The retina and the choroids are richly
vascularised structures and can therefore be
colonised by germs via the haematogenous route in
the course of a systemic infectious disease. The
germs responsible for this type of infection can be
fungi, viruses, bacteria and parasites. Ocular
candidiasis is outstanding amongst these
colonisations because of its frequency; it can
manifest itself as an endophthalmitis with a slow and
hidden course. The so-called ocular histoplasmosis
syndrome, although it is infrequent in our setting, is
an important cause of choroidal neovascularisation.
The viruses that most frequently affect the retina are
of the herpes type and can produce devastating
symptoms in immunoincompetent patients, named
acute retinal necrosis syndrome. Retinitis due to
cytomegalovirus is more frequent in
immunodepressed patients, as in the case of AIDS,
but it must also be contemplated in patients with
lymphoma and immunomodulatory treatment. The
most frequent bacterial diseases that affect the retina
are syphilis and tuberculosis. Disease due to cat
scratches, caused by a borrelia, can produce a
neuroretinitis. Toxoplasmosis is the most common of
the infectious diseases caused by a parasite and
gives rise to chorioretinitis. Toxocariasis, also
caused by a parasite, is second in importance, giving
rise to choroidal granulomas and retinal tractions
