Pinhole occluder

The stenopaic gap ( from Ancient Greek στενός Steno's "narrow" and the adjective ὀπαῖος opaios " provided with a hole" ) is a tool used in ophthalmology and optometry for the differential diagnostic assessment of reduced visual acuity. It consists usually of a round, opaque plastic disc of about three centimeters in diameter, which is provided in the center with a round, 1-2 mm large hole.

Operation

The stenopaic gap has the effect of a pinhole. It reduces the perception of interfering edge rays (spherical aberration), reduces the blur circles on the retina, thereby increasing the depth of field in vision. The result is that people with a not or only insufficiently corrected optical refractive error ( ametropia ) look sharper when looking through a stenopaic gap and the reduced visual acuity can be considered as refraktionsbedingt. However, are organic or functional causes of reduced visual acuity, such as a macular degeneration or amblyopia, so will the gap stenopaic do not improve.

Use

Because of the gap caused by the stenopaic reduction in luminance and a drastic reduction of the visual field it is unsuitable in the form described for everyday use. The principle of its action, however, can also be used on other way. Of people with nearsightedness or astigmatism is known for example that they squint in order to gain a stenopaic gap and be able to see better. Here the stenopaic gap therefore serves as a compensatory mechanism. In the U.S., a cornea implant was developed based on the principle of stenopaic gap is based correction for presbyopic people.

A further diagnostic application range of stenopaic gap is the assessment of monocular diplopia.

Even with the controversial pinhole glasses, the underlying principle is used.

The effect of a gap stenopaic you can make it clear in a simple way by the thumb, index and middle finger are brought together to that between them remains a small opening through which you look. With decreasing opening width of the gap formed the image is sharper and darker, near bright objects can be viewed as better.

History

The discovery of stenopaic action for the eye is the German Jesuit priest, astronomer Christoph Scheiner and Opticians (1573-1650) attributed to, who published his findings in 1619 in his work " Oculus ".