Nictitating membrane resection in the horse: A comparison of long-term outcomes using local vs. general anaesthesia A. L. LABELLE*, A. G. METZLER and D. A. WILKIE Department of Clinical Medicine, University of Illinois Urbana-Champaign, Urbana, Illinois, USA. Keywords: horse; third eyelid; nictitating membrane; neoplasia; squamous cell carcinoma Summary Reasons for performing study: Neoplasia, for which surgical excision is a frequent treatment, is the most common disease of the equine nictitating membrane. There is little long-term follow-up information available to the practitioner regarding the long-term effects of nictitating membrane excision on ocular health. No information is available to compare recurrence of primary neoplasia of the nictitating membrane after excision with local or general anaesthesia. Objectives: To evaluate the long-term complications of nictitating membrane resection in horses; recurrence of neoplasia of the nictitating membrane when nictitating membrane resection is performed under local vs. general anaesthesia and if the method of anaesthesia used to permit resection of the affected membrane influences the recurrence of neoplasia of the nictitating membrane after complete nictitating membrane resection. Methods: Records of 26 horses receiving resection of the nictitating membrane for primary neoplasia of the nictitating membrane 1999–2009 were reviewed. Clinical examination findings, surgical procedure, anaesthesia type, histopathological findings and details of adjunctive treatment were recorded. Owners were contacted via telephone regarding post operative outcomes. Data were analysed using a Fisher’s exact test (P<0.05). Results: The most common long-term complication of nictitating membrane excision was mild ocular discharge. Squamous cell carcinoma was the most frequent histopathological diagnosis. Recurrence of neoplasia was uncommon (2/26 horses). No significant difference in the number of horses experiencing recurrence of neoplasia was detected between groups receiving general anaesthesia vs. those receiving local anaesthesia. Conclusions: Resection of the nictitating membrane in horses following local anaesthesia is not associated with increased risk of recurrence of neoplasia compared with excision under general anaesthesia. Resection of the nictitating membrane is not associated with any long-term ocular side effects and can be an effective modality for cure of primary neoplasia of the nictitating membrane in selected cases. Introduction The nictitating membrane plays an important role in ocular health by acting to protect the globe and aid in both production and distribution of the precorneal tear film. The nictitating membrane is also a common site of ocular neoplasia in the horse, with squamous cell carcinoma (SCC) being the most frequent neoplasm (Blodi and Ramsey 1967; Lavach and Severin 1977). A wide variety of treatments for SCC have been evaluated, including surgical resection, cryotherapy, interstitial radiation, immunotherapy, photodynamic therapy and chemotherapy (Hilbert et al. 1977; Grier et al. 1980; Frauenfelder et al. 1982; Walker et al. 1986; King et al. 1991; McCalla et al. 1992; Theon and Pascoe 1995; Mosunic et al. 2004; Bosch and Klein 2005; Hewes and Sullins 2006; Ollivier et al. 2006; Rayner and Van Zyl 2006; Giuliano et al. 2008; Payne et al. 2009). Previous reports conflict on the ability of surgical resection of the nictitating membrane alone to effect a permanent cure for neoplasia of the nictitating membrane. A recent study from the UK suggests that surgical resection of the nictitating membrane is not associated with recurrence of neoplasia, while previous studies from the UK and USA suggest that surgery with no adjunctive therapy is associated with higher rates of recurrence (Walker et al. 1986; Dugan et al. 1991; Mosunic et al. 2004; Payne et al. 2009). Standing sedation using local anaesthesia for surgical procedures in the horse has become more commonplace as drugs that allow both sedation and analgesia without ataxia, toxicity or cardiorespiratory compromise become more widely available. Techniques for complete excision of the nictitating membrane under local anaesthesia have been previously described (Millichamp 2005; Harper 2009; Payne et al. 2009). There are currently no studies comparing the long-term outcomes of complete nictitating membrane excision for treatment of primary neoplasia of the nictitating membrane performed under local anaesthesia vs. general anaesthesia or documenting the long-term complications of nictitating membrane excision on ocular health. The aims of this study were to evaluate the long-term complications of nictitating membrane resection in horses, to evaluate recurrence of neoplasia of the nictitating membrane when nictitating membrane resection is performed under local vs. general anaesthesia and determine if method of anaesthesia influences *Corresponding author email: alabelle@illinois.edu [Paper received for publication 16.03.11; Accepted 01.06.11] © 2011 EVJ Ltd 42 EQUINE VETERINARY JOURNAL Equine vet. J. (2011) 43 (Suppl. 40) 42-45 doi: 10.1111/j.2042-3306.2011.00486.x