Breed predispositions to congenital and juvenile cataracts in horses at two academic institutions.

BACKGROUND: Determination of horse breeds predisposed to congenital and juvenile cataracts will enable investigations into potential genetic mechanisms for cataracts in horses. OBJECTIVE: To investigate horse breed predispositions to congenital and juvenile cataracts in two academic referral populations. STUDY DESIGN: Retrospective case series. METHODS: Medical record identification of horses diagnosed with congenital or juvenile cataracts at the Cornell University Equine Hospital (2000-2022) and the University of California-Davis (UCD) Large Animal Clinic (1990-2021). Signalment, examination findings and treatments were recorded. Descriptive statistics were performed, and breed over-representations were determined using Chi-squared or Fisher's exact tests. RESULTS: Thirty-one (Cornell) and 70 (UCD) horses with congenital or juvenile cataracts were identified, for a total of 101 affected horses. Seventy-eight horses were affected bilaterally and 23 were affected unilaterally, for a total of 179 affected eyes. Standardbreds were significantly over-represented at both institutions, comprising 32.5% of congenital/juvenile cataract cases and 10% of the equine hospital population at Cornell (p < 0.001) and 4.3% of cataract cases and 1.3% of the equine hospital population at UCD (p = 0.03). Thoroughbreds were under-represented for congenital and juvenile cataracts at both institutions (p = 0.03 Cornell, p = 0.01 UCD). MAIN LIMITATIONS: Retrospective study, potential for selection bias. CONCLUSIONS: The over-representation of the Standardbred breed for congenital and juvenile cataracts at two institutions suggests an underlying genetic basis in the breed. Future genetic and genomic studies are warranted to investigate heritable cataracts in Standardbred horses.

Macrodendritic ulcerative keratitis and conjunctival lymphoid hyperplasia in horses with equine herpesvirus-2 and equine herpesvirus-5 infections.

OBJECTIVE: The aim of this study was to describe the clinical, confocal microscopic, histologic, and virologic features of horses with macrodendritic ulcerative keratitis and conjunctival lymphoid hyperplasia associated with equine herpesvirus-2 and equine herpesvirus-5 infection. ANIMAL STUDIED: Four foals with bilateral ocular disease. PROCEDURES: Complete ophthalmic examination was performed for each horse, and corneal samples were collected for cytology and microbiologic evaluation, including virus isolation and molecular diagnostics for the equine herpesviruses. In vivo confocal microscopy examination of the cornea was performed in two horses. Conjunctival biopsies for histopathology were collected from two horses with nodular conjunctival thickening. RESULTS: Each horse had bilateral, large, superficial dendritic corneal ulcerations that covered extensive regions of the corneal surface. Corneal in vivo confocal microscopy examination in two horses detected inflammatory cells and populations of morphologically abnormal corneal epithelial cells adjacent to the ulcerations. The abnormal epithelial cells included round, relatively small, hyperreflective cells intermixed with elongated, enlarged, hyperreflective cells. Equine herpesvirus-2 was isolated from corneal samples of 2 horses and detected by PCR assay in the other two horses. Equine herpesvirus-5 was also detected by PCR assay in three of the horses. Conjunctival histopathology identified predominantly lymphocytic infiltrates. The macrodendrites and conjunctival masses resolved with topical antiviral therapy (cidofovir or idoxuridine) in all horses and did not recur. CONCLUSIONS AND CLINICAL RELEVANCE: The equine gammaherpesviruses may be associated with the development of macrodendritic ulcerative keratitis and conjunctival lymphocytic masses in foals. In vivo confocal microscopy of horses with macrodendrites revealed similar findings to other host species with herpetic dendritic keratitis.

Evaluation of the short- and long-term complications and outcomes of phacoemulsification surgery in alpacas.

