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The phenomenon that occurs when a patient's uncorrected vision improves by looking through an occluder with perforation is known as the pinhole effect. This effect is based on the principle of limiting the amount of light entering the eye to a smaller area, which reduces the impact of defocusing and aberrations.

When light passes through a small aperture, such as the holes in a perforated occluder, less peripheral light is allowed to enter the eye. This results in a sharper image being projected onto the retina because it minimizes the blur from optical imperfections. As the pinhole restricts the field of view to more directly focused rays of light, patients often experience an improvement in visual acuity, allowing the clinician to assess the potential for improved vision with corrective lenses.

The concept of refraction involves the bending of light as it passes through different mediums, which is not directly related to the improvement seen through a pinhole. The Snellen effect refers to the reference of visual acuity using the Snellen chart, and contrast sensitivity pertains to the ability to distinguish between finer increments of light versus dark and is not directly related to the phenomenon observed with an occluder. Therefore, recognizing the pinhole effect is crucial for understanding how vision can improve