title: Effect of ocular magnification on macular measurements made using spectral domain optical coherence tomography.
abstract: OBJECTIVE
  The aim of the present study was to study the effect of ocular magnification on macular measurements made using spectral domain optical coherence tomography (OCT).
  
  
  METHODS
  One hundred and fifty-one subjects were included from the normative study of foveal morphology carried out at our hospital. Subjects underwent comprehensive eye examination and macular scanning using Cirrus high-definition OCT and axial length (AXL) measurement. Macular cube 512 × 128 scan protocol was used for scanning the macula. Automated measurements of the fovea namely foveal diameter, foveal slope (lateral measurements) and foveal depth (axial measurement) were taken. A correction factor for ocular magnification was done using the formula t = p × q × s, where "t0" is the corrected measurement, "p" is the magnification of OCT, "q0" is the ocular magnification, and "s" is the measurement on OCT without correction. The difference between corrected and uncorrected measurements was evaluated for statistical significance.
  
  
  RESULTS
  Mean AXL was 22.95 ± 0.78 mm. Refractive error ranged from -3D to +4D. Mean difference between measured and corrected foveal diameter, slope and depth was 166.05 ± 95.37 ΅m (P < 0.001), 0.81° ± 0.53° (P < 0.001) and 0.05 ± 0.49 ΅m (P = 0.178) respectively. AXL lesser than the OCT calibrated value of 24.46 mm showed an increased foveal diameter (r = 0.961, P < 0.001) and a reduced foveal slope (r = -0.863, P < 0.001) than the corrected value.
  
  
  CONCLUSIONS
  Lateral measurements made on OCT varied with AXL s other than the OCT calibrated value of 24.46 mm. Therefore, to estimate the actual dimensions of a retinal lesion using OCT, especially lateral dimensions, we recommend correction for the ocular magnification factor.
authors.forename: Mohana Kuppuswamy
authors.initials: MK
authors.lastname: Parthasarathy
authors.affiliation: Department of Vitreoretinal Services, Sri Bhagwan Mahavir Vitreoretinal Services, Medical Research Foundation, Chennai, Tamil Nadu, India.
authors.forename: Muna
authors.initials: M
authors.lastname: Bhende
mesh_terms: D000328:Adult; D016477:Artifacts; D005260:Female; D005500:Follow-Up Studies; D005584:Fovea Centralis / Q000166:cytology; D006801:Humans; D008266:Macula Lutea / Q000166:cytology*; D008297:Male; D012016:Reference Values; D012029:Refraction, Ocular / Q000502:physiology*; D012030:Refractive Errors / Q000000981:diagnostic imaging*; D012189:Retrospective Studies; D041623:Tomography, Optical Coherence / Q000379:methods*