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Abstract

A prospective case control study was performed to evaluate the relative risk (RR) and population attributable risk percentage (PAR%) for all exposures of microbial keratitis and for a range of contact lens (CL) related disorders. The study population comprised new casualty attenders at Moorfields Eye Hospital presenting between 22nd April 1988 and 21st April 1989.

CL wear for the correction of low refractive errors was found to be the major cause of new keratitis cases in this population. Compared to eyes with no predisposing condition, the RR of keratitis in CL wearers was found to be 80.2x (95% confidence limits were 38.5-166.9x) greater. The RR for trauma and previous ocular surface disorders were estimated at 13.9x (6.0-32.2x) and 7.4x (2.2-25.3x) higher respectively. The PAR% for CL wear was found to be 62%. Increased RR for CL wear compared with other exposures were maintained for all severities of keratitis and persisted despite controlling for age, sex and socioeconomic class.

Hydrogel CL’s were found to account for 80% of all cases of lens related keratitis (n = 60). The RR for EWSCL was found to be 20.8-36.8x higher than for a gas permeable lens (GPCL). The RR for keratitis in DWSCL was found to be 3.6- 4. lx higher.

1611 lens wearers were identified from 29,242 new casualty attenders. Lens related disorders were classified according to their probable pathogenesis. EWSCL were found to have the greatest overall risk for any complication occurring at 2.7x (1.73-4.16x) higher than for GPCL. The overall risk for DWSCL was found to be 1.3x (1.0-1.72x) higher than for GPCL. EWSCL showed the greatest risk for metabolic disorders and sterile infiltrates at 2.1-3.7x and 2.4-4.7x that of GPCL. DWSCL were found to have the greatest RR for toxic and hypersensitivity disorders at 5.8-5.9x that of GPCL.

Possible relevant factors in the pathogenesis of lens related keratitis were investigated. Bacterial adherence to unworn hydrogel lenses was demonstrated using a lens homogenisation and colony counting technique. Using this technique, significant numbers of viable organisms, adherent to worn hydrogel CL from wearers with CL related keratitis, were recovered. Bacteria enclosed in a polysaccharide- rich film were demonstrated on the back surface of an EWSCL using scanning and transmission electron microscopy.

Publication Type:	Thesis (Doctoral)
Subjects:	R Medicine > RZ Other systems of medicine
Departments:	School of Health & Psychological Sciences > Optometry & Visual Sciences School of Health & Psychological Sciences > School of Health & Psychological Sciences Doctoral Theses Doctoral Theses

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