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.
Garner A, Griffiths P.The purpose of this paper is to describe congenital defects, having no direct counterpart in
the literature, that affected both eyes of a new-born foal of pedigree racing stock, which
otherwise appeared to be entirely healthy as were both the sire and the dam.
To compare ocular structures of Quarter Horses homozygous for hereditary equine regional dermal asthenia (HERDA) with those of Quarter Horses not affected by HERDA (control horses) and to determine the frequency of new corneal ulcers for horses with and without HERDA during a 4-year period. Methods: Cohort study of ocular structures and retrospective case series of horses with and without HERDA. Methods: The cohort portion of the study involved 10 Quarter Horses with HERDA and 10 Quarter Horses without HERDA; the retrospective case series involved 28 horses with HERDA and 291 horses without HE...
Bercovitz GR, Sullivan SN, Reed RA, Ryan CA, Diehl KA.To evaluate the effect of intravenous mannitol and hypertonic saline (HS) on intraocular pressure (IOP) and biometry parameters of horses with elevated intracranial pressure (ICP). Methods: Seven horses with normal ophthalmic exams were anesthetized and placed in lateral recumbency. A subarachnoid transducer was placed, and the head was lowered until ICP measured 40 mmHg +/- 2 mmHg. Five intravenous boluses of mannitol 20% (0.4 g/kg) or HS 7.2% (1 mL/kg) were administered, each 15 min apart. A 2-day washout period ensued, and the procedure was repeated with the other hyperosmotic age...
Ing ST, Pinard CL, James-Jenks EM, Leis ML.Our objective was to investigate the demographics and prevalence of ocular disease in a large referral population of horses in Ontario over a 10-year period. Unassigned: A retrospective analysis of medical records for 283 horses evaluated by Board-certified veterinary ophthalmologists at the Ontario Veterinary College (Guelph, Ontario) was conducted. Signalment and ocular disease were recorded. Unassigned: The 3 most common ocular abnormalities identified were uveitis (43.7%, 123 horses), ulcerative keratitis (42.0%, 119 horses), and cataract (25.1%, 71 horses). Uveitis was most often secondar...
Hefner EM, Stoppini R, McMullen RJ. This study is aimed at describing two unique case presentations of iris hypoplasia and the use of semiconductor diode laser for treatment in the horse. One 20-year-old American Quarter Horse gelding and one 11-year-old pony mare were studied. The presenting clinical signs, surgical technique, and postoperative results for two cases of iris hypoplasia treated with diode laser are described. Immediate postoperative complications-postoperative ocular hypertension (POH), corneal edema, and epithelial bullae-were possible anticipated effects but were controlled with topical medications in the fi...
Lam KP, Keys DA, McMullen RJ.To describe infracyanine green-based photodynamic therapy (InfraCG-PDT) and evaluate outcomes in horses with immune-mediated keratitis (IMMK). Methods: Medical records from 2014 to 2020 from the Equine Clinic Munich-Riem, Germany, and Auburn University Equine Ophthalmology Service identified horses diagnosed with IMMK following ophthalmic examination that had undergone InfraCG-PDT. Methods: Multiple intrastromal injections of EmunDo (InfraCG, A.R.C. Laser, Nuernberg, Germany) within an affected quadrant or the entire cornea were treated with diffuse diode laser energy (FOX A.R.C., Laser, Nuern...
Bandera L, Guerri G, Straticò P, Pincelli MC, Celani G, Varasano V, Vignoli M, Petrizzi L.Although lens diseases are uncommon in horses, they can be disabling in advanced stages. The B-mode ultrasound is useful for diagnosing and monitoring the progression of ocular diseases such as cataracts. Elastography is an ultrasonographic technique that allows the detection and measurement of tissue stiffness. This observational cohort prospective study aimed to determine the feasibility, reproducibility, and repeatability of 2D-shear wave elastography (2D-SWE) of lenses in horses. Forty-six eyes of 23 horses with no evidence of ocular disease were included in this study. The horses underwen...
Bazzano M, Laus F, Cerquetella M, Spaterna A, Marchegiani A.Phytocannabinoids have the potential to lower intraocular pressure in both normal and glaucomatous eyes and they have been tested in different animal species, but not in the horse. The present paper describes the tonometric curve of healthy adult Italian Saddle horses after oral administration of cannabidiol oil (CBD). Methods: CBD 20% was administered orally (oily solution) at the dose of 1 mg/kg to 8 adult horses and intraocular pressure (IOP) was evaluated by tonometric curve. Data were then compared to those of the same horses obtained the day before (blank) CBD administration. Results: ...
Moody LM, Hicks SL, Foote BC, Hendrix DV, Ward DA.Equine corneal disease is common and painful. Current pain mitigation strategies are often suboptimal, especially early in the disease. Objective: To evaluate the effects of local anaesthetic delivery via indwelling retrobulbar catheter on corneal sensitivity, pupil size, pupillary light responses (PLRs), and ocular motility in normal horses. Methods: Randomised, controlled crossover experiment. Methods: One eye was randomly selected from seven horses. A 20-gauge catheter was placed in the retrobulbar space and injected with 10 mL of 0.5% bupivacaine or 0.9% saline. Cochet-Bonnet esthesiomet...
