VN November 2022

Vetnews | November 2022 33 Regulars I Ophthalmology Column "Odds & Ends" Dr Antony Goodhead, Specialist Veterinary Ophthalmologist, Johannesburg and Cape Animal Eye Hospitals, www.animaleyehospital.co.za This month’s ophthalmology column is going to be devoted to some “Odds & Ends”. Things you may have wondered about and for which you may not have answers. 1] The development of corneal damage following general anaesthetic – does the eye need lubrication? The presence of corneal damage as a result of GA is a well-known and frustrating problem for all of us. In human patients, the incidence of corneal damage is reported to be between 0.01% and 2.3% in protected eyes and up to 44% in unprotected eyes. In dogs, the incidence of corneal damage is reported to be 1.9%– 18.6% in eyes protected with ocular lubricant. Corneal epithelial damage during GA arises from a combination of lagophthalmos due to the relaxation of the orbicularis oculi muscle and reduced tear production secondary to drugs used for the GA. Many opioids and alpha-2 adrenergic agents commonly used in anaesthetic protocols for sedation and analgesia have been shown to decrease tear production. Dexmedetomidine, medetomidine, butorphanol, pethidine, and fentanyl have all been shown to cause a significant decrease in tear production from baseline to below 15 mm/min, 15–20 min after administration. A combination of methadone and ACP has been shown to significantly decrease tear production from baseline, with 30% of dogs showing a decrease below 15 mm/min 30–45 min after administration. Inhalant agents for anaesthetic maintenance have also been shown to significantly decrease tear production in dogs. A retrospective study in dogs identified that patients undergoing prolonged GA, brachycephalic dogs and patients undergoing neurosurgery were at increased risk of developing corneal damage, whilst a further prospective study showed that these factors were not affecting the risk of damage. From our experience at JAEH, we have seen bad corneal ulcerations in patients undergoing prolonged surgical procedures. A recent study compared the presence of corneal damage in two groups of dogs where one group had a lubricant applied to the eyes, and the other group had a lubricant, and the eyelids taped closed during the surgical procedure. Corneal injury was described as corneal erosion or corneal ulceration. Corneal erosion was defined as superficial epithelial damage with no penetration into the epithelium’s basement membrane, that was seen as subtle, patchy uptake of fluorescein staining. Corneal ulceration was defined as loss of corneal epithelium exposing corneal stroma, with a pronounced, strong uptake of fluorescein stain. This study showed that the incidence of corneal erosion was 8%, and no signs of corneal ulceration were noted. Corneal erosions in the taped, and non-taped eyes and brachiocephalic breeds accounted for 31% of the cases. Regulars I Opht almol gy Column >>> 34