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Topic:Eyes
The study of equine eyes encompasses various anatomical, physiological, and pathological aspects of the horse's visual system. The equine eye is a complex organ adapted for a wide field of vision and low-light conditions, which is essential for the survival of prey animals. Key components include the cornea, lens, retina, and optic nerve, each playing a role in capturing and processing visual information. Common ocular conditions in horses include uveitis, cataracts, and corneal ulcers, which can affect vision and overall health. Diagnostic techniques such as ophthalmoscopy and ultrasonography are employed to assess eye health and detect abnormalities. This page compiles peer-reviewed research studies and scholarly articles that explore the anatomy, function, and diseases of the equine eye, as well as advancements in diagnostic and therapeutic approaches.
Equine Fungal Keratitis due to Cladorrhinum bulbillosum. To describe the case details and treatment of an equine fungal keratitis case caused by Cladorrhinum bulbillosum. Methods: A 14-year-old Bashkir Curly gelding with a complicated corneal ulcer of the left eye. Methods: Corneal cytology was performed, and intraoperative samples were collected for polymerase chain reaction and for aerobic and mycologic cultures. Under general anesthesia, an inferior eyelid subpalpebral lavage system (SPL) was placed to facilitate postoperative therapy. Anterior stromal keratectomy was performed followed by cryotherapy of the keratectomy bed. A biological scaffold...
Complications Following Nictitating Membrane Resection in Horses: 92 Eyes (2015-2024). The goal of this retrospective study is to evaluate the complications following nictitating membrane resection in horses with the aim of providing valuable information on the risks of this surgical procedure. Methods: 83 horses (92 eyes). Methods: Medical records for 83 horses that underwent nictitating membrane resection in 92 eyes between February 2015 and June 2024 were reviewed. Horses were included if they had at least 1 month of follow-up data available. Owners were contacted via telephone or email questionnaire to obtain follow-up information. Complications were recorded only when pre...
Efficacy of Therapeutic UVC Irradiation in Reducing Bacterial Load in Microbial Keratitis: A Retrospective Clinical Study in Veterinary Patients. To evaluate the immediate effect of therapeutic ultraviolet-C (UVC) irradiation on corneal bacterial load in veterinary patients with microbial keratitis (MK), using a retrospective analysis of clinical data collected at a UK referral ophthalmology hospital. Methods: Client-owned dogs, horses, and cats presented to a referral ophthalmology clinic with MK in 2025. Methods: Clinical records from MK cases were reviewed. For each case, paired corneal swabs were obtained immediately before and immediately after UVC irradiation with a commercially available 265 nm device (PhotonUVC). Treatment con...
Horses without ocular disease maintain similar electroretinographic responses and peripapillary retinal thicknesses across age groups. 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. Unassigned: 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 implici...
Antibiotics in Veterinary Ophthalmology: Resistance, Stewardship, and Emerging Antibiotic-Sparing Strategies. Antimicrobial resistance (AMR) is a growing challenge in veterinary ophthalmology, particularly in cases of bacterial keratitis, where progressive stromal infection can threaten vision and globe integrity within hours to days. This review synthesizes current evidence on pathogen distribution, antimicrobial susceptibility profiles, multidrug resistance (MDR) prevalence, and determinants of nonsusceptibility in veterinary patients, highlighting the emerging role of antibiotic-sparing alternatives. Across contemporary studies, Staphylococcus pseudintermedius, β-hemolytic streptococci, and Pseud...
The Early Ophthalmic Effects of Vatinoxan in Healthy Detomidine-Sedated Horses. To evaluate the short-term ophthalmic effects of vatinoxan, a peripherally selective alpha2-adrenoceptor antagonist, in detomidine-sedated horses. Methods: Seven healthy horses without ophthalmic disease in a randomized, masked, two-period crossover study design, with a ≥ 7-day rest period. Methods: After a bilateral palpebral block (lidocaine 40 mg) and baseline data collection, horses received intravenous detomidine (20 μg/kg [DET]) or DET with vatinoxan (200 μg/kg [DET-VAT]). Intraocular pressure (IOP) was measured from the left eye while tear production (Schirmer tear test -1; ...
Owner satisfaction and animal welfare after bilateral enucleation in horses. Bilateral enucleation in horses represents a challenging decision for owners, undertaken to relieve chronic, untreatable ocular pain. Emotional distress and uncertainty regarding postoperative welfare often lead to euthanasia instead of surgery. Objective: To evaluate owner perceptions of equine quality of life before and after bilateral enucleation, and to assess satisfaction with the procedure. Methods: Retrospective case series. Methods: Medical records from 21 horses that underwent bilateral enucleation between 2016 and 2024 were reviewed. Owners completed a structured survey assessing sat...
