Stenopean gap

The Stenopean gap (from ancient Greek στενός stenós “eng” as well as the adjective ὀπαῖος opaios “provided with a hole”) is an aid used in ophthalmology and optics for the differential diagnostic assessment of reduced visual acuity . It usually consists of a round, opaque plastic disc about three centimeters in diameter, which is provided with a round, 1-2 millimeter hole in the middle.

Mode of action

The stenopean gap acts like a pinhole . It reduces the perception of disturbing marginal rays ( spherical aberration ), reduces the circles of confusion on the retina and thus increases the depth of field when seeing. The result is that people with an inadequately corrected visual ametropia ( ametropia ) can see more clearly when looking through a stenopean gap and the reduced visual acuity can be viewed as being due to refraction . However, if there are organic or functional causes for reduced visual acuity, for example macular degeneration or amblyopia , the stenopic gap will usually not bring about any improvement.

use

Because of the reduction in luminance caused by the stenopean gap and a drastic restriction of the field of view , it is unsuitable for everyday use in the form described. The principle of their mode of operation, however, can also be used in other ways. People with nearsightedness or astigmatism , for example, are known to squint their eyes in order to create a stenopean gap and thus be able to see better. The Stenopean gap thus serves as a compensation mechanism here. In the USA, a corneal implant was developed that, based on the principle of the Stenopean gap, represents a correction for presbyopic people.

Another diagnostic application of the Stenopean gap is the assessment of monocular diplopia .

The underlying principle is also used for the controversial grid glasses .

The effect of a Stenopian gap can be made clear in a simple way by placing the thumb, index and middle fingers together in such a way that a small opening remains between them through which one can look. As the opening width of the gap that is formed decreases, the image becomes sharper and darker, and objects with a high intensity of light can be viewed better.

history

The discovery of the Stenopean mode of action for the eye is attributed to the German Jesuit priest , optician and astronomer Christoph Scheiner (1573–1650), who published his findings in 1619 in his work “Oculus”.

Individual evidence

^ Wilhelm Gemoll : Greek-German school and hand dictionary. 9th edition, reviewed and expanded by Karl Vretska . Freytag et al., Munich et al. 1965.
^ From Franz Grehn: Ophthalmology. 30th, revised and updated edition. Springer, Heidelberg 2008, ISBN 978-3-540-75264-6 , p. 26.
↑ Raster glasses - training or deception? ( Memento from November 19, 2009 in the Internet Archive ) Minutes of the press conference of the 38th Wiesbaden meeting of the Federal Association of Ophthalmologists, November 19, 1998.
↑ Th. Axenfeld (original), H. Pau (ed.): Textbook and atlas of ophthalmology. With the collaboration of R. Sachsenweger et al., Stuttgart: Gustav Fischer Verlag, 1980, ISBN 3-437-00255-4 . Page 32.
^ University Clinic for Ophthalmology and Optometry, Salzburg ( Memento from July 27, 2010 in the Internet Archive ).
^ F. Daxecker : Further studies by Christoph Scheiner concerning the optics of the eye. In: Documenta Ophthalmologica. Vol. 86, No. 2, ISSN 0012-4486 , pp. 153-161, doi : 10.1007 / BF01203559 .

[1] Wilhelm Gemoll : Greek-German school and hand dictionary. 9th edition, reviewed and expanded by Karl Vretska . Freytag et al., Munich et al. 1965.

[2] From Franz Grehn: Ophthalmology. 30th, revised and updated edition. Springer, Heidelberg 2008, ISBN 978-3-540-75264-6 , p. 26.

[3] Raster glasses - training or deception? ( Memento from November 19, 2009 in the Internet Archive ) Minutes of the press conference of the 38th Wiesbaden meeting of the Federal Association of Ophthalmologists, November 19, 1998.

[4] Th. Axenfeld (original), H. Pau (ed.): Textbook and atlas of ophthalmology. With the collaboration of R. Sachsenweger et al., Stuttgart: Gustav Fischer Verlag, 1980, ISBN 3-437-00255-4 . Page 32.

[5] University Clinic for Ophthalmology and Optometry, Salzburg ( Memento from July 27, 2010 in the Internet Archive ).

[6] F. Daxecker : Further studies by Christoph Scheiner concerning the optics of the eye. In: Documenta Ophthalmologica. Vol. 86, No. 2, ISSN 0012-4486 , pp. 153-161, doi : 10.1007 / BF01203559 .