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Parasitic Intraocular Infections- PSD B14

Terms in this set (35)

What systemic infection is caused by a Protozoa, infects humans after ingesting contaminated food or water (acquired) or by maternal transplacental spread (congenital), and causes anywhere from 1/4-1/2 of cases of posterior uveitis?
Toxoplasmosis
Toxoplasmosis can be acquired through 1 of 3 forms. What form is acquired transplacentally- oocysts, bradyzoites, or tachyzoites? How are the other two transmitted?
Tachyzoites are transmitted transplacentally. Oocysts are transmitted through unwashed fruits and vegetables. Tissue cysts containing bradyzoites are in undercooked or raw meats.
What is the most common cause of posterior segment infection and focal necrotizing retinitis in HEALTHY adults?
Ocular toxoplasmosis
What are some symptoms of ocular toxoplasmosis?
Most patients report UNILATERAL floaters and blurred vision (common findings). There may possibly be conjunctival injection and photophobia. The patient may also be asymptomatic (especially if it's inactive).
What condition is characterized by a "headlight in the fog" appearance? What represents the headlight in the fog?
Ocular toxoplasmosis. Headlight in the fog is from an active lesion (headlight) with an accompanying vitritis (fog). This is often found adjacent to a pigmented chorioretinal scar (from prior activation). The macula is involved in a majority of cases.
What other findings aside from the active retinochoroiditis may be seen in ocular toxoplasmosis?
Mild to moderate AC reaction and retinal vasculitis in the vicinity of the lesion or in far periphery.
What is the average amount of reactivations of toxoplasmosis?
Average ~3 per patient
Describe the pathogenesis of ocular toxoplasmosis.
Tachyzoites cause focal necrosis and exudation which progresses from the retina into the choroid. Once the infection is controlled, tachyzoites give way to bradyzoites and encystment. Inflammation then clears with resultant focal chorioretinal scar due to tissue damage.
What is the most effective way of reducing Toxoplasma-related morbidity?
Prevention
True or false- Medical treatment for toxoplasmosis is generally saved for cases that are sight threatening because it is often self-limiting, you can not eliminate the organism, and the medications are expensive, multiple, and have numerous side effects.
True- if the fovea or optic nerve are affected, treatment will generally be initiated.
What condition is spread through roundworms of puppies (more commonly) and kittens through eggs in contaminated raw veggies, water, or soil or infected raw/undercooked meat?
Toxocariasis
What are symptoms of ocular toxocariasis?
Blurred vision, floaters, and occasionally mild pain or photophobia. The patient may be asymptomatic as well. It is often not detected in children until they: fail a vision screening test or develop strabismus or leukocoria.
Ocular toxocariasis classically presents in one of three ways. What is the most common sign?
Peripheral granuloma (about 50%)
The other two signs are: posterior pole granuloma (25-50%) or dense vitreous inflammation resembling endophthalmitis (<25%)
**What condition is characterized by a peripheral granuloma with retinal folds?**
Ocular toxocariasis- fibrovascular tracts occur and are very common with toxocariasis; these can stretch the macula and start to affect vision
What is the pathogenesis of ocular toxocariasis? What damages the intraocular structures- the worm, the immune response, or toxins released by the worm?
Infectious larvae migrate through the wall of the small intestine and reach the eye via the bloodstream. Intraocular structures are damaged by the patient's immune-mediated inflammatory response (often after the worm dies).
If a patient presents with acute inflammation secondary to ocular toxocariasis and an anterior chamber reaction, what is the appropriate treatment?
Steroids (can be administered by various routes) to treat acute inflammation with an added cycloplegic/mydriatic agent if there is AC inflammation (to help prevent posterior synechiae).
What is the visual prognosis for ocular toxoplasmosis?
1/4 of patients have vision loss due to macular/optic nerve involvement, RD (serous, rhegmatogenous, or tractional), or late secondary CNV
What is the visual prognosis for ocular toxocariasis?
This is not near as common as toxoplasmosis. About 2/3 have some degree of vision loss, often due to vitreoretinal folds/traction extending from peripheral exudate or granuloma (peripheral or posterior pole).
What is the difference in treatment for toxoplasmosis vs. toxocariasis?
Toxoplasmosis requires treatment with steroids accompanied by anti-microbial therapy. Toxocariasis is treated with steroids with or without antimicrobial therapy.
What condition is caused by a single lone nematode found within the subretinal space and results in early findings of a mild vitritis, mild optic disc edema, and crops of gray-white outer retinal lesions?
Diffuse Unilateral Subacute Neuroretinitis (DUSN)
What age group is Diffuse Unilateral Subacute Neuroretinitis (DUSN) usually seen in? What type of climate is it more prevalent in?
It is usually seen in an otherwise healthy child or young adult. It is more prevalent in warmer climates.
In most cases, what is the only symptom seen in DUSN?
Unilateral vision loss (usually insidious). It is occasionally associated with TVOs (transient visual obscurations).
What are three late findings seen in DUSN?
Diffuse degenerative changes affecting the RPE and retina, optic atrophy, and narrowed retinal arterioles
What is the cause of the intraocular damage done in DUSN?
The worm's waste products are toxic to the retina and result in an inflammatory response.
What is the appropriate treatment of DUSN?
Photocoagulation of the nematode (visual prognosis is good if the worm is killed early) and oral medications (anti-helminths) are available if the worm is not detected/destroyed.
What is the second biggest infectious cause of blindness? (For fun, what is the first?)
The second biggest infectious cause of blindness is onchocerciasis. The first biggest is trachoma.
How is onchocerciasis contracted?
Infection of parasitic helminth Onchocerca volvulus contracted through the bite of a black fly
What systemic findings do we see with onchocerciasis?
Dermatologic lesions/nodules and occasional lymphatic obstruction/edema
What ocular findings do we see with onchocerciasis?
Sclerosing keratitis, anterior uveitis (floating microfilariae seen in AC), and chorioretinitis (bilateral chorioretinal atrophy with RPE clumping)
What is an effective way to slow the spread of onchocerciasis?
Spraying of rivers where the flies breed- treating the mass population decreases the spread
What is the individual treatment of onchocerciasis?
Anti-parasitic medication (Ivermectin), antibiotic medication against symbiotic bacterium, and steroids help quell the uveitis (chorioretinal lesions persist)
What ocular infection is acquired through the parasitic infection of the larval form of the pork tapeworm?
Cysticercosis - the presence of an adult tapeworm in the gut is reasonably harmless, but larva travel through the blood to become encysted in the brain, muscle, and eyes.
What causes the ocular findings in ocular cysticercosis?
Cyst death releases toxins which induce a severe inflammatory reaction- similar to toxocariasis in that the toxins induce an inflammatory response that causes the damage
What are three common symptoms of ocular cysticercosis?
Unilateral decreased vision, pain, and recurrent redness are common symptoms
**What is the appropriate treatment for ocular cysticercosis?**
*Surgical removal of larvae or cysts*, systemic steroids to control the inflammation, or anti-helminthic medication (controversial because sometimes killing the organism is worse because that's what leads to the inflammatory reaction)
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