Ocular Fundus Imaging for the Diagnosis of Progressive Retinal Atrophy - A Study in 31 Dogs.
During two years study, 31 cases of progressive retinal atrophy (PRA) were recorded in dogs with typical history of initial nyctalopia followed by hemeralopia. Out of 31 PRA suspected dogs, eight dogs (26%) were from the age group of 1-5 years, 15 (48%) 6-10 years and the rest (26%) 11-15 years. The most predominant breed was Spitz (18 dogs - 58%). Detailed ophthalmologic was conducted in all the dogs. Ophthalmoscopic and fundoscopic changes included hyper reflectivity and discoloration of the tapetal area, marked attenuation of retinal vessels, depigmentation in non-tapetal area and optic disc atrophy with scalloped borders. Funduscopy revealed typical signs of PRA with change in tapetal reflectivity. The signs were almost symmetrical for both eyes and severity of abnormalities was somewhat variable among the affected dogs.
Keywords: Attenuation; atrophy; funduscopy; progressive retinal atrophy; taptel hyper reflectivity
Ocular funduscopy elicits important aspects in pathological status of visual organ. Canine Progressive Retinal Atrophy (PRA) is a large group of progressive, hereditary, retinal degenerations causing visual impairment and eventually blindness in affected dogs. Approximately, 108 canine breeds are currently on the list for potentially being affected by progressive retinal atrophy (Whitley et al., 1995).
The diagnosis of progressive retinal atrophy is based on clinical history, ophthalmologic and complementary examination such as electro-retinography, ocular ultrasound and genetic testing (Gomes et al., 2013). This report describes funduscopic features of retinal atrophy in 31 dogs.
Materials and Methods
In a span of 2 years, 340 clinical cases of dogs underwent detailed ophthalmic examination for various ocular abnormalities which included complete history pertaining to visual abnormality including onset of troubled vision, nyctalopia, hemeralopia etc. and clinical assessment of visual functions by reflexes like menace, pupillary light, 4th purkinje and tapetal, different tests like fluorescein staining, schirmer's tear test, tonometry, complete ophthalmic examination with hand-held slit-lamp biomicroscope and binocular indirect ophthalmoscope with 20 D lens under pharma-cologic mydriasis with topical 1% Tropicamide ophthalmic solution and B-mode ultrasonographic examination in appropriate cases. All ocular abnormalities were documented and in many cases retinal photographs were taken with a hand-held fundus camera (Smartscope VET2: Optomed, Finland). Prior to fundoscopy recording, the dog's pupils were dilated with short-acting mydriatic 1% Tropicamide, 30 minutes prior to examination and after proper focusing of the camera, image of posterior segment was taken using ophthalmoscopic fundus imaging camera in a dark room. For each dog, tapetal and non-tapetal colour, tapetal reflectivity, shape of tapetal and non-tapetal area, homogenicity of tapetum and non-tapetal, the junction of tapetal and non-tapetal border and location, colour, shape, border and degree of myelination of optic disc were evaluated.
During the study period, out of 31 cases of PRA 18 dogs (58%) were male and 13 (42%) female, with age varying from 2-13 years, of which eight (26%) were from the age group 1-5 years, 15 (48%) between 6-10 years and the rest (26%) 11-15 years. The most predominant breed was Spitz (18, 58%) followed by Labrador retriever (8, 26%), Cocker Spaniel (2, 7%), Canadian pointer, Lhasa aphso and German shepherd (1 each, 3%).
Most of the dogs were presented with initial signs of nyctalopia, followed by progressive hemerlopia until the affected animal was totally blind. The age at onset of nyctalopia and rate of progression of vision loss varied widely. When examined almost all dog (n=27, 87%) had difficulty in avoiding objects in dim light, dilated pupils with slow pupillary light responses and characteristic shine from eye (tapetal hyper reflectivity).
