title: Cluster analysis of patients with ocular surface disease, blepharitis, and dry eye.
abstract: OBJECTIVE
  To develop a classification system for blepharitis and dry eye based on a classification-tree model of a large group of subjects who were given a variety of objective physiologic tests.
  
  
  METHODS
  We evaluated 513 subjects, some healthy and some with blepharitis and dry eye,with tests for tear volume, tear flow, and tear turnover and the Schirmer test for dry eye. Meibomian gland function was evaluated by meibomian gland lipid expression for lipid volume and lipid viscosity, evaporation, and eyelid transillumination for meibomian gland drop out. We subjected these data to cluster analysis and formulated a classification tree.
  
  
  METHODS
  The outcome measure of this study was the statistically valid groups of subjects with and without ocular surface symptoms identified by their physiologic characteristics.
  
  
  RESULTS
  Cluster analysis most successfully grouped subjects by initially dividing them into 2 groups based on the presence or absence of gland drop out and then by lipid viscosity and volume, Schirmer test results, and evaporation. The analysis created 9 categories. This division created an objective classification system that was found to have clinical relevance. Normal subjects were distributed across several groups.
  
  
  CONCLUSIONS
  Using a classification tree, blepharitis and dry eye can be classified with objective physiologic tests into clinically relevant groups that have common characteristics. The analysis establishes the central role of meibomian gland dysfunction in blepharitis and demonstrates the diverse characteristics of the normal population.
authors.affiliation: Department of Ophthalmology, Casey Eye Institute, Oregon Health and Science University, Portland 97201, USA. mathersw@ohsu.edu
authors.forename: William D
authors.initials: WD
authors.lastname: Mathers
authors.forename: Dongseok
authors.initials: D
authors.lastname: Choi
mesh_terms: D000328:Adult; D001762:Blepharitis / Q000145:classification*; D016000:Cluster Analysis; D003663:Decision Trees; D015352:Dry Eye Syndromes / Q000145:classification*; D005141:Eyelid Diseases / Q000175:diagnosis; D005260:Female; D015590:Fluorophotometry; D006801:Humans; D008297:Male; D008537:Meibomian Glands / Q000473:pathology; D008875:Middle Aged; D009994:Osmolar Concentration; D013666:Tears / Q000737:chemistry / Q000378:metabolism