Multifocal intraocular lens introduction _98961

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Multifocal intraocular lens introduction _98961 Powered By Docstoc
					?Multifocal intraocular lens


Single focus intraocular lens only one diopter, in the case of
single-focus lenses. Because of this artificial Crystal optical parts
of itself without accommodation, so it cannot be clearly see far and
look near the image.

In clinically observed pseudophakic of force, is the result of the
ciliary muscle contraction, vitreous and capsular role makes
artificial crystals before and after a slight movement, no special
loop construct artificial Crystal its movement is of no practical
significance. To overcome single focus this drawback of intraocular
lens, scholars research design a dual focus and multifocal
intraocular lens. Shanghai Dongfang hospital ophthalmic, Zhang Ying

The original double-focus lenses, is the use of thickened Crystal
optics Division of peripheral partially completed, i.e. in the same
Crystal optical parts, the central part of thinner, smaller degree,
Visual acuity for correction; and its surrounding parts thicker,
degrees, for the correction of near vision. However, in clinical
applications, often appears artificial lens dislocation or
displacement of the artificial Crystal optical part of the center of
the Central and the pupil does not exactly overlap. Cause patients to
see near cannot use Crystal optical part peripheral, and look far and
you cannot use artificial Crystal optical part of the Central
Department, with the result that patients see distant or close all,
and so this dual-focus lenses cannot get in I clinical application,
then after a study on improvement of scholars, designed with light
diffraction and refraction principles development of intraocular lens.

According to the principles of optics-Fresnel Huygens, incident light
by Diffractive intraocular lens, divided into 2 focus, first for the
refractive power of smaller long focus, the second is the refractive
power of larger near focus. Near refractive power size by the slope
of the height of the ring itself, and the size of the ring-asked by
distance, usually near refractive power far refractive power high +
4D, same time, only a focus on the retina. When the distance parallel
light rays entering the eye, focus on the retina, resulting in a
clear image, and close to the formation of matter like the focus
falls to the epiretinal, retinal overlays a blurred image, when near
scattered light enters the eye, focus on the retina retinal overlays
a blurred image. Diffraction pattern, multifocal intraocular lens far
and near focus light distribution has 2 kinds, one kind for equal
light allocation, far and near focus focus are 41 per cent, more than
18 per cent form-order diffraction. The other is not equal light
allocation, two focus for 70 per cent and 30 per cent (near: far = 7:
3 or near: far = 3: 7). Diffractive intraocular lens of maximum
advantages for 1 lens can produce 2 focus, and its large range of
Diffractive structures, with a diameter of about 4.7mm, any regions
are involved in the formation of double focus, so near and far focus
is not affected by the pupil size, Crystal translocation.

Refraction-multifocal intraocular lens, mostly made of PMMA double
convex lens, front surface central area consists of 3 ~ 5 diopter
concentric-truly change lenses, with a diameter of about 4.7mm;
smooth surface is a sphere, Crystal optical part diameter 6mm, loop
spacing: 12.5mm, no positioning holes. Crystal central part of
refractive power than the surrounding high + 3.50D, used to treat
nearly, surrounding refractive power is low, for as far. When the
incident light into the eye, 50-60 per cent of the light energy to
converge in focus, 22% to 28% of the light energy to converge more in
the near-focus, 15% ~ 18%, in intermediate focus, this artificial
crystal defects as far and near focus by pupil size, Crystal

As a result of intraocular lens is on the incident light by
refraction or diffraction and formation in the retinal image, so
neither the refraction of multifocal intraocular lens or Diffractive
intraocular lens the incident rays refraction or diffraction image
quality after some changes, that there is human brain needs to know
about things like the process and the like of contrast sensitivity
changes, etc.

Application of the principle of simultaneous perception, if distant
and near the light through the multifocal intraocular lens focused on
the retina of refractive power equal to or greater than the
difference between 3D, both in the retina produces image difference
is too great, the cerebral cortex cannot combine two image chuhe, but
select and be looks objects closer to a clearer image, another image.
So according to this principle, multifocal intraocular lens can
suffer from eye provides far, near, and good vision.

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