Refractive Errors

Ophthalmic Partners treats refractive errors for patients in Philadelphia, Pennsylvania and the surrounding communities.

WHAT ARE REFRACTIVE ERRORS?

Refraction of light is what allows us to see. A refractive error occurs when the eye cannot refract or bend the light to focus correctly, causing blurry or unclear vision. Refractive errors can also cause eye strain and headaches.

WHAT CAUSES REFRACTIVE ERRORS?

When light travels through a lens or a clear surface such as water, the light ray is bent. Refraction in the eye occurs when light rays enter the clear front of the eye (cornea) and travel through the lens. Other liquid surfaces in the eye, tears, and vitreous gel also bend light rays. After being refracted, the light rays are focused onto a sharp focal point on the retina at the back of the eye, which allows clear vision. If anything prevents the refracted light from landing at the right angle on that central point of focus, the quality of the image will be affected.Three anatomical features are involved in refractive errors: eye length, cornea curvature, and lens curvature. Optical imperfections in these features cause three main refractive errors:

1. Nearsightedness (Myopia).
   If the shape of the eye is too long, light will focus before it reaches the retina. The same will occur if the lens is too steeply curved, causing the inability to see beyond a short area in front of the eye.
2. Farsightedness (Hyperopia).
   If the eye shape is too short, or the lens curvature is too flat, the light will not be focused when it reaches the retina, causing an inability to see objects close at hand.
3. Astigmatism.
   A cornea that is not a perfect sphere will cause the image refraction to become irregular. A person may have myopia or hyperopia with or without astigmatism.

A few other less common refractive errors create conditions such as contrast sensitivity. Presbyopia is an age-related refractive error that occurs when the lens hardens and the ability to focus on close objects is hindered.

WHAT ARE THE RISK FACTORS FOR REFRACTIVE ERRORS?

Refractive errors are typically inherited. A family medical history of refractive errors places you at greater risk.

HOW CAN REFRACTIVE ERRORS BE PREVENTED?

Because refractive errors are typically inherited from your family, there are no preventative measures. Children, though, who are born with refractive errors, may outgrow the conditions as their eyes continue to develop.

HOW ARE REFRACTIVE ERRORS DIAGNOSED?

A refraction test is performed with an instrument called a phoropter, which allows the eye doctor at Ophthalmic Partners of Pennsylvania and New Jersey to test your refraction manually with different lenses.

HOW ARE REFRACTIVE ERRORS TREATED?

The test results are used to determine your eyeglass prescription. Contact lenses require an additional fitting. Your prescription designates precise measurements for lenses that will compensate for your eye’s refractive errors, bending the light rays, so they focus correctly on the retina. Laser refractive surgery changes the shape of the cornea so that it is more spherical and can refract the light rays correctly onto the retina.