International Equine Ophthalmology Consortium (IEOC) Symposium.

This first IEOC symposium met its goals of gathering a group of leading equine ophthalmology clinicians and researchers to identify the challenges of the field. To facilitate collaboration, notes from round-table discussions, including the ideas and plans that were discussed are being complied and will be distributed to the attendees. Development of an IEOC membership organisation and website was discussed and supported by the group in an effort further to advance the science of equine ophthalmology. To present results from the collaborations made at this first IEOC meeting, an IEOC mini-symposium will be held at the American College of Veterinary Ophthalmologists Annual Meeting in Chicago Illinois, on 6th November 2009. The second annual IEOC symposium will be held in Vienna, Austria on 4th and 5th June 2010.

Ocular distribution and toxicity of intravitreal injection of triamcinolone acetonide in normal equine eyes.

OBJECTIVE: To determine ocular distribution and toxicity of a single injection of intravitreal triamcinolone acetonide (TA) in normal horses. ANIMALS STUDIED: Six adult horses, donated to North Carolina State University. PROCEDURES: Six horses were injected intravitreally with either 10, 20, or 40 mg (n = 2 each) of TA. The opposite eye of each horse was injected with balanced salt solution (BSS). Ocular toxicity was assessed by biomicroscopy, tonometry, indirect ophthalmoscopy, and electroretinogram. Aqueous humor (AH), vitreous humor (VH), and plasma samples were collected. Horses were euthanized 7 or 21 days after injection and eyes enucleated for histopathology. TA concentrations in AH, VH, and plasma were measured by HPLC. RESULTS: Three control eyes and one TA eye developed inflammation after injection or collection of AH. Positive bacterial cultures (Corynebacterium spp., Staphylococcus spp., and Streptococcus spp.) were obtained from three of these eyes. Other than transient corneal edema in TA injected eyes, which resolved by 7 days after injection, no other changes were observed. TA crystals were visible within the vitreous body. No evidence of TA toxic effect was noted on histopathology. TA was detected in all AH and VH samples from treated eyes following injection. Drug was not detected in the plasma. CONCLUSIONS: There was no evidence of overt toxicity from intravitreal TA in normal horses and a single intravitreal injection resulted in TA ocular levels for 21 days. However, the risk for bacterial infections with intravitreal injection or anterior chamber aspirations in horses is high. Use of topical and systemic antibiotics after injection is recommended.

Ocular toxicity and distribution of subconjunctival and intravitreal rapamycin in horses.

In vitro photosensitivity of rapamycin (RAPA) and ocular toxicity and distribution of intravitreal and subconjunctival RAPA was evaluated in normal horses. RAPA (2.5 mg, 5 mg, and 10 mg) was placed in 10 mL of PBS and maintained in a water bath at 37 degrees C, kept in the dark or subjected to room light, and sampled for up to 3 months for RAPA levels. Six normal adult horses received either 5 mg (n = 2) or 10 mg (n = 2) of RAPA intravitreally or 10 mg (n = 2) subconjunctivally. Ophthalmic exams and electroretinography (ERG) were performed prior to injection and on days 1, 7, 14, and 21 post-injection. Eyes were enucleated and samples were collected for RAPA concentrations and histopathology. No difference in light vs. dark RAPA concentrations was observed, suggesting a lack of RAPA phototoxicity. No evidence of ocular toxicity was noted on ophthalmic examination or histopathology. RAPA was not detected intraocularly 7 days post-injection in eyes receiving subconjunctival RAPA, but was detected in the vitreous at 21 days post-injection. Drug could be detected in both the aqueous and vitreous humor after intravitreal injection. Further study is needed to determine the efficacy of intravitreal RAPA.

Prognosis and impact of equine recurrent uveitis.

