Reprinted in IVIS with the permission of the AAEP Close window to return to IVIS HOW-TO SESSION How to Prepare for Ocular Surgery in the Standing Horse Brian C. Gilger, DVM, MS, Diplomate ACVO; and Michael G. Davidson, DVM, Diplomate ACVO Authors’ address: Equine Ophthalmology Service, College of Veterinary Medicine, North Carolina State University, 4700 Hillsborough Street, Raleigh, NC 27606. © 2002 AAEP. 1. Introduction Therefore, learning the correct and latest methods for performing standing ocular surgery will increase There are many advantages to performing standing a veterinarian’s ability to provide excellent service surgical procedures and avoiding general anesthesia without a major outlay of infrastructure expense. in horses. Horses with orthopedic or other medical Because the cornea and conjunctiva of the problems may be at higher risk to develop anesthe- horse’s eye are thin and delicate, ophthalmic sur- sia-related complications and should not undergo gery must be precise to avoid damage. The use of routine general anesthesia. Even healthy horses small instruments, needles, and sutures is gener- can injure themselves on recovery from general an- ally required. In most instances, the surgeon will esthesia and are predisposed to develop colic, cecal benefit from the use of magnification, which allows impactions, and myositis in the post-anesthetic pe- precise cutting of tissues and suture placement, riod.1–3 Standing surgical procedures can also de- but exaggerates patient movement when the horse crease the time needed for hospitalization compared is not anesthetized. To perform ocular microsur- with horses receiving general anesthesia. This is gery, the eye must be immobile. In general, the advantageous because hospitalized horses, in gen- use of microsurgical technique and magnification eral, are predisposed to developing pneumonia, sal- during equine ocular surgery requires general an- monellosis or other forms of colitis, and laminitis.4,5 esthesia. However, with appropriate tranquil- Furthermore, with decreased hospitalization time ization, ocular nerve blocks (especially the and fewer anesthesia-related complications, there is retrobulbar nerve block), and restraint, many oc- decreased cost to the horse owner. For the veteri- ular surgeries can be performed adequately in narian, advantages of standing surgical procedures standing horses. include less technical support required, less cost The purpose of this paper is to describe the equip- incurred, less time required, and decreased need for ment needed and technique for performing ocular surgical and anesthetic equipment and facilities. surgical procedures in the standing horse. NOTES 266 2002 ր Vol. 48 ր AAEP PROCEEDINGS Proceedings of the Annual Convention of the AAEP 2002 Reprinted in IVIS with the permission of the AAEP Close window to return to IVIS HOW-TO SESSION Table 1. Ocular Surgical Procedures that May Be Done in a Standing Horse Adnexal Corneal Intraocular ● Small eyelid mass removal ● Corneal scraping for cytology ● Aqueocentesis ● Eyelid mass biopsy ● Ulcer debridement ● Intraocular injection (i.e., TPA) ● Eyelid lacerations—small ● Grid keratotomy ● Iris cyst laser ablation ● Conjunctival biopsy ● Superficial keratectomy—small ● Laser cyclophotocoagulation for glaucoma ● Third eyelid laceration repair ● Suture of non-perforating ● Intraocular mass laser ablation ● Third eyelid mass removal or biopsy corneal laceration ● Removal of superficial corneal foreign body 2. Materials and Methods Palpebral and Frontal Nerve Blocks Indications—Ocular Surgical Procedures that May Be To minimize eyelid movement and sensation of the Done in a Standing Horse upper eyelid, palpebral and frontal nerve blocks should be done. The palpebral nerve is a branch of With appropriate tranquilization, ocular nerve the facial nerve that controls the motor activity of blocks, and restraint, many short-duration ocular the upper orbicularis oculi muscle, which controls surgical procedures can be done in the standing upper eyelid function. To adequately block the pal- horse (Table 1). In general, these are procedures b involving the eyelids, conjunctiva, and cornea (tu- pebral nerve, 2 ml of 2% lidocaine HCl is injected mor removal, keratectomy, eyelid laceration, third SC along the dorsal zygomatic arch (Fig. 1). The eyelid removal) that take less than 30 min to per- frontal nerve is the branch of the trigeminal nerve form but do not include perforating lesions of the that provides sensory innervation to the medial two- cornea (or lesions pending perforation—such as cor- thirds of the upper eyelid. To block the frontal neal descemetoceles or infected deep corneal ulcers) nerve, 1 ml of 2% lidocaine HClb is injected over the or intraocular surgical procedures such as