Christopher G. Pirie

Photocrosslinking of Silk Fibroin Using Riboflavin for Ocular Prostheses

A novel method to photocrosslink silk fibroin protein is reported, using riboflavin (vitamin B2) as a photoinitiator and the mechanism of crosslinking is determined. Exposure of riboflavin-doped liquid silk solution to light results in the formation of a transparent, elastic hydrogel. Several applications for this new material are investigated including corneal reshaping to restore visual acuity and photolithography.

Manual corneal thickness measurements of healthy equine eyes using a portable spectral-domain optical coherence tomography device

REASONS FOR PERFORMING STUDY Corneal thickness measurements of the equine globe using spectral-domain optical coherence tomography (SD-OCT) have not been reported. OBJECTIVES To determine corneal thickness measurements and the intra- and interoperator reliability of a portable SD-OCT device in equine eyes. STUDY DESIGN Prospective observational study. METHODS Horses free of ocular disease were used for this study. Gentle manual restraint, in combination with detomidine hydrochloride and a head stand, were employed to ensure proper animal positioning. Corneal pachymetry measurements were obtained from both eyes of each animal 3 times by 2 operators in succession. A 6 mm corneal pachymetry protocol was performed using a portable SD-OCT device. All measurements were obtained manually by one operator (C.G.P.) using the integrated calliper function. Measurements included epithelial thickness, stromal thickness, Descemets membrane thickness and total corneal thickness. All recorded measurements were analysed to determine both intra- and interoperator reliability. RESULTS Thirty horses with a mean age of 10.6 ± 6.4 years were examined. Mean epithelial, stromal, Descemets membrane and total corneal thickness values obtained were, respectively, 174.7 ± 13.6, 599.2 ± 45.4, 38.4 ± 15.3 and 812.0 ± 44.1 μm for operator A and 175.9 ± 12.9, 599.2 ± 44.9, 38.4 ± 15.0 and 812.9 ± 42.9 μm for operator B. A positive correlation was found between Descemets membrane thickness and age, whereby Descemets membrane thickness increased by 2 μm/year (P<0.0001). The coefficients of variation for both operators were <4% for all measurements. Intraclass correlations ranged from 0.92 to 0.98. CONCLUSIONS Manual corneal thickness measurement using a portable SD-OCT device provides epithelial, stromal, Descemets membrane and total corneal thickness measurements with clinically acceptable intra- and interoperator reliability in healthy equine eyes.

Acute primary canine herpesvirus‐1 dendritic ulcerative keratitis in an adult dog

We present a report of dendritic ulcerative keratitis in a 4-year old locally immunosuppressed dog suspected to result from acute primary canine herpesvirus-1 (CHV-1) infection. The dog was presented for evaluation of mild blepharospasm and conjunctival hyperemia in the right eye (OD) shortly after attending a public boarding facility. For approximately 3 months, the dog had been receiving topical prednisolone acetate 1.0% and tacrolimus 0.02% in both eyes (OU) q12h for treatment of follicular conjunctivitis. Ophthalmic examination revealed three regions of corneal fluorescein retention OD. The lesions had a dendritic pattern, were approximately 2-3 mm in length, and were located at the dorsomedial, lateral, and ventromedial aspects of the cornea. No additional abnormalities were noted on complete ophthalmic and physical examinations. CHV-1 was identified in conjunctival samples OD by polymerase chain reaction, and paired CHV-1 serum virus neutralization antibody titers were positive and consistent with acute infection. Topical prednisolone acetate and tacrolimus were discontinued. The dog was treated with cidofovir 0.5% OU q12h for a period of 4 weeks, with resolution of corneal disease noted within 1 week of treatment. In conjunction with previous studies, this case report supports a central role for alterations in host immune status in the pathogenesis and clinical manifestations of CHV-1 ocular disease in dogs.

