Conditions of the anterior segment

• Keratitis can be caused by various microorganisms: Herpes simplex, Herpes zoster, onchocerciasis, microsporidiosis, Acanthamoeba, Staphylococcus aureus, Pseudomonas sp, fungi such as Fusarium, Candida and Aspergillus, Ophthalmia neonatorum caused by gonococci (Neisseria gonorrhoeae) can have very serious consequences. Corneal lesions frequently occur with measles and are aggravated by xerophthalmia (vitamin A deficiency).

• Vitamin A deficiency is characterized by night blindness (retina problem), followed by xerosis of the conjunctivae, with metaplasia (Bitot spots on the temporal conjuctivae). Drying out and cloudiness of the cornea occurs, which can lead to ulceration / perforation of the cornea. Keratomalacia can occur very quickly (in a few hours). The cornea becomes soft and visual capacity is totally lost. Phthysis of the eyeball can occur. Other residual lesions in case of xerophthalmia are staphyloma or a white spot on the cornea (leukoma).

• Keratitis due to chemicals, spitting cobra venom or to caustic / irritant plant sap (beware of euphorbias used in traditional medicine) can cause acute blindness. Some insects such as blister beetles are able to cause acute conjunctivitis and keratitis (Nairobi eye). When stinging urticating hairs of some caterpillars / bird spiders get into the eye they can cause a nodular conjunctivitis and/or keratitis.

• UV-keratitis (actinic conjunctivitis, snow blindness) can result in acute loss of sight (superficial burning of the cornea). This must not be confused with acute blindness in individuals who have looked directly at the sun. These individuals have macular lesions (eclipse retinitis).

• Uni- or bilateral blindness can occur in the context of leptospirosis, syphilis, toxoplasmosis, histoplasmosis and sarcoidosis. Uveitis frequently occurs in HTLV-1 infection, in brucellosis and in various autoimmune diseases.

• Cataract occurs frequently in the tropics. Cataract is generally considered to be the principal and most frequently seen cause of blindness: old age, diabetes, trauma, post-inflammation and congenital. Glaucoma (both closed and open angle) are responsible for a substantial loss of sight.

• Onchocerciasis (river blindness) is characterised by chronic itching (pruritus), subcutaneous noduli, swollen lymph nodes and diminishing sight. Keratitis punctata, and in a later stage sclerosing keratitis, is frequent. Microfilariae of Onchocerca volvulus can be found in the anterior chamber fluid. Subconjunctival migration of mature Loa loa filariae does not cause blindness. Other worms that can cause eye disease include Thelazia callipoeda and T. californiensis (usually ordinary conjunctivitis, occasionally keratitis or dacryocystitis). Angiostrongylus cantonensis can very occasionally be found inside the eye.

• Leprosy is a disease that is seldom imported into the West, but is a major cause of blindness in the third world. Destruction of the nervus facialis and/or of the nervus trigeminus, iridocyclitis and invasion by mycobacteria occur. Blindness can occur suddenly due to leprosy reactions.

• Trachoma (Chlamydia trachomatis) is a very important disease that can lead to blindness if it occurs repeatedly and is left untreated. Four clinical stages are differentiated. Trichiasis and entropion characterise the final phase.

• Dirofilaria repens tends to be found in the extraocular tissues. Trichinella spiralis infections and Romaña sign in Chagas's disease also do not affect the eye itself, but the extraocular tissues.

Category: Medicine Notes