Monday, May 08, 2006

Patient Q&A: LASIK Flap Wrinkles & Induced Astigmatism

Gary,

First of all, don't panic.  What you are going through is not common, but is well understood.  I'll give you some plain-language thoughts about what is happening, but if you are not familiar with any terms, feel free to use our glossary at http://www.usaeyes.org/glossary/glossary.html.

Striae (pronounced STREE-uh) are wrinkles that develop in the corneal flap after LASIK or ALK. When severe, striae can cause ghosting and very poor visual acuity.

Since the laser flattens the cornea centrally, it shortens the arc length across the front of the cornea and there is "extra" flap tissue when the flap is repositioned on the cornea. Think of the LASIK flap creation as opening your front door - if your door was made of soft rubber. Think of the excimer laser as making the doorframe smaller. After surgery, when you close your front door,! the full sized door can't fit into the smaller doorframe. To get it to fit you must squish the door. These squishes are wrinkles. This is the effect that can cause striae, especially in people who have high refractive change.

The wrinkles will cause light to scatter and not focus well. Light passing through striae will focus on a different area of the retina than light passing through unwrinkled areas of the cornea. This can cause multiple images or ghosting. Often someone with striae will experience more severe ghosting in dimly lit environments. In low light situations, the pupil size expands, allowing light passing through the striae at the edge of the cornea to reach the retina.

There are two types of LASIK induced striations.

The first and more common is flap fold (macro striae) and is usually at the outer edge of the flap. The first line of defense is often to lift the flap, irrigate the area, reposition the flap, and smooth it using a tiny sp! onge. This can help dramatically. Flap lift is appropriate if the wri nkles (and subsequent visual problems) are severe. Most doctors feel that the earlier the response the better, however if the wrinkles are minor the flap will usually settle as it heals.  It sounds to me like this is the kind of striae you have.

The second type is Bowman's crinkles (micro-striae). These usually occur in patients who have had LASIK for myopia over 6.00 diopters but can occur in any patient. Bowman's crinkles are when the Bowman's layer of the cornea constricts. This is similar to those fancy towels that have silk appliqu� on cotton. The one material shrinks different than the other. With Bowman's crinkles, the Bowman's layer constricts, causing the surrounding tissue to wrinkle. These usually resolve with time. During the initial surgery, these can be smoothed out but they are difficult to remove with secondary surgical intervention.  It is possible that you have micro-striae, but it seems less likely, based upon your description of! vision and the care you are receiving.

Astigmatism is when the cornea is not spherical like the top of a ball, but elliptical like the back of a spoon. Astigmatism can cause multiple focal points. The majority of the light focuses on the center of the retina and this provides the main image.  A small amount of light focuses slightly off the center of the retina providing a ghost image or generally poor visual quality, especially in low light environments.  Your small pupils may mean that light coming through the edge of your cornea where your astigmatism is located does not reach your pupils and is not "seen".  You could have astigmatism, but not be bothered by it at all.  Sometimes in refractive surgery astigmatism is induced by creation of the flap or other problems.  In your case, the astigmatism is undoubtedly caused or exacerbated by your flap problems. As your flap problems are resolved with treatment and healing, your astigmatism will undoubtedly settle down, perhaps even resolving completely.  If residual astigmatism is small enough that it does not cause vision problems, then leave it alone.  If you do have vision problems that are caused by the astigmatism, you can have an enhancement surgery to remove the astigmatism.

An enhancement is very likely in your case, but not just because of induced astigmatism.  You started as a very high myope (nearsighted). It is common for the cornea to regress back toward the original refractive error.  It may be that your doctor deliberately overcorrected you to accommodate regression and ultimately receive desired results.  It may be that the regression will make you slightly nearsighted again.

During healing after refractive surgery, both the epithelium and the deeper stroma can reshape and reform at different rates and can cause regression. This occurs mostly in myopic patients who have more than 6.0 dio! pters of refractive error and virtually all hyperopic patients.

Regression occurs more commonly with smaller ablation diameters and with abrupt transition zones at the edge of the treatment areas. Steroid medications can be used to regulate and control regression.

Although regression seems to be more prevalent the higher the refractive error, regression can occur in anyone.  For myopic patients, regression usually occurs within the first one to three months after surgery.  Depending upon the individual circumstances and the technique used for correction, hyperopic patients may continue to regress over a period of years until they return to their original refractive error.

At age 41, you probably are noticing more than ever, difficulty with reading or seeing clearly things close to you.  It is common for someone with early presbyopia to have difficulties like this after refractive surgery.  I call this "Sudden Presbyopia".!  You may want to read about this more at http://www.usaeyes.org/faq/subjects/sudden_presbyopia.htm.

Refractive surgery is more of a six-month process than a 20-Minute Miracle.  You are only two days out of surgery.  Follow your doctor's advice, seek outside research to satisfy your curiosity, feel free to ask me any questions, and if you get to a point where you think a second opinion is a good idea, I'll gladly help you find a qualified doctor.

I hope I have been of assistance.

Glenn Hagele Executive Director Council for Refractive Surgery Quality Assurance http://www.usaeyes.org

I am not a doctor.

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