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Astigmatism Correction

Astigmatism issues with Lasik, Bladeless Lasik, PRK, LASEK, Epi-Lasik, P-IOL, RLE, etc..


Diagram of light affected by astigmatism entering the eye.  
Astigmatism means the cornea is not spherical, like the top of a ball, but is elliptical, like the back of a spoon. Astigmatism is a corneal irregularity that causes multiple focal points and distorts vision.  
   

Conventional or custom wavefront  Lasik Bladeless Lasik, PRK, LASEK,and Epi-Lasik, can correct astigmatism. Most refractive surgeons consider it much more difficult to correct astigmatism than myopia (nearsighted, shortsighted) or hyperopia (farsighted, longsighted). As a very general rule, if your astigmatism is more than half your sphere, then the probably of a good outcome is diminished. If your astigmatism is more than 2.00 diopters, your probably of a good outcome is significantly diminished.

Lens Based Limitations

Lens based refractive surgery procedures like P-IOL and RLE do not correct astigmatism well, however RLE can correct lenticular astigmatism. Although toric intraocular lenses (IOL) are available, placement and rotation issues make astigmatic correction difficult.

The amount and type of astigmatism that can be corrected will depend upon many factors. Lasers are approved by the FDA for specific levels of astigmatic correction. More than the laser, the physiological features of your eye will determine if your astigmatism can be corrected with refractive surgery. Issues such as thickness of cornea, pupil size, plus type and amount of astigmatism will all be important considerations.

Indirectly Correct Astigmatism

P-IOL, and RLE do not directly correct astigmatism, however a minor amount of astigmatism can be corrected as a part of the surgical process of correcting myopia or hyperopia. P-IOLs available in the US do not correct astigmatism, but the incision through which the P-IOL is placed inside the eye can be manipulated to reduce preexisting astigmatism. Equally, the incision created during RLE through which the IOL is placed inside the eye can be manipulated to reduce preexisting astigmatism.

Laser Coupling Effect

Something important to remember is that with most laser assisted astigmatic refractive surgery techniques, for each diopter of astigmatism that is corrected, a certain amount of myopia is also automatically corrected - even if you don't need the myopia correction. This coupling of myopic correction and astigmatic correction is consistent with virtually all excimer lasers.

As an example, let us assume that for every one diopter of astigmatic correction the technique also corrects 0.25 diopter of myopia. If you have 2.00 diopters of astigmatism, you will receive 0.50 diopters of myopia correction (0.25 diopters of automatic myopia correction multiplied by the 2.00 diopters of astigmatism to be corrected) even if you do not need the myopia correction. If you have more than 0.50 diopters of myopia, a 2.00 diopter astigmatic correction should not be a problem with this technique. If you are plano then after surgery you would be 0.50 diopters hyperopic - not a desirable outcome.

Different Astigmatism Types

Irregular astigmatism is very, very difficult to correct and some techniques and technology cannot fully correct an irregular astigmatism at this time. Every person with irregular astigmatism is unique and needs to be individually evaluated.

Lenticular astigmatism is when the irregularity is in the natural crystalline lens, rather than in the cornea. RLE will eliminate lenticular astigmatism. Cornea-based surgery techniques conventional and wavefront Lasik, Bladeless Lasik, PRK, LASEK, and Epi-Lasik can correct lenticular astigmatism's effects, but making a reverse of the lenticular astigmatism in the cornea. While this can be a successful technique of lenticular astigmatism correction, there is a significant concern.

As we age the natural lens of the eye becomes clouded. This is called a cataract. The process to resolve a cataract is to remove the natural lens and replace it with an artificial lens. The problem is that the artificial lens will not have the pre-existing lenticular astigmatism and if the cornea has been reshaped to accommodate the lenticular astigmatism, the cornea will now cause an irregular astigmatism.

Discuss in detail with your doctor the type and amount of astigmatism you have and how it may be accommodated with refractive surgery. Discuss if the technology and techniques s/he intends to use may affect myopic correction and how this may be accommodated for your individual needs.

Looking For Best Lasik Surgeon?

If you are ready to choose a doctor to be evaluated for conventional or custom wavefront Lasik, Bladeless Lasik, PRK, or any refractive surgery procedure, we recommend you consider a doctor who has been evaluated and certified by the USAEyes nonprofit organization. Locate a USAEyes Evaluated & Certified Lasik Doctor.

Personalized Answers

If this article did not fully answer your questions, use our free Ask Lasik Expert patient forum.


Recent Astigmatism Island Medical Journal Articles...

Related Articles

Corneal coupling of astigmatism applied to incisional and ablative surgery.

J Cataract Refract Surg. 2014 Nov;40(11):1813-27

Authors: Alpins N, Ong JK, Stamatelatos G

Abstract
PURPOSE: To redefine measures of corneal coupling for use with incisional and ablation procedures for astigmatism.
SETTING: Private clinics, Melbourne, Victoria, Australia.
DESIGN: Retrospective nonrandomized study.
METHODS: The measures known as the coupling ratio (CR) and coupling constant (CC) were redefined to ensure validity in most cases of incisional procedures and laser vision correction procedures. In addition, a new measure--the coupling adjustment (CAdj)--was developed to quantify the amount of spherical adjustment that must be applied to compensate for coupling that occurs as a result of astigmatism treatment. These quantitative measures of coupling were applied to retrospective data to show their applicability.
RESULTS: Pure myopic, compound myopic, and compound hyperopic astigmatism excimer laser treatments showed a CR close to zero, a CC close to 0.5, and a CAdj close to zero. Incision LRIs showed a CR close to 1.0 and a CC close to zero. In all cases, the coupling measures were consistent for treatments with a larger astigmatic component (>1.0 diopter) but variable when the astigmatic component of the treatment was smaller.
CONCLUSIONS: The revised definitions of CR and CC can be used with incisional and ablative surgery. Incorporating the CAdj into the planning of spherocylindrical treatments allows one to factor in the effect of the astigmatic treatment on the spherical component and thus to more accurately target the desired spherical equivalent.
FINANCIAL DISCLOSURE: Dr. Alpins and Mr. Stamatelatos have a financial interest in the Assort software program. Dr. Ong is an employee of Assort.

PMID: 25442882 [PubMed - indexed for MEDLINE]

 


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