title: Microcysts: clinical significance and differential diagnosis.
abstract: BACKGROUND
  Microcysts are the most-distinctive and easily detectable indicator of contact lens-induced hypoxia. They should not be confused with cyst-like inclusions that occur in conditions such as Meesmann's dystrophy, bullous keratopathy, and Cogan's microcystic dystrophy, or with mucin balls, vacuoles, microcystic edema, and infiltrates.
  
  
  METHODS
  Data from published literature and recent data from The Cornea and Contact Lens Research Unit (CCLRU) clinical trials involving low Dk and prototype high Dk soft contact lenses (SCLs) were examined.
  
  
  RESULTS
  Extended wear with low Dk SCLs induces significant numbers of microcysts, whereas extended wear with high Dk SCLs does not. Subjects who transfer from low Dk to high Dk lenses have an initial increase in the number of microcysts after seven days that declines to normal levels over 1 to 3 months. Microcysts can be differentiated from other ocular conditions as they show reversed illumination, are 10- to 50-microm irregularly shaped dots, and are often associated with lens-induced hypoxia.
  
  
  CONCLUSIONS
  Microcysts are easily observed and differentiated from other conditions in clinical practice. On average, fewer than ten microcysts per eye occur in nonhypoxic lens wear and, on average, more than 20 microcysts per eye are an indication of chronic hypoxia. The increase in microcyst numbers after transfer from low to high Dk lens wear is transitory and does not necessitate a period of no lens wear.
authors.affiliation: Cornea and Contact Lens Research Unit, School of Optometry, and The Cooperative Research Centre for Eye Research and Technology, The University of New South Wales, Sydney, Australia.
authors.forename: L
authors.initials: L
authors.lastname: Keay
authors.forename: I
authors.initials: I
authors.lastname: Jalbert
authors.forename: D F
authors.initials: DF
authors.lastname: Sweeney
authors.forename: B A
authors.initials: BA
authors.lastname: Holden
mesh_terms: D003262:Contact Lenses, Extended-Wear / Q000009:adverse effects; D003316:Corneal Diseases / Q000175:diagnosis* / Q000209:etiology; D003560:Cysts / Q000175:diagnosis* / Q000209:etiology; D003937:Diagnosis, Differential; D019573:Epithelium, Corneal / Q000473:pathology*; D006801:Humans; D000860:Hypoxia / Q000209:etiology