19 Aug LASIK for Astigmatism
Laser eye surgery fixes astigmatism. If you have significant astigmatism, both LASIK and PRK do a great job of correcting your eye problems.
What is Astigmatism?
Those with astigmatism have eyes that are more football-shaped than round, making their vision blurry or doubled.
The cornea is the outer surface of your eye that allows light to pass through. It is like the outer glass crystal on an old style watch. It does most of the focusing for the entire eye. If a cornea has a perfect shape, all of the light rays that pass through it are brought to a perfect pinpoint focus on the retina at the back of your eye. A cornea that is relatively round (like a ball) creates this ideal and well-focused vision.
Glasses can correct this problem, which can restore focus. Because the correction sits out away from your eye, the correction glasses are thick.
A contact lens sits right on the surface of your eye so a very thin contact lens can carry the same correction.
Corneas that are not the ideal, rounded shape do not focus light rays to a pinpoint focus. The irregular shape makes light rays hit different parts of the retina (Fig 1), causing blurry vision or even double vision.
In LASIK astigmatism, the cornea has a toric shape, which means it is shaped more like an egg, a football, or a tablespoon instead of round. Notice how the toric shaped tablespoon distorts the image of the young woman like a “fun mirror” at a circus as it is rotated from vertical (Fig 2) to horizontal (Fig 3). This is what an astigmatic shaped cornea does to your vision.
I know it doesn’t seem fair that some have perfect corneas while others have eyes shaped like a football, but the good news is that you don’t have to put up with it as laser vision correction does a good job of correcting this focusing problem.
What causes Astigmatism?Most LASIK astigmatism is genetic, meaning you inherited the shape of your cornea from your parents (thanks for nothing). Trauma to the eye or even excessive eye rubbing can also change the shape of your cornea.
How does Astigmatism LASIK Work?
LASIK uses a laser to gently reshape the surface of your eye to return it to a more ideal round shape. For most patients, this restores balance so that your vision can focus for distance vision without glasses or contact lenses. This is a better and more natural correction for the problems from caused by astigmatism.The older style lasers flatten the steep parts of the cornea to create a rounder shape. This approach does a good job with astigmatism but the newer patterns have some distinct advantages. The Allegretto EX 500 that I use for the majority of my patients both flattens the steep parts and steepens the flat parts of the cornea. This combined treatment pattern gives an exquisite contour to the cornea with a full optical zone of treatment even with larger amounts of astigmatism. The older patterns don’t treat out as far in those with larger amounts of astigmatism, which can impact the quality of night vision for those with larger pupil sizes.
In conclusion, while no surgery is perfect, modern treatment patterns do a very good job of treating LASIK astigmatism to restore a more normal shape to your cornea and clarity to your vision without glasses.
If I can provide any further information, please schedule a time to meet with me at my office or post a comment.
How does an Eye Surgeon Measure LASIK Astigmatism?
We measure your astigmatism a number of ways before surgery.
We measure how much astigmatism you have in your old prescription glasses. We then use a corneal topographer to image your cornea. This machine displays a topographic map of your cornea. It compares the shape of your cornea to a perfectly round sphere, indicating the amount of work the laser will need to do to return your eye to a more natural shape.
We also use an auto-refractor to check your eyes and then do actual glasses measurements (you know, better one or two) before and after having your eyes dilated to compare the correction required for your clearest vision.
Finally, we use a wavefront imaging system that projects a column of light into your eye and then measures how your astigmatism has changed the light as it is reflected back out.
All of these instruments independently give us measurements of the amount of astigmatism you have. I insist on checking, and re-checking, before I use LASIK for problem.
How do you Measure Corneal Shape?The glasses machine has a series of round and non-round lenses inside. As the eye doctor rotates the different shapes in front of your eye, eventually they find one that best focuses your vision. The lens you like best indicates to the doctor the amount and the direction of your astigmatism.
There is another cleaver way of measuring the corneal shape directly called topography.
A series of perfectly round circles are projected onto your eye. As they reflect back a camera takes a picture of the rings. If a cornea is round, the circles are still round as they reflect back. If the cornea has LASIK astigmatism, the rings are bent out of round. Fig 4 shows an eye where the rings that are reflecting back are not perfectly round, but are distorted by an inperfect corneal shape. A computer uses edge detecting software to mark the rings then measures and mathematically calculates the astigmatism required to bend the rings to that shape (Fig 5).
Laser Eye Surgery For Astigmatism
Just before surgery, your particular problem, along with your age and visual goals, are entered into a sophisticated computer program that outlines the exact settings needed for the laser according to your individual eye problem. This program makes these recommendations based on the laser outcomes of all those that previously had their astigmatism corrected.
The laser then tracks the location of your eye and gently reshapes your cornea according to your custom settings. This return to a normal shape corrects your astigmatism.
Best Laser Eye Surgery
We strive to be the best laser center in America.
This requires constant focus on quality assurance and improvement. Several months after your surgery we check your eyes to make sure we have done a great job for you and your vision. We enter your exact outcomes back into the sophisticated computer program.
Your outcomes confirm and adjust the exact amounts needed for your friends that you refer in for their treatments. I guess you could call this the circle of light!
Laser eye procedures, like all surgery, carries some risk. If you have any further questions about astigmatism, please schedule a time to visit with me at the office or send me a note.