Evaluation of Circadian Variations of Central Corneal Thickness and Its Correlation With Intraocular Pressures in Healthy Horses. Circadian variations in central corneal thickness (CCT) and their correlation with intraocular pressure (IOP) have not been reported in horses. This information may be clinically relevant when interpreting IOP readings. Methods: Twenty-four eyes of 6 healthy adult gelded males and 6 healthy adult intact mares were evaluated. Rebound tonometry (TonoVet, Jorgensen Laboratories) followed by ultrasonic pachymetry (iPac Pachymeter, Reichert technologies) was performed in both eyes every 3 h over 24 h during the natural 14-h daylight summer photoperiod. Results: Central corneal thickness varied ...
Short-Term Daily Oral Administration of Cannabidiol Does Not Impact Rebound Tonometry Intraocular Pressure or Schirmer Tear Test Values in Healthy Adult Horses. To assess the effect of orally administered cannabidiol (CBD) on TonoVet measured intraocular pressure (IOP) and Schirmer tear test I (STT) in horses. Methods: Horse. Methods: This was a masked, randomized, balanced cross-over study of six healthy adult horses. Horses were randomly assigned and received 3 mg/kg CBD in sesame oil or volume matched placebo by mouth once daily for three days. Baseline and daily 4-, 12-, and 24-h post treatment IOPs were measured in triplicate without sedation or eyelid akinesia. Baseline and 24-h post final (day 3) treatment STTs were measured without sedation ...
From Concept to Perception: Equestrian Definitions of Harmony and Visual Attention in Horse-Rider Evaluation. In equestrian circles, horse-rider harmony is understood intuitively, yet clear criteria are lacking. This study examined how different equestrians conceptualized and visually assessed harmony and how this influenced scoring. Qualitative interviews were combined with eye tracking technology. Thirty equestrians assessed five videos of horse-rider combinations performing in dressage, showjumping, eventing, working equitation and Icelandic riding, with eye movements being recorded using a mounted eye tracker. Verbal definitions were analyzed using thematic analysis, revealing three overarching th...
Severe Macular Commotio Retinae Following a Fall from a Horse in a Pediatric Patient. Background and Clinical Significance: Blunt ocular trauma is a significant but often underestimated cause of visual impairment, particularly among adolescents involved in high-risk activities such as horseback riding. While most equestrian injuries affect the head and extremities, ocular trauma, especially commotio retinae, can result in severe visual complications. Case Presentation: We report the case of a 15-year-old girl who sustained blunt ocular trauma to the left eye following a fall from a horse and presented with decreased visual acuity. Multimodal imaging revealed outer retinal abnor...
Atropine induces narrowing of the superior and inferior iridocorneal angle and ciliary cleft in normal horse eyes. To investigate the effects of atropine on the iridocorneal angle (ICA) and ciliary cleft (CC) of normal equine eyes using ultrasound biomicroscopy (UBM). Unassigned: 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 pecti...
Adult Equine Optic Nerve Head Measurements Using Spectral Domain Optical Coherence Tomography. To compare equine optic nerve head (ONH) measurements using spectral domain optical coherence tomography (SD-OCT) to detect clinically relevant ONH cupping. Methods: Forty-five eyes from 34 horses were categorized as CONTROL or CUPPED based on indirect ophthalmoscopy and were measured using SD-OCT: Bruch's membrane opening (BMO), optic cup width (OC), anterior laminar depth (ALD), prelaminar thickness (PLT), and cup-to-disk ratio (OC: BMO) at superior (sup.), central (ctr.), and inferior (inf.) ONH locations. Results: The OC:BMO was 0.61 ± 0.09 (sup.), 0.64 ± 0.09 (ctr.), and 0.55 ...
Evaluation of episcleral silicone matrix cyclosporine implants for presumed equine immune-mediated keratitis: a retrospective study. Immune-mediated keratitis (IMMK) is a chronic inflammatory corneal disease in horses. Long-term topical therapy with cyclosporine is often impractical, highlighting the need for sustained-release alternatives. Objective: To assess clinical response, tolerability, and duration of effect of episcleral silicone matrix cyclosporine implants (ESMC) in horses with presumed IMMK. Methods: Medical records of 12 horses (14 eyes) treated between 2019 and 2023 were retrospectively reviewed. IMMK subtypes were classified as epithelial (n = 3 eyes), anterior stromal (n = 9), or mid-stromal (n =...
Septic Endophthalmitis Following Suprachoroidal Cyclosporine Implant Placement in Two Horses With Equine Recurrent Uveitis. This article presents the clinical and histopathological findings from two horses that developed severe postoperative complications following suprachoroidal procedures routinely employed in the management of equine recurrent uveitis (ERU). Case 1 was a 5-year-old warmblood stallion that initially received a unilateral suprachoroidal triamcinolone injection, followed later by bilateral suprachoroidal cyclosporine implant (CSI) placement. At 9 weeks postoperatively, the right eye (which had undergone both procedures) developed secondary glaucoma necessitating enucleation. Case 2 was a 14-year-ol...
