Microfluctuations of astigmatism

Abstract

Purpose : We aimed to quantify the microfluctuations (MF) of astigmatism at two distances in a large population. The relationship with MF of accommodation was also studied.

Methods : Dynamic measurements of spherical equivalent error (i.e., accommodation) and spherocylindrical refractive error were measured using the WAM-5500 while subject fixated a tumbling E either at 5.50 m or 0.40 m. One eye of 25 young subjects was measured. The spherical equivalent error was measured monocularly at 5 Hz for one minute. Spherocylindrical refractive error was measured at 2.5 Hz for four seconds. The four-second measurement periods were repeated five times in one minute at equal 10-second intervals. Each refractive error was recorded three times at each fixation distance.

Results : MF of astigmatism (i.e., standard deviation - SD) were 0.09 ± 0.03 D calculated on the four-second periods (i.e., short-time method) and 0.13 ± 0.05 D considering the full-time periods (i.e., SD calculated on five four-second periods considered as a unique period).
Near SD of accommodation is higher than distance SD of accommodation (p<0.001), near J0 (p<0.001) and J45 SD (p<0.001). Distance J₀ SD was lower than near J₀ SD (p=0.03). SD of J₀ was higher than SD of J₄₅ either at distance (p=0.03) or at near (p=0.01). Astigmatism can be represented in an orthogonal (J_0, J₄₅) radar graph. The area of the 95% confidence ellipse was calculated based on this radar graph. MF of astigmatism were twice as large in near vision. In near vision, half of the subjects showed similar mean astigmatism with greater MFs as compared to distance vision, while a third showed mean astigmatism changing in power or axis between the two distances but with fairly similar MFs of astigmatism.

Conclusions : J0 showed greater microfluctuations than J45, both in distance and near vision. MF of astigmatism were twice as large in near vision (i.e., area of the confidence ellipse) suggesting that the amplitude of astigmatism MF could be related to the tension exerted by the zonule on the lens.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.

 

Accommodation was measured at 5 Hz during one minute. Only one measure out of two was retained. In 2.5 Hz mode, spherocylindrical refractive error was measured during five four-second recording periods, each separated by a ten-second interval.

 

SD of MF of accommodation, J₀ and J₄₅ as a function of distance using the full-time method. Crosses represent mean, boxes correspond to the standard error and the whiskers to the standard deviation.