REASONS FOR PERFORMING STUDY: Equine recurrent uveitis (ERU) is a leading cause of vision loss in horses. OBJECTIVES: To assess the prognosis and impact of ERU on affected horses and their owners by evaluating the signalment, treatment and outcome (including the loss of use, vision assessment and economic loss). STUDY DESIGN: Retrospective impact study. METHODS: Medical records of horses presenting to the North Carolina State University Veterinary Health Complex (NCSU-VHC) with ERU between 1999 and 2014 were reviewed. Signalment, clinical signs, ophthalmic examination findings, treatments and outcomes were evaluated. Owner questionnaires were completed regarding vision, job/role, monetary value, diagnostic and treatment costs, concurrent illness and outcomes. RESULTS: Records of 224 horses (338 eyes) with ERU were reviewed. There was an overrepresentation of Appaloosas (54; 24.1%), Hanoverians (11; 4.9%) and other Warmbloods (13; 5.8%). Ninety-six eyes (28.4%) were diagnosed as blind and 38 eyes (11.2%) with glaucoma on initial evaluation. Leptospirosis titres of serum and/or aqueous humour were obtained in 88 horses and were positive in 40 horses (45.5%), with L. pomona being the most frequently isolated serovar. Globe loss at the NCSU-VHC occurred in 41 ERU eyes (12.1% of total). Owner questionnaires were evaluated in 194 horses (86.6%) and 91 horses (46.9%) were reported blind in the affected eye(s). Fifty-seven horses (29.4%) did not return to their previous role, while 61 (31.4%) performed at a reduced level. Equine recurrent uveitis decreased the monetary value of 164 horses. Twenty-nine horses (14.9%) were euthanised and 37 (19.1%) underwent change in ownership as a direct result of ERU. CONCLUSIONS: The impact of ERU is attributed to the high frequency of blindness, globe loss and loss of function. Euthanasia and change of ownership are common sequelae to the progressive nature of ERU. These factors, along with financial costs of the disease, have a significant impact on affected horses and their owners.

Low-dose oral administration of interferon-alpha for the treatment of immune-mediated keratoconjunctivitis sicca in dogs.

This preliminary study was designed to evaluate the effectiveness and dosage of oral use of interferon-alpha (IFN-alpha) in the treatment of naturally occurring, immune-mediated, canine keratoconjunctivitis sicca (KCS). Dogs with chronic immune-mediated KCS were selected from the two clinic populations. All medication, except topical artificial tears, was discontinued at least 2 weeks prior to beginning the clinical trial. IFN-alpha was administered orally once daily to the dogs by their owners as the sole therapy for the KCS. Examinations of the dogs were performed every 2 weeks for the duration of the trial (12 weeks). Each dog was given either two or three separate, escalating doses (20, 40, 80 IU of the IFN-alpha. A favorable response was observed in 55% (11/20) of all dogs treated. Clinical findings of those dogs that responded included increased wetting of the eyes, decreased mucus discharge, and fewer signs of discomfort. There was a nearly significant difference (p = 0.08) in pretreatment mean Schirmer's tear test (STT) between the dogs that responded (6.4 +/- SEM 0.62 mm/min) and those that did not respond (4.7 +/- SEM 0.69 mm/min) to the orally administered IFN-alpha. Seven of 11 dogs with favorable outcomes had an increased STT of at least 5 mm/min after treatment with oral IFN-alpha and the group had a post-treatment STT (10.5 +/- SEM 1.4 mm/min) significantly greater than baseline (p = 0.0004). The post-treatment STT of the dogs that did respond was significantly greater (p < 0.01) than the post-treatment mean STT of dogs that did not respond. All dogs that responded did so with the 20 or 40 IU dose of IFN-alpha. No side effects were noted and all dogs tolerated the treatment well.

Concomitant brainstem axonal dystrophy and necrotizing myopathy in vitamin E-deficient rats.