OBJECTIVE: To describe the complications and determine the visual outcomes associated with phacoemulsification surgery in alpacas. ANIMALS: Five alpacas (nine operated eyes). PROCEDURES: Medical records of alpacas with a clinical diagnosis of cataracts that received elective phacoemulsification surgery at Cornell University over a 15 year period were reviewed. RESULTS: The mean (± standard deviation) age of the five operated alpacas was 104 days (±64 days). The cataracts were suspected to be congenital in all alpacas. Concurrent congenital ocular abnormalities were common in the operated eyes and included microphakia, persistent patent hyaloid arteries, and persistent patent tunica vasculosa lentis. No significant intraoperative complications were identified in any cases. In the immediate postoperative period, uveitis was mild-to-moderate in most operated eyes, ocular hypertension was not detected, and clinically significant corneal edema did not occur in any eyes. The mean (± standard deviation) duration of clinical follow-up after surgery was 32 months (±25 months). A peri-incisional corneal stromal ulcer associated with fibrinous uveitis was identified in a single eye during recheck examination 4 weeks postoperative that resolved with medical therapy. Long-term complications included unilateral glaucoma in two alpacas that resulted in vision loss. On the final recheck ophthalmic examination, 78% (7 of 9) of operated eyes were visual and all operated alpacas had vision in at least one operated eye. CONCLUSIONS AND CLINICAL RELEVANCE: In this series, the visual outcomes associated with elective phacoemulsification surgery in alpacas were good. Glaucoma was the most common vision-threatening long-term postoperative complication.

Laser scanning in vivo confocal microscopic characterization of equine immune-mediated keratitis.

OBJECTIVE: To describe the corneal in vivo confocal microscopy (IVCM) findings in horses with putative immune-mediated keratitis (IMMK). ANIMALS: Sixty five horses with IMMK. PROCEDURES: Horses diagnosed with IMMK were examined with a modified Heidelberg Retina Tomograph II and Rostock Cornea Module. The findings from the IVCM examinations were correlated with clinical details from ophthalmic examination and diagnostic test results. RESULTS: Eighty eyes from 65 horses were examined. Clinical IMMK lesions were categorized as epithelial (n = 17 eyes), superficial stromal (n = 38), midstromal (n = 18), and endothelial (n = 7). Epithelial, superficial stromal, and midstromal lesions were characterized with IVCM by variable corneal leukocyte infiltrates and vascularization of the approximate corneal anatomic region that was clinically affected as determined by biomicroscopy. In addition, all horses displayed a dense network of dendritic cells in the epithelial basement membrane and immediate subepithelial stroma. Less consistent IVCM findings included epithelial disorganization, corneal edema, mineral deposition, stromal fibrosis, and epithelial pigment granules. Endothelial IMMK was distinct from the other forms of IMMK and characterized with IVCM by stromal edema, endothelium disorganization, endothelial cell loss, and multifocal accumulations of highly reflective material within the endothelium. CONCLUSIONS AND CLINICAL RELEVANCE: The distinguishing feature of epithelial and stromal forms of IMMK is a dense accumulation of dendritic cells in the epithelial basement membrane and immediate subepithelial stroma. Cellular changes in endothelial IMMK were largely confined to the endothelium and distinct from the other forms of IMMK evaluated.

In vivo confocal microscopy characteristics of equine epithelial and subepithelial nonulcerative keratomycosis.

OBJECTIVE: To describe the in vivo confocal microscopy features of horses with epithelial and subepithelial nonulcerative keratomycosis. ANIMALS STUDIED: Four horses with a clinical diagnosis of epithelial or subepithelial keratomycosis. PROCEDURES: Horses were examined on one or more occasions by in vivo laser scanning confocal microscopy of the cornea. Confocal microscopic examination characteristics were correlated with clinical, cytological, and histopathological findings for the horses. RESULTS: All horses had an irregular corneal epithelial surface during slit-lamp biomicroscopy examination. Epithelial or subepithelial corneal opacities were present in multifocal or diffuse patterns. Positive rose bengal corneal staining was present focally or diffusely in all cases. Fungal hyphae were detected in cytological or histopathological corneal samples from all horses. Aspergillus, Fusarium, and Penicillium spp. were cultured from corneal samples. Confocal microscopy detected hyphae diffusely distributed over the axial cornea in horses with epithelial clinical disease. Fungal hyphae were present in all layers of the corneal epithelium and associated with disorganized and sloughing epithelial cells with minimal leukocytes. Subepithelial keratomycosis was correlated with focal, dense accumulations of hyphae in the immediate subepithelial anterior stroma that were surrounded by moderate numbers of leukocytes. Two horses were examined by confocal microscopy on multiple occasions during the course of medical therapy, and fungal hyphae were observed to migrate from the epithelium into the subepithelial stroma as the clinical corneal disease progressed. CONCLUSIONS: With in vivo confocal microscopy, both epithelial and subepithelial keratomycosis appear as unique clinical entities. Equine epithelial keratomycosis is a potential precursor to subepithelial keratomycosis.

