title: Incidence of keratitis of varying severity among contact lens wearers.
abstract: OBJECTIVE
  To determine the incidence of non-severe keratitis (NSK) and severe keratitis (SK) among wearers of current generation contact lenses.
  
  
  METHODS
  A 12 month, prospective, hospital based epidemiological study was conducted by examining all contact lens wearers presenting with a corneal infiltrate/ulcer to a hospital centre in Manchester. A clinical severity matrix was used to differentiate between NSK and SK, based on the severity of signs and symptoms. The size of the hospital catchment population and the wearing modalities (daily wear (DW) or extended wear (EW)) and lens types being used were estimated from relevant demographic and market data.
  
  
  RESULTS
  During the survey period, 80 and 38 patients presented with NSK and SK, respectively. The annual incidences (cases per 10,000 wearers) for each wearing modality and lens type were: DW rigid--NSK 5.7, SK 2.9; DW hydrogel daily disposable--NSK 9.1, SK 4.9; DW hydrogel (excluding daily disposable)--NSK 14.1, SK 6.4; DW silicone hydrogel--NSK 55.9, SK 0.0; EW rigid--NSK 0.0, SK 0.0; EW hydrogel--NSK 48.2, SK 96.4; EW silicone hydrogel--NSK 98.8, SK 19.8. The difference in SK between EW hydrogel and EW silicone hydrogel was significant (p = 0.04).
  
  
  CONCLUSIONS
  A clinical severity matrix has considerable utility in assessing contact lens related keratitis. There is a significantly higher incidence of SK in wearers who sleep in contact lenses compared with those who only use lenses during the waking hours. Those who choose to sleep in lenses should be advised to wear silicone hydrogel lenses, which carry a five times decreased risk of SK for extended wear compared with hydrogel lenses.
authors.affiliation: Eurolens Research, Department of Optometry, The University of Manchester, PO Box 88, Manchester M60 1QD, UK. philip.morgan@manchester.ac.uk
authors.forename: P B
authors.initials: PB
authors.lastname: Morgan
authors.forename: N
authors.initials: N
authors.lastname: Efron
authors.forename: E A
authors.initials: EA
authors.lastname: Hill
authors.forename: M K
authors.initials: MK
authors.lastname: Raynor
authors.forename: M A
authors.initials: MA
authors.lastname: Whiting
authors.forename: A B
authors.initials: AB
authors.lastname: Tullo
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003261:Contact Lenses / Q000009:adverse effects* / Q000706:statistics & numerical data; D003262:Contact Lenses, Extended-Wear / Q000009:adverse effects / Q000706:statistics & numerical data; D003263:Contact Lenses, Hydrophilic / Q000009:adverse effects / Q000706:statistics & numerical data; D003320:Corneal Ulcer / Q000453:epidemiology / Q000209:etiology / Q000382:microbiology; D004209:Disposable Equipment; D004739:England / Q000453:epidemiology; D004812:Epidemiologic Methods; D015818:Eye Infections, Bacterial / Q000453:epidemiology / Q000209:etiology; D005260:Female; D006801:Humans; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate; D007634:Keratitis / Q000453:epidemiology* / Q000209:etiology* / Q000382:microbiology; D008297:Male; D008875:Middle Aged; D012720:Severity of Illness Index
chemical_list: D020136:Hydrogel, Polyethylene Glycol Dimethacrylate