Modified Medial Canthoplasty for Correction of Euryblepharon in Two Horses. To describe a medial canthoplasty surgical procedure in two horses for correction of euryblepharon, secondary to microphthalmia, and following excision of retrobulbar fat prolapse. Methods: A 1 year old thoroughbred mare was presented for small globes and chronic ocular discharge bilaterally. Ophthalmic examination revealed microphthalmos, euryblepharon, medial canthal pocket syndrome, and dacryocystitis bilaterally with no visual impairments. A 2 year old Appaloosa gelding was presented for evaluation of a smooth, subconjunctival mass anterior to the right globe in the medial canthus. Oph...
Effects of rectal examination on intraocular pressure and behavioral responses in pregnant and non-pregnant mares. Rectal examination is routine in equine reproduction but may trigger acute stress affecting welfare and safety. Intraocular pressure (IOP) responds rapidly to autonomic changes and may capture short-lived stress responses. Objective: To evaluate whether rectal examination acutely affects IOP and behavioral responses in mares, and whether reactions differ by reproductive status. Methods: Twenty Rahvan mares (10 pregnant, 30-40 days' gestation; 10 non-pregnant; 4-7 years) underwent transrectal examination without sedation. IOP was measured bilaterally at six time points: 2 min pre-exam (T1), dur...
Unilateral vision loss associated with corneal opacity and posterior lens luxation in the right eye of a Thoroughbred gelding: Case report. A 15-year-old Thoroughbred gelding was presented for examination due to chronic corneal opacity in the right eye, which had been noted for several years. An ophthalmic evaluation revealed dense, irregular corneal opacity; an absence of the direct pupillary light reflex; and a positive dazzle reflex. Fluorescein staining was negative and cytology of a corneal conjunctival swab identified nucleated squamous epithelial cells, but no inflammatory cells. Slit-lamp examination failed to visualize intraocular structure, and the lesion was deemed to be chronic and irreversible. An obstacle-avoidance t...
Standing superficial keratectomy provides long-term control of epithelial and stromal equine immune-mediated keratitis. 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. Unassigned: 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. Unassigned: 22 horses met the inclusion criteria. The mean age was 16.9 years (SD, ...
Cell and Gene Therapy in Equine Ocular Disease. Equine ocular disease is common and often challenging to treat using traditional methods. This has led to the development of new therapies. Like human medicine, veterinary medicine is adopting cellular and gene therapy as innovative approaches. Equine ocular disease is a particularly promising area for these techniques. Notably, immune-mediated diseases (such as immune-mediated keratitis and equine recurrent uveitis), ulcerative keratitis, and infectious ocular diseases are of interest. Several ocular gene therapy products are approved for use in humans, and more are currently being researched...
Evaluation of corneal sensitivity in 40 Pantaneiro horses using the Cochet-Bonnet esthesiometer. Corneal sensitivity is a crucial ophthalmic parameter for the protection and maintenance of ocular health in horses. Unassigned: This study aimed to evaluate the corneal sensitivity of 40 Pantaneiro horses using the Cochet-Bonnet esthesiometer, in order to establish reference values for this population. Unassigned: The animals were considered clinically healthy after a complete ophthalmic examination. Measurements were taken in both eyes, and the data were analyzed for mean, standard deviation, and potential differences between eyes, sex, and age groups. Unassigned: The average corneal sensiti...
Repeatability and reproducibility of intraocular pressure measurements in horses using rebound and applanation tonometry. Intraocular pressure (IOP) assessment is a fundamental component of ophthalmic examinations in both veterinary and human medicine. Due to variations in IOP across species and potential differences among examiners, knowledge of normal IOP values obtained using different tonometers is essential. Unassigned: This study aimed to compare the repeatability and reproducibility of IOP values in horses obtained by three different examiners using rebound (Tonovet) and applanation (Tonopen Avia) tonometers. Unassigned: Thirty healthy criollo horses were examined. IOP was measured by three veterinarians w...
Ocular Causes for Undesired Behaviors in the Horse. Numerous ocular diseases cause visual impairment and induce ocular pain that may be associated with undesired behaviors in horses. Horses with ocular pain, indicated by the presence of blepharospasm, blepharoedema, ocular discharge or rubbing the eye, should be rested from work to avoid worsening the ocular disease and to avoid undesired behaviors associated with pain or vision impairment. Horses with ocular disease are frequently head shy. Some stoic horses may not have obvious outward clinical signs despite significant visual impairment, and as such, undesired behaviors such as spooking, bal...
