Lecture Nine: Posterior Segment

what does the posterior segment include?

Vitreous

Retina, Choroid, Scleral

Optic Nerve

posterior chamber?

Sulcus between the lens and ciliary body (behind the iris).

tests to look at the posterior segment?

- Menace response

- Dazzle reflex

- Pupillary light reflex (PLR)

- indirect ophthalmoscopy (28D or 2.2D lens) vs direct

- Electroretinogram (ERG) - flash, multifocal -- flash lights --> get waveform like ecg

- Imaging: Ultrasound, CT, MRI

- Neurologic exam

- Systemic workup

what is this?

retinal detachment

primary vitreous

Hyaloid vascular system

secondary vitreous

adult

tertiary vitreous

lens/zonules

vitreous makes up ? % of the eye's volume in domestic animals

75%

vitreous attached to?

optic nerve, ora ciliaris retinae, posterior lens

Persistent Hyaloid Artery?

• Rarely clinical problem, can cause cataract

• Mittendorf's dot, Bergmeister's papilla

Persistent Hyperplastic Primary Vitreous?

persistent fetal vasculature -- Normally regressed at 3wk (dogs), 8wks (cats)

white opacity in pupil -- Leukocoria

leave alone vs cataract surgery

dobermans and staff terriers

staged 1-6

Asteroid Hyalosis?

aka floaters in vitreous

(Calcium/lipid complexes)

Vitreous Degeneration (Syneresis)?

Liquified, "sloshy" vitreous 🡪 predisposes to retinal detachment

other vitreous issues include ?

hemorrhage

inflammation

retina role?

Converts light into electrical signals for vision.

retina structure?

10 layers, including photoreceptors (rods & cones), ganglion cells, and retinal pigment epithelium (RPE).

choroid role?

Provides vascular supply to the retina

where is the tapetum?

choroid

retina layers (outside to in)?

Pigmented Epithelium

Photoreceptors (Rods/Cones)

External Limiting Membrane

Outer Nuclear Layer

Outer Plexiform Layer

Inner Nuclear Layer

Inner Plexiform Layer

Ganglion Cell Layer

Nerve Fiber Layer (optic nerve)

Internal Limiting Membrane

tapetum role?

Reflective to aid in dim light

Develops post-natally

Variable color between breed, coat color, species, etc.

Choriocapillaris?

Capillaries from choroid feeding posterior retina

Accumulation of ganglion cell axons leaving the eye within a fragile lamina cribrosa?

optic nerve

axonal flow goes from ? to ? for nutrients

CNS to eye

optic nerve & axon flow damaged during?

glaucoma

optic nerve shape in dog

triangle

optic nerve shape in cat

round

optic nerve shape in horse

ovoid

optic nerve shape in bird

cant see -- behind pecten

? effects the shape

myelination

puppy vs adult tapetum

blue vs yellow/green

do all dogs have pigment in the RPE?

no

Holangiotic retina vascular pattern?

in who?

whole retina

dog, cat, sheep, pig, human

Paurangiotic retina vascular pattern?

in who?

only extend out a little bit

horses, guinea pigs, Elephants

Merangiotic retina vascular pattern?

in who?

long meridian plains

rabbits

Anangiotic retina vascular pattern?

in who?

thinner retina (other than bat is thick)

birds, reptiles, bats

what does it mean when the tapetum is REALLY shiny from afar?

retinal thinning / atrophy

dull tapetum?

something in the way (retinal edema, other

causes of tapetum hemorrhage?

Hypertension, thrombocytopenia, coagulopathy, hyperviscosity, DIC, etc.

developmental Disorders of the Posterior Segment?

PHPV

Retinal Detachment

Retinal Dysplasia

Collie Eye Anomaly

Merle Ocular Dysgenesis

PHPV

Persistent Hyperplastic Primary Vitreous

Focal or generalized jumbling of retina in rosettes +/- folds, focal detachments?

retinal dysplasia

non-inherited forms of retinal dysplasia?

• Panleukopenia/FeLV in cats

• Adenovirus/Herpes in dogs

• BVD in cows

retinal dysplasia may be associated with?

oculoskeletal dysplasia in labs

what am i describing?

- Congenital, bilateral, asymmetric anomaly of choroid, optic nerve, sclera

- Choroidal hypoplasia, posterior pole colobomas, retinal detachment, tortuous vessels, hyphema, variable vision loss

Collie Eye Anomaly (CEA)

what percent of collies get Collie Eye Anomaly

85% !!!

what am i describing?

- failure of RPE development 🡪 failure of nearby retina, choroid, sclera to differentiate

- merling gene defect

- Homozygous = mostly white, multiple ocular defects

- Heterozygous = mild

Merle Ocular Dysgenesis

acquired posterior segment diseases include?

• Degeneration

• Inflammatory

• Detachment

• Neoplasia

• Generalized OMSD

what am i describing?

- Photoreceptor loss

- slow onset

inherited PRA (Progressive Retinal Atrophy)

inherited PRA (Progressive Retinal Atrophy) tx?

none

inherited PRA (Progressive Retinal Atrophy) in persians

recessive, early onset, rapid progression

inherited PRA (Progressive Retinal Atrophy) in abyssinians

early has rapid progression, can have gradual form

taurine deficiency causes ? due to ?

"Feline Central Retinal Degeneration"

+ heart disease

- Irreversible lesions, begin in area centralis 🡪 progress to entire retina if deficiency not corrected

home made diets

Enrofloxacin (Fluoroquinolone Associated Retinal Toxicity) causes what?

acute irreversible toxicity

destroys retina / blind

If must use enrofloxacin, only

5mg/kg/day

SARDs?

sudden acquired retinal degeneration

sards symptoms and signalment?

Acutely blind

Middle-aged +/- fat, female, Cushings common

NORMAL Fundus exam for quite some time

FLAT ERG

dark spots (hypo-reflective) in the eye may indicate

active inflammatory signs

Sharp borders + Hyperreflectivity =

inactive inflammation

acquired inflammatory dogs?

Distemper, Rikettsia, Fungi

acquired inflammatory cats?

FIV, FeLV, FIP, Toxo, Fungis (Crypto, Histo)

Uveodermatologic Syndrome?

• Attach on melanocytes

• Skin, uveal issues

• Great risk for secondary glaucoma

Uveodermatologic Syndrome tx?

steroids

Expect some damage to vision/blindness even if not detectable (focal)

underlying problem

causes of retinal detachment?

Hypertension, Exudative, Serous, Neoplasia, Congenital, Vitreous Traction

Rhegmatogenous retinal detachment?

hole/tear in retina

retinal detachment tx?

promptness critical!! -- Retina needs choroid for oxygen, degeneration can be fast (1mo)

1. Medical – treat underlying condition

2. Surgical (a must of there is a tear) – Retinopexy vs. intravitreal surgery

optic nerve coloboma?

portion of the optic nerve or surrounding structures (such as the retina or choroid) is missing or underdeveloped

optic nerve Micropapilla

vision

underdeveloped or abnormally small optic disc (the point where the optic nerve enters the eye)

optic nerve Hypoplasia/Aplasia

no vision

optic nerve Papilledema

vision

swelling of the optic nerve head (optic disc) due to increased intracranial pressure

Optic Neuritis

(no vision) - guarded prognosis (50%)

- Acute blindness, mydriasis, absent PLRs, swollen/red ON (may not see if retrobulbar portion of ON...