Surgical Techniques

There are a number of ocular conditions faced by both large and small animal veterinarians that require surgical intervention to prevent serious ocular dysfunction, blindness, or loss of an eye. They include conditions of some urgency, such as descemetoceles or corneal lacerations, as well as more routine clinical conditions, such as entropion or lid tumor removal. This handout will concentrate on some general principles of ophthalmic surgical instrumentation and technique, as well as brief descriptions of selected surgical procedures involving the eyelids, nictitans, conjunctiva, and cornea.

Ophthalmic Surgical Instrumentation

For most ocular surgeries, including those dealing with emergency situations, a small number of general purpose ophthalmic instruments will suffice. As the complexity of the procedure increases, the need for instruments with very specific functions increases. Additionally, surgeries requiring handling, cutting and suturing of the cornea or intraocular structures require specific microsurgical instruments to prevent undue trauma of the ocular tissues. Finally, for many of these procedures some sort of magnification is beneficial, and for some it is essential.

Magnification

• Plastic head loupes (or “Optivisors’) are quite adequate. They are inexpensive, and some come with multiple lens systems for different degrees of magnification. Three to five times mag is needed for most procedures. Some practice is required to work under magnification as the surgeon’s proprioceptive responses are altered by the altered visual environment. Also, as magnification increases the depth of field decreases, further compounding the difficulty working under high magnification.
• Spectacle mounted lenses (e.g., Keeler glasses or Zeiss-Gullstrand glasses) offer much improved optics and superior visualization, but are much more expensive.
• At the top of the magnification line are operating microscopes. Modern scopes contain optical and lighting combinations that can’t be approached by other means of magnification, but they exceed the cost of even spectacle mounted lenses many-fold.

Forceps

• Bishop Harmon - General purpose; grasping lids; can get with fine teeth for conjunctival and corneal work.
• Colibri or McPherson - Two types of corneal forceps. Light, well balanced and have delicate teeth for grasping cornea. Very helpful in corneal laceration repair and placement of conjunctival grafts that require suturing directly to cornea. They can be purchased with a “tying platform,” a flattened area behind the teeth which is used for grasping and tying fine suture materials. These forceps can also be used for manipulating the conjunctiva.

Scissors

• Stevens’ tenotomy scissors - Veterinary ophthalmic surgeons use these as general purpose scissors when cutting conjunctiva. The tips of both arms are blunted, and they are available in straight or curved models. These scissors should only be used on conjunctiva, never on skin.
• Wescott tenotomy scissors - Same general description as Stevens’, but have a springed mechanism.

Needle holders

• For suture sizes 6-0 and larger, a small pair of conventional needle holders are recommended. For sizes 7-0 and smaller, which are usually recommended for suturing cornea, special microsurgical needle holders are needed to offer proper control of the needle, to assist in grasping and tying suture, and to prevent bending the small needles. There are several varieties available that differ in only minor respects. Most are available in either locking or non-locking varieties.
  • Castroviejo
  • McPherson
  • Barraquer
  • Troutman

Eyelid Specula

• For keeping the lids out of the surgical field when operating on cornea or conjunctiva.
• Barraquer - A light, inexpensive wire speculum that is quite adequate for most procedures; only drawback is that retraction power can’t be increased beyond the tension inherent in the wire.
• Castroviejo (and similar models) - Have retraction jaws that are parted by twisting a threaded mechanism. Advantage is increased traction power, disadvantage is increased weight.

Miscellaneous

• Muscle or “Strabismus” Hooks - While intended for isolating extraocular muscles, these instruments are valuable in veterinary ophthalmology for general purpose retraction and probing.
• Cyclodialysis spatulas - Useful for replacing prolapsed iris into the anterior chamber.
• Lacrimal cannulas (23 - 27 gauge) - Useful for reinflating the anterior chamber following corneal laceration / perforation repair.
• Cellulose spears (e.g., Weck Spears) - For blotting blood and other fluids out of the surgical field when the interior of the eye is exposed. Unlike cotton tipped applicators, cellulose spears will not leave microscopic cotton fibers in the eye to act as an inflammatory nidus.

