Rani Sujatha1, Aabid Maqbool2
INTRODUCTION
A specific objective of the study was to look for correlations between myopia and optic disc measurements obtained by Primus SD-OCT. Retinal nerve fibre layer thickness was measured by Primus SD-OCT in both normal and myopic eyes.
MATERIAL & METHODS
This is a cross-sectional case control study conducted over a period of 18 months from July, 2014 to December, 2015 at DR. B. R. Ambedkar Medical College and Hospital, Bangalore, India on analysis of optic disc and peripapillary area using Primus spectral domain OCT in young Indian adult myopic eyes. A total of 108 eyes were studied in which 40 were normal (emmetropia), 27 were mild myopia (≤3D) and 41 were moderate to severe myopia (>3D). Patients in all three groups were age matched. All patients were of young age between 20 to 40 years. All images were acquired by Primus SD-OCT. Measurements of the ONH parameters and the peripapillary RNFLT were noted by OCT. The data was then analysed after dividing the patients into three groups: the normal group and the myopic group. The myopic group was further sub-divided into mild myopia (≤3D) and moderate to severe myopia (>3D).
The mean disc area of eyes in the control (emmetrope) group was 2.3±0.4mm.2 The mean disc area in the mild myopia group was 2.07±0.32mm2 while that of the eyes in the moderate to severe myopia group was 1.8±0.4mm.2 The difference between the groups was statistically significant, suggesting that as myopia increases disc area decreases. The other parameters were analysed statistically in a similar fashion and the results were tabulated and explained.
Myopic patients review periodically for their refractive error correction. Myopic disc findings may mimic optic disc changes suggestive of optic neuropathy. The data and results obtained in the current study suggest that optic disc parameters vary in myopic eyes compared to emmetropic eyes by SD-OCT. Therefore, in myopic eyes, OCT parameters should be interpreted with caution before labelling them as glaucomatous or any other disease causing RNFL thinning and variation in ONH values. Clinical correlation along with OCT parameters are essential before formulating a definitive diagnosis.
CONCLUSION
OCT is a non-contact, non-invasive imaging modality that is used to take high resolution, in-vivo, and cross-sectional pictures of the optic nerve head. OCT, thus, helps to quantify the structural damage that an eye has suffered due to glaucoma.
While performing OCT studies in normal (emmetrope) and myopic eyes in the current investigation, it was found that there was thinning in the retinal nerve fibre layer in superior, inferior, nasal and average thickness values in myopic eyes which was more marked in moderate to high myopia than in mild myopia. The disc area was smaller in high myopes compared to the normal eyes. The cup volume was smaller in high myopes which correlated with the smaller disc area. There was no significant correlation between spherical equivalent and RNFLT.
Myopic patients review periodically for their refractive error correction. Myopic disc findings may mimic optic disc changes suggestive of optic neuropathy. The data obtained in the current investigation suggests that optic disc parameters vary in myopic eyes compared to emmetropic eyes by spectral domain OCT. therefore, in myopic eyes, OCT parameters should be interpreted with caution before labelling them as glaucomatous or any other disease causing RNFL thinning and variation in ONH values. Clinical correlation along with OCT parameters are essential before formulating a definitive diagnosis.
