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Basics ⬇

Outline

BASICS

Overview!!navigator!!

  • IP follows ocular trauma, particularly sharp perforating corneal injuries, or blunt injuries causing rupture of the cornea, limbus, and/or sclera
  • IP can also occur secondary to rapid enzymatic degradation of stromal collagen in progressive melting or infected corneal ulcerations

Signalment!!navigator!!

All ages and breeds of horses are at risk.

Signs!!navigator!!

  • The eye may be cloudy or red. Blepharospasm and epiphora are present. Slight downward deviation of the upper eyelashes may be a subtle sign of corneal pain
  • A brown to red structure protruding through a corneal defect is diagnostic
  • The anterior chamber will be shallow or collapsed

Causes and Risk Factors!!navigator!!

Corneal perforation with IP may be a sequela to traumatic insult or to infectious and noninfectious corneal ulcerations.

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

Ocular pain may be found with corneal ulcers, uveitis, conjunctivitis, blepharitis, and dacryocystitis.

Diagnostic Procedures!!navigator!!

  • Fluorescein dye will indicate the site of corneal perforation, and the dye may leak into the anterior chamber
  • Seidel's test may indicate aqueous leakage through the corneal perforation

Treatment ⬆ ⬇

TREATMENT

  • Most IPs are ideally addressed with surgical repair. The decision to pursue surgery is initially based upon the possibility of useful vision and survival of the globe. Replacement of the missing cornea with a corneal transplant is recommended. The transplant site should be covered with a CF or an amniotic membrane graft
  • Key techniques in repairing an IP:
    1. Remove necrotic cornea before placing the corneal graft. Replace missing cornea with a larger diameter frozen corneal graft and suture in place
    2. Make CF thin before suturing it to the cornea atop the corneal graft. CF fibrosis and failure may be associated with aqueous leakage under the flap. Aqueous humor leakage induces fibroplasia such that the flap does not adhere well to the wound
    3. CF bruising may indicate flap ischemia
    4. A white CF has become avascular
    5. CF bulging may indicate IP. Check for low intraocular pressure and positive Seidel's test
    6. Continue anti-proteinase medications after flap placement or absorbable sutures may dissolve prematurely
    7. Anchor CF with sutures at the limbus to reduce tension

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

  • Topical antibiotics (every 1–4 h initially), atropine (1%; QID), and serum (every 1–4 h) are recommended. Systemic NSAIDs (flunixin meglumine 1 mg/kg BID PO, IV), and broad-spectrum parenteral antibiotics are indicated
  • Intensive postoperative medical therapy, especially use of systemic NSAIDs, is critical for successful management of iridocyclitis

Contraindications/Possible Interactions!!navigator!!

Horses receiving topical atropine should be monitored for colic.

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

  • Horses with IP and secondary uveitis should be stall rested until the condition is healed. Intraocular hemorrhage and increased severity of uveitis are sequelae to overexertion
  • The horse should be protected from self-trauma with a hard- or soft-cup hood
  • Ocular pain should gradually diminish following surgical repair

Possible Complications!!navigator!!

Infectious endophthalmitis is a complication that will require enucleation. Vision compromise may be minimal to complete.

Expected Course and Prognosis!!navigator!!

  • Prognosis of perforating corneal lacerations is guarded. Perforating wounds caused by sharp insults are associated with a better prognosis than those caused by blunt insults. High-energy blunt trauma may result in hyphema and/or globe rupture, most often occurring at the limbus or equator where the sclera is the thinnest
  • Iridocyclitis may predispose to fibropupillary membrane formation, posterior synechiae, and cataract development. Some of these eyes will become phthisical and permanently blind
  • Traumatic perforating wounds <15 mm have a better prognosis than those >15 mm
  • There is a direct relationship between a prolonged duration of ulcerative keratitis prior to IP and poor visual outcome. Eyes with IP due to ulcerative keratitis >2 weeks’ duration, and melting or infected ulcers, tend to have a poor visual outcome or may require enucleation due to endophthalmitis

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Associated Conditions!!navigator!!

Ulcerative keratitis in the horse frequently incites severe anterior uveitis.

Abbreviations!!navigator!!

  • CF = conjunctival flap
  • IP = iris prolapse
  • NSAID = nonsteroidal anti-inflammatory drug

Suggested Reading ⬆ ⬇

Brooks DE. Ophthalmology for the Equine Practitioner, 2e. Jackson, WY: Teton NewMedia, 2008.

Brooks DE, Matthews AG. Equine ophthalmology. In: Gelatt KN, ed. Veterinary Ophthalmology, 4e. Ames, IA: Blackwell, 2007:1165–1274.

Gilger BC, ed. Equine Ophthalmology, 3e. Ames, IA: Wiley Blackwell, 2017.

Author(s) ⬆

Author: Caryn E. Plummer

Consulting Editor: Caryn E. Plummer

Acknowledgment: The author/editor acknowledges the prior contribution of Dennis E. Brooks.