Main visual point
The main visual point is the area of a spectacle lens that represents the optimal refractive conditions for the correction of ametropia and thus guarantees the best possible visual acuity . With normal spectacle lenses, the main visual point corresponds to the so-called optical center point of the spectacle lens. However, if this has a prismatic effect, the position of the main visual point deviates from it according to the extent of its decentering.
It is important that the eyes always look through the main visual point when seeing , otherwise the visual acuity will be reduced. The line of sight that goes through the main visual point of the spectacle lens is also called the main line of sight in physical optics .
Knowing the exact distance between the eyes gives the optician the opportunity to determine the main visual point. A pupil statometer , a tool for determining the interpupillary distance , can be used here. The pupillary distance (PD) is an important parameter in the correct centering of the lenses. Progressive lenses should be centered towards the center of the pupil according to the zero line of sight with a natural head and body posture and a straight line of sight. An incorrectly centered spectacle lens leads to unintended prismatic side effects and possibly impairment of spatial vision . Because of the individuality of the glasses corrections and lens centering, wearing other glasses usually leads to asthenopic complaints and reduced visual acuity.
literature
- Eugene Hecht: optics . 4th edition. Oldenbourg, Munich 2005, ISBN 3-486-27359-0 .
Individual evidence
- ↑ servant optics lexicon
- ↑ Quality regulations in the optician trade. Issue 1961-12 Beuth-Verlag (DIN)