Central corneal thickness measurements in normal dogs: a comparison between ultrasound pachymetry and optical coherence tomography

OBJECTIVE To compare central corneal thickness (CCT) measurements obtained from normal canines using a spectral-domain optical coherence tomography device (SD-OCT) and an ultrasonic pachymeter. ANIMALS Fifteen clinically normal dogs. PROCEDURES Dogs were briefly anesthetized with propofol. Central corneal thickness measurements were obtained from both eyes of each animal four times by one operator using a SD-OCT system. The CCT was automatically calculated using the pachymetry software generated from eight radial scans, 6 mm in length. Ultrasonic pachymetry was then performed in both eyes of each animal by one operator five times in succession. The CCT was recorded for each modality and compared statistically for agreement and bias. RESULTS Fifteen dogs (seven castrated male, eight spayed female) with a mean age of 2.3 ± 1.3 years were examined. The mean CCT for all eyes examined via SD-OCT and ultrasonic pachymetry (velocity set at 1636 m/s) was 587.72 ± 32.44 μm and 598.54 ± 32.28 μm, respectively. Ultrasonic pachymetry consistently overestimated CCT as compared to OCT by a mean value of 10.82 μm (P < 0.0001). No significant difference in CCT was found based on the age or sex of the animal. There was no significant difference in CCT measurements between replicates performed by the same operator for each modality. The coefficient of variation within and between imaging modalities was low (range 0.63-2.5%). The intraclass correlation coefficient comparing methods was 0.92. CONCLUSIONS Correlation between modalities was excellent; however, ultrasonic pachymetry set at a standard velocity of 1636 m/s overestimates CCT as compared to OCT.

Corneal epithelial inclusion cyst in a Llama.

A 13-year-old, female Llama presented for evaluation of a limbal based corneal mass involving the OD of 4 months duration. The mass was excised en bloc by a nonpenetrating keratectomy, followed by placement of a conjunctival advancement flap covering the keratectomy site. The mass was submitted for histological evaluation. Histopathology identified the mass to be a corneal epithelial inclusion cyst filled with necrotic squamous and neutrophilic debris. Surgical excision was complete and considered curative with no signs of recurrence 3 months postoperatively. There was no known prior ocular trauma; however, a previously performed corneal biopsy for evaluation of recurrent epithelial erosions may have been an initiating cause.

Glaucoma associated with uveal cysts and goniodysgenesis in American Bulldogs: a case series

We present a series of three American Bulldogs with clinical signs of glaucoma and intraocular inflammation accompanied by bilateral uveal cysts and abnormal gonioscopic findings. All dogs proved refractory to medical management and were enucleated. Histopathologic findings were similar in all three and included significant preiridal fibrovascular membranes and mononuclear inflammatory infiltrates in the anterior uvea. On microscopic evaluation, cysts appeared to arise primarily from the ciliary body and iridociliary sulcus, with smaller cysts also budding from the posterior iris. Pigment dispersion was variable but consistent, involving deposition of a small number of pigment-laden cells in the dependent trabecular meshwork. Cataract formation was not noted. Glaucoma associated with uveal cysts has been described previously in Golden Retrievers and Great Danes, although clinical and histopathologic findings in those breeds are not identical to those described here. American Bulldogs with uveal cysts should have gonioscopy performed and should be monitored carefully for signs of increased intraocular pressure and intraocular inflammation. Furthermore, documentation of cyst-associated glaucoma in a third breed suggests clinicians should exercise caution in dismissing uveal cysts in dogs as incidental findings.

Intra and inter-user reliability of central corneal thickness measurements obtained in healthy feline eyes using a portable spectral-domain optical coherence tomography device

OBJECTIVE To determine the intra and inter-user reliability of central corneal thickness (CCT) measurements obtained using a portable spectral-domain optical coherence tomography (SD-OCT) device in healthy feline eyes. ANIMALS Twenty clinically normal cats. PROCEDURES Gentle manual restraint was utilized for proper animal positioning. Central corneal thickness measurements were obtained from both eyes of each animal three times by two operators in succession. A 6 mm, corneal pachymetry protocol was performed using the Optovue® iVue SD-OCT system. The CCT was automatically calculated using the pachymetry software generated from eight radial scans, 6 mm in length. The CCT was recorded for each operator and compared statistically for both intra and inter-user reliability. RESULTS Twenty cats (11 CM, 9 SF) with a mean age of 4.7 years were examined. The mean CCT for all eyes examined was 629.08 ± 47.05 μm. No significant difference in CCT was found based on the eye examined (OD vs. OS) or age of the animal. However, the CCT of spayed females was significantly higher (42.64 ± 18.0 μm) as compared to castrated males (P = 0.03). There was no significant difference in CCT measurements between replicates performed by the same operator or between operators. The mean difference in CCT between operators was 0.38 μm. The coefficient of variation for each user and between users was very low (range 0.68-1.5%). The intra-class correlation coefficient comparing operators was 0.975. CONCLUSIONS The Optovue® iVue SD-OCT device is capable of obtaining CCT measurements with excellent intra and interoperator reliability in healthy feline eyes.

