What is “pinholing” a patient?

The pinhole can be used when checking vision. A pinhole changes the eye from a lens focusing system into a pinhole camera … thus removing a lot of potential refractive error by removing the misaligned rays of light. If a patient’s vision improves when looking through a pinhole, then the patient may be using the wrong glasses.

People see better when squinting because their eyelashes turn into multiple “pinholes.”