The purpose of this study was to simultaneously evaluate in rats the effects of vitamin E depletion on tissue alpha-tocopherol (alpha-T) concentrations, electrophysiologic measurements and histopathology. Rats (21-day-old male Wistar) were fed either vitamin E-deficient or supplemented (control) diets (n = 6/group) for 10, 16, and 61 weeks. At these times, electrophysiologic tests (electromyography, spinal and somatosensory evoked potentials, and motor nerve conduction velocity) were performed, the rats were killed and alpha-T concentrations of adipose tissue, sciatic nerve, and cervical and lumbar spinal cord were measured along with histopathologic evaluation of skeletal muscles and the nervous system. By 61 weeks, depletion of alpha-T from adipose tissue and peripheral nerve was more severe (< 1% of controls) than from cervical and lumbar spinal cord (15 and 8% of controls, respectively). Electrophysiologic tests were normal at all times. Histopathologic evaluation at 61 weeks revealed normal peripheral nerve structure, but necrosis of type 1 muscle fibers and increased numbers of spheroids in the gracile and cuneate nuclei. Our results confirm that low alpha-T concentrations in tissues precede histologic changes in peripheral nerves and skeletal muscle. Furthermore, pathologic changes associated with vitamin E deficiency occur independently in muscle and nervous tissue of rats.

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 month's 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.

Characterization of T-lymphocytes in the anterior uvea of eyes with chronic equine recurrent uveitis.

Equine recurrent uveitis (ERU), a chronic, recurrent inflammation primarily of the anterior uveal tract, is the most common cause of blindness in horses. Recently, T-lymphocytes have been found to be the most numerous cell type to infiltrate the anterior uveal of horses with ERU. In the present study, we characterized the T-lymphocyte population in the anterior uveal tract of eyes of horses with chronic ERU by evaluating the microscopic appearance (histopathologic features), the T-lymphocyte subsets, and the relative levels and amounts of T-lymphocyte cytokine mRNA in the anterior uvea. Seven inflamed eyes (from six horses with chronic ERU) and 5 normal eyes (from five horses with nonocular problems) were studied. After clinical examination, the eyes were removed, ocular fluids were aspirated, and anterior uveal tissues (iris and ciliary body) were processed for histologic and molecular (RNA isolation) analyses. Histologic examination by hematoxylin and eosin (H and E) staining and immunohistochemistry evaluating T-lymphocyte subsets (anti-CD4, CD8, CD5) were performed for each sample. RNA samples were analyzed for levels of messenger (m) RNA specific for interleukin (IL)-2, 4, and interferon-gamma (IFNgamma) by quantitative reverse transcriptase polymerase chain reaction (QRT-PCR). Eyes with ERU exhibited characteristic clinical signs, including corneal edema, aqueous flare, posterior synechia, corpora nigra degeneration, and cataract formation. Histologically, infiltration of the uveal tract with lymphocytes, plasma cells, and macrophages was most evident in the ciliary body and base of the iris. Loss of tissue structure (destruction) was most evident in the ciliary processes. Infiltrating lymphocytes were predominantly CD4+ T-cells (e.g. 48% CD4+ and 18% CD8+ in the ciliary body stroma), as determined by immunohistochemistry. Few inflammatory cells were observed in the normal eyes. The QRT-PCR results revealed increased transcription of IL-2 and IFNgamma and low IL-4 mRNA expression in eyes with chronic ERU compared to normal eyes, demonstrating a Thelper (Th) 1-like inflammatory response in eyes with ERU.

Effect of an intravitreal cyclosporine implant on experimental uveitis in horses.

The purpose of this study was to determine the effects of an intravitreal device releasing cyclosporine A (CsA) on recurrent inflammatory episodes in experimental uveitis. Nine normal horses were immunized peripherally with H37RA-mTB antigen twice, and then received 25 microg of H37RA-mTB antigen intravitreally in the right eye and an equal volume of balanced salt solution intravitreally in the left eye. Two weeks later, the animals randomly received either a CsA or a polymer implant (without CsA) in both eyes 1 week following implantation of the devices, 25 microg of H37RA-mTB antigen was reinjected into the right eye of each animal. Clinical signs of ophthalmic inflammation were graded following injections and implantation. The animals from each group were euthanized at 3, 14, and 28 days following the second injection. Aqueous and vitreous humor protein concentrations were measured. The presence, number, and type (CD4, 5 and 8) of infiltrating inflammatory cells and amount of tissue destruction were determined. Total RNA was isolated and quantitative reverse transcriptase-polymerase chain reaction was performed for equine specific interleukin (IL) 2 and 4, interferon-gamma (IFN gamma) and beta-actin. In addition, aqueous and vitreous humor and peripheral blood were collected at the termination of the experiments and analyzed for CsA concentration by HPLC. Within 4h of the first intravitreal H37RA-mTB antigen injection, each animal developed epiphora, blepharospasm, mild corneal edema, aqueous flare, myosis, and vitreous opacity. The severity of signs peaked 48 to 72 h after injection and subsequently decreased back to normal within 14 days. Following the second injection, clinical signs in the eyes with the CsA device were less severe and significantly shorter in duration than signs with the polymer only implant eyes. Aqueous and vitreous humor protein levels, infiltrating cell numbers, total number of T-lymphocytes, and levels of IL-2 and IFN gamma-mRNA were significantly less in eyes with the CsA implant compared to eyes with the polymer only. CsA implants did not completely eliminate the development of a second ('recurrent') experimental inflammatory episode in these horses. However, the duration and severity of inflammation, cellular infiltration, tissue destruction, and pro-inflammatory cytokines RNA transcript levels were significantly less in those eyes implanted with the CsA device.