360-degree conjunctival grafting for management of diffuse keratomalacia in a dog.

We present a report describing use of a 360-degree conjunctival graft for management of progressive keratomalacia refractory to medical treatment in a 5-month-old American Cocker Spaniel. In the dog of this report, the extension of melting to nearly the entire corneal surface limited surgical options. Following surgery and later resection of the graft, the patient is visual with minimal corneal opacity. Numerous corneal grafting techniques have been described in companion animals, but require special materials and may not be possible when melting is extensive. Although older animals or animals with additional corneal pathology may have less ideal outcomes in terms of corneal clarity than the patient of this report, we believe that 360-degree conjunctival grafting offers a viable and cost-effective option for management of cases with extensive keratomalacia that may otherwise have resulted in enucleation.

Measurement of corneal sensitivity in 20 ophthalmologically normal alpacas

OBJECTIVE To determine corneal sensitivity in 20 healthy adult alpacas (40 eyes) in order to establish reference values. DESIGN Prospective study. ANIMALS Twenty healthy, adult alpacas. PROCEDURES Corneal sensitivity was determined by the corneal touch threshold (CTT) using a Cochet-Bonnet esthesiometer. Five different regions of the cornea were evaluated (nasal, ventral, lateral, dorsal, and central). RESULTS Corneal touch threshold values (in mm filament length) obtained from five corneal regions demonstrated varying corneal sensitivities. The central region (34.5 ± 7.1 mm) was the most sensitive, followed by the ventral (29.5 ± 7.2 mm), medial (29.3 ± 7.3 mm), dorsal (25.6 ± 6.3 mm), and lateral (21.8 ± 5.7 mm) regions. All pairwise comparisons of regional differences were statistically significant (P < 0.05), except for the comparison between the ventral and medial regions (P = 0.88). Evaluation of the CCT while controlling for age (2-5 years vs. 6-10 years) demonstrated an increased CTT with an increasing age for the central, ventral, medial and lateral regions. A decrease in the CTT of the dorsal region was noted with increasing age. CONCLUSION AND CLINICAL RELEVANCE Corneal touch threshold values in 40 eyes of 20 healthy adult alpacas were determined using a Cochet-Bonnet esthesiometer. This study demonstrated the central corneal region to be most sensitive. Values obtained may serve as reference values in subsequent studies.

Surgical treatment of epibulbar melanocytomas by complete excision and homologous corneoscleral grafting in dogs: 11 cases

OBJECTIVE The aim of the study was to evaluate the efficacy, outcome, and complications following penetrating sclerokeratoplasty and frozen homologous corneoscleral grafting for the management of extensive canine epibulbar melanocytomas. METHODS Medical records of canine patients treated at three different veterinary hospitals between 1999 and 2010 were reviewed. Signalment, location and extent of melanocytomas, recurrence rate, and early and late complications were reported. Patients were re-examined postoperatively to provide follow-up information. RESULTS Patients included one intact male, three castrated males, six intact females, and one spayed female, with a median age of 5 years (range, 3-9). German Shepherds were overrepresented. Tumors extended from 2 to 4 clock hours at the limbus and up to 17 mm from clear cornea to globe equator. One case showed iridocorneal angle invasion; corneal involvement was present in all cases, and lipid keratopathy was present in four cases. In two cases, there was incomplete resection owing to tumor extent. Follow-up time ranged from 3 to 72 months (median, 17 months), with one case of intraocular tumor progression. Early complications included anterior uveitis (11/11), intracameral fibrin (5/11), hyphema (4/11), corneal edema (4/11), exuberant corneal granulation tissue (2/11), focal retinal edema (1/11), dyscoria (1/11), and partial suture dehiscence (1/11). Late complications included corneal fibrosis and/or pigmentation (11/11), faint anterior cortical cataracts (3/11), and lipid keratopathy (1/11). Vision was retained in all cases. CONCLUSIONS This technique offers a surgically challenging but effective treatment for extensive epibulbar melanocytomas. In this case series, complications were mild and transient, with preservation of ocular anatomy and function.