Astigmatism and optical coherence tomography measurements

Background To evaluate the effect of astigmatism change on measurement of retinal nerve fiber layer (RNFL) and macular thickness by Cirrus HD spectral-domain optical coherence tomography (Cirrus HD OCT; Carl Zeiss Meditec, Dublin, CA, USA). Methods A total of 30 right eyes from 30 healthy young subjects underwent RNFL and macular thickness measurements using Cirrus HD OCT. Measurements were performed at the baseline state and induced with-therule (WTR) and against-the-rule (ATR) astigmatism states by wearing toric soft contact lenses (+1.50 .3.25 diopter × 90° and +1.50 .3.25 diopter × 180° respectively). Dfferences in RNFL and macular thickness between the baseline state and induced astigmatism states were analyzed. Results Wearing toric soft contact lenses induced a mean 2.92 diopter WTR and 3.18 diopter ATR astigmatism respectively. After signal strength change adjustment, RNFL thicknesses of average, superior quadrant, 12 and 6 o'clock hour sectors decreased after induction of a WTR astigmatism (mean difference range, 1.58 to 6.88 μm); RNFL thicknesses of average, nasal, temporal quadrants, 2, 3, and 9 o'clock hour sectors decreased after induction of an ATR astigmatism (mean difference range, 0.75 to 5.11 μm) (all P values<0.05). Macular thickness was not significantly affected by astigmatism changes (all P values≥0.250). Conclusion Although the amount of change was not substantial, RNFL thickness measured by Cirrus HD OCT was affected by astigmatism changes induced by contact lenses. It may be warranted to consider the effect of astigmatism on RNFL thickness measured by OCT in eyes with higher degrees of astigmatism.