title: Corneal thickness in keratoconus: comparing optical, ultrasound, and optical coherence tomography pachymetry.
abstract: OBJECTIVE
  To compare the central and peripheral pachymetry measurements determined using Orbscan IIz (Bausch & Lomb, Rochester, NY), Visante optical coherence tomography (OCT; Carl Zeiss Meditec, Dublin, CA), and RTVue OCT (Oculus Technologies, Wynwood, WA) with ultrasound pachymetry in eyes with established keratoconus and to evaluate the agreement between them.
  
  
  METHODS
  Evaluation of diagnostic technologies.
  
  
  METHODS
  One hundred six eyes of 67 consecutive patients with a clinical diagnosis of keratoconus ranging in age from 12 to 40 years.
  
  
  METHODS
  Central corneal thickness (CCT) was determined by all the 4 techniques. Peripheral corneal thicknesses were determined using Orbscan IIz, Visante OCT, and RTVue at 8 points (superior, inferior, temporal, nasal, superior-temporal, inferior-temporal, superior-nasal, and inferior-nasal) all in the 5.0- to 7.0-mm arcuate zone.
  
  
  METHODS
  Central and peripheral keratoconus thickness.
  
  
  RESULTS
  Ultrasound pachymetry determined significantly higher CCT values than Orbscan IIz (P<0.001), Visante (P<0.001), and RTVue (P = 0.037), with a mean ± standard deviation difference of 14±3 μm, 13±2 μm, and 5±3 μm, respectively. The mean CCT difference was minimal (1±3 μm; P = 0.69) between the Orbscan IIz and Visante. A strong correlation was found (r>0.80) between all the CCT measurement techniques. Orbscan IIz significantly overestimated the peripheral thickness compared with the rest, and the mean differences ranged between 21 and 60 μm. Mean peripheral thickness differences between RTVue and Visante OCT always remained less than 20 μm. Weak correlations and larger limits of agreement were found between the techniques in thinner and peripheral zones.
  
  
  CONCLUSIONS
  Orbscan IIz, Visante, RTVue, and ultrasound pachymetry show high correlation, although Orbscan IIz and Visante significantly underestimated CCT measurements compared with ultrasound pachymetry in keratoconus. Orbscan IIz significantly overestimated peripheral corneal thickness compared with RTVue and Visante.
authors.affiliation: L. V. Prasad Eye Institute, Hyderabad, India. Electronic address: duttadebarun@gmail.com.
authors.forename: Debarun
authors.initials: D
authors.lastname: Dutta
authors.affiliation: L. V. Prasad Eye Institute, Hyderabad, India.
authors.forename: Harsha L
authors.initials: HL
authors.lastname: Rao
authors.affiliation: L. V. Prasad Eye Institute, Hyderabad, India.
authors.forename: Uday K
authors.initials: UK
authors.lastname: Addepalli
authors.affiliation: L. V. Prasad Eye Institute, Hyderabad, India.
authors.forename: Pravin K
authors.initials: PK
authors.lastname: Vaddavalli
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D003315:Cornea / Q000473:pathology*; D063171:Corneal Pachymetry / Q000295:instrumentation* / Q000379:methods; D019781:Corneal Topography; D005260:Female; D006801:Humans; D007429:Intraocular Pressure; D007640:Keratoconus / Q000175:diagnosis*; D008297:Male; D011446:Prospective Studies; D015203:Reproducibility of Results; D041623:Tomography, Optical Coherence; D014065:Tonometry, Ocular; D014463:Ultrasonography; D055815:Young Adult