Difference between revisions of Eyeballs
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give rough estimate of focusing power.
Viceroy Sam (talk | contribs) m (added Category:Articles using HotCat) |
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* '''Vitreous detachment''' is attached to the outer wall of the eye in multiple locations, but can become separated. When separated from the retina it does not support the retina fully, and puts you at higher risk for [[retinal detachment]]. It can also leave behind a large [[floater]] that impairs vision. | * '''Vitreous detachment''' is attached to the outer wall of the eye in multiple locations, but can become separated. When separated from the retina it does not support the retina fully, and puts you at higher risk for [[retinal detachment]]. It can also leave behind a large [[floater]] that impairs vision. | ||
==Focusing Power== | |||
As a back-of-the-envelope calculation for the focusing power of an [[emmetropic eye]], we might estimate the [[axial length]] as around 2.5cm. For [[distance vision]] (parallel incident light) that number is simply the [[focal length]] of the eye at rest, giving 40 [[Diopters]]. If we take the near point as about 25cm, that requires an additional 4 dpt of focusing power from the lens. (For example using the thin lens equation <math>\frac{1}{x} + \frac{1}{y} = \frac{1}{f}</math>.) | |||
== Axial Length == | == Axial Length == | ||
The primary cause of differences in [[refractive state]] is the length of the eye, referred to as axial length, relative to the focusing power. Long eyeballs are associated with myopia, as the natural lens of the eye focuses light too far forward of the retina. | The primary cause of differences in [[refractive state]] is the length of the eye, referred to as axial length, relative to the focusing power. Long eyeballs are associated with myopia, as the natural lens of the eye, even when fully relaxed, focuses light too far forward of the retina. | ||
==See Also== | ==See Also== | ||