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Ocular Funduscopy of Different Canine Breeds in India - A Clinical Study of 70 Normal Dogs.

Abstract

The morphological, structural and functional particularity of eye fundus is an important elements in diagnostic ophthalmology irrespective of species or examination method. In the present study, a total of 70 canines of 19 different breeds were included. Green-blue was the most common color (18.57%, n=13) followed by yellow-green-blue (17.14%, n=12) green (11.42%, n= 8) and combinations of these colors in rest of animals. The canine ocular fundus showed enormous variations in normal ophthalmoscopic appearance. The present study facilitated a mini 'memory reference library' of fundic images in different species in Indian clinical settings advocating ocular funduscopy to be a routine in diagnostic ophthalmic armamentarium.

Keywords: Canine; dog; funduscopy; ocular

Introduction

Ocular funduscopy elicits important aspects in pathological status of the visual organ. Because of its morphological, structural and functional particularity, eye fundus represents important elements in diagnostic ophthalmology, no matter of species or examination method (Alina et al., 2008).

The fundus of each domestic species has a characteristic appearance that varies greatly among species and to a lesser extent among individuals of same species. However, fundic appearance varies very little between eyes of one individual, making diagnosis of unilateral fundic changes easier (Maggs, 2013).

The canine ocular fundus is a challenge for the examiner because of its enormous variations in normal ophthalmoscopic appearance (Crispin, 2005). The hardest thing about interpretation of ocular fundus is knowing what is normal. There is a tremendous amount of normal variation in ocular fundus and one must examine many animals to truly understand what normal is. Until variations of normal are understood, determination of pathologic changes is impossible (Morreale, 2010).

In India there is paucity of documented literature regarding the study of ocular fundus in different species of animals. Hence the present study was undertaken to study and evaluate the variations in ocular fundus of different dog breeds in India.

Materials and Methods

The study was conducted in 70 canines of different breeds without any vision abnormalities. Prior to fundus examination, all the animals had undergone basic ophthalmic examination for diagnosis of any ocular condition. The pupils were dilated with a short-acting mydriatic (0.5%-1% Tropicamide) 30 minutes prior to examination. For accurate fundus examination, the diagnostic area was selected as a dark room. Detailed fundus examination was carried out using fundus imaging camera (a) in nineteen different dog breeds and normal variations of fundus were analysed.

The images were evaluated and characterized according to its breed which included a) Tapetal color b) Tapetal reflectivity c) Shape of tapetal area d) Homogenicity of tapetum e) The junction of tapetal and non tapetal border.

Results and Discussion

Among 70 dogs, 19 different canine breeds were included in study. The most prevalent breeds examined were Doberman Pinscher (n=8; Fig. 1), Labrador Retriever (n=8; Fig. 2) and non descript (n=8; Fig. 3) followed by Spitz (n=7; Fig. 4), Pug (n=6; Fig. 5), German Shepherd (n=5; Fig. 6),Great Dane (n=4; Fig. 7), Lhasa Apso (n=4; Fig. 8), Saint Bernard (n=3; Fig. 9), Beagle (n=3; Fig. 10), Golden Retriever (n=2; Fig. 11), Dalmatian (n=2; Fig. 12), Rottweiler (n=2; Fig. 13), Boxer (n=2; Fig. 14), Cocker Spaniel (n=2; Fig. 15), English Mastiff (n=1; Fig. 16), Neopolitan Mastiff (n=1; Fig. 17), Chihuahua (n=1; Fig. 18) and Old English Sheep Dog (n=1; Fig. 19).

The color of tapetum varied a lot. Colors observed include yellow, green, blue or orange and combinations of these colors. Green-blue was the most common color (18.57%, n=13), followed by yellow-green-blue (17.14%, n=12), green (11.42%, n=8) and combinations of these colors in rest of animals. The tapetal area was absent in 08.57% (Labrador-1, nondescript-2, Great Dane-2, Spitz-1) of animals examined. The color of tapetal area was almost same in right and left eye in all dogs except one. The color distribution varied considerably between breeds. For example Doberman breeds of dogs often showed yellow green tapetum with blue border, while German Shepherds were with yellow orange tapetum and blue border.

The junction between the tapetal and non tapetal area were uneven with scattering of some tapetal cells while in long haired breeds like Golden Retriever, Cocker Spaniel, sharply demarcated in short haired breeds like Pugs.

Areas of pigmentation of retinal pigment epithelium overlying tapetum were noticed in all seven pugs dogs especially near the tapetal- non tapetal junction. The size of tapetal area was considered to be full sized covering about one third of dorsal fundus with optic nerve situated near border between tapetal and the non tapetal area. Based on this, full sized tapetum was observed in Golden Retriever, Beagle etc. Tapetal area was smaller in Chihuahua and Pug breed of dogs where optic disc was in non tapetum. Neopolitan Mastiff and Old English Sheep dog showed larger tapetal area with OD in tapetum.

