The short-term effect of diffuse and defocus blur on axial length and vision

Abstract

Purpose : It is not clear what aspects of the retinal image are important for guiding eye growth in humans. This study investigates the axial length (AxL) changes with short-term exposure to different types and levels of blur (both diffuse and defocus blur).

Methods : This experiment involved 20 participants (7 males, 13 females), aged 20 to 41 years, and right eye mean spherical equivalent refraction of -0.46 ± 0.93 D (range: +0.50 D to -2.63 D). At each of five visits, axial length measurements of the right eye were taken with the Lenstar LS 900, before blur exposure (baseline), and after 10, 20 and 30 min exposure to blur. Subjects watched TV at 5 m binocularly with the right eye exposed to blur while the left eye had clear vision. Blur conditions included: Bangerter foil density 0.2 (BF0.2), Bangerter foil light perception (BFLP), +2.25 D, BF0.2 combined with +12.50 D (BF0.2/+12.50D) and a control condition (no diffuser). Right eye visual acuity (VA) was measured with all blur conditions using the FrACT vision test.

Results : AxL changed significantly with blur conditions (F_4,76 = 9.36, p < 0.00001), with no significant time by blur condition interaction (F_8,152 = 1.15, p = 0.33). Post-hoc testing with Bonferroni correction showed that the +2.25 D condition significantly shortened the AxL compared to the other blur conditions (p < 0.05). AxL with +2.25 D was -7 ± 2 µm shorter compared to BF0.2 (p = 0.03), even though both conditions caused an equal loss in VA. The BF0.2 and BFLP produced similar, non-significant AxL changes, while BFLP caused 0.28 ± 0.02 logMAR greater VA loss than BF0.2 (p < 0.0001). The AxL changes with the BF0.2/+12.50 D condition and the control condition were not significant (+0.5 ± 1 µm, p = 1.00).

Conclusions : The myopic vergence appears to explain the axial length shortening in myopic defocus blur compared to diffuse blur that produced equivalent VA loss. Further investigation is required to understand the interaction of diffuse and defocus blur, and the role of the retinal image spatial and contrast information in regulating short-term axial length changes.

This is a 2020 ARVO Annual Meeting abstract.

 

Figure 1: Change in AxL from baseline (µm) after 30 minutes of exposure to different blur conditions. Error bars indicate the standard error of the mean. Data displaced slightly on the x-axis to make the error bars visible.