected tissues are completely excised, and there is no eyelid or cutaneous involvement. Horses diagnosed with the nodular form of extraocular lymphoma seem to have the best prognosis with complete excision.

Extra-adrenal paraganglioma of the equine orbit: six cases.

At The Ohio State University from 1994-2006 six of seven horses evaluated for primary orbital disease were diagnosed with extra-adrenal paraganglioma (EAPG). The horses ranged in age from 14 to 24 years, with a mean of 16.8 years. Duration of clinical signs was 1.5 years to 5 years, with a mean of 2.8 years. Clinical signs varied, but all six had non-painful exophthalmus of the right eye. Five horses had complete ocular exams reported; three of five had decreased to absent vision, two of five had pale optic nerves, and in three of five, difficulty of retropulsion of the globe was noted. Diagnostic tests performed included complete blood count, serum profile, radiography, ultrasound, computed tomography, true-cut biopsy, ocular examination, guttural pouch endoscopy, oral examination, and physical examination. Expulsive hemorrhage during orbital exenteration occurred in all horses. In five of six cases, tumor extension through the orbital foramen was apparent intra-operatively. Histopathologic appearance of all surgically removed tissues consisted of sheets of polygonal cells with abundant lightly granular cytoplasm, round nuclei with vesicular chromatin, and rare mitoses. Neoplastic cells were arranged into small groups separated by a fine fibrovascular stroma. All six cases were chromagranin positive on immunohistochemical staining. Follow-up ranged from six months to six years, with a mean of two years. Four of the five horses that recovered from surgery had no apparent tumor recurrence in 6-48 months.

Cellular immunity in dogs with keratoconjunctivitis sicca before and after treatment with topical 2% cyclosporine

Peripheral cellular immunity of ten dogs with keratoconjunctivitis sicca (KCS) that had not been treated with topical corticosteroids or cyclosporine was evaluated (by use of in vitro lymphocyte proliferation assays and CD4+/CD8+ lymphocyte subset analysis) before and after 1 and 3 months of treatment with topical ocular 2% cyclosporine (CsA). In vitro lymphocyte proliferation and CD4+/CD8+ lymphocyte subset analysis was done in eight normal dogs at the 0, 1 and 3 month time periods to use for comparison. There was no significant difference in lymphocyte proliferation or numbers of CD4+ or CD8+ lymphocytes in dogs with KCS and normal dogs prior to CsA treatment. However, by 1 months time, lymphocyte proliferation had decreased in the CsA-treated Dogs with KCS, and by 3 months there was a significant difference (P < 0.0001) from the normal dogs. These results suggest that dogs with KCS may not have altered peripheral cellular immunity and that use of topical 2% cyclosporine for treatment of KCS causes a suppression of lymphocyte proliferation after 1 to 3 months of use.

Ultrasound biomicroscopy of the iridocorneal angle of the eye before and after phacoemulsification and intraocular lens implantation in dogs

OBJECTIVE To compare the iridocorneal angle (ICA) and angle opening distance (AOD) in dogs with cataractous and noncataractous lenses; evaluate cataractous eyes ultrasono-graphically for association of postoperative ocular hypertension (POH) with the ICA, AOD, and postoperative echogenic anterior chamber debris; and evaluate intraobserver reliability associated with ICA and AOD measurements. ANIMALS 56 dogs with 102 cataracts, and 23 clinically normal dogs. PROCEDURES Ultrasound biomicroscopy was performed on 102 eyes of 56 dogs before and after cataract surgery and on 46 nondilated and dilated eyes of 23 clinically normal dogs. Cataract stage, ICA, AOD, and association with POH were assessed. RESULTS Cataract stage and ICA or AOD were not significantly associated; however, ICA and AOD typically decreased with increasing cataract maturity. Before and after pupillary dilation, AODs were significantly smaller in cataractous eyes than in noncataractous eyes. Before surgery, ICA and AOD in eyes without pupillary dilation were significantly associated with POH. At > 13 degrees , odds of developing POH increased by 11% for each degree increase in the ICA. Postoperative anterior chamber debris was not associated with POH. Coefficient of variation for repeated measurements was 10% for the ICA and 9.5% for the AOD, suggesting good intraobserver reliability. CONCLUSIONS AND CLINICAL RELEVANCE In this study, dogs with larger ICA and AOD measurements before surgery were at greater risk of developing POH. This information may be useful for future studies to determine whether preventative treatment for POH administered prior to surgery may be beneficial.

Update on veterinary cataract surgery.

Purpose of review The purpose of this review is not to specifically discuss the techniques of veterinary cataract surgery, but rather to emphasize some of the differences between the veterinary and human cataract patients, procedures and outcomes. Recent findings In general, veterinary cataract surgery has more similarities than differences when compared to its human counterpart. This is especially true when comparing pediatric cataract patients. Veterinary cataract surgery has changed dramatically in recent years with regards to surgical technique, ocular pharmacology, viscoelastic devices, phacoemulsification, and the most recent advancement, intraocular lens implantation for dogs, cats, and horses. Summary It is hoped that the exchange of information between the human and veterinary specialties can be of benefit to both groups as we all work to improve outcomes and resolve complications.