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Abstract
Abstract
Pathophysiology of Ocular Toxoplasmosis
Garweg J. G.
Dept. Ophthalmology, University of Bern, Bern, Switzerland
Purpose: Ocular toxoplasmosis is a local manifestation of systemic Toxoplasma infection, which affects mainly the posterior eye segment. Reactivation of the initially retinal condition presumably results from the rupture of quiescent parasitic cysts lying adjacent to pre-existing scars, and may secondarily involve the choroid (leading to retino-choroiditis).
Conclusions: Although the genomic mechanisms underlying host-parasite interaction are largely unknown, toxoplasmic retinochoroiditis is clearly a local event, which may fail to evoke a detectable systemic immune response. Local immune tolerance referred to as anterior-chamber-associated immune deviation (ACAID) may likewise thwart attempts to confirm the clinical diagnosis. Aqueous humour may be analyzed for the presence of parasitic DNA or of specific antibodies, but the DNA burden therein is low, and a surer confirmation would necessitate risky puncturing of the vitreous. Laboratory confirmation of the diagnosis is also frustrated by marked individual differences in the time elapsing between the onset of clinical symptoms and the activation of specific antibody production, which results in a high proportion of false negatives. A delay in the onset of specific local antibody production could reflect immune tolerance in cases of congenital infection but not obviously in instances of acquired toxoplasmosis as might the incidence of cases with confirmed local antibody production. Against this background, curr