title: Corneal densitometry in keratoconus.
abstract: OBJECTIVE
  The aim of this study was to compare corneal densitometry measured by Scheimpflug tomography in normal and keratoconic eyes and to assess the differences in densitometry values among the stages of keratoconus.
  
  
  METHODS
  Keratoconic and normal corneas were examined using the Pentacam. Corneal densitometry was measured over a 12-mm diameter area, divided by annular concentric zones and depths. Keratoconus was classified according to the topographic keratoconus classification.
  
  
  RESULTS
  We enrolled 1 eye randomly selected from each of 172 patients with normal corneas (N) and 98 patients with bilateral keratoconus (KC). There were significant differences between the groups for densitometry measurements in 2 annuli: central 2.0 mm in diameter (N = 16.85 ± 2.42, KC = 18.93 ± 2.78, P = 0.0001) and annulus 2.0 to 6.0 mm in diameter (N = 15.18 ± 2.18, KC = 16.16 ± 1.71, P = 0.005), and total diameter (N = 24.89 ± 6.18, KC = 16.71 ± 2.3, P = 0.033). Divided by layers, the inner parts of anterior (120 μm), central (from 120 μm to the last 60 μm), and posterior (last 60 μm) layers were also higher in the KC group (P < 0.001). There were differences according to the stages of KC for corneal densitometry of the central annuli at total thickness, anterior and central layers. More advanced cases presented a higher backscatter (P < 0.05). The anterior layer presented the smallest overlap between groups and KC stages.
  
  
  CONCLUSIONS
  The densitometry map reveals that light backscatter was higher in the central portion of the anterior keratoconic cornea than in the normal cornea. The densitometry level is higher in more advanced stages.
authors.affiliation: *Rio de Janeiro Corneal Tomography and Biomechanics Study Group, Rio de Janeiro, Brazil; †Instituto de Olhos Renato Ambrósio, Rio de Janeiro, Brazil; and ‡Department of Ophthalmology, Federal University of São Paulo, São Paulo, Brazil.
authors.forename: Bernardo
authors.initials: B
authors.lastname: Lopes
authors.forename: Isaac
authors.initials: I
authors.lastname: Ramos
authors.forename: Renato
authors.initials: R
authors.lastname: Ambrósio
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D003315:Cornea / Q000473:pathology*; D063171:Corneal Pachymetry; D003720:Densitometry; D005260:Female; D006801:Humans; D007640:Keratoconus / Q000145:classification / Q000175:diagnosis*; D008297:Male; D008875:Middle Aged; D010781:Photography / Q000379:methods; D012189:Retrospective Studies; D014054:Tomography