Olympics shooting competitors wear mechanical irises on their faces to fine-tune their gunsights. These allow them to adjust to changing light conditions and eye fatigue throughout the day. However, South Korean competitor Oh Ye-jin, who won Gold in the 10 Meter Air Pistol event, opts out of using mechanical irises. The irises provide a unique advantage in competition compared to relying solely on prescription glasses. Manufacturer Gehmann offers frames for those who do not wear glasses, ensuring that all competitors have the tools needed for sharp focus during events.
https://www.core77.com/posts/133176/What-are-the-Olympics-Shooting-Competitors-Wearing-On-Their-Faces