Refractive errors

Light rays enter the eye through the clear cornea, pupil and lens. These light rays are focused directly onto the retina. The light sensitive tissue lining the back of the eye, the retina converts light rays into impulses sent through the optic nerve  to the brain where they're recognized as images 70% of the eyes focusing power comes from the cornea and 30% from the lens when we can't see clearly it's often caused by a refractive error. 

There are four types of refractive error

1. Myopia or nearsightedness

This is where the distance between the cornea and the retina is too long so that light rays focus in front of the retina instead of on it with myopia close objects will look clear but distant objects will appear blurred.

2. Hyperopia or farsightedness 

This is where the distance between the cornea and the retina is too short. Here light rays are focused behind the retina instead of on it. Distant objects will look clear but close pbjects will appear blurred.

3. Astigmatism 

This occurs when the cornea is curved unevenly shaped more like a football than a basketball light passing through this uneven cornea is not properly focused on the retina. Distance and close vision may both appear blurry.

4. Presbyopia 

This is a normal condition that typically starts around middle age when the eye lens becomes less flexible and less able to focus on closed objects a typical sign of presbyopia is the need for reading glasses the most common method for correcting refractive errors is the use of eyeglasses. The prescribed lenses in the glasses refocus light rays onto the retina contact lenses float on the tear film that coats the cornea and they also refocus light rays onto the retina over the past decades a variety of surgical procedures collectively known as refractive surgery has become an increasingly popular method of correcting refractive errors in most cases these procedures permanently alter the shape of the cornea so that light rays are refocused on the retina.

To improve vision the most common refractive surgical procedures are as follows:

1. LASIK 
2. Epi-LASIK 
3. PRK
4. LASEK
5. CK  
6. AK
7. RK
8. Phakic IOLs
9. Accomodative IOLs
10. Multifocal IOLs
11. Refractive Lens Exchange
12. INTACS

Each of these procedures offer a different technique for refocusing light more accurately on the retina. 

For many people with refractive errors who are content to wear glasses or contacts there is no need to consider refractive surgery but millions of people have elected to have a fact of surgery to reduce their dependence on glasses or contacts. 

A patient considering refractive surgery should consult with their ophthalmologist  and have a complete eye exam to determine which procedure is  appropriate for their particular case.