Unilateral choristoma of the nictitating membrane in a horse.

The study discusses the case of a 2-year-old horse that had a rare condition causing hair growth and corneal ulceration in its eye. This was treated through surgical removal of the abnormal tissue, leading to satisfactory recovery.

Condition Observation

• The research focuses on a 2-year-old Morgan mare that was brought in for evaluation due to a corneal ulceration in its left eye.
• An irregular, deep stromal corneal ulcer was observed, situated in an area of malacia (an area of softened tissue).
• The condition of the eye was further complicated by the presence of hypopyon, which involves pus in the anterior chamber of the eye, and a moderate aqueous flare, usually indicating inflammation.
• The horse’s nictitating membrane (third eyelid) had hairs growing from its leading edge, which were coming into contact with the corneal surface potentially causing further discomfort and damage.

Intervention and Analysis

• Upon determining these factors, the researchers decided on performing a bulbar pedicle conjunctival graft after inducing general anesthesia in the horse.
• The surgery involved excising (cutting out) the conjunctiva, or the mucous membrane that covers the front of the eye and lines the inside of the eyelids, at the leading edge of the nictitating membrane. The aberrant (unusual or abnormal) hair follicles were also removed.
• Upon microscopic examination, the researchers found a non-keratinized stratified squamous epithelium (a type of protective tissue), sebaceous glands, and hair shafts, confirming the diagnosis of a choristoma of pilosebaceous origin.

Post Treatment Observation and Conclusion

• Six weeks after the surgical procedure, the horse displayed no signs of discomfort, and there was no regrowth of the previously present hairs. Importantly, the horse showed no loss of vision.
• The paper concludes by stating that ocular choristomas, which are tumorous growths made up of normal cells but in inappropriate places, develop secondary to defective fetal cellular differentiation. The condition is rarely reported in equines.
• This variant of choristoma contained ectopic hair follicles with hair growth, as well as sebaceous glands.
• The study emphasizes the importance of a detailed adnexal examination (evaluating the structures surrounding the eye such as the eyelids and tear glands) in horses with corneal disease.