Transnasal, Endoscopically Guided Skull-Based Surgery by Pharyngotomy for Mass Removal from the Sphenopalatine Sinus in a Horse.

OBJECTIVE: To report a transnasal, endoscopically guided ventral surgical approach for accessing the cranial and caudal segments of the sphenopalatine sinus for mass removal in a horse. STUDY DESIGN: Case report. ANIMAL: Adult horse with acute onset blindness referable to a soft tissue mass within the sphenopalatine sinus. CLINICAL REPORT: A 7-year-old Warmblood gelding presented with a history of running into a fence and falling. No neurologic signs were identified at initial examination but acute blindness was noted 3 weeks later. On computed tomography (CT) the sphenopalatine sinus was filled with a large homogeneous mass with poor contrast enhancement that extended dorsally with thinning to the dorsal cortex of the sphenoid bone, just rostral to the entrance of the optic canals into the cranial cavity. Surgical access to the sphenopalatine sinus was achieved using a transnasal, endoscopically guided ventral pharyngotomy approach and the mass lesion was removed. A presumptive diagnosis of chondroma was made based on histopathology. The horse recovered well from surgery, and although it has not regained vision as of 6.5 years postoperatively, the disease has not progressed. CONCLUSION: Transnasal, endoscopically-guided ventral surgical access to the sphenopalatine sinus is possible in horses and may improve access in horses with disease extending caudally beyond the palatine portion of the sinus. Use of smaller diameter or specialized instruments, such as various endoscopic bone cutting instruments, and CT image guidance may improve sinus access by this route.

CORRELATIONS AMONG ULTRASONOGRAPHIC MEASUREMENTS OF OPTIC NERVE SHEATH DIAMETER, AGE, AND BODY WEIGHT IN CLINICALLY NORMAL HORSES.

Early diagnosis of high intracranial pressure (ICP) is critical for minimizing progressive brain injury due to reduced cerebral perfusion. In people, detecting enlargement of the optic nerve sheath diameter (ONSD) by transpalpebral ultrasonography has been found to be an accurate test for high ICP. Aims of this prospective, observational, cross-sectional study were to test hypotheses that (1) ultrasonographic measurement of ONSD would be repeatable in horses, (2) have acceptable interobserver agreement, and (3) would be correlated with age and body weight. The sample population included 48 horses without clinical signs of high ICP and with varying ages and body weights. Two observers independently performed ONSD measurements in both eyes. All measurements ranged from 2.6 to 6.5 mm. The mean difference of repeated measures within observers was ≤0.1 mm and the coefficients of variation ranged from 5.0% to 8.8%. The mean difference of measures between observers was ≤0.2 mm. After correcting for performing multiple tests, no significant rank correlation (all r < 0.4 [absolute value]) was detected between ONSD and age or body weight. However, we observed smaller ONSD in foals versus adults (all P ≤ 0.002). In the foals, all observed measures of rostrocaudal and dorsoventral ONSD were <5 mm. In the adults, all observed measures of rostrocaudal and dorsoventral ONSD were ≤6.5 mm. Findings indicated that ultrasonographic ONSD measurement is a feasible test for use in horses of varying ages and sizes. Further investigation of this ultrasonographic measure as a clinical test for horse with suspected high ICP is warranted.

In vivo confocal microscopy of corneal microscopic foreign bodies in horses.

