The Impact of Surgical Excision of the Orbital Lacrimal Gland on the Aqueous Tear Production and Ocular Surface Health in Donkeys (Equus asinus)

Abstract

The exact contribution of the orbital lacrimal gland (OLG) is unknown and is still a subject of debate and inconsistency in literature. Currently, there are no detailed studies addressing the influence of the OLG removal on tear production in equines. This study aimed to address the influence of surgical excision of the OLG on aqueous tear production and ocular surface health in donkeys. The study was conducted on six clinically healthy donkeys with no ophthalmic abnormalities. In each donkey, the OLG of the left eye was surgically excised, whereas the right eye was served as a control. External ophthalmic examination, Schirmer tear test (STT) I and II, tear pH, fluorescein staining test were conducted on both eyes, preoperatively and at one-week intervals for 60 days, postoperatively. There were significant decreases in STT I and II values (P = .0001 and .0001, respectively), whereas tear pH values showed a significant increase (P = .0001) in the operated eyes compared with the control ones. There were no overt clinical signs characteristics of keratoconjunctivitis sicca (KCS) in the operated eyes. However, there was evidence of microinjury of the keratoconjunctival epithelium evidenced by positive fluorescein uptake, postoperatively. Surgical excision of the OLG significantly diminished the aqueous tear production and threatened the corneal epithelium as a result of corneal dehydration. On the contrary to the recommendations of other studies, eyes subjected to this procedure should receive treatment of dry eye to prevent development of KCS, postoperatively.