In normal dogs, the ophthalmoscopic and fundoscopic examinations showed normal reflectivity of tapetal region, normal vascular size and normal coloration of tapetal fundus (Fig. 1). Ophthalmoscopy in dogs with PRA, showed bilateral and generalized changes. Only subtle color changes were noted in central parts of ocular fundi, but in peripheral parts there were signs of choroidal spoking and slight hyper-reflectivity. Lesions of fundus were variable and at early stages (n=13), focal or multifocal hyper reflective lesions of tapetum resulting in thinning of retina, with an inconsistent symmetry were frequently observed but the hyper reflective band surrounding tapetal-nontapetal junction was rare and blood vessels were not completely attenuated (Fig. 2) but narrowed away from the disc; while at advanced stages (n=15), generalized hyper reflexion coexisted either with hyper reflective coalescent foci in tapetum and only ghost vessels are visible with pallor of disc and hypopigmentation of nontapetum area (Fig. 3). Fundoscopy revealed shrinking of blood vessels, decreased pigmentation of nontapetal fundus, increased reflection from tapetum and atrophied optic disc with scalloped borders. There was a generalized but mild vascular attenuation with decrease in number and size of retinal vessels and pigmentary changes along with circular and atrophied optic disc with scalloped or indistinct borders and early loss of myelin over the optic nerve head. Fundus changes were not detected in any of the examined dog below 4 years of age (n=3) though the owners had complaints regarding their dog showing signs of fear in dark.
Funduscopy changes noted in PRA affected dogs included one or more of following changes: diffuse hyper reflectivity of tapetal area (n=31, 100%), moderate or severe attenuation of major venules and arterioles (n=31, 100%), severe tan-brown discoloration of tapetal fundus (n=4, 12.9%), depigmentation in non-tapetal area (n=3, 9.6%) and optic disc atrophy (n=8, 25.8%). Ophthalmoscopic observation of abnormalities of retina that included bilateral symmetric pale optic nerve heads, severely attenuated retinal vessels and tapetal hyper reflectivity. The signs of retinal degeneration were symmetrical for both eyes in each dog and severity of ophthalmoscopic fundus abnormalities was somewhat variable among affected dogs.
All 31 affected dogs described in present report showed no obvious visual impairment except nyctalopia at initial stage which gradually progress to day blindness in few months to years resulting in complete blindness. Dogs of both genders, 18 males and 13 females were affected by PRA, which makes it unlikely that the condition is sex-linked.
The ophthalmoscopic signs are similar for each type of PRA, but the aetiologies vary considerably (Bedford, 2006). Although ophthalmoscopic findings at various stages of PRA were rather similar, the variation in age of onset of disease in few dogs was remarkable. Through the genealogy of affected dogs, it was found that certain families were affected early with more rapid progression of disease, compared to other dogs that developed PRA at a later time. PRA in Spitz is late onset form and is diagnosed in middle aged dogs.
The disease is characterized by progressive attenuation and thinning of retinal blood vessels. As the disease progresses, arteries decrease in number and large veins become noticeably thinner. The optic disc becomes pale to gray brown owing to loss of capillaries on its surface and demyelination and atrophy of nerve fibers caused by extensive degeneration of retina (Maggs, 2013). The most obvious and consistent finding in affected dogs is a greyish discoloration of peripheral tapetal fundus that slowly spreads toward central part of tapetal area. Funduscopy revealed typical signs of PRA. It included change in tapetal reflectivity i.e. tapetum showed focal or multifocal areas of hyper reflectivity in early stages and progressed to diffused hyper reflectivity in advanced stage.
Bedford, P. (2006). Hereditary Retinal Diseases. World Congress WSAVA/FECAVA/CSAVA, p. 609-10.
Gomes, D., Otsuki, D.A., Lisaki, R., Angelica De Mendonga and Safatle, V. (2013). Generalized progressive retinal atrophy in Cocker Spaniel dogs. Ciencia Rural, Santa Maria, 43:1405-14.
Maggs, D.J. (2013). Basic diagnostic techniques. In: Maggs D. J., Miller, P. and Ofri, R. (Eds), Slatter's Fundamentals of Veterinary Ophthalmology. 5th Ed., Saunders, Philadelphia. p. 1-12.
Whitley, R.D., McLaughlin, S.A. and Gilger, B.C. (1995). Update on eye disorders among purebred dogs. Vet. Med. 90: 574-92.
D.N. Kelawala (1), D.B. Patil (2), K.R. Sini (3), P.V. Parikh (4) and E.A. Parulekar (3)
Department of Veterinary Surgery and Radiology
College of Veterinary Science and Animal Husbandry
Anand Agricultural University (AAU)
Anand - 388001 (Gujarat)
(1.) Ph.D. Scholar and Corresponding author. E-mail: email@example.com
(2.) Director of Research and Dean (Post Graduate Studies), Kamdhenu University, Gandhinagar
(3.) Post Graduate Scholar
(4.) Professor and Head
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|Title Annotation:||Research Article|
|Author:||Kelawala, D.N.; Patil, D.B.; Sini, K.R.; Parikh, P.V.; Parulekar, E.A.|
|Date:||Jul 1, 2016|
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