Purpose:
Previous studies have measured the horizontal and vertical diameters of the optic nerve and distance between optic nerve and fovea from histological studies and fundus photographs. Both these methods are prone to errors - histological measurements are not accurate because of desiccation of tissue and fundus photographs induce some magnification errors. With the advent of spectral-domain optical coherence tomography (SD-OCT), it may be possible to more accurately measure these dimensions. This study was done to evaluate the distance between the foveal center and the temporal nerve border and dimensions of the optic nerve using the Spectralis OCT (Heidelberg Engg., Germany) to provide normative data for future trials.
Methods:
Fifty-four subjects with best-corrected visual acuity of 20/20 or better with no known optic nerve or retinal diseases were included in the study. The ages ranged from 22 to 78 years. These subjects were part of a prior study done to establish normative data for retinal thickness and hence SD-OCT scans had been done for the original study. The scale on the OCT screen was used to measure the horizontal and vertical diameters of the optic nerve. The distance between the temporal margin of the optic nerve to a point just above the fovea in the horizontal plane was measured as the ‘nerve to fovea’ distance. The ‘nerve to fovea’ measurements were done on 104 eyes of 54 subjects. However, optic nerve was not scanned in some of the patients - hence the horizontal and vertical diameters could be measured in 84 eyes of 42 subjects.
Results:
The average ‘nerve to fovea’ distance, measured in 104 eyes, was 3627µ +/- 246.5µ (range, 2928 - 4037µ). The horizontal and vertical diameter of the optic nerve, as measured in 84 eyes, was 1545µ +/- 206µ and 1692µ +/- 205µ, respectively.
Conclusions:
The SD-OCT is an excellent tool for making the measurements of various landmarks at the posterior pole. The measurements were similar to what has been reported in the literature in histological and photographic studies. However, this seems to be a more convenient and accurate way of measurement.
Keywords: anatomy • optic nerve • imaging/image analysis: clinical