The act of partially closing the eyelids to narrow the aperture through which light enters the eye improves visual acuity, particularly when encountering blurriness or refractive errors. This action effectively creates a pinhole effect, reducing the diameter of the incoming light beam. A smaller aperture decreases the amount of unfocused light reaching the retina, leading to a sharper, more focused image. For example, individuals with nearsightedness or astigmatism may find that this action temporarily clarifies distant objects.
This method offers a temporary compensatory mechanism for refractive errors. The benefit lies in the enhanced clarity it provides in situations where corrective lenses are unavailable or impractical. Historically, this action represents a natural, instinctive response to poor vision, employed long before the advent of modern vision correction techniques. Its simplicity and accessibility render it a universally applicable, albeit temporary, solution.