Published: May 4, 2009
Updated: July 8, 2009
Myopia causes images to focus in front of the retina making close objects appear more clearly than distant objects. Myopia is caused either by a cornea that has a steeper curvature than normal or by an eye that is too long from front to back.
Hyperopia causes images to focus behind the retina making distant objects appear clearer than closer objects. Hyperopia is caused by a cornea that is flatter than normal or by an eye that is too short, causing the light rays to focus at a point behind the retina.
Hyperopia is often confused with presbyopia -- a condition which results from aging -- since they both affect your ability to see close objects. Although they are different, hyperopia aggravates presbyopia, making this age-related change occur earlier in life and more severely than in non-hyperopic individuals.
Astigmatism can occur by itself or with myopia or hyperopia and is caused by a cornea that has an uneven, irregular, or asymmetric curvature. Without correction, astigmatism prevents the eye from properly focusing at any distance resulting in blurred vision and multiple images.
Modern vision correction surgery remains remarkably stable for years and even decades after the procedure; however, aging continues to impact the eye and the rest of your body.
While vision correction surgery does not appear to accelerate any of the changes associated with aging, it also does not prevent degenerative eye conditions that often occur with aging eyes. Therefore, it is important to continue your regularly scheduled, routine eye examinations to screen for these conditions. Common conditions associated with aging include presbyopia and cataracts.
Presbyopia results from a progressive loss of focusing range that develops as a natural consequence of aging. Aging reduces the flexibility of the lens inside the eye and the muscles around the lens lose their focusing power and ability to change shape. This is most noticeable when trying to see close objects, especially reading material.
Presbyopia is inevitable and often occurs first between 40 and 50 years of age. This is why many people begin to wear bifocals, and people who previously had normal vision begin using reading glasses. Anyone considering vision correction surgery should understand the impact of presbyopia and the eventual need for reading glasses.
Patients experiencing presbyopia may consider using contact lenses or vision correction surgery in a manner that corrects each eye differently. This option attempts to preserve reading vision by sacrificing some quality of distant vision in the nondominant eye.
In this approach, called monovision, the doctor determines ocular dominance and corrects the dominant eye for distant vision. The non-dominant eye is treated for partial myopia or intentional nearsightedness so that it can be used for reading.
In addition to sacrificing some distant vision in the nondominant eye, there is also some loss of depth perception, most noticeable when performing activities within arms length such as threading a needle. This sacrifice is made in an effort to preserve some reading or computer vision in the nondominant eye.
Monovision may not be a permanent solution for the elimination of reading glasses, and therefore is best thought of as an option that postpones this need. The best candidates for monovision are successful wearers of contact lenses; you may want a contact lens trial before undergoing surgery as patients who can't wear contact lenses are usually poor candidates for surgical monovision.
This surgical option is best discussed with the experienced Duke surgical staff and is typically reserved for patients over 45 years of age desiring a functional compromise as an alternative to reading glasses.
As your eyes age, the lens not only loses its flexibility as with presbyopia, it begins to harden and change color. This process eventually produces a cloudy lens that blocks the transmission of light -- this lens is known as a cataract.
While vision correction surgery does not cause cataracts, it also does not prevent this process from slowly progressing over time.
The doctors at Duke are among the most experienced in the world at diagnosing and treating cataracts, including cataracts that develop in patients previously treated with vision correction surgery. These doctors are also very experienced with the latest intraocular lens technology that includes lenses that address the treatment of presbyopia simultaneously with distance vision in an effort to reduce the need for reading glasses after cataract surgery.