What are your diagnoses, and therapeutic recommendations?

History and clinical signs

A 1-year-old, female English springer spaniel was examined at a Canine Eye Registration Foundation (CERF) clinic. The owner had noted anisocoria; and the right pupil was larger than the left. Findings on neuro-ophthalmic examination were normal, except for an absent right menace reflex. Biomicroscopic (Osram 64222; Carl Zeiss Canada, Don Mills, Ontario) examination failed to reveal abnormalities in either anterior segment. Indirect ophthalmoscopy (Heine Omega 200; Heine Instruments Canada, Kitchener, Ontario) confirmed a right retinal detachment. A left fundus photograph is provided for your assessment (Figure 1).

Figure 1. Photograph of the left fundus of an English springer spaniel. Note the grey streaks in the peripapillary tapetal region. The right retina was completely detached and similar peripapillary lesions were present.

Discussion

Our diagnoses were bilateral geographic retinal dysplasia and retinal detachment in the right eye. Geographic retinal dysplasia in English springer spaniels is inherited as an autosomal recessive disease (1). We advised the owners not to breed the dog and to contact the original kennel and advise its owners to have their breeding dogs certified by the CERF. We also recommended a prophylactic, peridysplastic, transcorneal laser retinopexy in order to permanently scar the retina of the left eye to the retinal pigment epithelium and choroid, to prevent retinal detachment in that eye. Vitrectomy and retinal reattachment in the right eye were considered. However, a poor visual prognosis was given, based on the generalized retinal degeneration and the history of the right pupil being dilated for several months.

Retinal dysplasia is an abnormal development of the retina. Light microscopic examination of affected eyes will confirm linear folds and rosettes within the outer retinal layers. Retinal dysplasia has multiple etiologies, including viral infections (2), toxins (3), nutritional deficiencies (3), intrauterine trauma (3), radiation exposure (3), and genetic mutations (3). Heritable retinal dysplasia is the most common etiology; it has been described in many breeds of dogs, including the English springer spaniel (4).

The clinical manifestations of retinal dysplasia include multiple retinal folds that appear grey in the nontapetal regions and grey-green in the tapetal fundus (4). Retinal dysplasia in English springer spaniels develops predominately in the peripapillary tapetal fundus, and the folds are present at birth (5). The dysplastic areas are nonprogressive. Ophthalmologists have noted ophthalmoscopically less prominent folds as affected dogs age (5). The vitreous overlying a dysplastic area is often degenerate and large areas of dysplasia predispose to retinal elevation and detachment. Retinal detachment often occurs in these dogs within the first 6 mo of life (5). Geographic retinal dysplasia is an autosomal recessive condition in springer spaniels (6), and affected dogs will not be certified for breeding.

The pathogenesis of retinal dysplasia in English springer spaniels has been investigated with light and electron microscopy of eyes from cesarian-derived puppies at various days of embryologic development (7). The earliest light microscopic lesions were detected at day 45 of embryologic development (7). These early lesions were an inward folding of the neuroblastic retina, focal loss of integrity of the external limiting membrane, and disorganization of neuroblastic cells (7). By embryologic day 55, distinct rosettes were formed within the outer nuclear layer. There was retinal pigment epithelial hypertrophy, and retinal detachment developed within the dysplastic areas (7). The retinal pigment epithelium may play a role in the pathogenesis of retinal dysplasia in English springer spaniels, although this epithelial layer is morphologically normal in affected dogs (7). O'Toole (5) suggested that the dysplasia may be attributed to abnormal development of the Müller cells and retinal capillaries.

We completed a transcorneal diode laser retinopexy with a double layer of burns around the perimeter of the dysplastic areas of the left eye to prevent further detachment. No complications were noted and the retina remains unchanged 1 y later.