1. Why Perform a Fundus Examination?

 Vision impairment related to the retina

 Systemic disease and associated retinal changes

 Breed certification--CERF, ACES, European Eye Certificate

2. Methods of Examining the Fundus

 Use dim or no room light

 Dilate pupil using mydriatic (tropicamide)

 Ophthalmoscopy is needed to visualize the posterior segment (vitreous, retina and optic nerve and their associated blood vessels)

 Two different types of ophthalmoscopy: direct and indirect

Direct ophthalmoscopy: Requires less practice; cheaper; more magnification (varies inversely with size of eye; e.g., about 20 X in the cat and about 8 X in the horse); can be used with miotic pupils; is of some use in most species.

Indirect ophthalmoscopy: Survey instrument with less magnification (varies inversely with the dioptric power of the lens used and inversely with the size of the eye; e.g., about 4 X using a +20 diopter lens in the cat), but wider field allowing more fundus to be visible at one time (35 degrees instead of 9 degrees)--facilitates examination of peripheral fundus; permits exam at safe distance from fractious patients; provides stereoscopy; brighter illumination (for translucent ocular media); excellent teaching device because a prism can be used to give students a simultaneous view of what the examiner is seeing

3. Equipment Needed

 Finoff transilluminator

 Indirect ophthalmoscope & 20D or 28D lens

 Direct ophthalmoscope (not as useful because it is designed for human optics NOT dogs and cats). Useful in horses.

4. Anatomy of the Retina

 Ten layers--outermost layer is the retinal pigment epithelium which faces the choroid

 The other nine layers referred to as sensory retina (including the photoreceptors)

5. Normal

 Important to recognize normal

 Regular examination of normal patients is important

 Takes many years to become competent

 Variations from normal

 Many variations, mainly related to colour

 Blue irides = tigroid (no overlying pigment) fundus--Siamese cats, merle Collie, Old English sheepdog, etc.

 Dark coated dogs = small tapetal fundus, occasionally no tapetum visible e.g., Chocolate Labradors

 Optic disc anatomy can vary especially in dogs (variations in myelination)

 Blood vessel appearance varies--note in dogs, vessels cross over optic disc

6. Retinal Diseases Recognised with Funduscopy

Retinal Haemorrhage/Detachment

 Especially older cats with hypertension

 Also coagulopathies, hyperviscosity and some canine systemic diseases

 Best seen using indirect ophthalmoscope but can be often seen with naked eye

 Look for areas of detachment (dull, out of focus) and haemorrhage (association with blood vessels and retinal layers determines appearance)

 Later, look for areas of hyperreflectivity

Retinal Atrophy

 Includes progressive retinal atrophy (PRA), progressive rod-cone degeneration, rod-cone dysplasia and retinal degeneration in Abyssinian cats

 Signs very subtle in early stages (attenuation of the peripheral retinal vessels) but will have poor vision in dim light)

 Later on, obvious hyperreflectivity and retinal vessel attenuation accompanied by vision impairment including in day light

 Taurine deficiency in cats causes retinal degeneration in the area centralis

Collie Eye Anomaly

 Defect is choroidal hypoplasia dorsotemporal to optic disc and focal absence of tapetum and RPE revealing abnormal choroidal vasculature

 Defects in optic nerve

 Occasionally accompanied by retinal detachment and haemorrhage

 Seen in collies, Shetland sheepdogs, Australian shepherds and some non-shepherd breeds

Inflammatory Disease

 Chorioretinitis (as seen in feline infectious peritonitis--FIP and fungal disease) and retinochoroiditis (as seen in neurotrophic viruses such as canine distemper)

 Often see hypertrophy of the retinal pigment epithelium, easily visible in the nontapetal fundus

 Perivascular cuffing (vasculitis in FIP)

Congenital Disorders

 Retinal dysplasia (also in maternal viral infections such as canine herpes and feline panleukopaenia)

Sudden Acquired Retinal Degeneration (SARD)

 Cause unknown but retinitis is suspected as the initiator in some cases

 Some cases have endocrinological abnormalities

 Fundus changes occur sometime after clinical signs noticed