General Principles

• Positioning - Not so critical for procedures of the lids and nictitans, but for corneal surgery this is a major key to a successful surgery. Placing animals in dorsal recumbency and placing the neck in flexion so that the plane tangential to the corneal axis is horizontal makes for the best exposure. In this position, however, it is important to remember that the tight bend placed on the endotracheal tube may kink it; an armoured tube should be used to prevent this complication.
• Surgical prep - In most instances eyelid hair should be clipped and the lashes trimmed. A 10:1 dilution of Betadine solution (not scrub) can safely be used to irrigate the lids, conjunctiva and cornea. Three applications to each surface separated by a flush with sterile saline (not alcohol) are adequate. The final application of Betadine should be followed by a thorough sterile saline flush to make certain all traces of betadine have been rinsed away. If there is a full thickness corneal or scleral wound, prep the cornea with sterile saline only as betadine solution can cause uveitis if it gets inside the eye.
• Draping - A non-fenestrated clear plastic adhesive drape (e.g., Steri-drape®, 3-M) or Huck towels may be used as the initial drape. We prefer to follow this with a 20" X 20" cloth drape with a 2-3 inch diameter round, hemmed, centrally placed fenestration. This drape is clamped into place and a slit is cut in the plastic drape over the surgical field. A large area drape may then be placed over the entire surgical field to prevent contamination during instrument passage.

Tissue handling

• Any time ocular tissues are being manipulated, sutured, cut, etc., the surgeon should be seated with his/her arms resting on chair mounted arm supports or on the edge of the surgery table.
• Eyelids - The edge of a lid laceration or incision should be handled as little as possible to avoid induction of excessive swelling and loss of proper anatomic orientation.
• Conjunctiva - The conjunctiva should only be handled with lightweight forceps; if using toothed forceps, they should have delicate teeth to avoid unnecessary tearing of this fragile tissue. Remember that the conjunctiva itself is very thin; the bulk of the tissue superficial to the sclera is Tenon’s capsule and other fibrous tissue, which must be dissected away from the conjunctiva for most conjunctival grafting techniques.
• Cornea - Should only be handled with forceps made for this purpose. Never grasp the full thickness of the cornea, as the “underside” arm of the corneal forceps will abrade the corneal endothelium. Similarly, whenever an instrument is introduced into the anterior chamber (for example, a spatula for breaking down synechiae or removing fibrin clots associated with a corneal perforation) care must be taken not to let the instrument contact the endothelium. When the cornea is being manipulated, the surgeon’s eyes should never stray from the cornea. If one attempts to look away even for an instant (to locate another instrument on the Mayo stand, for instance), the hand holding the corneal forceps will invariably shift a small amount which could result in corneal damage. When placing corneal sutures, the needle should be driven with a rolling motion of the fingers, not gross movements of the wrists as in other suturing techniques. Most other instruments applied to the cornea should also be manipulated with finger movements. Finally, the cornea should be moistened periodically with a LRS or BSS irrigation solution to prevent dessication, which can occur rapidly when the lids are held open under hot surgical lights.

Sutures

• Sizes - Conjunctiva and lids are usually best sutured with 5-0 or 6-0. 7-0 is the largest suture that should be used in the cornea, with 8-0 and 9-0 being the preferred sized for corneal work. The optimal suture for many corneal procedures is 10-0, but special microsurgical instruments (beyond the capabilities of the forceps and needle holders described above) are usually needed to handle material of this size.
• Materials
  • Braided absorbables - e.g., Polyglactin 910 (Vicryl®) or Polyglycolic acid (Dexon®). These materials can be used in lids, conjunctiva or cornea. In lid surgeries it is best to use a braided material if there is a danger of the suture ends rubbing across the cornea (e.g., entropion surgery).
  • Monofilament nonabsorbables - e.g., Nylon (Ethilon®) or polypropylene (Prolene®). Very good material for cornea and lids, as it is considerably less reactive than polyglactin or PGA; however, it needs to be removed and removal of these small materials can be difficult, especially from the cornea (it should be pointed out that, in selected circumstances, nylon can be left in the cornea indefinitely if 8-0 or smaller with special knotting). In lid surgeries it is best to use a monofilament material if there is a danger of the shaft of the suture rubbing across the cornea (e.g., temporary tarsorrhaphy).
• Needles - For work on lids, conjunctiva or cornea, a cutting needle or some variant of a cutting needle (e.g., micro-point, spatula, or micro-point spatula) is preferred. All of these tissues contain a significant connective tissue component, so that tapered needles as small as those swaged onto ocular surgery suture material will often bend and not drive properly. Much of the ophthalmic suture material on the market is available double armed. It is best to use double armed suture because these small needles become dull quickly, and it is more efficient and cost effective to have a new needle available without having to open another package of suture material.

Surgical Procedures of the Eyelids

Entropion

• Most commonly seen in Chow Chows, Shar Peis, English Bulldogs, Rottweilers, and retriever breeds.
• The severity of the clinical signs depends on the severity of the entropion, and can range from mild blepharospasm and epiphora to chronic corneal ulceration.
• The majority of cases respond well to a simple removal of a crescent shaped piece of skin adjacent to the affected area (the “modified Holz- Celsus” procedure).
  • The first incision is 2.5-3 mm from and parallel to the lid margin. The haired/non-haired junction is a good landmark, as it is about 1.5-2 mm from the margin. This is facilitated by use of a lid plate.
  • The second incision connects the medial and lateral extents of the first in a crescent shaped fashion, and the intervening piece of skin is removed. The amount of skin removed varies and depends on the severity of the entropion. For beginners, a 5 mm width will often prove effective.
  • The incisions are then sutured in a simple interrupted pattern, thus everting the offending lid away from the cornea. The first suture should be in the middle of the crescent with subsequent sutures bisecting the remaining incision.

