The results of the presurgical blood work (complete blood count and serum chemistry profile) were normal except for a mature
lymphocytosis (7.2 × 103/µl; normal = 1 to 4.8 × 103/µl) and an eosinophilia (2.4 × 103/µl; normal = 0.1 to 1.2 × 103/µl). Preoperative medications included atropine (0.04 mg/kg), acepromazine (0.01 mg/kg), and morphine (1 mg/kg) subcutaneously.
Anesthesia was induced with thiopental intravenously and maintained with isoflurane inhalation anesthesia. In preparation
for surgery, we flushed the eye with dilute povidone-iodine solution (1:50).
We used an eyelid speculum to open the palpebral fissure and used tenotomy scissors to incise the conjunctiva over the mass.
We then used the scissors to dissect through the tissues surrounding the mass. The mass seemed separate from the underlying
sclera but involved Tenon's capsule. We removed all apparently affected tissue. The mass seemed to peel out well, although
there was no distinct capsule. Two other nodules were adjacent to the gland of the nictitating membrane on the bulbar conjunctiva.
Three threadlike worms were adhered to these nodules but broke off as they were being extracted with Bishop-Harmon thumb forceps
(Figure 1). We also excised these nodules with tenotomy scissors and placed all excised tissues in formalin and submitted them for
histopathologic evaluation. Simple interrupted sutures of 7-0 polyglycolic acid were used to close the conjunctiva, and all
the knots were buried. We also evaluated the right eye for small nodules; none were found.
Figure 1: Surgical removal of a subconjunctival mass in a dog (not the dog in this case report) with ocular onchocerciasis.
The conjunctiva has been incised to help identify the type of parasite; the surgeon is removing a threadlike worm from the
mass. Photo courtesy of Dr. David Williams.
The dog's recovery from anesthesia was uneventful. The dog was discharged from the hospital, and the owners were instructed
to administer topical neomycin-polymyxin B-dexamethasone ointment in the left eye every eight hours. A follow-up examination
was scheduled for seven days later.
Diagnosis and treatment
The results of the initial histopathologic examination of the masses suggested that the parasite was a Thelazia species. Two days later, after consulting with a parasitologist, the diagnosis was changed to a parasitic episcleral mass
due to Onchocerca species. The submitted sample consisted of loose, vascular connective tissue surrounding a moderately well-demarcated, multilobular
granulomatous mass containing numerous nematode cross sections and free microfilariae (Figures 2 & 3). The nematode intestines were uniformly small, and gravid females contained both microfilariae and ova within the uteri
(Figure 2). The nematodes had thick cuticles with regularly spaced cuticular ridges overlying dorsal and ventral bands of coelomyarian
somatic musculature separated by elongated and flattened lateral cords (Figure 4); these features are characteristic of Onchocerca species.1,2
Figure 2 : A granulomatous mass containing numerous nematode cross sections (40X). The inset shows microfilariae (arrow)
within a section of uterus (hematoxylin-eosin stain; 100X).