The uveal tract Flashcards
What are the parts of the uveal tract
The uveal tract is the middle vascular layer of the globe
The anterior uvea consists of the iris and ciliary body
The posterior uvea is the choroid
What are the roles of the ciliary body
The ciliary body:
- is the principal source of aqueous humor production (by active secretion and ultrafiltration)
- controls accomodation
- is important in the control of intraocular pressure (uveoscleral pathway of aqueous outflow)
What are the roles of the blood-aqueous barrier
The blood-aqueous barrier:
- prevents most large molecules and cells from entering the eye
- limits the immune response against the internal eye thus making it an immune-privileged site
What is the Waardenburg syndrome
Waardenburg syndrome occurs in some blue-eyed white cats and consists of deafness, heterochromia irides and a white coat color
It is inherited as a dominant trait with complete penetrance for the white coat and blue irides
What are the ocular implications of Chediak-Higashi syndrome
Chediak-Higashi syndrome is inherited as an autosomal recessive trait and has been reported in Persians with a blue-smoke coat color and pale irides
Affected cats have platelet function defects and may develop:
- cataracts
- tapetal degeneration
- nontapetal fundus hypopigmentation
What is iris coloboma
Congenital absence of some or all iris tissue is termed iris coloboma
- “typical” colobomas arise in the area of the optic fissure (approximately 6 to 7 o’clock)
- “atypical” colobomas arise in other areas of the eye
What is persistent pupillary membrane
Persistent pupillary membrane is the most common form of anterior segment dysgenesis
- it arises due to incomplete regression of embryonal tissues, which normally disappear by six weeks of age
They appear as thin strands of iridal tissue arising from the iris colarette
- they may be attached to other PPMs, to the anterior lens capsule, or to the posterior cornea
How can you make the difference between persistent pupillary membrane and acquired synechial adhesions
The distinctioon can usually be made by determining whether the uveal tissue arises from the iris colarette (PPM) or the pupil margin (synechiae)
What can you say about synechiae
Synechiae are adhesions between the iris and other ocular structures
- anterior synechiae are most often caused by perforing ocular injury with incarceration of the iris within the wound
- posterior synechiae are fibrinous adhesions of the pupillary margin of the iris or the posterior iris epithelium to the anterior lens capsule
Adhesions forming around the entire circumference of the pupil, termed iris bombe, obstructs aqueous flow into the anterior chamber and almost invariably result in glaucoma
What are the key features for lipaemic aqueous
Lipaemic aqueous results from leakage of lipid from the systemic circulation into the anterior segment of the eye giving rise to a “milky” appearance of the aqueous humour
Lipaemic aqueous can occur:
- as a result of primary inherited hyperlipoproteinemia, such as inherited hyperchylomicronemia in the Burmese
- secondary to conditions such as endocrinopathies (e.g. diabetes mellitus), obesity or iatrogenic drug therapy (e.g., glucocorticoids, megestrol acetate)
Clinical signs:
- the most common presentation is transient lipemic aqueous after a fatty meal
- uveitis can be a predisposing factor, as breakdown of the blood-aqueous barrier allows lipid to enter the anterior chamber (the inverse is also right)
- the fundus should be examined to assess whether there is also lipemia retinalis
Diagnosis:
- triglycerides high (> 25mmol/l)
- lipoprotein analysis and electrophoresis could help
What are the two types of uveitis and their characteristics
Anterior uveitis
- the most common
Posterior uveitis
- is almost always accompanied by inflammation of the adjacent retina, and is thus usually termed chorioretinitis
- it arises most often from systemic infections, especially with fungal organisms
What would be your main differentials for uveitis
Uveitis may be infectious or noninfectious
Infectious causes include:
- FeLV
- FIV
- FIP
- Toxoplasmosis
- Bartonellosis
- systemic fungal infections
Noninfectious causes include:
- trauma
- immune-mediated inflammation
- neoplasia
- reflex uveitis occurs in most cases of corneal ulceration
According to one histopathological study the main causes were:
- FIP
- FeLV-associated lymphoma
- trauma
Explain why it is important to perform a thorough physical examination in cats with uveitis
Cats with serious systemic diseases may present with signs of uveitis before other clinical signs become evident
- therefore it is imperative to perform a thorough physical examination of every cat presenting with either unilateral or bilateral uveitis
What are the goals in treating uveitis
The goals in treating uveitis are:
- to eliminate infectious agents
- control inflammation
- stabilise the blood-aqueous barrier
- minimise bystander damage to intraocular structures
What would be your treatment plan for uveitis
Treat the specific cause if identified
Use topical and systemic antiinflammatory drugs
- prednisolone acetate or dexamethasone phosphate up to six times daily
- contraindicated with corneal ulcer or stromal infection
Topical mydriatics are useful to:
- stabilise the blood-aqueous barrier,
- reduce pain through paralysis of the iridal sphincter and ciliary body musculature
- reduce the likelihood of synechiae
- should be avoided if the IOP is raised
- 0.5-1% tropicamide can be used
Enucleation is required for blind, painful eyes that are not responsive to medication
When is aqueocentesis the most useful
Aqueocentesis is the most useful for the diagnosis of lymphoma
What are the key features for diffuse iris melanoma
Diffuse iris melanoma is the most common primary intraocular neoplasm
- it tends to be more rapidly progressive over time than benign iris melanosis
Signs such as:
- progression of pigmentation
- anterior uveitis
- dyscoria
- reduced pupil motility
- thickening or altered texture of the iris
- pigment invasion into the iridocorneal angle
- free pigment in the anterior chamber
are considered to be indicative of melanoma rather than melanosis
There is a high potential for metastasis, principally to the liver and lungs, which has been reported as late as 1-3 years after enucleation
What are the key features for feline intraocular sarcoma
Feline intraocular sarcomas are highly malignant intraocular neoplasms that involve the uveal tract
- there is a high potential for hematogenous metastasis and local invasion through the sclera and optic nerve
They are most frequently associated with a history of significant ocular trauma, and an average interval of seven years from the traumatic event to the diagnosis of the tumor has been reported
Clinical signs include:
- a visile intraocular mass
- uveitis
- hyphema associated with pre-iridal fibrovascular membranes
- secondary glaucoma
Treatment:
- early enucleation
What are the key features for Spastic Pupil Syndrome
Spastic Pupil Syndrome is a condition unique to cats
Clinical signs:
- cats are healthy and visual
- no ocular abnormalities other than unusual pupil behavior
- Anisocoria that may sometimes be transient and independent of ambient light levels
- failure to achieve complete mydriasis in dark conditions
- sluggish PLRs
Pathomechanism:
- it is claimed that all cats with SPS test positive for FeLV, although this is not always the case at the initial examination
- the lesion is thought to result from viral-induced neuritis involving cranial nerve III
Treatement and prognosis:
- no treatment
- long-term prognosis may be poor for cats aaffected by FeLV
