Kelly E. Knickelbein

Objective: To determine the impact of age on equine electroretinography (ERG) parameters and retinal thickness in horses with healthy eyes. We hypothesized that ERG b-wave amplitudes would be significantly lower in older horses and that total retinal thickness would not vary significantly with age. Methods: Horses with clinically normal eyes comprising 3 age groups (≤ 10, 11 to 20, and ≥ 21 years) underwent scotopic and photopic ERGs, high-resolution fundus photography, and spectral-domain optical coherence tomography. Electroretinography results were compared between age groups using mean implicit times and amplitudes of the a- and b-waves for scotopic (3.0 cd⋅s/m ² white) and photopic (3.0 cd⋅s/m ² white at 2 Hz; background, 30 cd/m ² white) tests obtained with the RETevet. Optical coherence tomography–derived total retinal thickness (TRT) of the nasal, dorsal, and temporal peripapillary regions was compared between age groups. Results: 15 horses were included, with 5 horses in each age group. No statistically significant differences in ERG implicit times or amplitudes were observed between age groups. No significant differences in nasal, dorsal, or temporal peripapillary TRT were identified between age groups. Conclusions: No significant differences in retinal function as measured by ERG nor peripapillary TRT as assessed by optical coherence tomography were identified in young relative to middle-aged and aged horses without ocular disease. Clinical Relevance: While individual variation can be expected, aged horses maintain similar ERG parameters and TRT to young horses. In the clinical setting, reduced retinal function detected on ERG and retinal thinning should be considered pathologic and unrelated to the normal aging process.

Objective: To describe the clinical presentation and histopathology of a meibomian gland epithelioma that clinically resembled squamous cell carcinoma in a steer. Animal Studied: A 15 year‐old Hereford‐Lowline cross steer presented for evaluation of an approximately 2 × 4 cm ulcerated, pedunculated eyelid mass arising from the right inferior eyelid margin. Procedures: Excision of the mass followed by adjunctive cryotherapy was performed. The mass was submitted for histopathologic analysis. Results: Histopathologic evaluation revealed the mass to be consistent with a meibomian gland epithelioma, a neoplastic proliferation of the basal/reserve cells of the meibomian gland. The steer recovered routinely from the procedure with no evidence of regrowth of the mass at 13 months post‐operatively. Conclusion: Meibomian gland epitheliomas are one of the most common eyelid tumors of dogs; however, this is the first known report of a histologically confirmed meibomian gland epithelioma in cattle. Clinically, the mass resembled the appearance of squamous cell carcinoma, a common eyelid tumor in Hereford cattle. The clinical misclassification of a benign eyelid mass as squamous cell carcinoma could lead to unnecessary aggressive management such as enucleation, exenteration, or culling. This case confirms the importance of histopathologic analysis of excised tissues to reach an accurate diagnosis and appropriate treatment and follow‐up plans.

Objective: To describe the demographics and treatment outcomes of horses definitively diagnosed with epithelial or stromal immune-mediated keratitis (IMMK) by use of in vivo confocal microscopy (IVCM) and/or histopathology. Methods: Medical records of horses presented to the Cornell University Equine Hospital definitively diagnosed with epithelial or stromal IMMK with IVCM and/or histopathology between 2020 and 2024 were reviewed. Patient signalment, affected eye(s), diagnostics, treatments, and outcomes were assessed. Results: 22 horses met the inclusion criteria. The mean age was 16.9 years (SD, ± 7.3 years). There were significantly more geldings (n = 16) than mares (6). Nineteen horses were unilaterally affected (11 right eyes and 8 left eyes) and 3 bilaterally affected. Twenty horses underwent IVCM, of which 8 had histopathology following superficial keratectomy with agreement in diagnosis. Two horses had corneal histopathology without IVCM. All horses were initially managed medically. Seven horses subsequently underwent episcleral cyclosporine implantation, of which 2 were controlled at last follow-up (median, 532 days). Standing superficial keratectomy was performed in 10 horses, with IMMK controlled in 9 of 10 horses at last follow-up (median, 692 days). Recurrence was documented in 1 horse 12 months after keratectomy. Conclusions: IVCM allowed for a rapid noninvasive diagnosis of equine IMMK that correlated with histopathology. Standing superficial keratectomy was an effective diagnostic and therapeutic option for equine IMMK. Clinical Relevance: Standing superficial keratectomy was an effective diagnostic and treatment for equine IMMK that provided long-term control of disease and minimized the need for long-term daily medications.