There were variations in color of non tapetal area in different dog breeds. The color observed include shades of brown, dark brown, chocolate brown, black and red. The most common color was dark brown (72.72%, n= 40), followed by brown (9.09%, n= 5), black (7.27%, n= 4) and in others different shades of brown (chocolate, greyish brown) and red color could be seen. Some breeds (Lhasa Apso, Spitz) with less pigmented non tapetal fundus, in which choroidal blood vessels were visible, had a tigroid or striped pattern. These choroidal blood vessels were lighter in color than the retinal blood vessels.

Subalbinotic fundus was observed in two dogs (Spitz, Old English Sheep dog-1, 02.85%). These were characterized by absence of pigmentation in retinal pigment epithelium and in choroid, causing white sclera to become visible between choroidal blood vessels.

The optic disc of all dog breeds was well developed. The physiological cavity in centre could be observed and venous circulation was evident in some dogs. In most dogs, the disc was situated close to junction of tapetal to nontapetal fundus (50.00%, n= 35). It was often inside the tapetal area (18.57%, n= 13) especially in breeds like Old English Sheep dog, Neapolitan Mastiff and Saint Bernard. In some dogs (Chihuahua, Pugs, 22.85%, n= 16), the disc was situated entirely in non tapetal fundus. In dogs with absence of tapetum, position of OD could not be differentiated.

There were variations in shape and color of disc. Most common shape observed was triangular (57.14%, n=40) followed by circular (28.57%, n=20) and polygonal (14.28%, n=10). Border of disc appeared irregular due to pronounced myelination in some dogs. The color also varied, ranging from white to pink. Pink (47.88%, n=33) was the most common color observed followed by pinkish white (43.66%, n=31) and white (8.45%, n=6). When the disc was entirely situated in dark nontapetal fundus, it appeared paler than it was surrounded by tapetal fundus.

The disc also varied a lot in size. In some dogs, due to presence of myelinated nerve fibres on anterior side of lamina cribrosa, disc appeared a lot larger and it did not have a sharply demarcated rim. It was mainly noticed in dogs with more than 2yrs of age. Sometimes myelination of the nerve fibers could be seen as white streaks converging on the optic disc which is a normal variation (Great Dane-2, GSD-1, and Cocker Spaniel-1). Relatively small optic disc was observed in Pug breeds of dogs and micropapilla in Lhasa Apso.

There were lots of normal variations observed among dogs. When the disc was entirely surrounded by tapetum, pigmented ring (partial or complete) was seen around the disc (German Shepherds-1, Old English Sheep Dog-2). Normal zone of hyperreflectivity surrounding the optic nerve head (peripapillary conus) was not observed in any dogs.

Dogs had a holangiotic fundus. There were three or four and sometimes even five primary retinal veins. The primary veins were wider, darker, less in number and less tortuous than arterioles. The veins formed a venous circle in central part of disc. This circle was fully closed in some dogs and incomplete in others. There were more than fifteen to twenty arterioles. These arterioles appeared finer, lighter in color and sometimes more tortuous than veins. Visual streak or area centralis, area in tapetum where large retinal blood vessels were absent, situated laterally and somewhat dorsally from the disc was seen in three dogs.

Discussion

In the study, the most common color of tapetal area was green-blue (24.07%, n=13), followed by yellow-green-blue (22.22%, n=12) and green (14.81%, n=8), whereas in a retrospective study on Swedish dogs yellow-green was the most common color (48.4%, n=261), followed by orange (29.7%, n=160) and yellow (12.2%, n=66) (Granar et al., 2011). The tapetal area was absent in 08.57% (Labrador-1, non-descript-2, Great Dane-2, Spitz-1) of animals examined. There is absence of tapetal region in Blue Merle Collies or Shetland Sheep dogs (Narfstrom and Ekesten, 1999) and 1.9% of Swedish dogs were without tapetum (Granar et al., 2011).

The non tapetal area of fundus may also vary considerably in color from almost black to brown, red and stripped. Coloring of this part depends on degree of pigmentation in the choroid and also in Retinal pigment epithelium (RPE). When RPE lacks pigmentation, the nontapetal area is often stripped red and brown with visible straight choroidal vessels in brown pigmented choroid (Narfstrom and Petersen-Jones, 2007). A retrospective study in Swedish dogs revealed that most common color of the nontapetal area was dark brown, followed by black (Granar et al., 2011). In this study, the most common color obtained was dark brown (72.72%, n=40), followed by brown (9.09%, n=5) and black (7.27%, n=4).

These areas are characterized by absence of pigmentation in RPE and in choroid, causing the white sclera to become visible between choroidal blood vessels (Janssens, 2002). Subalbinotic fundus was observed in two dogs (3.27%, Spitz-1, Old English Sheep Dog-1).

