title: Ultrasonography and optical low-coherence interferometry compared in the chicken eye.
abstract: OBJECTIVE
  To compare ocular biometry [anterior chamber depth (ACD), lens thickness (LT), vitreous chamber depth (VCD), and axial length (AL)] using A-scan ultrasonography and optical low-coherence interferometry (OLCI) in the chicken eye.
  
  
  METHODS
  Two-week-old chicks (n = 42) were measured. Bland-Altman plots and repeatability and correlation analyses were calculated for both methods.
  
  
  RESULTS
  There was a high correlation between both methods for ACD (r = 0.6144, p < 0.0001), VCD (r = 0.9595, p < 0.0001), and AL (r = 0.9290, p < 0.0001) but not for LT (r = 0.1604, p = 0.144). Measurements by OLCI were more consistent (smaller coefficients of variation and higher intraclass correlation). Bland-Altman plots showed that ultrasound provided larger values for LT, VCD, and AL but not for ACD [differences between ultrasound and OLCI (mean ± SD): ACD = -0.11 ± 0.12 mm; LT = 0.10 ± 0.09 mm; VCD = 0.25 ± 0.08 mm; AL = 0.50 ± 0.16 mm].
  
  
  CONCLUSIONS
  A high correlation between both techniques was found for three of the four parameters (ACD, VCD, and AL). However, as the absolute values were different, both techniques cannot replace each other mainly because (1) one is non-contact and the other contact and can induce a minor indentation of the cornea and (2) each device uses different types of waves that cross the ocular interfaces differently. While consistency and repeatability were better by OLCI, a disadvantage is that, different from humans, it can only be used in anesthetized chicks.
authors.affiliation: Institute for Ophthalmic Research, Section of Neurobiology of the Eye, University Eye Hospital, Tuebingen, Germany.
authors.forename: Alexandra Marcha
authors.initials: AM
authors.lastname: Penha
authors.forename: Eva
authors.initials: E
authors.lastname: Burkhardt
authors.forename: Frank
authors.initials: F
authors.lastname: Schaeffel
authors.forename: Marita P
authors.initials: MP
authors.lastname: Feldkaemper
mesh_terms: D000818:Animals; D000867:Anterior Chamber / Q000000981:diagnostic imaging*; D002645:Chickens; D003315:Cornea / Q000000981:diagnostic imaging*; D004195:Disease Models, Animal; D007368:Interferometry; D007908:Lens, Crystalline / Q000000981:diagnostic imaging*; D009216:Myopia / Q000000981:diagnostic imaging* / Q000503:physiopathology; D012029:Refraction, Ocular; D015203:Reproducibility of Results; D014463:Ultrasonography