The principle of correcting refractive errors is to modify the refractive power. Refractive power is the ability of the eye to focus light onto the retina in the back of the eye. A refractive error means there is a mismatch between the curvature of the cornea and distance from the cornea to the retina so that light does not come to a focus on the retina, but rather in front or behind it. In farsightedness, the corneal power is too weak, and light is focused behind the retina. To correct this, the refractive power must be increased. In nearsightedness, the corneal power is too strong, and light is focused in front of the retina. In this case the refractive power of the cornea must be decreased.
Spectacles or Glasses. The most widely used form of vision correction,glasses are considered to be the safest because they are the least invasive. However for various reasons, many people will find that spectacles are not necessarily the answer to their vision problems. For example, they are not suitable for people whose refractive errors differ greatly between the two eyes, they are not allowed in certain professions, and they are often not practical for sports or active lifestyles.
Contact Lenses. Contact lenses are another popular choice. They provide convenience and are reasonably safe. However, they are not risk-free. Although the risk can be somewhat reduced when the guidelines given by your eye doctor are strictly followed, contact lens users are always at a higher risk to develop eye infections than the general population. Some people cannot use contact lenses at all because of dry eyes or they are allergic to the lens materials or disinfecting solutions. Certain environments are also prohibitive to the use of contact lenses, such as very dusty or smoky surroundings. A number of activities are also contraindicated with contact lens wear, such as swimming or scuba diving.
Refractive Surgery. Refractive surgery has been developed as a means to correct vision problems for people who cannot (or prefer not to) wear spectacles or contact lenses for various reasons. Refractive laser surgery has been continuously developed for decades, progressing from Photorefractive Keratectomy (PRK), which uses an excimer laser to directly reshape the top of the cornea’s middle layer, to Laser In-Situ Keratomileusis (LASIK), which uses the same type of laser to reshape the inside of cornea’s middle layer. The main difference between these two surgeries is that LASIK involves making an incision in the cornea to create a flap so that the inside of the middle layer can be accessed by the laser. Both surgeries are proven to be safe and effective. Phakic Intraocular Lenses are a more recent development in the field of refractive surgery. In this vision correction procedure, a lens is placed inside of the eye to correct the refractive error. This lens does not need to be replaced but can be removed at any time if necessary. The two most common cases where this procedure is recommended over PRK and LASIK is for patients whose corneas are too thin, or their prescription is too high.