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Effect of ocular magnification on measurements made on spectral domain optical coherence tomography

Session Details

Session Title: Quick Fire Free Paper 2

Session Date/Time: Thursday 11/09/2014 | 11:00-12:30

Paper Time: 11:05

Venue: Boulevard D

First Author: : M.Bhende INDIA

Co Author(s): :    M. K P              

Abstract Details

Purpose:

To study the effect of ocular magnification on macular measurements using Spectral Domain Optical Coherence Tomography.

Setting:

Tertiary referral vitreoretinal center in South India

Methods:

151 subjects were included from a normative study on foveal morphology . Subjects underwent macular scanning using Cirrus HDOCT instrument and axial length measurement. Macular cube 512 x128 scan protocol was used for scanning the macula. Lateral measurements of the fovea namely foveal diameter and foveal slope, axial measurement named as foveal depth were measured automatically using a custom written program in Matlab. A correction factor for Ocular magnification using the formula t=p*q*s was used, where t = corrected length, p = magnification of OCT camera, q = ocular magnification, and s = measurement on OCT without correction. The difference between the two measurements was evaluated for statistical significance.

Results:

Mean axial length was 22.95 ± 0.78 mm ranging from 21.35 to 24.98 mm. Refractive error ranged from -3 to +4 diopters with 58 (38.4%) subjects being emmetrope. The measured mean foveal diameter, foveal slope and foveal depth were 2490.97 ± 259.19 microns, 11.35 ± 2.61 degree and 113.68 ± 17.26 microns respectively. Corrected mean foveal diameter, foveal slope and foveal depth were 2323.16 ± 228.19 microns, 12.16 ± 2.86 degree and 113.62 ± 17.3 microns respectively. The mean difference between measured and corrected parameters was statistically significant for lateral measurements. Axial length lesser than 24.46mm showed a decrease in foveal diameter and an increase in foveal slope from the measured value.

Conclusions:

Lateral measurements made on OCT tend to vary with axial lengths that differ from the standard OCT calibrated value of 24.46mm. Therefore, to estimate the actual dimension of a retinal lesion using OCT, especially the lateral dimension, measurements should be corrected for ocular magnification factor.

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