Retinal diseases: Dusting off the ophthalmoscope (Proceedings)

"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

Infectious

a. Most causes of uveitis can result in RD, (see uveitis notes)

b. Fungal

i. Subretinal granulomas- tan, raised lesions

ii. May result in concurrent vitritis

iii. Often associated uveitis

c. Tick borne

i. Retinal hemorrhages and serous detachments

2. Inflammatory

a. Hypertension

i. Older cats most common, can see in Cushingoid dogs.

ii. "Sudden" blindness or "red eye" described by the client

iii. Hemorrhage is variable, often a bullous retinal detachment

iv. Work up the systemic disease and treat accordingly

v. Anti-inflammatory therapy for the eye, topical and systemic

vi. Most retinas will reattach physically, but prognosis for regaining vision is guarded

b. Auto-immune

i. Steroid responsive retinal detachment

ii. Dog problem presenting with sudden blindness

iii. Bullous retinal detachment, usually OU

iv. Work-up is normal

v. Responds well to topical/systemic immunosuppressive therapy (prednisone/immuran)

vi. Often requires lifelong or protracted treatment

3. Degenerative/Traction/Rhegmatogenous

a. Usually breed related (genetic) or post-operatively subsequent to lensectomy

b. Breed predisposition for spontaneous RDs= Shi tzu, Labrador retriever, Cocker spaniel, Springer spaniel, Italian grey hound

c. Breed predisposition for lensectomy associated: bichon fries, Cocker spaniel

d. Often resulting from a form of vitreal degeneration resulting in liquefaction of the vitreous and subsequent retinal tear and detachment.

e. Surgical correction is available and can carry a good (75-90%) chance of visual outcome if surgery is accomplished quickly enough (1-3 weeks).

f. Exudative RDs are not surgical candidates

4. Traumatic

a. Poor prognosis when accompanied by significant hemorrhage

b. May have globe compromise resulting in RD

c. Anti-inflammatory therapy may be useful

d. Monitor for secondary glaucoma

4. Optic neuritis

i. Not truly retinal disease, but noticed in blind patients with normal appearing retinas

ii. Examination reveals edematous retina around optic nerve and swollen optic nerve, remainder of retina normal

iii. ERG normal

iv. Work-up with an MRI and CSF tap for elucidation of cause and prognosis

v. Treatment often long term anti-inflammatory therapy systemically

5. Retinal neoplasia

i. Choroidal melanoma

a. Black lesion in the fundus, usually raised, poor prognosis for eye long term

Blind dog client education:

• Animals rely heavily on senses of hearing and smell

• Quality of life is generally fair

• Don't redecorate frequently

• Fence in yard and be very careful around in ground pools

• Living with Blind Dogs Excellent resource for owners to cope and learn

• Alternative training methods for their pets.