Histological findings in corneal stromal abscesses of 11 horses: correlation with cultures and cytology.

Histopathology was compared to culture results and cytology from horses with corneal stromal abscess at the Auburn University and the Ohio State University Veterinary Teaching Hospitals. Significant bacteria were not isolated in culture or seen on histopathology in any of the horses. Although most bacteria infecting equine corneas can be isolated with blood and MacConkey's agars, failure to detect bacterial growth may not rule out infection because anaerobic or intracellular bacteria would not be isolated. The inability to visualise bacterial organisms on histological sections did not rule out their presence in the tissue, because there is often destruction of bacteria by neutrophils, macrophages and antibiotic therapy greatly reducing their numbers. Fungal keratitis was diagnosed by histopathology in 4 of 11 eyes (36%) and keratitis with no aetiological agent in 7 of 11 eyes (64%). Nine of 11 horses (82%) had a prominent neutrophilic stromal infiltrate and 2 (18%) had a predominantly pyogranulomatous reaction. Two of the 4 lesions that showed histological evidence of fungal infection were positive for identifiable fungi on culture and cytology. Fungal cultures of the other 2 cases with histological evidence of mycotic keratitis were negative or grew unidentifiable fungi which were considered pathogenic because, on histopathological sections, fungal hyphae were found deep in the corneal stroma surrounded by an inflammatory reaction. In 3 of 6 cases where fungi were recovered on culture, they were considered contaminants based on lack of evidence of organisms in histopathological sections. Histopathology and the use of special stains were important in the interpretation of culture and cytology results.

Effect of single- and multiple-dose 0.5% timolol maleate on intraocular pressure and pupil size in female horses.

OBJECTIVE: To determine the effect of single and multiple-dose 0.5% timolol maleate on intraocular pressure (IOP) and pupil size between 8 AM and 8 PM. Animals Nine female horses with normotensive eyes. Procedure IOP, horizontal and vertical pupil size were measured on a single day, between 8 AM and 8 PM at hours 0, 0.5, 1, 2, 4, 6, 8, 10, and 12. A single dose of 0.5% timolol maleate was applied to both eyes immediately after the first measurement at 8 AM. IOP and pupil size were measured at 8 AM and 4 PM in a 5-day experiment of twice-daily application of 0.5% timolol maleate. RESULTS: A significant decrease in IOP from 24.9 +/- 4.2 mmHg prior to application of timolol maleate to 20.7 +/- 3.1 mmHg (4.2 mmHg = 17%) was observed 8 h after single-dose application. A significant decrease in horizontal pupil size (2.0 mm = 11%) was present 6 h after single-dose application. In the multiple-dose experiment, a significant decrease in IOP was present on days 4 and 5 as compared to IOP measured prior to application of timolol maleate. A significant decrease in horizontal and vertical pupil size was present throughout the 5-day study as compared to the values obtained prior to treatment. CONCLUSIONS: 0.5% timolol maleate significantly decreased IOP and pupil size in normo-tensive eyes of this group of female horses in both single and multiple twice daily applications.

Orbital fibroma in a horse.

