Fundus Findings Examining the fundus can be challenging, but having the right equipment makes the process a lot easier. We use indirect ophthalmoscop

Fundus Findings

Examining the fundus can be challenging, but having the right equipment makes the process a lot easier. We use indirect ophthalmoscopy to examine the fundus. The main advantage of this is that you get a wide field of view, and this makes seeing tapetal hyper-reflectivity and blood vessel attenuation much easier.

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To do Indirect Ophthalmoscopy you will need

A light source eg a focal light or a head mounted light source
A condensing lens. We commonly use a 28 D Indirect lens, these are available from Scan Optics in Adelaide, and a 2.2 Volk PanRetinal Lens available from Dan Scott & Associates in the USA. If you are going to use just one lens, then the 2.2 PanRetinal lens has the widest range of applications.

The normal fundus is examined with reference to

Blood vessels. The most common abnormality is attenuation (thinning) or loss of the blood vessels and this is seen with retinal atrophy

Reflectivity. This can either be increased (hyper-reflectivity) eg retinal atrophy, or decreased (hypo-reflectivity) with retinal detachment or infiltrates. If retinal atrophy ie hyper-reflectivity is seen you would also expect to see blood vessel attenuation.

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Normal Feline Fundus

Optic disc. The optic disc is always small and dark in cats. In dogs the optic disc tends to be larger and whiter. The size of the optic disc can vary greatly in dogs, depending on how much myelin is present. A small dark optic disc is suggestive of optic nerve atrophy. Remember the pupil should be dilated and non responsive in such a case and the eye blind.

Pigment changes. The retinal epithelium in the non-tapetal fundus is usually heavily pigmented. Remember in light coloured animals you may be able to see the choroidal blood vessels. A loss of pigment in the non tapetal fundus is a sign of retinal inflammation. The retinal epithelium overlying the tapetum is normally unpigmented and is usually quite resistant to becoming pigmented. Pigment in the tapetal area is usually a sign of severe retinal and/or choriodal disease.

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Fundus Photo of a cat that had Toxoplasmosis

Note the areas of localised inflammation in the retina. These inflamed areas have caused the normally unpigmented retinal epithelium to become pigmented. These are seen as the dark lesions in the tapetum.

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Fundus photo of an older cat

This shows retinal haemorrhages. This is characteristic of
systemic hypertension particularly if seen in older cats.

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Another older cat with systemic hypertension

In this case we can see a bullous lesion. Fluid is coming out of the choroid due to the hypertension causing this circular area of retina to lift off.

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PRA—progressive retinal atrophy in a cat

This is very rare in cats, but is seen in Siamese and other pure bred cats. Note the flash intensity has been turned down, but the tapetum is hyper-reflective. The tapetum is granular. The blood vessels are very attenuated, we can only see a remnant of the dorsal vein. Dogs with advanced PRA look similar to this on fundus exam.

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