Other Equine Keratopathies

Take Home Message  

The horse cornea is large and predisposed to several important inflammatory and non inflammatory diseases.  

Corneal Stromal Abscesses  

Focal trauma to the cornea can inject microbes and debris into the corneal stroma through small  epithelial ulcerative micropunctures. Some stromal abscesses may be secondary to systemic  disease.  

A corneal abscess (Figs. 1-3) may develop after epithelial cells adjacent to the epithelial  micropuncture divide and migrate over the small traumatic ulcer to encapsulate infectious agents  or foreign bodies in the stroma. Epithelial cells are more likely to cover a fungal than a bacterial  infection.
 

Reepithelialization forms a barrier that protects the bacteria or fungi from topically administered  antimicrobial medications. Reepithelialization of stromal abscesses interferes with both routine  diagnostics and treatment.  

Corneal stromal abscesses can be a vision threatening sequelae to apparently minor corneal  ulceration in the horse. A painful, blinding chronic iridocyclitis may result.  

Most stromal abscesses involving Descemet's membrane are fungal infections. The fungi seem  "attracted" to the type IV collagen of Descemet's membrane.

Both superficial and deep stromal abscesses do not heal until they become vascularized. The  patterns of corneal vascularization are often unique suggesting that vasoactive factors are being  released from the abscess that influences the vascular response.  

Medical therapy consists of aggressive use of topical and systemic antimicrobials, topical  atropine, and topical and systemic NSAIDs.  

Superficial stromal abscesses may initially respond positively to medical therapy. If reduced  inflammation of the cornea and uvea are not found after two to three days of medical treatment,  surgical removal of the abscess should be considered.  

Deep lamellar and penetrating keratoplasties (PK) are utilized in abscesses near Descemet's  membrane, and eyes with rupture of the abscess into the anterior chamber. PK eliminates  sequestered microbial antigens, and removes necrotic debris, cyotokines and toxins from  degenerating leukocytes in the abscess.

Penetrating Keratoplasty and Lamellar Keratoplasty (LK) for Deep Corneal Stromal  Abscesses  

Corneal transplantation is performed to restore vision, to control medically refractory corneal  disease, and to re-establish the structural integrity of the eye. Full thickness (PK) (Fig. 4) or split  thickness (LK) transplants can be done successfully in the horse.  
 

Penetrating and lamellar keratoplasty is considered high-risk for rejection in infected, vascularized corneal tissue. Nearly all PKs in horses are in high-risk corneas.  

Fresh corneal grafts are preferred in horse PK, but frozen tissue can be utilized. Vascularization of the grafts, indicating rejection, begins at 5-10 days postoperatively.  

Few equine PK grafts remain clear following their vascularization. They form a therapeutic and tectonic function.  [...]