Diagnostic Ophthalmology

History and clinical signs

A 6-year-old, neutered male miniature poodle dog was referred to the ophthalmology service at the Western College of Veterinary Medicine (WCVM) for evaluation of acute blindness. The neuro-ophthalmologic examination revealed absent menace responses bilaterally with normal pupillary light, palpebral, and oculocephalic reflexes. Schirmer tear test (Schirmer Tear Test Strips; Alcon Canada, Mississauga, Ontario) values were 21 and 19 mm/min in the right and left eyes, respectively. The intraocular pressures were estimated with a rebound tonometer (Tonvet; Tiolat, Helsinki, Finland) and were 11 and 13 mmHg in the right and left eyes, respectively. Fluorescein staining (Fluorets; Bausch & Lomb Canada, Markham, Ontario) was negative bilaterally. The pupils were dilated with 0.5% trop-icamide (Mydriacyl; Alcon Canada, Mississauga, Ontario) and biomicroscopic examination (Osram 64222; Carl Zeiss Canada, Don Mills, Ontario) and indirect ophthalmoscopic (Heine Omega 200; Heine Instruments Canada, Kitchener, Ontario) examinations were completed bilaterally. Biomicroscopic examination was within normal limits, bilaterally, and fundic photographs are provided for your assessment (Figure 1).

Figure 1.

Photographs of the right and left fundi of a 6-year-old miniature poodle.

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Discussion

The ophthalmic diagnosis was bilateral complete rhegmatogenous retinal detachments with vitreal degeneration. In the clinical photographs (Figure 1) the retina is hanging ventrally in the vitreous over the optic nerve head due to a giant dorsal peripheral retinal tear at the ora ciliaris retinae. The grey membrane is the neurosensory retina hanging from and obscuring direct visualization of the optic nerve head. A physical examination, complete blood (cell) count (CBC), serum biochemical profile, urinalysis, and blood pressure measurements were performed and no abnormalities were noted. Routine chest radiographs were also performed and were unremarkable. Bilateral vitrectomy with retinal reattachment surgery was recommended but declined by the owner. Annual examinations to monitor for inflammation secondary to the retinal detachments were recommended and 6 mo following initial presentation the dog re-presented to the WCVM for blepharospasm and hyphema in the left eye. Due to the presence of discomfort and chronic uveitis in the face of blindness, evisceration and placement of an intrascleral prosthesis was performed on the left eye with continued annual examinations for the right eye.

Retinal detachments occur as the neurosensory retina separates from the underlying retinal pigment epithelium (RPE). They can develop in one of 3 ways: i) exudative, in which effusions, exudations, or solid accumulations of cells push off the neurosensory retina; ii) rhegmatogenous retinal detachments, in which a tear or hole in the retina causes disinsertion allowing liquefied vitreous to accumulate under the tear; and iii) traction detachments, in which proliferation of pre-retinal (i.e., vitreal) membranes pulls the neurosensory retina away from its underlying RPE (1). Causes of retinal detachment are variable and include infectious disease (including bacterial, rickettsial, and mycotic infections), systemic hypertension, trauma, and congenital ocular disease (1). Rhegmatogenous retinal detachments are most common in the shih tzu, whippet, and Italian greyhound breeds in which a primary vitreal degeneration and liquefaction predisposes to peripheral retinal tears and sudden, total detachment. The diagnosis of rhegmatogenous retinal detachment is confirmed by ophthalmoscopic examination unless opacification of the anterior segment (cornea, anterior chamber, lens) precludes fundic examination. In such cases ultrasonographic examination can often confirm the diagnosis. Ophthalmic examination by a veterinary ophthalmologist is often helpful in confirming the diagnosis. Further diagnostic testing in cases of retinal detachment should include a systemic work-up consisting of a physical examination, CBC, serum biochemical profile, blood pressure, urinalysis, and chest radiographs to rule out any systemic disease resulting in the retinal detachment. In this particular case all diagnostics were within normal limits. Vitreal degeneration and liquefaction resulting in vitreal traction bands and a retinal tear were the suspected cause of retinal detachments.

Complete rhegmatogenous retinal detachment results in blindness in the affected eye(s). Once the retina is detached there is rapid degradation of the photoreceptors when they are detached from the RPE. The recommended treatment in cases with rhegmatogenous retinal detachments is vitrectomy with retinal reattachment surgery. In such cases, reattachment surgery is the patient’s only chance to restore vision. The duration of the retinal detachment is important in predicting any anticipated return of vision but in animals, the timeline of events is often unknown. This case presented with a history of acute bilateral blindness; however, it is important to note that in many cases of bilateral rhegmatogenous retinal detachments the detachments do not happen simultaneously in both eyes. Astute owners may notice acute unilateral vision loss in their pet; however, most cases presenting with acute bilateral retinal detachments have one retina that has been detached long-term and it is only when the retina detaches in the fellow eye that the owner is aware of a visual disturbance (2). It has been demonstrated that if the retina is reattached within 4 wk, there is a reasonable chance of return of some functional vision (3). Obviously, the sooner the repair, the better the odds of good vision.

Without surgical correction, chronic retinal detachments release vascular endothelial growth factors, which induce vascular membranes that predominate on the anterior and posterior iris surfaces and extend into the vitreous. These membranes are fragile, and often leak serum and blood, resulting in chronic uveitis and secondary glaucoma (4). In cases of chronic retinal detachment there is a 90% chance that a dog will develop secondary complications such as chronic uveitis and secondary glaucoma within the animal’s lifetime (4). In this particular case, the dog developed hyphema and pain from chronic uveitis necessitating an evisceration and intrascleral prosthesis in the left eye 6 mo after initial presentation. Owners with dogs suffering from retinal detachment who are unable to arrange for surgical correction should be made aware of the risk of secondary complications necessitating enucleation or evisceration. Annual complete ophthalmic examinations including Schirmer Tear Tests, intraocular pressures, and fluorescein staining are recommended in patients affected with chronic retinal detachment.