Pinhole occluder
A pinhole occluder is an opaque disk with one or more small holes through it, used not only by ophthalmologists but also optometrist to test visual acuity. The occluder is a simple way to focus light, as in a pinhole camera, temporarily removing the effects of refractive errors such as myopia. Because light passes only through the center of the eye's lens, defects in the shape of the lens (errors of refraction) have no effect while the occluder is used. In this way the ophthalmologist can estimate the maximum improvement in a patient's vision that can be attained by lenses to correct errors of refraction.[1] This can be used to distinguish visual defects caused by refractive error, which improve when the occluder is used, from other problems, which do not.[2]
Squinting works similarly to a pinhole occluder, by blocking light through the outer parts of the eye's lens.[3] An improvised pinhole has a similar but better effect. The same principle has also been applied as an alternative to corrective lenses: a screen of pinholes is mounted on an eyeglass frame and worn as pinhole glasses.
References
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- ↑ Renner, Eric (1999). Pinhole Photography. Focal Press. ISBN 0240803507. Retrieved 2008-12-09.
- ↑ Naidoo, Kovin (2002). "Case Finding in the Clinic: Refractive Errors". J Comm Eye Health. 15 (43): 39–40. Retrieved 2008-12-09.
- ↑ Lloyd, Dr. Bill (November 4, 2008). "How does squinting improve eyesight?". WebMD. Retrieved 2008-12-09.