Lid Tumor Removal

• Most tumors of the eyelids are benign, but can interfere with lid function if large enough. Therefore removal is often indicated.
• The most useful technique for tumor removal is the full thickness wedge resection.
  • An imaginary triangle is outlined around the tumor, with the lid margin serving as the base of the triangle. The length of the base and sides should be adequate to allow for 1-2 mm of grossly normal skin all the way around the tumor.
  • Incisions for the sides of the triangle are made full thickness through the eyelid, and should include the skin, orbicularis oculi muscle, tarsus, and conjunctiva using a #15 blade. This is facilitated by use of a lid plate.
  • The eyelid stroma (the tissue between the conjunctiva and the skin; includes orbicularis muscle and tarsus) is closed in a simple continuous pattern or several interrupted sutures beginning at the apex of the wedge. Use care to prevent perforation of the conjunctiva with the suture as the suture would abrade the cornea.
  • The skin is closed, starting with a figure-8 suture at the lid margin and progressing toward the apex of the wedge with simple interrupted sutures.
  • A topical antibiotic/corticosteroid preparation may be applied 3 times a day for 5 days.
• If the tumor is large, a pentagonal resection can be performed in a manner similar to that just described, but the pentagonal shape will allow for wider surgical margins .
• In either technique, placement of the figure-8 suture at the margin is critical to assure a smooth margin, thus preventing postoperative cicatricial entropion.
• If the tumor is large enough to require removal of more than 1/3 the length of the lid in a large-fissured dog (e.g., Cocker Spaniel) or 1/4 the lid length of a cat or tight-fissured dog (e.g., Schnauzer), more extensive blepharoplastic procedures are required.

Lid Laceration

• Always inspect the globe for damage.
• Primary closure always advised to prevent exposure keratitis and/or cicatricial entropion.
• Frequently presents as an “L” shaped tear with one arm perpendicular to the lid margin and the other along the base of the tarsus.
• The sooner the lacerated flap is replaced, the less tissue devitalization. Even if considerable time has passed between injury and repair, the flaps will often heal with primary intention due to excellent conjunctival and palpebral vascular supply.
• Wounds should be checked thoroughly for embedded foreign material, then rinsed well with physiological saline. If the wound is more than 24 hours old, it should be considered infected and cultured. If less than 24 hours, it should be considered contaminated.
• Broad spectrum perioperative antibiotics are always indicated, with postoperative antibiotics being used as well if the wound is infected.
• Flush the wound with a 8:1 dilution of Betadine solution, then re-flush with saline.
• Full thickness wounds should be closed in 2 layers: subconjunctival and skin. Most often no debridement is necessary; however, when it is needed minimal debridement should be done.
  • Subcutaneous/stromal layer is simple continuous or interrupted pattern. Start suture at point farthest from the lid margin. Suture throws should be parallel to the skin surface and should not penetrate the conjunctiva. Final throw should result in good margin-to-margin apposition with the knot buried away from the margin and away from the conjunctiva.
  • For skin sutures, always start with the marginal suture. A figure-8 suture results in good apposition and leaves the knot away from the cornea. If the wound is in the canthal area, however, the figure-8 pattern should be avoided as it results in rolling in of the lids. In this instance a horizontal mattress may be used. Subsequent sutures are simple interrupted. Good margin-to-margin apposition is the single most important step in this procedure to help prevent post- operative keratitis.
  • If the wound is in the area of the medial canthus, the nasolacrimal puncta should be identified and the integrity of the canaliculi verified. If torn, the canaliculi should be cannulated with a 2-0 or 3-0 monofilament suture or small bore polyethylene tubing. This cannula should be drawn out of the nostril if possible and secured to the skin at both ends. The wound is then closed as described above, and the cannula is removed in 3-4 weeks. A topical antibiotic/corticosteroid solution is used to help maintain potency of the duct.

