Retina

Question 1

Posterior segment

Answer 1

is the area behind the lens and includes the vitreal body, retina, choroid and optic nerve.

Question 2

Vitreal body

Answer 2

the largest area of eye filling the posterior segment between the lens and retina. It is filled with a clear gel-like fluid (vitreous).

Question 3

Asteroid hyalosis

Answer 3

age-related, degenerative change in vitreous (lipid & calcium) and looks like a snow-globe when viewed with a transilluminator.

Question 4

Fundus is the area viewed behind the lens and includes

Answer 4

Optic nerve, retinal vessels, tapetum (if present) and non-tapetal, pigmented area.

Question 5

Retinal degeneration causes thinning of the retina

Answer 5

tapetum to be seen as more reflective. This is called hyper-reflectivity. These areas are seen and bright and sharp.

Question 6

Retinal dysplasia

Answer 6

is seen in many breeds of dogs by 6-8 weeks of age. Folds or rosettes are seen due to defective development of retinal layers.

Question 7

Collie Eye Anomaly (CEA)

Answer 7

1) choroidal hypoplasia: the area lateral to the optic nerve is void of normal choroidal vessels. The white sclera can be seen and the vessels are disorganized. This is seen in the majority of collies and does not eliminate them from the breeding pool because vision is not affected. 2) Tortuous retinal vessels – not clinically significant. 3) Coloboma - a ‘hole’ in the retina or optic nerve forms during development and may cause hemorrhage, detachment and blindness.

Question 8

Progressive Retinal Atrophy (PRA),

Answer 8

or retinal degeneration, is an umbrella term that encompasses several hereditary rod/cone degenerative diseases.

Question 9

Clinical signs of PRA

Answer 9

These animals initially exhibit decreased vision at night that progresses to total blindness. As the nerve layer of the retina thins, more light reflects off the underlying tapetum resulting in hyper-reflectivity. The retinal vessels thin (attenuate) and the optic nerve atrophies. These findings are bilaterally symmetrical and can be distinguished from traumatic, toxic and infectious causes of degeneration that may or not be bilateral and are not symmetrical.

Question 10

Optic nerve hypoplasia

Answer 10

is a congenitally small optic nerve; these patients are blind.

Question 11

Micropapilla

Answer 11

is a congenitally small optic nerve, but in a visual eye.

Question 12

Optic nerve coloboma (hole)

Answer 12

is seen in CEA (Collie Eye Anomaly) with variable degrees of vision loss relative to the size of the defect.

Question 13

Papilledema

Answer 13

is the passive swelling of optic nerve, often associated with brain tumor or increase CSF pressure. The nerve is raised but not hyperemic. Vision is not lost with edema alone.

Question 14

Optic neuritis clincal signs

Answer 14

These patient present with acute blindness, dilated pupils, with a sluggish, if any, response. The fundus may be normal on exam (if an extraocular lesion) or the optic nerve may be swollen, fuzzy and hyperemic.

Question 15

SARDS vs optic neuritis

Answer 15

These patients have a normal ERG which distinguishes the blindness from SARDS (flat ERG).

Question 16

SARDS – Sudden Acquired Retinal Degeneration Syndrome

Answer 16

History of acute blindness or vision loss over a few days to weeks
Inappropriately dilated pupils, often sluggish response
Fundus appears normal on exam in early stages; subtle changes are slight episcleral injection, mild retinal vascular attenuation and optic nerve pallor.
Predisposed breeds: Dachshund, Schnauzer, Brittany, Beagle, others
Signalment: Female, Middle-age

Question 17

SARDS prodromal signs

Answer 17

recent weight gain, PU/PD/PP (polyuria/polydypsia/polyphagia); 50% of dogs’ lab work is consistent with hyperadrenocorticism (HAC); many of these dogs may be atypical Cushings with elevated sex hormones and normal cortisol.

Question 18

Dx of SARDS

Answer 18

Diagnosis is made by ERG (electroretinogram). The ERG assesses the function of the photoreceptor cells (rods & cones) and measures amplitudes achieved in response to light stimulus. No response is an extinguished ERG=SARDS
There is no effective treatment at this time to restore vision in SARDS.

Question 19

retinal detachment

Answer 19

occurs between the neurosensory retina and the RPE (retinal pigmented epithelium-outermost layer of retina adjacent to the choroid) due to fluid and/or cells escaping the choroidal vessels and lifting the retina.

Question 20

Key sign of retinal detatchment

Answer 20

Dilated pupils are present and are usually not responsive to light. If the detachment is unilateral, the affected pupil will constrict from consensual input from a normal fellow eye, and re-dilate when light is redirected back to affected eye (Marcus-Gunn pupil). This is a localizing lesion to the retina or optic nerve.

Question 21

Causes of retinal detatchment

Answer 21

Immune mediated, hypertension, UVD, ERU, infectious, neoplasia and steroids

Question 22

UVD targets

Answer 22

this is an auto-immune disease directed at melanocytes which are found in the retina, ciliary body & iris of the eye and the skin

Question 23

ERU (Equine recurrent uveitis):

Answer 23

Retinal detachments in horses cause irreversible vision loss