Surgical CO2 laser corrects a common canine eye condition

    By Noel Berger DVM, MS, DABLS For The Education Center
    Originally Published In Veterinary Practice News, May 2018 –
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    Better surgical outcomes, faster surgical completion times, less postoperative pain and reduced operative bleeding are among the common benefits touted by CO2 laser surgeons. One such procedure that general practitioners commonly face is surgical correction of an inflamed gland of the nictitans, or “cherry eye.” It is not an emergency; however if left untreated, the patient can have chronic corneal irritation and a reduced visual field, in addition to an unsightly appearance that can be a concern for most pet owners (Figure 1). If improperly managed, removal of the inflamed gland will lead to keratoconjunctivitis sicca, or dry eye. The following description of a successful conjunctival burial of the gland using a CO2 laser to perform the procedure is a modification of Morgan’s (1993) pocket technique that has a reported 95 percent success rate.

    Surgical procedure

    Any dog can be affected by this condition; however there is a predilection for puppies and brachycephalic breeds. Commonly, pet owners request this unsightly malady to be repaired at the time of surgical sterilization; however, it is easily corrected at any age as long as the patient is a good candidate for anesthesia. Once anesthetized, minimal preparation is required, and I generally irrigate the eye with sterile saline to remove any mucus, debris, or other potential sources of contamination (Figure 2).

    To perform the procedure, I use a CO2 laser to make a circumferential incision around the markedly inflamed gland. Experienced practitioners will understand that when this procedure is initiated with a scalpel that appreciable bleeding is expected. That should not occur when a CO2 laser is used. The effect of CO2 laser light on capillaries smaller than 0.5 mm in diameter causes denaturation of capillary endothelial cells, constriction of their lumen, and “capping,” or sealing, of the vessels in a process called photothermolysis or coagulation. This is the basic mechanism of cauterization in free-beam mode that provides for a clean and dry incision made by a surgical CO2 laser.

    To guard against inadvertent exposure of the cornea to the 10.6 μm CO2 laser wavelength, I recommend covering the eye with a moistened and flattened piece of soft cotton or several layers of saturated soft gauze. Other commercially available eye shields can be purchased as well.

    It doesn’t matter if the incision begins medially or laterally as long as it transects a large supporting capillary seen coursing over the bulbar conjunctiva of the nictitans (Figure 3). This CO2 laser exposure should be made no more than one half the distance between the top of the gland and the protected globe. To make the first portion of the incision in a single pass, I use 2-4 W continuous wave with a 0.25-mm-diameter spot, behind the posterior aspect of the inflamed gland (Figure 4).

    To continue the incision around the anterior aspect of the gland (Figure 5), I often change the output mode of the CO2 laser to superpulse (SP). This provides for significantly reduced char formation due to the nature of this waveform. Although still using 2-4 W SP, the average amount of energy deposited into the tissue is reduced significantly, which results in more cutting effects and less burning effects. This is referred to as photovaporolysis, or the sudden vaporization of target tissue without causing excessive heat to nearby tissue that needs to be preserved.

    Once the incisions are made around the gland, the procedure is completed as described in the literature. The bulbar conjunctiva of the nictitans is undermined bluntly with iris scissors (Figures 6 and 7). The suturing begins from the palpebral conjunctiva laterally, through the nictitans. The incision is closed using 4-0 or 5-0 absorbable braided suture material, with a taper needle, in a continuous pattern, causing the gland to be tucked into a pocket made by the surgeon’s previous incision and undermining. A second row of an inverting continuous oversewing suture is then placed in the opposite direction. Bear in mind that excessive suture material can irritate the cornea, causing edema, ulceration, infection, and pain. It should be noted here that a clean and dry surgical field enhances surgical accuracy and reduces anesthesia time, which together improve patient outcomes. These features are possible only when a surgical CO2 laser is used instead of a scalpel. Additionally, the use of a CO2 laser reduces the amount of thermal necrosis at the surgical site compared to the use of electrocautery to complete the procedure.

    Postoperative care

    Following the procedure, I recommend the patient to be fitted with an Elizabethan collar or other suitable device to prevent self-mutilation. Additionally, an ophthalmic antibiotic ointment should be used twice daily for one week postoperatively. At a recheck appointment two weeks after the procedure, an examination should show complete healing of the bulbar conjunctiva and resolution of any tissue swelling. This is one more adaptation of a surgical CO2 laser used in an accepted surgical technique that improves upon existing surgical standards to provide even better patient care.

    This Education Center article was underwritten by Aesculight of Bothell, Wash., the manufacturer of the only American-made CO2 laser.