The canine optic disc exhibits a wide range of normal variations in ophthalmoscopic appearance. It is located in center of fundus, sometimes in non tapetal fundus and sometimes in tapetal region, depending on the extension of latter (Narfstrom and Petersen-Jones, 2013). In our study, the disc was situated close to junction of tapetal to non tapetal fundus (56.06%, n=37) in majority of dogs. It was often inside the tapetal area (19.69%, n=13) especially in breeds like Old English Sheep dog, Neapolitan Mastiff and Saint Bernard. In some dogs, the disc was situated entirely in non tapetal fundus i.e. Chihuahua, Pugs etc (24.24%, n=16). These findings showed similarity with that of Janssens (2002) observations that disc was often situated just inside the tapetal area especially in large breeds. In some dogs, especially smaller ones, the disc situated entirely in non tapetal fundus. These differences in situation are not due to a different position of optic nerve in eyeball, but to a variation in extent of tapetal fundus.

There is an obvious variation in size of optic disc between different individuals and different breeds. There is no strict relationship, however between breed or size of dog and size of OD. The extent of myelinization affects the size of ONH. The shape of ONH may be round, oval, triangular, or polygonal and sometimes, the disc edge may be clearly indented. The color of ONH varies from pinkish white to deep pink, depending on extent of visible vasculature (Narfstrom and Petersen-Jones, 2013). The most common shape of optic disc noticed was triangular (56.94%) and color was pink (47.88%).

Narfstrom and Petersen-Jones (2013) observed central prominence of medullated nerve fibers that extend into surrounding fundus, mostly along retinal blood vessels in some dogs, especially Golden Retrievers and German Shepherds. Medullated nerve fibres could be seen as white streaks converging on optic disc in two Great Danes, one GSD and one Cocker Spaniel in our studies. When the disc was entirely surrounded by tapetum, pigmented ring (partial or complete) was seen around the disc (German Shepherds-1, Old English Sheep dog-2) which was a normal funduscopic variation due to the absence of tapetum and the visible choroidal pigmentation (Janssens, 2002).

The present study facilitated a mini 'memory reference library' of fundic images in different breeds of dogs enabling clinician to instantaneously distinguish between normal variations and signs of pathology.

References

Alina, D., Muste, A., Beteg, F. and Briciu, R. (2008). Morphological aspect of tapetum lucidum at some domestic animals. Bulletin USAAM. Vet Med. 65: 166-70.

Crispin, S. (2005). Notes on Veterinary Ophthalmology. Blackwell Science Ltd, UK. p. 158-171.

Granar, M., Nilsson, B.R. and Nystrom, H.L. (2011). Normal color variations of the canine ocular fundus, a retrospective study in Swedish dogs. Acta Vet Scand. 53: 13.

Janssens, G.H.R.R. (2002). Normal variation of the ocular fundus in dogs. EJCAP. 12: 193-98.

Maggs, D.J. (2013). Basic diagnostic techniques. In: Maggs D. J., Miller, P. and Ofri, R. (Eds), Slatter's Fundamentals of Veterinary Ophthalmology. 5th Edn., Saunders, Philadelphia. p. 1-12.

Morreale, R.J. (2010). Interpretation of Fundus Changes. In: Evaluation of the ocular fundus Manual. Michigan Veterinary University.

Narfstrom, K. and Ekesten, B. (1999). Diseases of the canine ocular fundus. In: Gelatt, K.N. (Eds), Veterinary Ophthalmology. 3rd Edn., Williams and Wilkins, Baltimore. p. 869-32.

Narfstrom, K. and Petersen-Jones, S.M. (2007). Diseases of the Canine Ocular Fundus. In: Gelatt, K. N. (Eds), Veterinary Ophtalmology. 4th Edn., Blackwell Publishing: Iowa. p: 944-1025.

Narfstrom, K. and Petersen-Jones, S.M. (2013). Diseases of the Canine Ocular Fundus. In: Gelatt, K. N., Gilger, B. C. and Kern, T. J. (Eds), Veterinary Ophtalmology. 5th Edn., John Wiley & Sons, Inc. Iowa. p. 1303-93.

K.R. Sini (1), D.N. Kelawala (2), D.B. Patil (3), P.V. Parikh (4) and E.A. Parulekar (1)

Department of Veterinary Surgery and Radiology College of Veterinary Science and Animal Husbandry Anand Agricultural University (AAU) Anand - 388001 (Gujarat)

(1.) Post Graduate Scholar

(2.) Ph.D. Scholar

(3.) Director of Research and Dean (Post Graduate Studies), Kamdhenu University, Gandhinagar and Corresponding author. E- mail: db1608@gmail.com

(4.) Professor and Head

(a) - Brand of Smartscope VET2, Optomed, Finland
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Title Annotation:Research Article
Author:Sini, K.R.; Kelawala, D.N.; Patil, D.B.; Parikh, P.V.; Parulekar, E.A.
Publication:Intas Polivet
Article Type:Report
Date:Jul 1, 2016
Words:2378
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