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Emmetropia is the state of vision in which a faraway object at infinity is in sharp focus with the ciliary muscle [1] in a relaxed state. That condition of the normal eye is achieved when the refractive power of the cornea and eye lens and the axial length of the eye balance out, which focuses rays exactly on the retina, resulting in perfectly sharp distance vision.
The power of any lens system can be expressed in diopters, the reciprocal of its focal length in meters. Corrective lenses for myopia have negative powers because a divergent lens is required to move the far point of focus out to the distance. More severe myopia needs lens powers further from zero (more negative).
Generally refractive surgery can be broadly divided into: corneal surgery, scleral surgery, lens related surgery (including phakic IOL implantation, clear lens extraction, photophacoreduction and photophacomodulation for correction of presbyopia) For presbyopia correction, a corneal inlay consisting of a porous black ring surrounding a small ...
Additionally, many of these people have reached the age where presbyopia occurs. Some also develop cataracts. Their vision can still be restored with Epi-LASIK, photorefractive keratectomy, LASIK or phakic lens extraction, or cataract surgery. The corneal curvature has to remeasured and modified by history, central keratometry, or contact lens ...
A corrective lens is a lens worn on or before the eye. They are used to treat myopia , hypermetropia , astigmatism , and presbyopia . The main article for this category is Corrective lens .
A corrective lens can be used to correct hyperopia by imaging an object at the typical near point distance D onto a virtual image at the patient's actual near point, at distance NP. [2] From the thin lens formula, the required lens will have optical power P given by [3] [4].
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