title: Pre-corneal tear film thickness in humans measured with a novel technique.
abstract: OBJECTIVE
  The purpose of this work was to gather preliminary data in normals and dry eye subjects, using a new, non-invasive imaging platform to measure the thickness of pre-corneal tear film.
  
  
  METHODS
  Human subjects were screened for dry eye and classified as dry or normal. Tear film thickness over the inferior paracentral cornea was measured using laser illumination and a complementary metal-oxide-semiconductor (CMOS) camera. A previously developed mathematical model was used to calculate the thickness of the tear film by applying the principle of spatial auto-correlation function (ACF).
  
  
  RESULTS
  Mean tear film thickness values (±SD) were 3.05 μm (0.20) and 2.48 μm (0.32) on the initial visit for normals (n=18) and dry eye subjects (n=22), respectively, and were significantly different (p<0.001, 2-sample t-test). Repeatability was good between visit 1 and 2 for normals (intraclass correlation coefficient [ICC]=0.935) and dry eye subjects (ICC=0.950). Tear film thickness increased above baseline for the dry eye subjects following viscous drop instillation and remained significantly elevated for up to approximately 32 min (n=20; p<0.05 until 32 min; general linear mixed model and Dunnett's tests).
  
  
  CONCLUSIONS
  This technique for imaging the ocular surface appears to provide tear thickness values in agreement with other non-invasive methods. Moreover, the technique can differentiate between normal and dry eye patient types.
authors.affiliation: Biomedical Engineering, University of California Irvine, Irvine, CA 92697-2715, USA.
authors.forename: Kaveh
authors.initials: K
authors.lastname: Azartash
authors.forename: Justin
authors.initials: J
authors.lastname: Kwan
authors.forename: Jerry R
authors.initials: JR
authors.lastname: Paugh
authors.forename: Andrew Loc
authors.initials: AL
authors.lastname: Nguyen
authors.forename: James V
authors.initials: JV
authors.lastname: Jester
authors.forename: Enrico
authors.initials: E
authors.lastname: Gratton
mesh_terms: D000293:Adolescent; D000328:Adult; D001767:Blinking; D016022:Case-Control Studies; D003315:Cornea / Q000000981:diagnostic imaging* / Q000187:drug effects / Q000503:physiopathology; D005260:Female; D019793:Fluorescein / Q000032:analysis; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000295:instrumentation / Q000379:methods; D007834:Lasers; D008297:Male; D008432:Mathematical Computing; D008856:Microscopy, Fluorescence; D009883:Ophthalmic Solutions / Q000008:administration & dosage; D011859:Radiography; D015203:Reproducibility of Results; D013666:Tears / Q000187:drug effects / Q000502:physiology*; D014985:Xerophthalmia / Q000175:diagnosis / Q000000981:diagnostic imaging* / Q000503:physiopathology; D055815:Young Adult
chemical_list: D009883:Ophthalmic Solutions; D019793:Fluorescein