Objective: To describe ocular abnormalities of pet and sanctuary-housed domestic pigs presented to an academic veterinary hospital. Methods: Electronic medical records at the Cornell University Hospital for Animals were searched for pigs having undergone a complete ophthalmic examination by a Diplomate of the American College of Veterinary Ophthalmologists between 2011 and 2024. Signalment, examination findings, diagnoses, and treatments were reviewed. Results: 36 domestic pigs of a variety of breeds were represented, including Vietnamese pot-bellied (22 of 36), American Miniature (4 of 36), Yorkshire (2 of 36), Berkshire (1 of 36), mixed breed (2 of 36), and unknown breeds (5 of 36). Most ocular abnormalities were adnexal with the following abnormalities diagnosed: excessive periocular fat (“fat blindness”; 8 of 36), corneal ulceration (8 of 36), blepharitis/periocular dermatitis (7 of 36), conjunctivitis (7 of 36), entropion (3 of 36), and eyelid neoplasia (melanoma; 1 of 36). Cataracts were diagnosed in 2 (3 eyes) of 36 pigs. Conclusions: A wide range of ocular disease impacted pet and sanctuary-housed pigs. Vision-threatening ophthalmic disease appeared to be rare, aside from functional blindness associated with excessive periocular fat. Clinical Relevance: This study provided veterinarians with new information on the ophthalmic diseases that affect pigs as well as approaches to treatment.

Objective: To investigate the effects of atropine on the iridocorneal angle (ICA) and ciliary cleft (CC) of normal equine eyes using ultrasound biomicroscopy (UBM). Methods: 12 normal adult horses underwent measurement of intraocular pressure (IOP), vertical and horizontal pupil diameter, and UBM of the superior, temporal, inferior, and nasal ICA/CC in both eyes. Measurements were repeated 2 hours following ophthalmic atropine 1% solution application. Measurements of the ICA and CC, including pectinate ligament distance (PLD), CC length (CCL), height of opening distance (HOD), CC area (CCA), and pectinate ligament angle (PLA) were performed. Results: Mean IOP significantly decreased following atropine administration (14.17 ± 2.34 mm Hg vs 12.67 ± 1.14 mm Hg). No significant differences in pre- or post-atropine ICA/CC measurements occurred nasally or temporally. Superiorly, a significant decrease in mean CCL (2.74 ± 0.52 mm vs 2.62 ± 0.43 mm), CCA (2.67 ± 0.72 mm ² vs 2.42 ± 0.66 mm ² ), HOD (1.15 ± 0.26 mm vs 1.06 ± 0.20 mm), and PLA (80.33 ± 7.02° vs 73.67 ± 8.50°) occurred. Inferiorly, a significant decrease in PLD (1.46 ± 0.23 mm vs 1.39 ± 0.17 mm), HOD (1.44 ± 0.24 mm vs 1.33 ± 0.15 mm), and PLA (73.18 ± 6.81° vs 69.98 ± 8.92°) occurred. Conclusions: Atropine causes narrowing of the superior and inferior ICA and CC in normal horse eyes. Clinical Relevance: Due to its effect in narrowing the ICA and CC, atropine should be used with caution in horses with elevated intraocular pressure or glaucoma.

Background: Use of photodynamic therapy (PDT) for the treatment of immune‐mediated keratitis (IMMK) in horses is becoming common. The safety and morphologic impact on the normal equine cornea have not been investigated, and the mechanism of its efficacy is unknown. Objective: To investigate the morphologic effects and safety of in vivo PDT on healthy equine corneas. Study Design: In vivo experiment. Methods: Six university‐owned horses underwent unilateral corneal PDT with intrastromal infracyanine green (EmunDo®) and photoactivation with an 810 nm diode laser (500 mW for 2.5 min = 75 Joules). Complete ophthalmic examinations, clinical scoring, digital and infrared photography, ocular thermography, in vivo confocal microscopy (IVCM), and ultrasound biomicroscopy were performed pre‐treatment and post‐treatment on study days 1, 5, 15, 33, and 103. Results: Post‐treatment, corneal ulceration occurred in all treated eyes. In all horses, IVCM identified destroyed keratocytes immediately post‐treatment followed by keratocyte depopulation on days 5 and 15. Slow keratocyte repopulation was evident on days 33 and 103. Stromal keratitis was seen on day 5 and persisted through day 103. EmunDo® remained visible in the cornea on study day 103 in 5/6 horses. No horses developed blinding complications. Main Limitations: Limited sample size included horses of various ages. Conclusions: Corneal ulceration, keratocyte depopulation, prolonged stromal keratitis, and prolonged corneal dye retention occurs with PDT in normal equine corneas. Corneal stromal cellular depopulation is proposed as the mechanism by which PDT is effective in the treatment of equine IMMK.

