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).
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 “ t” is the corrected measurement, “ p” is the magnification of OCT, “ q” 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.
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 µm ( P < 0.001), 0.81° ± 0.53° ( P < 0.001) and 0.05 ± 0.49 µm ( 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.