About Refractive Errors

Vision Problems Corrected by LASIK

The natural shape and curve of your cornea and eye dictates how clearly you see. If they are shaped just right, you will have clear vision at all distances.

However, if your cornea is too steep or flat – or your eye is too long or short – you will end up with blurry vision at near, far or all distances. This is because the cornea is not allowing light to properly bend (refract) and focus on the retina (the back of the eye).

These irregular corneal and eye shapes are called refractive errors and they are very common:

Myopia (Nearsightedness):

Nearsighted people can see close objects clearly but objects in the distance are blurry. Being nearsighted means the curve of the cornea is too steep, or the eye itself is elongated, which results in images being focused in front of the retina. LASIK corrects this condition by flattening the curvature of the cornea. This allows the cornea to focus images on the retina.

Hyperopia (Farsightedness):

Farsighted people see distant objects better but intermediate and close-up objects are blurred. In a farsighted eye the shape of the cornea is too flat, or the eye is too short, causing light rays to focus behind the retina. LASIK corrects this condition by steepening the cornea so that it focuses images onto the retina.


Astigmatism is the inability to focus clearly at any distance due to an irregular or misshapen cornea. With astigmatism the cornea is shaped more like a football than a basketball and light rays focus at differing points on the retina. This causes both distant and near images to be distorted. LASIK corrects this oval shape so images can be clearly focused on the retina.

LASIK is performed to permanently alter the shape of the cornea using laser technology. Only a miniscule amount of corneal tissue is typically removed to create the ideal shape so light focuses more precisely on the retina.

Presbyopia is Not a Refractive Error

The condition of presbyopia (the need for reading glasses or bifocals) is not a refractive error. By age 40, many people start to develop what they might think is farsightedness because they need glasses to read things up-close. Presbyopia is actually the stiffening of the eye lens that occurs naturally over time – even to people who have had 20/20 vision their whole lives. As the lenses become less flexible, it becomes harder to focus on images like text messages, restaurant menus, medicine labels and more without some type of magnifier.

LASIK cannot correct presbyopia. However, a technique called monovision LASIK, where one eye is corrected for vision distance and the other eye is corrected for up-close vision, may be an alternative to reading glasses or bifocals.

While LASIK can help many people achieve clear vision, it is not recommended for everyone. To find out if your refractive error, corneal thickness and overall eye health is right for this amazing procedure, contact us today to schedule a free LASIK Consultation. Our LASIK doctors in San Francisco will perform a comprehensive exam and discuss your options.