Diagnostic Ophthalmology

History and clinical signs

An 8-year-old spayed, female Llasa apso dog was referred to the ophthalmology service at the Western College of Veterinary Medicine because of blindness. The menace responses were negative and the dog failed photopic and scotopic maze tests. The direct and consensual pupillary light reflexes, palpebral, and oculocephalic reflexes were present in both eyes. Schirmer tear tests (Schirmer Tear Test Strips; Alcon Canada, Mississauga, Ontario) were 28 and 23 mm/min in the right and left eye, respectively. The intraocular pressures, estimated with a rebound tonometer (Tonovet; Tiolat Oy, Helsinki, Finland), were 25 mmHg bilaterally. The pupils were dilated with tropicamide (Mydriacyl; Alcon Canada, Mississauga, Ontario), and biomicroscopic (Osram 64222; Carl Zeiss Canada, Don Mills, Ontario), and indirect ophthalmoscopic (Heine Omega 200; Heine Instruments Canada, Kitchener, Ontario) examinations were completed. Abnormalities were limited to the posterior segments bilaterally and fundic photographs (Kowa RC2, Kowa, Japan) are provided for your assessment (Figure 1). Fluorescein stain (Fluorets; Bausch & Lomb Canada, Markham, Ontario) was applied and rinsed from the corneal surfaces and the surfaces of both eyes were examined under cobalt filtered light and staining was negative.

Figure 1.

The fundic photographs of the right and left eyes of an 8-year-old Llasa apso dog.

What are your clinical diagnoses, diagnostic and therapeutic plans, and prognosis?

Discussion

Our clinical diagnoses were bilateral rhegmatogenous retinal detachments with giant retinal tears. There are multiple right vitreous hemorrhages, and the left retina is hanging over the optic nerve, as that the retina is torn completely off the ora ciliaris. A physical examination, complete blood (cell) count, and urinalysis were advised and completed. The systolic and diastolic blood pressures were assessed, and routine chest radiographs were completed. No abnormalities were noted in any of these diagnostic evaluations. Repeated indirect ophthalmoscopic examinations documented vitreous degeneration and vitreous traction bands. Bilateral vitrectomies were advised and completed, and the retinas were reattached surgically in a fashion similar to that used in previous references (1–3). The dog was treated with prednisone (Apoprednisone; Apotex, Toronto, Ontario), 1 mg/kg, PO, for 1 wk. The dosage was reduced gradually over 3 wk, and then it was discontinued. Both eyes were treated topically with ciprofloxacin (Ofloxacin; Pharma Science, Montreal, Quebec) for 3 wk. No complications were noted, and vision was restored within 1 mo based on the ability of the dog to traverse a maze and find its favorite toys.

Rhegmatogenous retinal detachments with giant retinal tears commonly develop secondary to fibrous vitreous traction bands (1). These traction bands form secondary to vitreous inflammation and vitreous degeneration, and a variety of etiologies have been incriminated including trauma (1). The diagnosis is confirmed by ophthalmoscopic examination unless opacification of the cornea, anterior chamber, and lens, preclude posterior segment examination. In that instance, an ultrasonographic examination will confirm the diagnosis (4). Complete retinal detachment induces blindness in the affected eye. To restore vision, a surgical vitrectomy and reapposition of the retina to the retinal pigment epithelium is required (1). This has recently become a vision restoring surgical procedure in dogs (1–3). The prognosis for restoring vision is good, provided that the retinal degeneration, which is progressive from the time of detachment until surgical attachment to the retinal pigment epithelium, has not destroyed the entire outer retina (3). Determining the precise time of detachment of the first eye is difficult in the dog (3). Generally, the earlier the retina is reattached the better the visual prognosis, and reattachment within a month of detachment is preferable. The presence of a brisk pupillary light reflex in an eye with a complete retinal detachment and a giant retinal tear is considered by some to be a useful indicator of a potentially viable retina (1). However, most chronically detached retinas maintain a pupillary light reflex in our experience (3). The degeneration of a detached retina is progressive and begins initially within hours of detachment as a wave of apoptosis spreads across the outer nuclear layer. After several weeks, the outer and inner segments of the photoreceptors atrophy, and the entire outer retina will eventually degenerate including the outer nuclear and plexiform layers and the inner nuclear layer as well. The apoptosis and degeneration are related to the sudden loss of nutrient supply from the choroid as the photoreceptors detach from the retinal pigment epithelium. However, the proximity of the outer retina to the retinal pigment epithelium varies, and the nontapetal or ventral retina is generally closer to this important epithelial layer. Therefore, the ventral retina may not degenerate as quickly as the dorsal retina during complete detachments (3). Chronic retinal detachments release vascular growth factors during degeneration and these induce vascular membranes that predominate on the anterior and posterior iris surfaces and extend into the vitreous. These membranes are common in chronic retinal detachments in dogs and the capillaries are fragile; they leak serum and blood, and induce uveitis and often secondary glaucoma (3).