Evidence Based

Astigmatic Keratotomy (AK)

Astigmatic keratotomy, also known as arcuate keratotomy or AK, is a procedure that corrects astigmatism. Astigmatism occurs when your cornea's curvature is not spherical like a basketball, but oval like an egg. As a result, one meridian (curvature) of your cornea is flatter, while the other is steeper.

AK is a type of corneal relaxing incision (CRI) surgery. These surgeries correct astigmatism by flattening the steeper areas of your cornea.

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Who Is a Candidate for Astigmatic Keratotomy Surgery? 

Astigmatic keratotomy may be ideal for people who have:

  • A desire to reduce their dependence on glasses or contact lenses
  • Mild to moderate astigmatism
  • Stable eyeglass prescription for at least one year
  • Good general health; diabetes and connective tissue diseases may affect the healing process
  • No eye problems that may affect recovery, such as severe dry eyes

Most times, AK is performed on people who have residual astigmatism after previous eye surgery, such as:

  • Cataract surgery
  • Corneal transplant (penetrating keratoplasty or partial-thickness corneal transplants)
  • Radial keratotomy 
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What To Expect Before, During & After Surgery

AK is an outpatient procedure, meaning you can go home shortly after the surgery. The surgery itself only takes about 5 minutes per eye.

Before surgery

Before the procedure, the surgeon obtains a corneal topography. This serves as a map to guide the surgeon on where to make the incisions. Another measurement called corneal pachymetry tells the surgeon how thick your corneal tissue is, which helps determine how deep the incisions can go. 

During surgery

To numb your eyes, the surgeon instills anesthetic eye drops. Then, they place a lid speculum to hold your eye open during surgery. The surgeon places temporary markings on your cornea that indicate where they will make the incisions.

Traditionally, the surgeon uses a diamond surgical blade. Many surgeons are now using a laser to create the incision, which may result in more precise outcomes.

The surgeon typically makes one or two incisions parallel to the edge of your cornea. These incisions are located along the steepest meridian of your cornea.

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Generally, the deeper or longer the incision, the more astigmatism is corrected. Shallower or shorter incisions result in less correction. Reducing the distance between the two incisions also increases the amount of astigmatism correction.

AK tends to be more effective in older patients. The surgeon can make shorter incisions in these cases. For younger patients, the surgeon may create longer incisions.

After surgery

The surgeon prescribes antibiotic eye drops (and possibly steroid eye drops) to use for several days after surgery. You may need to use eye shields to protect your eyes. If you experience discomfort, you can take some over-the-counter pain relievers. Other post-surgical symptoms include:

  • Tearing
  • Mild swelling
  • Light sensitivity
  • Redness
  • Scratchy eyes

These symptoms are normal and usually go away within a day or two. Full healing time is about 2 to 3 months, although your vision should improve within a day or so. Most people can return to work and resume normal activities the next day.

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Pros and Cons of Astigmatic Keratotomy

Another type of corneal relaxing incision surgery is limbal relaxing incisions (LRI). The techniques involved are similar to those of AK. Currently, LRI surgeries are performed more often than AK. Here are some pros and cons that highlight the differences between these procedures.

Pros of AK
  • Quick and safe procedure
  • Shorter incision length
  • Corrects higher amounts of astigmatism
  • Less costly than laser refractive surgery, such as LASIK
Cons of AK
  • Deeper incisions, which carries a higher risk of penetrating the cornea
  • Incisions are placed further from the edge of your cornea (closer to the center), which may result in increased glare and other vision problems
  • More discomfort 
  • Longer visual recovery
  • Higher risk of overcorrection
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Side Effects of Astigmatic Keratotomy Surgery

Astigmatic keratotomy is considered safe and effective. However, a small percentage of people experience side effects that may be temporary or permanent. Some side effects and complications include:

  • Overcorrection or undercorrection
  • Light sensitivity, glare, and halos, which can be permanent for some people
  • Infection, although rare
  • Weaker corneal structure, which makes your cornea more vulnerable to injury

Alternative Surgical Options

In addition to astigmatic keratotomy and limbal relaxing incisions, there are other procedures that correct astigmatism, including:

  • LASIK (laser in-situ keratomileusis) is a form of laser eye surgery that corrects refractive errors, including astigmatism, myopia, and hyperopia. This procedure may be more suitable for those who have a combination of refractive errors (not only astigmatism).
  • PRK (photorefractive keratectomy) is another type of laser refractive surgery that also corrects astigmatism, myopia, and hyperopia. Some people receive PRK instead of LASIK because they have thinner corneas or high prescriptions. Others elect PRK to avoid having a corneal flap, such as in LASIK. This may include athletes who participate in high-impact sports.
  • Refractive lens exchange (RLE) is a procedure that removes the natural lens in your eye and replaces it with an intraocular lens implant (IOL). The surgeon places a toric IOL into your eye, which is a type of implant that corrects astigmatism. This surgery may correct higher astigmatism levels than AK.
  • Cataract surgery involves the same steps as an RLE, except that the natural lens has developed into a cataract at the time of surgery. For this reason, older patients who have cataracts may choose this surgery over other types of procedures to correct astigmatism.
  • Phakic intraocular lens implant (IOL) surgery differs from RLE in that your natural lens is not removed. The implant is placed in front of the iris (anterior chamber) or behind the iris (posterior chamber). This procedure primarily treats high myopia, but can also correct astigmatism with the use of toric phakic IOLs. 

In modern eye surgery, many surgeons favor laser refractive surgery (LASIK or PRK) over corneal relaxing incision surgeries. However, combining laser eye surgery with AK may benefit patients with high astigmatism. The laser can correct a majority of the prescription, while AK treats any residual astigmatism. This combination may lead to a better quality of vision and less glare at nighttime. 

Author: Melody Huang, O.D. | UPDATED June 18, 2020
Resources

Chang, John S. M. “Femtosecond Laser-Assisted Astigmatic Keratotomy: a Review.” Eye and Vision, vol. 5, no. 6, 2018, doi:10.1186/s40662-018-0099-9.

Emerah, Sherif. “Evaluation of Axis Alignment and Refractive Results of Toric Phakic IOL Using Image-Guided System.” International Journal of Ophthalmology, vol. 13, no. 4, 2020, pp. 667–670., doi:10.18240/ijo.2020.04.21.

Hays, James. “Astigmatic Keratotomy for the Correction of Astigmatism.” Medscape, 6 Apr. 2017, emedicine.medscape.com/article/1220380-overview#a6.

Kozak, Alex, et al. “Limbal Relaxing Incisions.” EyeWiki, 22 Oct. 2019, eyewiki.aao.org/Limbal_Relaxing_Incisions.

Roberts, Harry W., et al. “Refractive Outcomes after Limbal Relaxing Incisions or Femtosecond Laser Arcuate Keratotomy to Manage Corneal Astigmatism at the Time of Cataract Surgery.” Journal of Cataract & Refractive Surgery, vol. 44, no. 8, Aug. 2018, pp. 955–963., doi:10.1016/j.jcrs.2018.05.027.

Yoo, Aeri, et al. “Femtosecond Laser-Assisted Arcuate Keratotomy Versus Toric IOL Implantation for Correcting Astigmatism.” Journal of Refractive Surgery, vol. 31, no. 9, 1 Sept. 2015, pp. 574–578., doi:10.3928/1081597x-20150820-01.

Zheng, Lin-Yan, et al. “Comparison between Toric and Spherical Phakic Intraocular Lenses Combined with Astigmatic Keratotomy for High Myopic Astigmatism.” Eye and Vision, vol. 4, no. 20, 18 Aug. 2017, doi:10.1186/s40662-017-0085-7.

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