March 28, 2019
The retinal dysplasias (RDs) represent a group of inherited retinal diseases, associated with the abnormal differentiation & proliferation of one of more retinal layers. The RDs may involve;
- Multifocal linear folds of tissue (notably affecting the Labrador Retriever, American Cocker Spaniel, Beagle, Rottweiler & Yorkshire Terrier)
- Large irregular or “geographic” areas of tissue (notably affecting the Labrador Retriever, Golden Retriever, English Springer Spaniel & Cavalier King Charles Spaniel)
- Complete dysplasia with or without retinal detachment (notably affecting the Labrador Retriever, Australian Shepherd, Samoyed, Doberman Pincher, Akita & Chow Chow)
Genetic testing is also available for multiple breed-related retinal dysplasias (www.optigen.com). No medical therapy is likely to be beneficial. Surgical management of retinal detachments may be indicated in selected cases.
The retinal atrophies (RAs) represent a group of inherited retinal diseases, which result in photoreceptor dysfunction and death, leading to visual impairment/blindness. Various forms have been described as affecting a large (and increasing) number of dog breeds as well as some cat breeds. The classification of the retinal atrophies is complex, however may be simplified into;
- early and late onset progressive retinal atrophy (PRA)
- congenital stationary night blindness (CSNB)
- cone degeneration (“day blindness”)
- the feline RAs
Genetic testing is also available for multiple breed-related RAs (www.optigen.com). Accurate gene-based testing facilitates breeding programs designed to help reduce the incidence of disease within a breed.
Sudden acquired retinal degeneration syndrome/immune-mediated retinitis (SARDs/IMR) describes a spectrum of disease resulting in acute onset blindness, which is generally irreversible. The mechanism of photoreceptor death in SARDs/IMR appears to be antibody-mediated retinopathy. Ophthalmic examination (including funduscopic assessment) is initially unremarkable (although signs of generalized neuroretinal degeneration including tapetal hyper reflectivity and vascular attenuation become evident in the ensuing months). Affected animals are commonly middle-aged, female, small-breed dogs, which may additionally be overweight and/or exhibit symptoms of polyuria/polydipsia/polyphagia. Intermittent associations have been made with paraneoplastic syndromes, hyperadrenocorticism &/or sex hormone imbalances. The diagnosis if SARDs/IMR supported by electroretinographic testing. Attempted treatment of fully extinguished photoreceptor function is fruitless. In rare cases of peracute IMR (associated with a degree of residual visual and/or electroretinographic function), experimental treatment using immunomodulating therapy comprising systemic doxycycline, corticosteroids and/or immunoglobulin therapy has been described.
Ocular changes are often the presenting symptom of systemic hypertension. Blood-ocular barrier breakdown results in variable combinations of sub-retinal fluid leakage, retinal hemorrhage &/or detachment, hyphema or visual deficits. Systemic hypertension may be primary or may occur secondary to systemic disease (including renal or cardiovascular dysfunction), endocrinopathy (including hyperthyroidism, hyperadrenocorticism, diabetes mellitus) or neoplasia (including lymphoma, multiple myeloma & phaeochromocytoma). Treatment comprises addressing underlying disease where present. Blood pressure may be directly regulated, typically using amlodipine, and/or an ACE-inhibitor where indicated. Retinal hemorrhage will typically resolve, and retinal detachment may spontaneously re-attach (notably in cats), depending on the chronicity & severity of the pre-exiting detachment. Surgical re-attachment may also be considered in select cases, once underlying pathology has been addressed.
Clinical symptoms potentially associated with chorioretinitis (posterior uveitis) may include: chorioretinal edema, exudation, hemorrhage and/or retinal detachment, visual impairment and/or blindness. Potential etiologies include trauma, systemic disease, exposure to infectious organisms, the presence of (local or systemic) neoplasia and/or hereditary factors. Treatment encompasses addressing underlying systemic, infectious or neoplastic disease. Additionally, topical and/or systemic anti-inflammatory therapy is typically warranted.
Primary bullous retinal detachment represents a separation of the neurosensory retina from the underlying pigment epithelium due to sub-retinal fluid accumulation. This process is suspected to be immune-mediated in etiology. Clinical symptoms typically comprise bilaterally dilated poorly, or non-responsive pupils in association with acute onset blindness. Commonly affected breeds include the German Shepherd, Australian Shepherd and Labrador Retriever. Bullous detachments are typically promptly responsive to anti-inflammatory therapy
Rhegmatogenous retinal detachment, represents a separation of the neurosensory retina from the underlying retinal pigment epithelium stemming from a break in the retinal tissue.
Rhegmatogenous detachments may be;
- primary – frequently in association with vitreoretinal degeneration
- secondary – arising as a result of inflammation and/or trauma
Clinical symptoms may include dilated, poorly responsive pupil(s), vitreous degeneration, herniation, and/or hemorrhage visual deficits and/or blindness. Funduscopically retinal tears may visualized. Frequently affected breeds include the Shi Tzu & Bichon Frise’. Medical therapy is unlikely to result in resolution of rhegmatogenous retinal detachment. Where pathology is relatively recent (1-3 weeks) & significant secondary complications have not developed, surgical repair may be indicated.
Dr Esson is a board-certified veterinary ophthalmologist with more than twenty years of clinical experience and multiple areas of interest & expertise. His clinic Veterinary Ophthalmic Consulting (www.veterinaryophthalmicconsulting.com) is family owned & operated and he takes great pride & pleasure in working closely with his friends and colleagues in the greater Southern California veterinary community.