Título

COMPARISON OF SS-OCT AND SD-OCT IN ANALYSIS OF THE RETINAL NERVE FIBER LAYER THICKNESS IN NORMAL TENSION GLAUCOMA

Objetivo

To compare swept-source optical coherence tomography (SS-OCT) and spectral-domain OCT (SD-OCT) in analysis of the peripapillary retinal nerve fiber layer (RNFL) thickness in normal tension glaucoma (NTG).

Método

This was an observational cross-sectional study including 90 eyes of 45 patients with NTG, and 52 eyes of 27 healthy subjects. Optical coherence tomography images were obtained from the optic nerve heads using a SS-OCT 1.050 nm (DRI OCT, Triton) and a SD-OCT (Spectralis). Peripapillary RNFL thickness was measured on a circle of 3.4-mm in diameter, centered on the optic disc. Average thicknesses of global peripapillary RNFL and superior, inferior, nasal and temporal quadrants were calculated. Statistical analyses were performed using the SPSS software (version 22.1; SPSS Inc., Chicago, IL). The x2 was used to compare categorical data. Student t-tests were used for group comparison for normally distributed variables and Mann-Whitney U test for non-normally distributed variables. The threshold for statistical significance was set at p<0.05. All the investigations were in agreement with the tenets of the Declaration of Helsinki.

Resultado

For both SS-OCT and SD-OCT, glaucomatous eyes also had significantly thinner RNFL than healthy eyes in all zones. The mean peripapillary RNFL thickness measured in glaucomatous eyes was 81,91 ± 27.77 µm using the SS-OCT and 76,86 ± 16,63 with SD-OCT (p<0,05). The difference in the RNFL thickness between the systems was significant in all quadrants except for the temporal in the NTG group.

Conclusão

A new generation of OCT, swept-source OCT (SS-OCT) has recently been introduced, which has the ability to image deep ocular structures such as the choroid and lamina cribrosa, as well as the RNFL thickness. This study evaluated that the peripapillary RNFL thickness measurements with SS-OCT were higher than those obtained with SD-OCT. However, it is unclear what might contribute to this discrepancy between the systems, and which system would provide more accurate measurements.