OBJECTIVE: To describe in vivo corneal confocal microscopy of horses with microscopic corneal foreign bodies and to correlate findings with clinical, cytological, and histopathologic evaluations of clinical cases and foreign body morphologies observed in vitro with the confocal microscope. ANIMAL STUDIED: Five horses with microscopic corneal foreign bodies. PROCEDURES: Sedated and anesthetized horses were examined with a modified Heidelberg Retina Tomograph II and Rostock Cornea Module. Confocal microscopy images were compared with images from cytologic and histopathologic corneal samples. To establish microscopic morphologic features, confocal microscopy images of burdock pappus bristles and surgical glove powder were obtained by in vitro examination. RESULTS: Horses were examined by in vivo confocal microscopy to assist in identifying corneal opacities detected by slit-lamp biomicroscopy, to determine the etiology of clinically idiopathic keratitis, or to localize corneal opacities presumed to be foreign bodies for surgical planning. Corneal foreign bodies presumptively identified by confocal microscopy included burdock pappus bristles, other plant foreign materials, and surgical glove powder. The corneal foreign bodies appeared as moderately or hyper-reflective linear, circular, or oval structures by confocal microscopy and did not resemble any normal anatomic structures. The confocal microscopic identification of the foreign bodies was corroborated by cytologic and histopathologic findings in some horses. The in vivo confocal microscopic appearance of the foreign bodies was consistent with morphologies observed during examination of foreign bodies in vitro. CONCLUSIONS: In vivo corneal confocal microscopy provides a noninvasive method for the detection, characterization, and localization of microscopic foreign bodies in the equine cornea.

Use of a formal assessment instrument for evaluation of veterinary student surgical skills.

OBJECTIVES: To (1) evaluate the design and use of a global rating scale assessment instrument in veterinary medical education and; (2) examine the effectiveness of 2 surgical techniques courses for improving the surgical skills of veterinary students. STUDY DESIGN: Instrument development; observational; survey-based. SAMPLE POPULATION: Students (n = 16) registered for 2 elective surgical techniques courses were enrolled on a volunteer basis. METHODS: A 5-point global rating scale instrument was designed for the evaluation of 12 basic surgical skills by faculty evaluators and used to obtain student start and end scores during the courses. Upon conclusion of the courses, students completed a survey from which their opinions on their improvement as well as their desire for feedback were obtained. RESULTS: All authors agreed the instrument was easy to use. As groups, 3rd year students, 4th year students, and all students combined had significantly higher total skill scores at the end of the courses compared to the start of the courses. Individually, 10 students (63%) had significant improvement in surgical skills as a result of their participation in the courses: 4 (100%) 3rd year and 6 (50%) 4th year students. Student survey responses revealed a strong desire for feedback as well as support of formal assessment methods. Only weak agreement was found between student opinions on their improvement and the authors' assessment scores. CONCLUSIONS: Assessment instruments are useful for (1) student evaluation and (2) for providing students with feedback on their surgical skills.

Bilateral parotid duct transposition for keratoconjunctivitis sicca in a Connemara stallion.

A 7-year-old Connemara stallion was presented with a 4 month history of blepharospasm, recurrent corneal ulcerations, mucopurulent ocular discharge, and keratoconjunctivitis sicca (KCS) in both eyes unresponsive to medical therapy. Ophthalmic examination revealed lackluster corneas, axial corneal scarring and pigmentation with associated neovascularization, and absolute KCS in both eyes. Computed tomography scan and endoscopic evaluation of the upper airway and guttural pouches revealed no structural abnormalities to indicate neurogenic KCS. The stallion was diagnosed with immune-mediated dacryoadenitis as all other causes of KCS were excluded. Parotid duct transposition (PDT) was performed in the right eye followed by PDT in the left eye 4 weeks later. The right PDT was functional 2 years post-operatively with significant improvement in ocular comfort and reduced corneal fibrosis and neovascularization. The left PDT developed a salivary-cutaneous fistula over the left masseter muscle post-operatively due to avascular necrosis of the distal parotid duct (PD). Surgical reconstruction of the PDT using an expanded-polytetrafluoroethylene (e-PTFE) tube graft, an e-PTFE tube graft to autogenous caudal auricular vein graft, and an autogenous saphenous vein graft were all unsuccessful. Tear production in the left eye improved at 1 year post-surgery as a result of long term lacrostimulant therapy, and a permanent PD-cutaneous fistula was performed on the left PD at the level of the ventral mandible. Bilateral PDT in the horse is effective in resolving clinical signs associated with KCS; however, morbidity associated with avascular necrosis of the transposed PD may be significant and can result in surgical failure.