cataract opening to the supraorbital foramen (Fig. 2), in surgery. However, minimally invasive intraocular which the frontal nerve exits. The frontal nerve procedures such as iris cyst laser disruption,6 laser block also denervates branches of the palpebral cyclophotocoagulation,7 and anterior chamber cen- nerve and thus helps to decrease upper eyelid motor tesis can be performed adequately with the horse activity; therefore, a combination of both the palpe- standing. bral and frontal nerve block provides an excellent Standing surgical procedures should be performed denervation to the upper eyelid resulting in minimal in a specific order. Supplies should first be gath- eyelid movement. ered, equipment should be set up, the horse should be tranquilized, eyelid nerve blocks performed, the retrobulbar nerve block area prepared aseptically and performed, the eye surgically prepped, topical Table 2. Equipment and Supplies Needed for Standing Ophthalmic Surgical Procedures in the Horse anesthetics and vasoconstrictors applied, and finally the surgery should be performed. General Equipment Medications ● Syringes: 1, 3, and 12 cc ● 2% Lidocaine HCl Supplies and Equipment Needed ● 25-gauge needles ● 1% Proparacaine All supplies and equipment should be gathered and ● 22-gauge 2.5-in spinal ● 2.5% Phenylephrine be accessible before positioning the horse. A list of needle ● Tranquilizer supplies is provided in Tables 2 and 3. It is also ● Ocular surgical preparation ● Eye lubrication ointment recommended that the standing procedure be per- (Betadine scrub and formed in stocks to protect the surgeon and solution) ● assistants. Eye wash ● Clean clippers ● Sterile surgical gloves Tranquilization ● Scalpel blades The best tranquilizer for ophthalmic procedures in ● Sterile cotton-tipped the horse is detomidine HCla (0.01–0.02 mg/kg IV). applicators This medication has a rapid onset and is effective for ● Sterile gauze 30–45 min. The major advantage of this drug is ● Kimura spatula* ● Glass slides* that, during its effect, the horse’s head remains still ● and does not tremor. Use of xylazine and/or butor- Culture tubes and/or plates* ● Formalin* phanol should be avoided because each causes head movement and exaggerated response to stimuli. *Needed depending on type of procedure. AAEP PROCEEDINGS ր Vol. 48 ր 2002 267 Proceedings of the Annual Convention of the AAEP 2002 Reprinted in IVIS with the permission of the AAEP Close window to return to IVIS HOW-TO SESSION Table 3. Basic Ophthalmic Surgical Instrument Pack Surgical Equipment Disposable Surgery Supplies Surgical Magnifying Loupes ● Bishop Harmon forceps ● 6-0 or 7-0 Vicryl or Dexon ● Keeler Loupes on a headmount 1 over 2 tissue forceps on ophthalmic spatula ● Zeiss Prism Loupes on a headmount 0.8-mm teeth needles (4ϫ with 450-mm working distance) ● Derf needle holder ● 4-0 or 5-0 Monofilament on ● Microsurgical needle holder—Barraquer an ophthalmic cutting curved, without lock needle (nylon, surgilene, 9–11 mm with medium or fine jaw prolene, etc.) ● Stevens tenotomy scissors—curved ● Blades: ● Eyelid speculum—Castroviejo or Guyton-Park #64 Beaver blades 14- to 16-mm blades) #15 Bard-Parker blades ● Beaver blade handle ● Irrigating solution ● Bard Parker blade handle Fig. 1. Palpebral nerve block in the horse. A: Location of palpebral (top white marker) and frontal nerve (bottom white marker) blocks in the horse. B: Two milliliters of 2% lidocaine HCl is injected SC along the dorsal zygomatic arch to block the palpebral nerve, which controls the motor activity of the upper orbicularis oculi muscle. Retrobulbar Nerve Block prepped, a 22-gauge, 2.5-in spinal needlec is placed The orbital fossa above the dorsal orbital rim and through the skin perpendicular to the skull in the zygomatic arch is first clipped and aseptically orbital fossa, just caudal to the posterior aspect of prepped with Betadine scrub and alcohol (Fig. 3). the boney dorsal orbital rim. The needle is ad- Care must be taken to avoid getting surgical scrub vanced caudally to the globe until it reaches the or alcohol on the ocular surface because severe irri- retrobulbar orbital cone. When the needle ad- tation and corneal ulceration may develop. Once vances to this location, the eye will have a slight 268 2002 ր Vol. 48 ր AAEP PROCEEDINGS Proceedings of the Annual Convention of the AAEP 2002 Reprinted in IVIS with the permission of the AAEP Close window to return to IVIS HOW-TO SESSION Fig. 2. Frontal nerve block in the horse. One milliliter of 2% lidocaine HCl is injected SC over the opening to the supraorbital foramen, from which exits the frontal nerve, a branch of the trigeminal nerve. This blocks sensory innervation to the medial two-thirds of the upper eyelid. dorsal movement as the needle passes through the