THE EFFECT OF CORNEAL ASTIGMATISM ON RETINAL NERVE FIBER LAYER THICKNESS AND OPTIC NERVE HEAD MEASUREMENTS BY OPTICAL COHERENCE TOMOGRAPHY

Abstract

ABSTRACT Background: Optical Coherence Tomography (OCT) is a non-invasive investigative technique that functions as a type of optical biopsy. It has been an important diagnostic tool in evaluation of optic nerve head (ONH) and macula. Evaluation of OCT ONH is essential, since the thickness of the RNFL and ONH parameters can be affected in various optic neuropathies like glaucoma, optic atrophy and optic disc edema. Objective: To evaluate the effect of corneal astigmatism on retinal nerve fiber layer (RNFL) thickness and optic nerve head (ONH) parameters measured with spectral-domain optical coherence tomography (OCT). Methods: Forty eyes of 32 patients were included in this study.Group I; 20 non/low astigmatic eyes to be compared with Group II; 20 astigmatic eyes (10 eyes have with the rule corneal astigmatism WTR and 10 eyes have against the rule corneal astigmatism ATR). The average corneal astigmatism in group I was -0.33±0.17 D (range -0.5-0 D), in group II it was -3.18±0.87 D (range -4.5- -2 D) in eyes of with the rule corneal astigmatism, and -3.13±0.84 D (range -4.5- -2.25 D) in eyes of against the rule corneal astigmatism. All forty eyes underwent full ophthalmic examination and performed OCT ONH imaging by SD-OCT Angio Vuein Ophthalmology Department, Faculty of Medicine, Al-Azhar University, Cairo, from January to November 2019. Results: No significant difference was noted in the disc area, rim area, vertical C/D ratio and cup volume (all P values > 0.05). There were no significant differences between the two groups in global average RNFL thickness, as well as superior, inferior, nasal and temporal quadrant RNFL thickness (P values > 0.05). Conclusions: corneal astigmatism had statistically insignificant effect on optic nerve head parameters and retinal nerve fiber layer thickness measured with spectral domain optical coherence tomography.