Chapter 147

Eyelid Lacerations

Amber L. Labelle

The eyelids are a common site of ocular trauma in the horse. Restoring normal anatomic relationships is essential to preserving normal eyelid function and long-term ocular health. Eyelid lacerations must be repaired promptly and precisely. Surgical repair may be done with the horse sedated and standing or under general anesthesia, but the principles of eyelid laceration repair are the same regardless of the method of anesthesia used.

Anatomy and Physiology

Eyelids are essential for corneal health. The eyelid provides protection to the cornea, disperses the tear film across the ocular surface, removes debris, and plays an important role in producing the tear film and providing immunologic protection of the cornea. Eyelid skin is no different than skin elsewhere on the body, but the eyelid margin and the underside of the eyelid are highly specialized. Only the smooth and hairless eyelid margin and palpebral conjunctiva come into contact with the cornea, helping to maintain normal corneal epithelial health and integrity. Just external to the eyelid margin are the robust cilia, which are an important sensory component of the blink reflex. The eyelids of the horse are at risk for trauma because of their external location over the prominent equine globe and because of the quick resorting to a fight-or-flight response that is inherent to the nature of horses. When the eyelid is lacerated, restoration of the normal anatomy of the eyelid margin is the most important part of the laceration repair. An irregular eyelid margin or one with a step defect does not maintain even corneal contact and may lead to tear film deficiencies, chronic irritation, exposure keratitis, chronic epiphora, or chronic ulceration. Worse, if the laceration heals with haired skin touching the cornea, chronic ulceration, perforation, and vision loss can result. Restoration of the normal eyelid margin anatomy is an essential component of eyelid laceration repair.

Evaluation of the Laceration

Most horses need sedation to permit thorough examination after an eyelid laceration. A complete ophthalmic examination should be performed, including fluorescein staining of both eyes. Occasionally, underlying ophthalmic disease such as equine recurrent uveitis or glaucoma is detected as a cause for ocular pain, rubbing, and eyelid trauma. Corneal trauma is frequently detected concurrently with eyelid trauma, so application of fluorescein stain to assess corneal integrity is important. After both eyes have been thoroughly assessed, the practitioner must make a decision about when to repair the laceration. Unless the laceration is very fresh (<2 hours old), packing the laceration overnight and repairing the next day is most prudent. Eyelids are very vascular and rapidly become edematous and distorted, making accurate tissue apposition more challenging. A wet-to-dry bandage helps keep wound edges moist, reduces edema, and allows the practitioner to schedule the repair as an elective procedure the following day. A generous quantity of nitrofurazone gel can be applied to 4- × 4-inch cotton gauze squares, which are placed directly over the laceration and held in place overnight with a self-adherent stretch bandage material such as Elastikon.¹ Nitrofurazone does not appear to have adverse effects on the cornea.

Surgical Repair

Most horses are amenable to standing eyelid laceration repair with the use of local anesthesia and sedation, although particularly young or fractious patients may be more easily operated on while under general anesthesia. If sedation of the standing horse is used, a ring block with a combination of 2% lidocaine and 0.5% mepivacaine provides effective local anesthesia for most patients. This block has the advantage of inducing local anesthesia without the necessity of anatomic precision in administering the block but may require larger quantities of local anesthetic to provide complete local anesthesia; 15 to 20 mL is typically needed to completely encircle the globe. Direct injection of local anesthetic into the laceration site is not recommended because this will distort the tissues and make repair more challenging.

Alternatively, the four nerves innervating the eyelids can be blocked: the frontal, lacrimal, and infratrochlear (all branches of the ophthalmic branch of cranial nerve V) nerves and the zygomatic (a branch of the maxillary branch of cranial nerve V) nerve can be blocked. The frontal nerve is most easily blocked as it courses through the supraorbital foramen located in the dorsolateral aspect of the orbital rim. The supraorbital foramen is located by the veterinarian placing the thumb under the ventral aspect of the dorsolateral orbital rim and using the index finger to palpate a distinct depression in the frontal bone. A 25-gauge 5/8-inch–long needle is inserted directly into the foramen, and 1 to 2 mL of local anesthetic is injected after aspiration to confirm extravascular needle location. Alternatively, 1 to 2 mL of local anesthetic is injected subcutaneously over the foramen, followed by gentle digital massage. The lacrimal nerve is blocked by injecting 1 to 2 mL of local anesthetic slightly medial to the lateral canthus, with the needle directed medially beneath the orbital rim. The infratrochlear nerve is blocked by injecting 1 to 2 mL of local anesthetic rostrocaudally beneath the orbital rim into the infratrochlear notch, which is palpable on the cranial surface of the dorsomedial aspect of the orbital rim. The zygomatic nerve is blocked by injecting 1 to 2 mL of local anesthetic along the lateral 2 cm of the ventral orbital rim. Additionally, the administration of topical anesthetic (proparacaine or tetracaine hydrochloride) will help desensitize the conjunctiva and cornea and decrease patient movement during the procedure.

Clipping is not required for many eyelid lacerations unless the hair of the eyelid skin is particularly long. Application of a water-soluble lubricant to the wound bed before clipping is recommended because it is easily rinsed, along with any clipped hairs, away from the wound. The cilia and vibrissae should be preserved whenever possible. The laceration site should be prepared with dilute (1 : 50) povidone-iodine solution. It is essential that solution, rather than scrub, is used because povidone-iodine scrub contains detergents that may cause significant ocular irritation and corneal ulceration. If the laceration is to be repaired with the horse standing, resting the sedated horse’s head at a comfortable level for the surgeon is recommended. A stack of hay bales covered with a tarpaulin makes a stable head stand, as would a tall trashcan with a flat lid.

Minimal instrumentation is required for an eyelid laceration repair (Table 147-1). The first step in laceration repair is to assess the laceration site and determine how to reappose the tissues. The wound edges can be gently debrided with a #15 blade in a scraping motion until fresh hemorrhage occurs. Amputating any eyelid tissue should be avoided because there is little redundant skin around the eyelids, and amputation of any tissue, particularly eyelid margin, will distort the eyelid. Tissue should only be excised if it is grossly necrotic, and then as minimally as possible.