General examination of the eye is a routine part of equine practice, both to determine the cause of ocular pain and as part
of a prepurchase examination.
Figure 1: Lateral schematic of the head. Peripheral nerve blocks are highlighted. Lidocaine is deposited with a 25-gauge
needle. Deeper nerves require a 1.5-in. 22-gauge needle.
This article features some new technology together with useful techniques that greatly enhance the ease and amount of information
obtained, as well as safeguarding the damaged globe. While the general principles to be described are familiar to all equine
specialists, there are some clinical pearls that can greatly enhance your satisfaction and ultimate confidence in clinical
findings, yielding more rapid resolution.
The eye has been the source of wonder to many for generations, yet it induces frustration and anxiety for veterinarians. Our
intention within the scope of this article is to encourage and stimulate interest in the eye. Remember, there are many practical
and simple additions to your approach that are rewarding. Be warned, however; this is addictive!
Most normal horses and those with minor injuries often will permit an ophthalmic examination in their stall with minimal restraint.
When transported to the hospital or examined under more difficult circumstances, additional restraint is necessary to protect
the eye, the examiner and to permit a thorough evaluation. Painful globes are a profound sensory stimulus, and a variety of
techniques might be required to examine a potentially ruptured globe.
Figure 2:(a) Cross section through the eyelid showing correct placement of the lavage system to avoid corneal contact. (b)
If the lavage is closer to the eyelid margin, it may abrade the cornea during blinking, and result in ulceration. (c) Note
incorrectly positioned lavage system, which may result in a corneal ulcer.
When serious injury is suspected, sedation should be performed before handling. Xylaxine (Rompun®) at 0.3-0.6 mg/kg IV is
usually sufficient if the patient has not been overly stimulated. It is imperative that adequate effect is permitted before
proceeding, otherwise, further sedation is difficult to achieve.
Routinely, I wait five minutes to 10 minutes after the initial head drop to avoid a rapid rebound when the eyelids are touched.
Peripheral nerve blocks also are useful. More profound sedation can be achieved with detomidine (0.015-0.025 mg/kg, IV). Supplementation
with butorphanol may be useful in particularly painful patients, but is frequently complicated by head tremors and jerky motions.
Standing the horse in a stock is very helpful if profound sedation is to be used. Acepromazine is minimally effective. I prefer
to avoid manual restraint with a twitch unless the examination is a brief recheck, or a mild supplement to sedation is required.
Dosages might require adjustment for miniature horses, warmbloods and draught horses.