Uvea- Iris, Ciliary Body, and Choroid

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Anatomy

General
Extremely vascular
Highly pigmented
Smooth muscle (iris and ciliary body)
Function = nutrition
Aqueous for the cornea and lens
Choroidal vessels supply the outer retina

Anterior uvea (iris, ciliary body)

Iris
Forms a diaphragm with an opening (pupil)
Iris sphincter muscle (parasympathetic control)
Iris dilator muscle (sympathetic control)
Corpora nigra (granula iridica) in equine and ruminants
Ciliary body
Posterior to the iris (not visible on exam)
Epithelium of the ciliary processes produce aqueous
Ciliary body muscle is under parasympathetic control and functions in lens accomodation

Blood-Ocular Barriers

Protect intraocular structures from infectious agents, toxins, drugs, neoplastic cells
Tight junctions
Blood-aqueous barrier
Ciliary body epithelium
(iris capillary endothelium)

Blood-retina barrier
Retinal pigmented epithelium
(retinal capillary endothelium)

IRIS Neoplasia

Canine
Benign but locally invasive (low metastatic potential)
Consider laser ablation when small
If large usually enucleate globe once secondary glaucoma develops and the eye is blind, painful
Feline
Higher metastatic potential
Recommend enucleation when the lesion is raised, causing dyscoria or anisocoria (larger pupil
Lymphoma (always considered metastatic)
Diffuse iris infiltration
Hemorrhagic

IRIS Non-inflammatory conditions-Iris atrophy

Normal aging change in geriatric dogs (especially miniature and toy poodles!) and cats
Not pathologic
Appears as an irregular thinning of the iris at the pupil; or can be as advanced as holes in the iris
Causes an EFFERENT pupillary light reflex deficit

IRIS Non-inflammatory condition Iris cysts

Originate at the pupil margin from the posterior pigmented epithelium of the iris
Non-pathologic EXCEPT in Golden Retrievers (associated with pigmentatry uveitis syndrome)
Locations within the anterior chamber
Attached at the pupil margin
Floating in the ventral anterior chamber
Ruptured cysts appear on the ventral corneal endothelium
Differential diagnosis from melanoma
Cysts are smooth and round
Cysts transilluminate (can see tapetal reflection through it)

IRIS Non-inflammatory condition Persistent pupillary membranes

Congenital
Remnants of blood vessels spanning the pupil in embryonic development  as the eye develops there is not complete atrophy of the membrane tissue
Iris to iris (most common): not clinically significant
Iris to lens or iris to cornea (uncommon): can be clinically significant if it results in a large lens or corneal opacity at the point of attachment

Posterior uvea (choroid)

Lies between sclera and retina
Nutrition and removal of waste products for retina
Contains the tapetum
Highly reflective layer
Improves night vision by acting as a reflector or "mirror" to incoming light; light not absorbed by the photoreceptors on the first pass is reflected back to the photoreceptors for a second chance to stimulate

Uveitis

inflammation of the uvea with breakdown of the blood-ocular barrier(s)
Anterior vs. posterior uveitis
Physiology of uveitis
Disruption of BOB tight junctions & dilated, leaky blood vessels allow cells and protein to leak into tissue
Prostaglandin-mediated
Miosis (prostaglandin effect on iris sphincter)
Pain (prostaglandin effect on ciliary muscle)

Uveitis Clinical signs

Non-specific clinical signs
Blepharospasm  pain from ciliary muscle spasm
Inflamed conjunctiva
Engorged scleral vessels
Discharge (tearing or mucoid)
Corneal edema  inflammatory cells in the aqueous affect endothelial cell function
Vision loss  when uveitis is severe from cloudy aqueous, scarred or closed pupil, cataract, retinal detachment

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