Polyhexanide, Povidone-Iodine, and Hypochlorous Acid Show High In Vitro Antimicrobial Efficacy Against Pathogens Commonly Associated With Equine Infectious Keratitis. To determine the in vitro antimicrobial activity of specific antiseptics against common equine ocular surface pathogens. Methods: Staphylococcus aureus (S. aureus) (n = 12), Streptococcus equi subspecies zooepidemicus (S. zooepidemicus) (n = 9), Enterobacter hormaechei (E. hormaechei) (n = 6), and Bacillus cereus (B. cereus) (n = 5) were collected from corneal samples of horses with ulcerative keratitis. Reference strains were included. Minimum bactericidal concentrations (MBC) of polyhexanide, povidone-iodine, and hypochlorous acid were tested using the microdilution method. ...
Evaluation of Laboratory Techniques for the Diagnosis of Leptospira-Associated Equine Recurrent Uveitis (ERU) With Focus on the Goldmann-Witmer Coefficient. To evaluate different laboratory procedures for determining the etiologic diagnosis of equine recurrent uveitis regarding intraocular infection with Leptospira spp. and to establish a diagnostic guideline. Methods: Eighty horses with a history of ERU were ophthalmologically examined. Serum and aqueous humor were collected. Total protein, albumin level, and MAT against Leptospira spp. were evaluated on serum and aqueous humor. PCR for Leptospira spp., EHV-1 and -4 was performed on aqueous humor. Goldmann-Witmer coefficient (GWC) and C-value (CC) were calculated based on MAT. In 42 cases, an add...
Green Light-Activated Rose Bengal Cross-Linking in 81 Horses With Complex Corneal Ulcers and Stromal Abscesses. To assess the efficacy and safety of Rose Bengal and green light corneal cross-linking (RGX) as an adjunctive treatment for complicated corneal ulcers and stromal abscesses in horses. Methods: A retrospective analysis included 81 horses (82 eyes) treated with RGX between 2018 and 2024. Cases involved complicated corneal diseases such as melting keratitis, fungal keratitis, deep stromal defects, and stromal abscesses. Treatment consisted of topical or iontophoretic administration of 1% Rose Bengal followed by green light irradiation (550 nm; 150 J/cm) for 10 min. Most procedures (76.8%) w...
Use of a Fogarty balloon catheter for management of distal nasolacrimal duct atresia in a standing sedated horse. A 4-year-old Arabian cross paint mare was referred for evaluation of chronic mucopurulent discharge and epiphora of the left eye. Ophthalmic and radiographic evaluations confirmed distal nasolacrimal duct atresia with absence of the nasolacrimal orifice. Initial minimally invasive treatments, including guidewire-assisted catheterization and diode laser photoablation, were unsuccessful. Definitive treatment was achieved using a Fogarty arterial embolectomy catheter under standing sedation. Controlled balloon inflation and deflation enabled progressive dilation of the obstructed duct, and a surg...
Traumatic injuries in polo players. To determine the frequency of traumatic injuries in polo players in England. Methods: The survey included data on body location and reason for injury derived from accident reports using a retrospective cohort design from 26 participating English polo clubs between the years 2018 and 2024. Results: The study population included injuries in 236 polo players. The most common injury site was the limb (arm, hand, leg, wrist, shoulder) 47.9% (95% CI: 41.4-54.5), and face or head 38.6% (95% CI: 32.3-45.1), of which 12.1% (95% CI: 6.2-20.6) affected the eyes. The most common reason to require hospital...
Tear Film Osmolarity in Horses With Bacterial Conjunctivitis. Conjunctivitis is an inflammation of the conjunctiva caused by infectious or non-infectious factors. Infectious conjunctivitis comes in two forms: viral and bacterial. Bacterial conjunctivitis is commonly caused by organisms such as Staphylococcus and Streptococcus, with the severity of the disease influenced by the specific bacterial species involved. Because both viral and bacterial conjunctivitis are highly contagious, preventive measures are essential to reduce transmission-especially to the unaffected eye. Objective: To evaluate the tear film osmolality in horses with bacterial conjunctiv...
Computed Tomographic Assessment of Normal Ocular Dimensions and Densities in Cadaveric Horses (Equus ferus caballus). This study aimed to characterize the computed tomographic (CT) dimensions and contrast attenuation properties of the equine eye. CT scans from 21 horses without ocular abnormalities were analyzed to obtain detailed ocular measurements and attenuation values. In addition, cranial measurements, such as nasal-occipital length and zygomatic width, were incorporated to explore potential anatomical relationships between the skull and intraocular structures. Although most correlations between cranial and ocular parameters were weak, statistically significant associations-particularly those involving ...