An 11-year-old American Quarterhorse gelding presented for moderate periorbital swelling and exophthalmia of the left eye. The menace response, and direct and consensual pupillary light reflexes were absent in the left eye. Conjunctival hyperemia, blepharedema, a mydriatic pupil, resistance to retropulsion, and an increased intraocular pressure were present. A soft-tissue mass could be palpated in the left retrobulbar space by pressing onto the orbit over the supraorbital fossa. Incomplete surgical resection of the mass was performed and histopathologic evaluation was consistent with a fibroma. Normal pupillary light reflexes and vision returned following surgery. The mass has not recurred 14 months after surgery.

Angioinvasive pulmonary carcinoma with posterior segment metastasis in four cats.

The objective of the research was to characterize the clinical, fluorescein angiographic, pathologic and microscopic features of feline pulmonary carcinoma with ocular metastasis that resulted in ischemic chorioretinopathy. Four cats with confirmed or presumed primary pulmonary neoplasia with posterior segment metastasis were studied. The medical records from four cats with a diagnosis of bronchogenic carcinoma and intraocular metastasis were reviewed. Physical and ophthalmic examinations and thoracic radiographs were performed in all cases, and fluorescein angiography was performed in two cases. Classification of the neoplasms was determined by fine-needle aspiration and biopsies of peripheral metastatic lesions, and/or complete necropsies. All four cases had unilateral or bilateral blindness and ophthalmoscopic lesions characterized by a wedge-shaped, tan discoloration in the tapetal fundus, variable but mild serous exudation under the retina, and profoundly attenuated retinal vasculature. Painful swelling and necrosis of the distal extremities and/or mass lesions in the appendicular musculature were also present. Clinical findings, along with microscopic findings from biopsy specimens or complete postmortem examination, documented widespread metastasis of variably differentiated, neoplastic, columnar epithelial cells presumed to be of bronchial origin. Tumor cells were predominately located within the systemic vasculature, consistent with classification of angioinvasive pulmonary carcinoma. Fluorescein angiographic and histopathologic findings in the affected globes suggested that the posterior segment lesions resulted from invasion and growth of neoplastic cells within the chorioretinal vasculature, resulting in secondary ischemic necrosis of the retina and choroid. Ischemic chorioretinopathy and necrosis of the distal extremities, associated with primary bronchogenic carcinoma, appear to be a unique neoplastic syndrome in the domestic cat.

Long-term effect on the equine eye of an intravitreal device used for sustained release of cyclosporine A.

OBJECTIVE: To determine the long-term toxicity of an intravitreal device releasing continuous cyclosporinee A (CsA) in normal eyes of horses by evaluating clinical signs, electroretinography, and histopathology. Animals Studied Ten adult horses with normal ophthalmic examinations were used in this study Procedure(s) Four horses had one eye implanted with a CsA device, and six horses had the right eye implanted with a CsA-containing device (10 eyes with CsA in total) and the left eye (six eyes in total) with the device without drug (control). The implants were placed in the vitreous of the eyes through a sclerotomy 1 cm posterior to the limbus in the dorso-temporal quadrant of the eye. Scotopic electroretinograms were performed prior to implantation and at 1 week, and at 1, 3, 6, 9, and 12 months postimplantation. Two of the unilaterally implanted horses were euthanized at 1 weeks postimplantation, and two at 6 weeks postimplantation. Two of the bilaterally implanted horses were euthanized at 6 months, two at 9 months, and two at 12 months postimplantation. At euthanasia, the eyes were removed, aqueous and vitreous humor aspirated, and tissues fixed in 10% buffered formalin and processed for histopathology. CsA concentrations were measured by high pressure liquid chromatography in the aqueous and vitreous humors, and in peripheral blood. RESULTS: The devices were tolerated well in 14 of 16 eyes. There was minimal postoperative inflammation in most eyes, with a normal appearance within 7 days. In two eyes implanted with the CsA device, severe inflammation resulted in phthisis bulbi by 28 days. One of these eyes exhibited suspected bacterial endophthalmitis, and one had a sterile endophthalmitis and cataract presumably from trauma to the lens during implantation. In the other 14 eyes, no change was observed in the scotopic electroretinograms (ERG) from preoperative results, and no significant differences between the right (CsA) and left (control device) eyes were observed. CsA levels in the aqueous and vitreous humor, and peripheral blood were below the detection limit of the HPLC. Histologic findings revealed only a mild lymphoplasmacytic cellular infiltrate in the ciliary body and pars plana near the implantation site. CONCLUSIONS: The CsA devices were well tolerated with no long-term complications from the implants themselves. However, complications may occur from inadvertent implantation trauma or contamination during surgery. The long-term safety of the device may make it useful for delivery of CsA in the control of equine recurrent uveitis.

