ISSN 2398-2977      

Eye: neoplasia - overview



  • Cause: primary and secondary neoplasms.
  • Signs: depend on type of tumor.
  • Diagnosis: primarily via clinical examination; additional diagnostic imaging and biopsy (histology and cytology) may provide more information and allow a definitive diagnosis
  • Treatment: variety of options depending on type of tumor and precise location. Most treatments are limited by the need to preserve eyelid or ocular function.
  • Prognosis: fair to grave. Most primary ocular and periocular tumors do not metastasize in the horse, but they are often locally aggressive and they may have profound effects on the welfare and use of the horse. Periocular sarcoids may be especially invasive into the upper eyelid. When treated early and aggressively, the prognosis is much better than those left to become invasive and extensive prior to attempting treatment. Early treatment is paramount to achieve a reasonable end result.



Predisposing factors


  • Squamous cell carcinoma predisposed by ultraviolet light and non-pigmented skin/conjunctiva.
  • Palpebral/iridal melanomas far more commonly found in gray horses.
  • Periorbital sarcoids are rarely solitary lesions; the majority of horses with periocular sarcoids will have sarcoids in other locations as well.


  • Primary tumors of the orbit are rare, but primary tumors of the periorbital structures are common.
  • Sarcoid, melanoma and squamous cell carcinoma are the most common ocular, orbital and periorbital tumors.
  • Lymphoma, tear gland adenoma and extension of carcinoma and ethmoid hematoma are the most common masses occurring within the orbit itself.
  • Orbital tumors may also be secondary to tumors of the paranasal sinuses or as extension of ocular/adnexal structures
  • Others types of neoplastic diseases are rare.
  • Papilloma (warts):
    • Common on the head and neck of young horses (12-24 months) Papillomatosis.
    • Infection with equine papilloma virus Papilloma virus or non-infectious irritants.
    • Benign.
    • Usually self-resolving around the face/eyes.
  • Nerve sheath tumors:
    • Neurofibroma and Schwannoma arise from tissue of neuroectodermal origin, eg nerve sheath or Schwann cells and perineural fibroblasts.
    • One report suggested they comprised 4.2% of all equine neoplasms but this is not confirmed elsewhere.
  • Adenocarcinoma:
    • Usually secondary to sinus adenocarcinoma - direct extension from sinus or ethmoidal region.
    • Eyelid, orbit, third eyelid.
    • Tendency to metastasize Eye: pituitary adenoma.
  • Basal cell tumor:
    • Benign, slow growing.
    • Uncommon in horses (much more common in humans).
  • Hemangiosarcoma:
    • Eyelid, bulbar conjunctiva, cornea, third eyelid, orbit.
    • Vascular origin tumor which may metastasize.
  • Hemangioma:
    • Benign, vascular origin tumor.
    • Cornea, conjunctiva.
  • Lymphoma:
    • Uncommon in eye; has been reported to affect the orbit, eyelid, cornea, conjunctiva, uvea.
    • Malignant tumor which may be primary or secondary and has a high likelihood of systemic involvement elsewhere Lymphosarcoma: overview.
    • Can present as a solitary nodular lesion with an appearance similar to a nodular sarcoid.
  • Mast cell tumor
    • Rare tumor affecting limbus, and occasionally the eyelids.
    • Differential diagnosis includes habronemiasis; both conditions stimulate mast cell invasion and require careful histopathology to differentiate.
  • Medulloepithelioma:
    • Rare congenital intra-ocular tumor of neuroepithelial tissues; usually arises from the ciliary body or, occasionally, the retina/optic nerve.