Objective: To describe the clinical and in vivo confocal microscopy (IVCM) characteristics of horses with corneal stromal invasive squamous cell carcinoma (CSI‐SCC). Animals Studied: Retrospective study of 7 horses with histopathologically confirmed unilateral CSI‐SCC. Procedures: Horses with corneal CSI‐SCC were examined by laser scanning IVCM. Signalment, clinical findings, and histopathology results were compared with IVCM findings. Results: Clinical ocular lesions in all horses included a heavily vascularized, opaque, gray or tan, anterior or midstromal opacity invading the cornea from the limbus. The corneal epithelium overlying the stromal opacities was intact and the abnormal corneal regions were markedly thickened. Crystalline, white, linear, branching stromal opacities emanated from the leading edge of the corneal lesions in 2 horses. Polygonal neoplastic epithelial cells, with prominent anisocytosis and pleomorphism, were visible in the corneal stroma by IVCM and appeared enlarged and hyperreflective. Islands and cords of neoplastic epithelial cells that occasionally branched could be followed by IVCM as they transversed the corneal stroma. The islands of neoplastic cells were occasionally arranged as circular whirls of cells grouped around concentric layers of hyperreflective cells or amorphous materials within a dark cyst‐like space consistent with keratin pearls. Dense accumulations of blood vessels and leukocytes were present within and around the neoplastic cells. Conclusions: This report demonstrates the unique ability of IVCM examination to provide a rapid and noninvasive method for the presumptive diagnosis of CSI‐SCC and to contribute to the formulation of diagnostic and therapeutic clinical plans for individual horses.

Background: Little information describing the biologic behaviour and therapies for corneal lymphoma exist. Objectives: To characterise histologically confirmed equine corneal lymphoma considering breed, age or sex predisposition, histologic and immunologic features, therapies and outcomes. Study design: Retrospective case series. Methods: A multicentre retrospective medical record review was used to identify horses that presented with corneal disease confirmed morphologically as corneal lymphoma from 2012 to 2022. Results: Mean age at diagnosis was 10.5 years. Males represented 18/26 cases. Warmblood (14) and Thoroughbred (6) breeds were most commonly represented. 25/26 had unilateral ocular involvement. No cases had evidence of multicentric lymphoma. Most eyes (77.7%) had a history of suspected immune‐mediated keratitis (IMMK) or eosinophilic keratitis. Morphological diagnosis confirming lymphoma was available for all cases. B‐cell lymphoma was diagnosed in 19/24 eyes for which immunohistochemistry was performed, with intermediate to large B‐cell lymphoma being most common. Fifteen of 27 eyes received at least one form of adjunctive therapy following keratectomy. Four eyes, which did not receive adjunctive therapy following keratectomy, experienced recurrence. No horses treated with adjunctive therapy following keratectomy experienced recurrence. Malignant transformation of IMMK to lymphoma was morphologically documented in one eye and suspected in three others based on recurrence of clinical signs. All globes were retained and visualised at the last follow‐up. Main limitations: Incomplete medical records, owner subjectivity concerning onset of disease and cases being lost to follow‐up. Conclusions: Malignant transformation of IMMK to corneal lymphoma likely occurs in horses. Lymphoma should be a differential for nonulcerative keratitis in horses. Keratectomy and histopathology may be considered in progressive or refractory cases of IMMK to rule out neoplastic disease. Recurrence of corneal lymphoma is unlikely following excision and adjunctive therapy. Cases with large corneal surface area or deep stromal involvement may have a likelihood for recurrence.