Experimental implantation of posterior chamber prototype intraocular lenses for the feline eye.

OBJECTIVE: To measure postoperative anterior chamber depth (ACD), corneal curvature, and refractive state of feline eyes after lens removal and implantation of a prosthetic intraocular lens (IOL) and determine appropriate IOL use in cats. ANIMALS: 8 clinically normal adult cats. PROCEDURE: A-scan ultrasonic biometry, keratometry, and streak retinoscopy were performed on both eyes of each cat before and after lens removal and implantation of a prosthetic IOL. Three diopter (D) IOL strengths were used: 48, 51, and 60 D. Measurements were recorded for 12 weeks after surgery. RESULTS: IOL were well tolerated by cats, with no serious complications attributable to implantation or presence of the IOL. The ACD was significantly greater after (8.30 mm) than before (4.97 mm) surgery; however, it became slightly more shallow during the 4 weeks after surgery, suggesting that the IOL shifted anteriorly in the eye. Significant difference in corneal curvature was not detected before or after surgery among eyes with various IOL. Twelve weeks after surgery, eyes with 48-, 51-, and 60-D IOL had mean +/- SD refractive state of +2.1 +/- 0.49, +0.42 +/- 0.20, and -2.6 +/- 0.78 D, respectively. Linear regression analysis of refractive state on IOL power for all eyes at 12 weeks after surgery predicted that +52.8-D IOL was necessary to best approximate emmetropia in these cats. CONCLUSION AND CLINICAL RELEVANCE: IOL of substantially higher diopter strength than that needed in dogs was required to achieve emmetropia after lens extraction in cats. A 52- to 53-D IOL is required to correct feline eyes to near emmetropia after lens removal.

Keratometry, ultrasonic biometry, and prediction of intraocular lens power in the feline eye.

OBJECTIVE: To determine ocular dimensions (using A-scan ultrasound biometry) and corneal curvature (using keratometry) in the feline eye and to calculate the appropriate dioptric power for a prototype posterior chamber intraocular lens (IOL) necessary to achieve emmetropia in the eyes of cats undergoing lens extraction. ANIMALS: 25 clinically normal adult mixed-breed cats and 10 eyes from 10 clinically normal adult mixed-breed cat cadavers. PROCEDURE: A-scan ultrasonic biometry was performed on both eyes of each live cat. Cats were tranquilized, and keratometry was performed on each eye. Biometry was performed on the cadaver eyes. Five of the cadaver eyes had the lens extracted and an IOL, designed for use in dogs, was implanted. Biometry was repeated to estimate postoperative IOL position. Using 3 theoretical IOL formulas, data from biometry, keratometry, and postoperative IOL position were used to predict IOL strength required to achieve emmetropia after lens extraction in cats. RESULTS: Mean axial length of eyes in live cats was 20.91 +/- 0.53 mm. Mean preoperative anterior chamber depth (ACD) was 5.07 +/- 0.36 mm, and mean lens thickness was 7.77 +/- 0.23 mm. Predicted postoperative ACD was calculated to be 10.84 mm. Measured postoperative ACD in the 5 cadaver eyes was 8.28 mm. Required IOL strength calculated, using the predicted postoperative ACD, was 73 to 76 diopters. The required IOL strength calculated, using the measured postoperative ACD, was 53 to 55 diopters. CONCLUSIONS AND CLINICAL RELEVANCE: An IOL of substantially higher diopter strength than that needed in dogs is required to achieve emmetropia after lens extraction in average cats; an IOL strength of approximately 53 to 55 diopters will likely be required.

