Characterization and outcome following excision of masses in the nictitating membranes of horses: 50 cases (1998-2012).

This research evaluates the characteristics and outcome of nictitating membrane (third eyelids) surgery in horses. Basing its findings on historical cases, it identifies squamous cell carcinoma as the predominant type of tumor affecting this part of the eye. The study found a relatively high rate of recurrence and mortality, so underlines the importance of long-term monitoring following surgery.

Study Design and Methods

• The study is a retrospective review of 50 cases involving horses with masses in their third eyelid. The cases span from September 1998 to November 2012.
• The researchers included cases in which detailed follow-up information was available for at least one year post-surgery.
• The study focused on horses that underwent partial or complete excision of the third eyelid, submitting the removed part for histologic evaluation.
• Data collected from medical records included information about the horse (signalment) and the treatment administered.
• The histopathology reports were evaluated to determine surgical margins and any vascular invasion.
• The data was analyzed using a χ(2) test to determine the association between the recurrence of the mass and factors such as the type of excision, surgical margins, vascular invasion, and the use of chemotherapy.
• The association between partial excision prior to referral and the outcome was also assessed.

Key Findings

• The predominant tumor type in the third eyelid of horses was found to be squamous cell carcinoma.
• Of the 50 horses, 10, or 20%, had a recurrence of the mass. Recurrence happened, on average, 2.25 years after surgery, with the median being 1.5 years post-surgery.
• There was an identified association between conducting a partial excision of the third eyelid prior to referral and the outcome of the treatment.

Conclusions

• The rate of recurrence and mortality was notably high in horses that underwent surgery for masses in the third eyelid.
• Long-term monitoring following partial or complete third eyelid excision was recommended due to these findings.