The human crystalline lens is situated behind the iris, the color of the eye. In the ideal world the eye can focus on objects in the distance, and the lens will then change shape and the focus of the eye will change permitting near vision. This change in the shape of the lens is called accommodation. Interestingly, the lens is the only human organ that grows throughout your life. The lens does not enlarge much though, but do increase in its density, and therefore becomes stiff and loses its compliance. This is an age related phenomena and affects all individuals, irrespective of their spectacle dependence.
The net result of all these changes is presbyopia. After the age of around 43 to 45 most individuals will experience difficulty in focusing on near objects. People that are nearsighted (myopic) will often compensate for this by removing their spectacles for reading, but most individuals will need some kind of correction to help them with close work.
There is no universal solution to this problem. Essentially three solution are available, i.e. spectacles, contact lenses or surgery. The choice between these is of course personal.
The surgical choices depend on the age of the patient and his or her spectacle error. Surgery can in no way restore the accommodative powers of the human lens but will reduce the dependency on either spectacles or contact lenses for performing near activities like reading. Essentially our demand for vision is focused at three distances: distance, intermediate and near. Only having two eyes therefore means that there will always be a compromise. With monovision one eye focuses for distance and the other for near. This situation can be created with the use of contact lenses but also with surgery. LASIK surgery or phakic intra-ocular lenses can be used to change the refraction of each eye within certain parameters to alleviate spectacle dependence for both distance and near. Before surgery the success of the outcome can be confirmed with a contact lens trial that will simulate the same effect.
With further aging the human crystalline lens hardness increases further and the lens fails completely, therefore having no accommodative effect, leaving a person completely dependent on spectacles for all closer activities. This situation generally presents itself at the age of 52 to 55 years. Due to the fact that the lens is the root of the problem, the ideal solution will be to remove the failed human lens, replacing it with an intra-ocular lens. Importantly, the new lens will not accommodate, but will reduce spectacle dependence for near work. This solution is most commonly achieved with the use of lenses that permit monovision as described above, but also with the use of multifocal lenses in some instances. The multifocal intra-ocular lenses permit good distance, intermediate as well as near vision and permit complete spectacle independence for most. The intra-ocular lenses are a permanent solution. They do not need to be replaced or explanted in the future.
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