Diagnosis of Borrelia-associated uveitis in two horses.

Borrelia burgdorferi, the etiologic agent of Lyme disease is a tick born spirochetal infection. Clinical signs of Lyme borreliosis are uncommon in horses, but when present they are often vague and nonspecific. In horses, Lyme borreliosis has been implicated in musculoskeletal, neurological, reproductive, and ocular disorders, including uveitis, but definitive diagnosis can be challenging as the causative agent is rarely isolated and serologic tests can be unreliable and do not confirm active disease. Here, we report two cases of equine uveitis associated with B. burgdorferi based on the identification of spirochetes within ocular fluids and confirmed with PCR testing. The two cases illustrate some of the challenges encountered in the recognition and diagnosis of equine Lyme borreliosis. Although only one of many possible causes of equine uveitis, Lyme disease should be considered a differential diagnosis, especially in endemic areas. Given the possibility for false negative results of serum tests during uveitis associated with B. burgdorferi and the failure of such tests to confirm active infection, a combination of cytologic assessment, antibody, and/or PCR testing of ocular fluids may be worthwhile if the clinical suspicion for Lyme uveitis is high.

Neuro-ophthalmology in horses.

A complete neuro-ophthalmologic assessment is relatively simple, requires minimal instrumentation and should be performed as part of every complete ophthalmic and neurologic examination. This article has summarized the tests that comprise and the species-specific details of the complete neuro-ophthalmologic of the equine patient. Selected causes of sudden blindness in the horse were summarized and some common neuro-ophthalmic conditions with significant ophthalmic consequences, such as facial nerve paralysis, were discussed. Split-lid tarsorrhaphies, which are indicated but rarely used in cases of facial nerve paralysis were strongly recommended for all facial paralysis cases and were described in detail.

In vivo confocal microscopy of equine fungal keratitis.

OBJECTIVE: To describe in vivo corneal confocal microscopy of horses with fungal keratitis and correlate findings with clinical, histopathological, and microbiological evaluations of clinical cases and an ex vivo experimental equine fungal keratitis model. ANIMALS STUDIED: A total of 12 horses with naturally-acquired fungal keratitis and ex vivo equine corneas experimentally infected with clinical fungal isolates. PROCEDURES: Horses with naturally-acquired fungal keratitis were examined with a modified Heidelberg Retina Tomograph II and Rostock Cornea Module. Confocal microscopy images of clinical isolates of Aspergillus fumigatus, Fusarium solani, and Candida albicans were obtained by examination of in vitro cultures and experimentally infected ex vivo equine corneas. RESULTS: Non-specific in vivo corneal confocal microscopic findings in horses with fungal keratitis included leukocyte infiltrates, activated keratocytes, anterior stromal dendritic cell infiltrates, and vascularization. Linear, branching, hyper-reflective structures that were 2-6 µm in width and 200 to >400 µm in length were detected in all horses with filamentous fungal keratitis. Round to oval hyper-reflective structures that were 2-8 µm in diameter were detected in a horse with yeast fungal keratitis. The in vivo confocal microscopic appearance of the organisms was consistent with fungal morphologies observed during examination of in vitro cultures and infected ex vivo equine corneas. CONCLUSIONS: In vivo corneal confocal microscopy is a rapid and non-invasive method of diagnosing fungal keratitis in the horse. This imaging technique is useful for both ulcerative and non-ulcerative fungal keratitis, and is particularly advantageous for confirming the presence of fungi in deep corneal stromal lesions.