ABSTRACT

If an uncorrected visual acuity is less than 6/9 for example, in order to discover whether this is attributable to a refractive error without refracting the patient, the pinhole acuity test may be performed. In this test the patient views the Snellen chart through a pinhole occluder, a hand-held device which completely covers one eye and allows the other to view the chart through a tiny, central opening. A pinhole only admits central rays of light which do not require refraction by the cornea, allowing an eye to resolve fine detail on the chart without optical correction. Thus, if use of the pinhole improves a patient’s poor, uncorrected acuity to 6/6 or even 6/9 or 6/12, the chances are the patient has a significant refractive error. If poor, uncorrected acuity is not improved with a pinhole, the visual problem may be due to a cause other than a refractive error, eg problems with the optical media (transmission of light) or the retina (visual perception).