Surgical Procedures of the Cornea

• Lamellar Keratectomy
  • Common indications for lamellar keratectomy include corneal neoplasia, feline corneal sequestration, and corneal dermoids. Less common indications include dense corneal pigmentation and indolent corneal ulceration.
  • The lesion to be excised is identified and the perilesional surgical margin is determined.
  • Proper magnification is very helpful for this procedure. - A #15 scalpel blade on a Bard-Parker handle or a #64 Beaver ophthalmic scalpel is used to incise the cornea around the lesion.
  • Attaining proper depth of the outlining incisions requires some degree of practice, as determination of depth is more tactile than visual.
  • Once the outlining incisions have been completed, one of the incised edges is grasped with a corneal forceps and elevated. Either the scalpel blade or a spatula is inserted between the elevated flap and underlying corneal stroma in a tangential fashion and used to undermine the lesion.
  • This process is continued until the lesion has been removed.
  • In severely diseased corneas, neovascularization may result in bleeding, thus obscuring the surgeon’s view. In these cases topical application of phenylephrine or epinephrine during the procedure may be helpful, as will frequent lavage of the surgical field with balanced salt solution and blotting with sterile cotton tipped applicators.
• Conjunctival Graft
  • Medical therapy may be attempted initially in treatment of MMP-type ulceration. If the ulceration continues to progress rapidly despite medical therapy, or if descemetocele formation or perforation has already occurred, immediate surgical intervention is indicated.
  • All such ulcers should be cultured and aggressive antibiotic therapy (i.e., every 1-2 hours) instituted if indicated.
  • The most useful surgical technique for these cases is conjunctival grafting, of which several varieties are available. These grafts not only provide much needed structural support, they also provide a healthy blood supply to promote healing and several serum anti-collagenase compounds (e.g., alpha-2 macroglobulin and alpha-2 antitrypsin) to retard corneal melting. In all varieties of conjunctival grafting an attempt should be made to harvest only the thin conjunctiva, as adherent Tenon’s capsule will result in graft retraction 2-3 days postoperatively. The bed of the ulcer should be gently scraped with a scalpel blade to ensure that all epithelium has been denuded from its surface. This will help promote graft retention. Also, all necrotic and malacic corneal stroma should be removed. Six to eight weeks following graft placement, the graft is incised at its limbal attachment and at the edge of the ulcer (this does not apply to island grafts or the corneoconjunctival transposition). The graft will have adhered over the ulcer. Some advocate therapy with topical steroids at this point, to accelerate reduction in scar tissue, but the ultimate degree of scarring will probably be the same with or without the use of steroids.
  • Pedicle graft (see Figure 6A/B). Can be used for essentially any ulcer except those that occupy a large portion of the cornea (i.e., approximately 75% of the diameter of the cornea) or those that are melting so rapidly that the sutures would be in danger of dehiscence.
    • The diameter of the area to be covered is determined, as this will determine the width of the pedicle (Figure 6A).
    • In most cases it is easiest to harvest the conjunctiva from the lateral aspect of the globe. An incision using tenotomy scissors is made in the conjunctiva perpendicular to the limbus leaving about 1 mm of conjunctiva at the limbus then extending the incision the width of the lesion plus 3 mm to allow for tissue contraction. For a centrally located lesion on the right eye, this incision is begun at the 9 o’clock position.
    • The incised conjunctival edge is grasped with a fine forceps and tenotomy scissors are used to undermine and thin the conjunctiva dorsally.
    • A 2nd incision is then made from the lateral extent of the first incision and extended dorsally. This incision should extend to a point tangential to the lateral edge of the ulcer. The pedicle should be hinged dorsally in most cases.
    • A 3rd conjunctival incision is made parallel to the limbus and 1 mm peripheral to it; this incision also begins at the 9 o’clock position, but is continued dorsally to a point tangential to the medial edge of the lesion.
    • The pedicle is then rotated down over the lesion and sutured to the edge of the lesion. If the lesion being covered is a melting ulcer, the necrotic edges should be debrided to healthy cornea so that there will be a healthy edge on which to suture. Simple interrupted sutures should be placed every 1-2 mm all the way around the lesion (Figure 6B). If perforation has occurred, an additional suture should be placed through the rotated arm of the pedicle, taking care not to place the suture in such a location that major blood vessels are ligated. If this “pedicle arm” suture is needed, it is usually easiest to place it first. The precise location of the pedicle can be altered from the scenario above in order to facilitate conjunctival harvesting. However, the final direction of the pedicle should not stray from the vertical for more than 45° or blinking will tend to encourage dehiscence of the pedicle. Also, for very large lesions, placement of a temporary lateral tarsorrhaphy will help prevent dehiscence; this can be taken down in one to two weeks.

Temporary Tarsorrhaphy

A tarsorrhaphy is used to protect the eye. It is most frequently used in horses but is indicated in small animals with exophthalmic eyes. It is used to prevent corneal exposure and protect the cornea after surgery in exophthalmic dogs and horses and to replace a proptosed globe. It can be partial or complete. Usually a space is left medially to allow globe visualization and to allow for application of medications.