Retinal detachment is a relatively common ophthalmic disorder of dogs characterized by separation of the retina from the underlying retinal pigment epithelium and is a leading cause of vision loss in this species.
The retinal pigment epithelium, which is the primary site for various retinal diseases, is sandwiched between the photoreceptors and choriocapillaries. The tight junctions formed between the retinal pigment epithelium cells prevent passive diffusion of molecules and serve as a blood–retina barrier. Unlike most epithelia, which have their apical side face toward the lumen, the apical surfaces of retinal pigment epithelium cells are in close contact with the subretinal space and neural photoreceptors throughout development.
Although trauma has been cited as an initiating factor in retinal detachment, retinal detachment in dogs is commonly associated with underlying systemic or local ocular disease. Regardless of cause, pathologic intraocular neovascularization is a key component in separation of the retina from the underlying retinal pigment epithelium.
After the retina detaches in dogs, the retinal pigment epithelium changes rapidly, with hypertrophy and hyperplasia, and the epithelial cells may detach from their basement membrane and become migrating cells with macrophage-like properties. When the detachment is chronic, hyphema and uveitis are common sequelae, due to the development of pre-iridal fibrovascular membranes.
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. When photoreceptors are separated from the retinal pigment epithelium, the outer and inner segments of the rods and cones degenerate quite rapidly and the retinal pigment epithelium hypertrophies.
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.
A number of forms of retinal detachment can occur but the most common in dogs is rhegmatogenous retinal detachment which commonly develops secondary to fibrous vitreous traction bands, as a result of trauma or vitreous inflammation and degeneration, frequently resulting in giant retinal tears, commonly seen in Shih Tzu, Springer Spaniel, Poodle, Bichon Frise, Labrador Retriever.
Other forms of retinal detachment include bullous retinal detachment (separation of the neural retina from the retinal pigment epithelium, due to accumulation of fluid and or cellular debris), tractional retinal detachment and posterior vitreous detachment.
Causes of retinal detachment include:
- - Vitreous degeneration in Shih Tzu, Boston Terrier, Poodle, Brussels Griffon, Chihuahua, Havanese, Italian Greyhound, Lowchen, Papillon, Whippet
- - Retinal pigment epithelial dystrophy (retinal dysplasia) in English Cocker Spaniels, Springer Spaniel, Labrador Retriever, Miniature Schnauzer
- - Uveodermatologic syndrome
- - Oculoskeletal dysplasia in Labrador Retrievers and Samoyeds
- - Multifocal retinopathy in Great Pyrenees dogs
- - Collie eye anomaly in Collie breeds, Australian shepherds
- - Persistent hyperplastic primary vitreous
- Diabetes mellitus
- Hyperviscosity syndrome
- Lens luxation
- Postoperative complications following cataract phacoemulsification
- Intraocular foreign body
- - Toxocara spp
- - Anaplasma phagocytophilum infection
- - Ehrlichia spp
- - Leptospira spp
Retinal detachment in dogs may be partial or focal, and not perceptibly affect vision, or it may be complete and the affected eye is blind. However, in most dogs retinal detachment, unless bilateral, is usually subclinical and manifest with only mild pupillary dilation (anisocoria) to the affected eye. In many cases, the menace responses and the palpebral, oculocephalic, and direct and consensual pupillary light reflexes are present in both eyes. A Schirmer tear test should be performed to exclude keratoconjunctivitis sicca and tonometry (<25 mmHg) to exclude concurrent glaucoma. The pupils are usually dilated with tropicamide for a full fundic examination.
Diagnosis is usually confirmed by ophthalmoscopic examination, and in cases complicated by corneal opacity, ultrasonographic imaging may be required.
Medical treatment involves use of topical glucocrticoids to minimize vitreous inflammation and antiglaucoma medications.
Surgical repair of retina detachment requires retinal reattachment via a pars plana vitrectomy, followed by transscleral cryopexy or retinopexy. This is usually reserved to cases where large portions or complete retinal detachment has occurred.
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.
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