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Retinal diseases: Dusting off the ophthalmoscope (Proceedings)

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Aug 01, 2008

"More is missed for not looking than for not knowing"—author unknown

The key to understanding retinal disease is in knowing there is a problem. You must know all the variations of normal to be able to identify the abnormal. Many blind patients would be sighted if someone took the time to examine the retina of patients with systemic diseases.

The retinal exam

1. Direct ophthalmoscopy

a. Can be useful, but understand the limitations

b. Very small field of view, very magnified

c. Difficult on an awake moving patient

2. Indirect ophthalmoscopy

a. Handheld lens and transilluminator

i. Better than direct, larger field of view

ii. Need a good technician to hold patient still

iii. Dilation is very helpful

iv. Best lens is a 22D Panretinal by VOLK

b. Indirect headset

i. Best option as view is large and three dimensional

ii. YOU control the head which makes the exam MUCH easier

iii. Variety of lenses from 20D to 28D useful on small animals

3. ERG

a. Electrical testing of the retinal function

b. Useful when retina cannot be visualized, or a blind patient with a normal appearing retina in a blind patient

c. Can be useful in diagnosing genetic diseases

4. Ultrasound

a. Helpful when the retina cannot be visualized

b. 9MHz probe up to 50MHz probe depending on what you are wanting to evaluate

Assorted retinal diseases

1. SARDS

i. "sudden" onset of blindness, days to weeks

ii. middle-aged, spayed female predisposed

iii. Often pu/pd

iv. normal retina on exam initially, progresses into an atrophic looking retina over months

v. ERG is diagnostic with the absence of waveforms

vi. No therapy currently

vii. Higher prevelance of hyperadrenocorticism in SARDS patients

viii. Always perform Cushing's testing regardless of Chem profile results

2. PRA

i. Genetic basis in many breeds (toy poodles, cocker spaniel, Labrador, miniature schnauzer, etc.)

ii. Visual impairment usually occurs slowly

iii. Begins with impairment in dim to lowlight situations

iv. Progresses to daytime blindness

v. Age of blindness varies with breed

vi. Usually by time of presentation disease is fairly progressed and marked thinning of the retina is seen on examination

vii. Hyperreflective tapetum and vessel attenuation hallmark

viii. No treatment available at this time.

ix. Some retroviral work shows promise for eventual therapy

3. Retinal detachment

i. Treatment and prognosis depends on the cause

ii. Types of detachment: exudative, traction and rhegmatogenous

iii. Etiologies