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How the Eye Works:
To understand how IOLs work it is necessary to understand how the eye works.
  • Light enters the eye through the clear outer covering called the cornea
  • Light passes through the pupil, the opening in the center of the iris, and through the natural crystalline lens to the retina where it stimulates the optic nerve
  • In non-presbyopic patients, typically under 45 years of age, the shape of the lens changes involuntarily so that the eye can accommodate or change focus on objects that are at far, intermediate, or close distances
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  • People who are nearsighted (myopic) see near objects clearly, but have poor distance vision.
  • Depending on their age, those who are farsighted (hyperopic) can see distance objects clearly, but they have poor near vision.
  • Those with astigmatism have blurred vision at all distances.
Treatment Options
Means for Managing Presbyopia
Monovision, Multifocality and Accommodation

Most commonly, individuals employ reading glasses, bifocals or progressive bifocal glasses to be able to see far and near–and they work well. However, the annoyance of eyeglasses has caused many patients to seek alternative solutions and considerable research and energy has been applied to helping with this problem.

Monovision: a commonly used strategy with contact lenses or some forms of surgery refers to making one eye see clearly at distance, usually the dominant eye, and the fellow eye focus at a near point. Patients subconsciously select the distant or near object to see.

Advantages
  • Monovision can be achieved with contact lenses, LASIK, Conductive Keratoplasty (CK) and cataract or lens replacement surgery
  • A majority of patients adjust well to monovision
Disadvantages
  • Eliminates the use of both eyes (binocularity) for the
    same viewing target
  • Reduces image sharpness and the ability to judge
    distances well
  • A compromise between good depth of focus and the
    elimination of full time eyeglass use
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Those interested in learning if a monovision surgical solution might be acceptable to them should consider a trial using contact lenses—one selected for good distance vision and one selected for good near vision—to simulate the surgical effect. The majority of patients, but not all, adapt well to monovision.

Multifocality: Provides each eye with the ability to see at far and near distances.

Advantages

  • Allows for better depth perception than monovision
  • Contact lenses, implanted artificial lenses and multifocal laser vision correction, although the latter is still under investigation, are all devises that achieve multifocality
  • A trade-off against the use of reading glasses

Disadvantage

  • Multifocal devices split light energy into two or more images, causing a number of patients to experience undesired optical effects and a reduced quality of vision
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While bifocal and gradient lens glasses are not truly multifocal in the above sense, they do have distance and near vision prescriptions ground onto the surface of a single lens. By looking down or up the patient can select the near or distant prescription to look through.

Accommodation: A change of optical power by the natural lens or by an artificial lens system. Lenses can do this inside the human eye by changing their shape or by moving forward in the eye to change magnifying power.

Advantage

High quality of vision because light is not split between different focal points.

Disadvantage

Some patients may not achieve sufficient accommodation to perform all near tasks with currently available accommodating intraocular lenses.