Singh A, Johnson T, Wotman K, Leary D.Veterinary personnel exposure due to scattered x rays, when present during superficial radiation treatment (SRT), was evaluated. Veterinary personnel presence is needed during SRT to minimize the degree of required aesthesia to horses. Animal treatment was simulated, and exposure rates determined for 50, 70, and 100 kV x rays using eight different SRT applicators. Exposure rates at the surface of a solid water phantom (SWP) phantom ranged from 3.9 mR h-1 to 396 mR h-1 for 50 kV, from 41 mR h-1 to 2,880 mR h-1 for 70 kV, and from 235 mR h-1 to 7,500 mR h-1, for 100 kV, respectively. A horse pha...
Graham AE, Carslake HB, Malalana F.Evidence for optimal location of subpalpebral lavage (SPL) systems is lacking. Objective: To compare the rate and types of complications with SPL systems located in central upper- compared with medial lower-eyelid in hospitalised patients. Methods: Prospective, randomised treatment trial. Methods: Horses admitted for ophthalmic treatment using an SPL system from February 2015 to January 2024 were included if ocular pathology did not necessitate SPL system placement in a specific location. Coin toss was used to determine location. SPL systems were monitored at least daily, and complications wer...
Kirmse L, Thieme K, Doherr MG, Eule JC.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...
Bourassi S, Jack H, Florczyk A.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...
Knickelbein KE.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...
Young KAS, Schnabel LV, Gilger BC.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...
Toddy T, Ledbetter EC, Knickelbein KE.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, ...
Imai S, Sato R, Fujiwara R, Terui S, Kimura A, Ichijo T, Kasashima Y, Miyazaki T.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...
Çortu A, Çınar H.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...
Letourneau AR, Butler BA, Martinez PS, da Costa Martins B, Monk CS, Plummer CE.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...
Martin de Bustamante MG, Plummer CE, Caddey B, Gomez DE.Information regarding the impact of topical antibiotics with or without corticosteroids on the microbiota of the horses' eyes is limited. This study aimed to describe the bacterial ocular surface microbiota in healthy horses and evaluate the effect of topical antibiotics or antibiotic-corticosteroid medication on the ocular surface microbiota. Unassigned: This was a prospective, randomized, longitudinal, blinded study in which one eye of 12 horses was treated 3 times daily for 7 days with neomycin, polymyxin B and bacitracin ophthalmic ointment ( = 6) or neomycin, polymyxin B and dexametha...
Roth LSV, McGreevy P.To improve human-horse interactions and reduce the risk of injury, it is essential to adopt an equi-centric perspective that prioritizes how horses perceive their environment. This review focuses on the equine visual system, both because it is the most studied of the horse's senses and because misunderstandings about how horses see can lead to unsafe or unsustainable handling. By applying two complementary frameworks, namely Tinbergen's Four Questions and the Five Domains model, we examine equine vision from both a biological and a welfare-oriented perspective. We explore the anatomical and fu...
Plotsker NM, Taylor R, Coffin HR, Beatty A, Newbold G, Knickelbein KE.To describe the clinical and histologic features of a sarcoid arising from the medial caruncle with spread to the third eyelid of a horse. Methods: A 20-year-old Quarter Horse gelding. Methods: An incisional biopsy of the medial caruncle mass was initially performed, with histopathology suggesting a sarcoid or other spindle cell neoplasm. The mass grew rapidly following the biopsy, expanding to affect the third eyelid and adjacent superior palpebral conjunctiva. A complete third eyelid and medial caruncle excision with resection of affected palpebral conjunctiva and adjunctive cryotherapy was ...
Tucker-Retter EK, Yamagata M, Gilger B, Oh A.To assess whether topical carbonic anhydrase inhibitors (CAIs) with or without episcleral brinzolamide implants control intraocular pressure (IOP) in horses with glaucoma. Methods: 12 client-owned horses diagnosed with glaucoma. Methods: Medical records of horses treated with topical CAIs for ≥ 14 days, with a subset receiving episcleral brinzolamide implants, were reviewed. Diagnosis, signalment, concurrent ocular disease, medications, IOP, visual status, and additional procedures were recorded. Treatment failure was defined as horses with IOP > 30 mmHg resulting in phthisis bulbi o...
Esdaile E, Houston K, Till BJ, Sutton RB, Scurrell E, Ling M, Hartley C, Bellone RR.Although several inherited ocular disorders have been extensively studied in horses, few reports of equine ectopia lentis exist and no genetic investigations have been reported. Ectopia lentis in humans and other species is reported to be caused by trauma, genetic variants, and systemic diseases. The most commonly reported genetic causes are dominant alleles in FBN1. Here we examined a 3-day old Oldenburg x Thoroughbred colt due to concerns over bilateral ocular anomalies and hypothesized that either a recessively inherited allele or a dominant de novo allele was the genetic cause. Examination...
Díaz-Bertrana ML, Pitti L, Ramírez AS, Encinoso M, Fumero-Hernández M, Morales I, Arencibia A, Jaber JR.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 ...
Saberinia A, Ozmaei S, Anoushepour A.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...
Goetz M, Cremoux M, Lassalle L, Douet JY.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...
Ken-Dror G, Chua V, Sharma P.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...
Stolle LM, Oltmanns H, Meißner J, Heun F, Schieder AK, Wolff HT, Ohnesorge B, Busse C.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. ...