Clinicopathologic findings after experimental implantation of synthetic intraocular lenses in dogs.

Clinical findings indicate that canine eyes tolerate implantation of polymethylmethacrylate (PMMA) intraocular lenses (IOL) well, although inflammation and ocular damage attributable to the implants is not known. The use of silicone or polyhydroxyethylmethacrylate (HEMA) IOL has not been reported in dogs. In this study, 15 conditioned, mixed-breed dogs were allotted to 3 groups: 5 received PMMA IOL; 5 received silicone IOL; and 5 received HEMA IOL. The IOL optic was inserted into the anterior chamber of the right eye and anchored to the cornea. An identical surgical procedure was done on the left eye, except that no lens optic was inserted. Clinical examination and measurement of corneal thickness were done immediately prior to and after surgery. Aqueous humor samples were collected at the time of surgery and 28 days after surgery. Only mild and transient inflammation was observed in IOL-implanted eyes. On several postoperative days, it was found that PMMA IOL induced significantly greater corneal thickness, aqueous flare, anterior uveal irritation, and corneal edema than did other IOL. Significantly more anterior uveal irritation and increased aqueous humor protein concentration was observed with HEMA IOL than with PMMA or silicone IOL. Silicone IOL induced significantly less fibrin deposition than did PMMA or HEMA IOL.

Effect of auriculopalpebral nerve block and intravenous administration of xylazine on intraocular pressure and corneal thickness in horses.

Intraocular pressure (IOP) was measured, using applanation tonometry, in both eyes of 20 horses after topical application of 0.5% proparacaine to the cornea. Ultrasonic pachymetry was used to measure central, mid-peripheral, and peripheral corneal thickness (CT) in all 4 quadrants of both eyes of 25 horses. All measurements were repeated after auriculopalpebral nerve block, sedation by IV administration of xylazine, or combination of nerve block and sedation. Mean IOP after topical anesthesia of the cornea was 20.6 +/- 4.7 mm of Hg for the left eye and 20.35 +/- 3.7 mm of Hg for the right eye. Mean central CT was 793.2 +/- 42.3 microns. The peripheral part of the cornea was significantly (P < 0.05) thicker, on average, than the central part of the cornea. Auriculopalpebral nerve block had no significant effect on IOP or CT. Intravenous administration of xylazine resulted in a significant (P < 0.05) decrease in IOP, but had no effect on CT.

Canine corneal thickness measured by ultrasonic pachymetry.

Ultrasonic pachymetry was used to measure central, superior peripheral, and temporal peripheral corneal thicknesses of 75 dogs (150 eyes) with normal corneas, anterior chambers, and intraocular pressure. Mean corneal thickness averaged over the 2 eyes, 3 locations, and 75 dogs was 562 +/- 6.2 microns. The peripheral cornea was thicker on average than the central cornea by 49.43 +/- 8.45 microns and this difference increased with age at 6.97 +/- 1.3 microns/month of age. Mean corneal thickness changed with age (14.23 +/- 2.26 microns/month), and weight (1.83 +/- 0.38 microns/kg). Females had significantly thinner corneas (22.43 +/- 11.03 microns than males) after adjusting for age and weight.

Scanning electron microscopy of intraocular lenses that had been implanted in dogs.

Scanning electron microscopy was used to evaluate changes on the surfaces of polymethylmethacrylate (PMMA), silicone, and polyhydroxyethylmethacrylate (HEMA) intraocular lenses (IOL) that had been implanted in the anterior chambers of the right eyes of 15 dogs. Five dogs received PMMA IOL; 5 dogs received silicone IOL; and 5 dogs received HEMA IOL. Twenty-eight days after surgery, the IOL were removed and processed for scanning electron microscopy. Nonimplanted IOL of each type were processed identically for comparison. Implanted PMMA IOL had significantly more debris and macrophages on their surfaces than did silicone IOL or HEMA IOL. Silicone IOL had significantly less fibrin deposition than did PMMA or HEMA IOL. Silicone IOL had surface defects attributable to handling by surgical instruments. Implanted HEMA IOL had multiple pits that appeared to be caused by biodegradation.