How the eye forms an image.
The ability to see the world in sharp focus is mainly determined by the shape of your cornea. The crystalline lens also plays a role in the formation of the retinal image.

Presbyopia
The crystalline lens within the eye is extremely elastic during childhood and early adult life.  However with time, it becomes rigid and looses it's ability to adjust focus, with the result that one experiences difficulty in adjusting the focus of the eye.

Glasses and contact lenses compensate for all these abnormalities, by bending light in such a way that, before it reaches the eye, it leads to a focused image on the retina after passing through the abnormally shaped cornea.

However, due to the rapid advance in medical science, a new way of enhancing your vision is now available - refractive surgery.  During the early 90’s, this technology would have sounded like science fiction, but today it is an ophthalmologic reality, with an astonishing track record.

There are different techniques that may be employed to correct refractive errors, depending on the type and extent of the error.  The modern trend is not only to correct a person's visual acuity, but also to provide the best quality of vision under all possible conditions of illumination. Among the various techniques are PRK (photorefractive keratectomy), Intra-stromal corneal ring segments, a variety of modern modalities namely Advanced Surface Ablation, LASEK, LASIK, phakic intra-ocular lenses, and clear crystalline lens replacement.