Friday, November 1, 2013

Eye infections

Conjunctivitis and keratitis. The healthy conjunctiva and cornea usually bear a few albus staphylococci and diphtheroid bacilli, mainly derived from the edges of the eyelids. in the newborn, a severe form of acute conjunctivitis, ophthalmia neonatorum, may be caused by the gonococcus in the first 2 or 3 days of life and is liable to damage the cornea unless promptly treated with antibiotics. A much less dangerous infection. ‘sticky eye’. may be caused by S. aureus during the first week or two. At any age, Haemophilus aegypzius may cause acute epidemic conjunctivitis and H. influenzae. Pneumococcus and Meningococcus may cause sporadic cases. Pseudornonas aeruginosa may cause serious superficial or deep infections after trauma or surgery to the eye, and Moraxella Izicunata is found in a rare, subacute or chronic angular conjunctivitis.
Many cases of conjunctivitis are due to viruses of different kinds, e.g. adenovirus type 8 which causes epidemic kerato-conjuctivitis in factories, shipyards and hospitals, whilst herpes simplex virus may cause keratitis. Chlamydia trachornatis causes trachoma, a common cause of corneal scarring and blindness in many undeveloped countries, and also a much milder, inclusion conjunctivitis in developed countries, e.g. swimming pool conjunctivitis in older subjects and congenital conjunctivitis within a few days of birth.
The principal difficulty in laboratory diagnosis is that of obtaining an adequate specimen in which the viability of the more delicate pathogens is preserved, it is best to make smears and seed culture plates beside the patient immediately after collecting, material from the eye.
Because the volume of exudates obtainable is generally small, a dry cotton-wool swab, which would absorb and retain most of the specimen, is unsuitable as a means of collection .
The exudates should be picked up with a sterile platinum loop or on the smoothly rounded tip of a thin glass or plastic rod; otherwise, on the tip of a thin, serum-coated swab. It should be collected from the conjunctiva, e.g. from under an everted eyelid, and contamination from the skin and margin of the eyelid should be avoided . A separate collection should be made for inoculation on to each culture plate and for the making of a smear. The cultures should be on blood agar and heated-blood agar plates incubated in air with 5-10% CO2.
When the specimen material is little, the smear should be confined to a small marked area of the slide, e.g. 5-10 mm in diameter; it should be stained by Gram’s method with a strong counterstain.
If it is necessary to dispatch a specimen to the laboratory before inoculation on to Culture media, it should be taken on an albumen-coated swab which is placed at once in Stuart’s transport medium.
For examination for chlamydia by immuno-fluorescence or culture in cells, scrapings must be taken from the affected conjunctIva after wiping off the exudate. For examination for viruses, a swab from the conjunctiva should be submitted in a virus transport medium.
Infections of orbit and eyeball. These may be caused by any of a variety of aerobic and anaerobic bacteria of the types found in pyogenic and wound infections. Any exudates obtainable should be examined for such organisms and a blood culture should be done. Iritis and choroidoretinitis may occur in the course of systemic viral infections, e.g. with cytomegalovirus, and toxoplasmosis, for which serological diagnosis should be attempted.
Styes are small boils affecting the follicles or the eyelashes on the edges of the eyelids; they are usually caused by S. aureus and treated without bacteriological investigation.