  • Variable timecourse.
  • Some very slow, others rapid enlargement and extensive tissue destruction.
  • Bovine papilloma virus is implicated in the development of sarcoids, which are a neoplastic disorder of fibroblasts.
  • Secondary effects on keratinocytes.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Clode A B, Miller C et al (2012) A retrospective comparison of surgical removal and subsequent CO2 laser ablation versus topical administration of mitomycin C as therapy for equine corneo-limbal squamous cell carcinoma. Vet Ophthlamol 15 254-262 PubMed.
  • Henson F M D & Dobson J M (2004) Use of radiation therapy in the treatment of equine neoplasia. Equine Vet Educ 16 (6), 315-318 VetMedResource.
  • Rebhun W C (1998) Tumors of the eye and ocular adnexal tissues. Vet Clin North Am Equine Pract 14 (3), 579-606 PubMed.
  • Rebhun W C et al (1998) Ocular lesions in horses with lymphosarcoma - 21 cases (1977-1997). JAVMA 212 (6), 852-854 PubMed.
  • Basher A W et al (1997) Orbital neuroendocrine tumors in three horses. JAVMA 210 (5), 668-671 PubMed.
  • Bacon C L et al (1996) Bilateral Horner's syndrome secondary to metastatic squamous cell carcinoma in a horse. Equine Vet J 28 (6), 500-503 PubMed.
  • Theon A P et al (1995) Iridium-192 interstitial brachytherapy for equine periocular tumors - treatment results and prognostic factors in 115 horses. Equine Vet J 27 (2), 117-121 PubMed.
  • Ueda Y et al (1993) Ocular medulloepithelioma in a Thoroughbred. Equine Vet J 25 (6), 558-561 PubMed.
  • Dugan S J (1992) Ocular neoplasia. Vet Clin North Am Equine Pract 8 (3), 609-626 PubMed.
  • Wilkie D A (1991) Ophthalmic procedures and standing surgery in the standing horse. Vet Clin North Am Equine Pract 7 (3), 535-547 PubMed.
  • King T C et al (1991) Therapeutic management of ocular squamous cell carcinoma in the horse - 43 cases (1979-1989). Equine Vet J 23 (6), 449-452 PubMed.
  • Davidson H J et al (1991) Anterior uveal melanoma, with secondary keratitis, cataract, and glaucoma, in a horse. JAVMA 199 (8), 1049-1050 PubMed.
  • Dugan S J et al (1991) Epidemiological study of ocular/adnexal squamous cell carcinoma in horses. JAVMA 198 (2), 251-256. PubMed
  • Riis R C et al (1990) Intraocular medulloepithelioma in a horse. Equine Vet J Suppl. 10, 66-68 PubMed.
  • Rebhun W C (1990) Treatment of advanced squamous cell carcinomas involving the equine cornea. Vet Surg 19 (4), 297-302 PubMed.
  • Wilkie D A et al (1990) Combined treatment of ocular squamous cell carcinoma in a horse, using radiofrequency hyperthermis and intersitial 198Au implants. JAVMA 196 (11), 1831-1833 PubMed.
  • English R V et al (1990) Carbon dioxide laser ablation for treatment of limbal squamous cell carcinoma in horses. JAVMA 196 (3), 439-442 PubMed.
  • Hum S et al (1989) Ocular mastocytosis in a horse. Aust Vet J 66 (1), 32 PubMed.
  • Schwink K (1987) Factors influencing morbidity and outcome of equine ocular squamous cell carcinoma. Equine Vet J 19 (3), 198-200 PubMed.
  • Szymanski C M (1987) Malignant teratoid medulloepithelioma in a horse. JAVMA 190 (3), 301-302 PubMed.
  • Hacker D V et al (1986) Ocular angiosarcoma in four horses. JAVMA 189 (2), 200-203 PubMed.
  • Moore P F et al (1986) Ocular angiosarcoma in the horse - morphological and immunohistochemical studies. Vet Pathol 23 (3), 240-244 PubMed.
  • Junge R E et al (1984) Papillomas and squamous cell carcinomas of horses. JAVMA 185 (6), 656-659 PubMed.
  • Bistner S et al (1983) Neuroepithelial tumour of the optic nerve in a horse. Cornell Vet 73 (1), 30-40 PubMed.
  • Murphy J et al (1979) Intraocular melanoma in a horse. Vet Pathol 16 (5), 539-542 PubMed.
  • Lavach J D et al (1977) Neoplasia of the equine eye, adnexa, and orbit - a review of 68 cases. JAVMA 170 (2), 202-203 PubMed.
  • Gelatt K N et al (1974) Conjunctival squamous cell carcinoma in the horse. JAVMA 165 (7), 617-620 PubMed.

Other sources of information

  • Knottenbelt D C, Patterson-Kane J C & Snalune K L (2015) Clinical Equine Oncology. Elsevier, London.

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