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Visual performance and visual acuity
Visual performance(Visus sine correctione, VCS; raw visus): Vision without correction by glasses.
Special text: ametropia and its degree of dioptre
Reading sample boards for the visual acuity test at a distance of 5 m. Letters, numbers, E-hooks, Landolt rings, children's pictures. The ophthalmologist or optician uses these different optotypes in different sizes to check the eyesight.
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Visual acuity(Visus cum correctione, VCC): Vision with optimal correction through glasses or contact lenses.
Visual performance and visual acuity for the distance (Distant vision) and proximity (Near vision) are checked individually for each eye. To test the distance vision, different sizes are used Optotypes(Optotypes) offered: letters, numbers, E-hooks, Landolt rings. Domestic items are suitable for children. The signs are located on well-lit boards that are not backlit at a distance of 5 m or are projected onto a screen. The size of the respective characters is chosen so that they are barely recognizable to a normal-sighted eye from a certain distance (target distance).
The visual acuity is calculated according to the formula "actual distance divided by target distance". The normal vision is 1.0, ie the target and actual distance are equal. This corresponds to a vision of 100%. Statistically, this is the normal case However, there are definitely people who can see better: A visual acuity of 120% is not uncommon, especially with younger people. The optimal optical correction is selected by connecting different lenses. Visual acuity is determined by the lens with which the person examined can see best can.
The near vision is checked with reading texts of different font sizes at a distance of 30–40 cm.
In small children or non-cooperative adults, the visual defect cannot be determined from the patient's information. Here, objective methods are chosen to diagnose ametropia, such as the Retinoscopy(Shadow sample): If the pupil is widened by the medication, the light source of the retinoscope is guided over the pupil of an eye at a distance of 50 cm. The ophthalmologist or optician observes the flashing red light reflex in the pupil, which is caused by the reflection of the light on the retina. If the examiner moves the retinoscope mirror, this shadow moves with normal and farsightedness when the mirror is rotated, and in the case of nearsightedness in the opposite direction. Now gradually stronger and stronger test glasses are inserted in between until the shadow no longer moves in the pupil or when there is no more shadow when changing from light to dark. At this moment, the interposed glass effects a full correction of the visual defect.
AuthorsDr. rer. nat. Katharina Munk, Dr. med. Arne Scäffler in: Gesundheit heute, edited by Dr. med. Arne Schäffler. Trias, Stuttgart, 3rd edition (2014). Revision and update: Dr. med. Sonja Kempinski | last changed on at 16:39
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