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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

Comparison of visual and refractive outcomes following femtosecond laser- assisted lasik with smile in patients with myopia or myopic astigmatism.

J Refract Surg. 2014 Sep;30(9):590-6

Authors: Ganesh S, Gupta R

Abstract
PURPOSE: To compare the visual and refractive out-comes of femtosecond laser-assisted LASIK with small-incision lenticule extraction (SMILE) in terms of visual acuity, contrast sensitivity, aberrations, and dry eye.
METHODS: A single-center prospective randomized study in which patients diagnosed as having myopia presenting for refractive correction were allocated to either a LASIK or SMILE group. The primary outcome measures were refractive efficacy, predictability, and safety, postoperative contrast sensitivity, aberrations, and dry eye status. Patients were followed up at days 1 and 15 and 3 months; postoperative uncorrected visual acuity (UCVA), aberrations, dry eye, and contrast sensitivity were recorded and compared to preoperative data. Two postoperative subjective questionnaires were used to assess pain, pricking sensation, redness, glare, and overall patient satisfaction.
RESULTS: At day 1 postoperatively, 48 (96%) of 50 eyes in the SMILE group achieved a UCVA of 20/20 compared with 46 (92%) of 50 eyes in the LASIK group. At day 15 postoperatively, contrast sensitivity was similar in the two groups (P = .15), but by 3 months, it was better in the SMILE group than the LASIK group at all spatial frequencies (P < .0001). At 3 months postoperatively, 42 (84%) eyes in each group achieved a UCVA of 20/20, with 6 (12%) eyes in the SMILE group and 2 (4%) eyes in the LASIK group achieving 20/15. Higher-order aberrations at 3 months postoperatively were significantly higher in the LASIK group (0.437 + 0.103 pm) than in the SMILE group (0.267 + 0.07 pm; P < .001). Postoperative dry eye and glare were significantly more common following LASIK (P < .001).
CONCLUSIONS: Three-month results demonstrate that refractive accuracy, dry eye, contrast, and induced aberrations are better following SMILE rather than LASIK.

PMID: 25250415 [PubMed - indexed for MEDLINE]

 


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