Pinhole Function

A pinhole acts like a universal lens. By limiting the incoming light to a small central ray, the optical effects of refractive error are markedly reduced, regardless of the type of refractive error.

Pinhole viewing can therefore be used in the clinic to help determine if a patient’s poor visual acuity is due to underlying refractive error. If the visual acuity is significantly improved by viewing through a pinhole, it can be inferred that at least some of the reduced acuity is due to refractive blur.