Astigmatic Defocus Leads to Short-Term Changes in Human Choroidal Thickness

Area of Science:

• Ophthalmology
• Optometry
• Vision Science

Background:

• Choroidal thickness (ChT) is a key indicator of ocular health and a potential factor in myopia progression.
• Understanding the eye's response to different types of visual defocus is crucial for myopia control strategies.

Purpose of the Study:

• To investigate the short-term impact of with-the-rule (WTR) and against-the-rule (ATR) simple myopic astigmatic defocus on choroidal thickness.
• To compare the ChT response to astigmatic defocus with responses to spherical myopic defocus and clear vision.

Main Methods:

• Healthy adults underwent four experimental sessions, each involving 60 minutes of a specific visual condition: clear vision, spherical myopic defocus, WTR astigmatic defocus, or ATR astigmatic defocus.
• Macular ChT was measured using optical coherence tomography at multiple time points before and during defocus exposure.

Main Results:

• Spherical myopic defocus significantly increased ChT by +8 µm after 60 minutes.
• WTR astigmatic defocus led to a significant increase in ChT (+5 µm), whereas ATR astigmatic defocus caused a significant decrease (-4 µm).
• These changes in ChT due to astigmatic defocus were independent of the meridian measured and differed significantly from the clear vision control.

Conclusions:

• The orientation of astigmatic blur influences the human choroidal thickness response.
• These findings suggest that the direction of astigmatism may play a role in signaling myopic changes in the eye.