October 2018

COVER FEATURE

Revisiting astigmatism
Views on astigmatic keratotomy


by Rich Daly EyeWorld Contributing Writer


A patient undergoes a manual AK.

Slit lamp exam of a patient who received an AK treatment

A patient undergoes a manual LRI in the OR.

A patient undergoes a manual LRI at the slit lamp.
Source (all): Eric Donnenfeld, MD

The use of astigmatic keratotomy continues to change amid newer options

Astigmatic keratotomy (AK), one of the two primary ways of surgically treating astigmatism, has changed in recent years with newer technology and understandings of its anatomical impacts.
Treating corneal astigmatism at the time of cataract surgery remains critical to improve visual outcomes and decrease reliance on glasses. Although the newer option of toric IOLs to offset corneal astigmatism by neutralizing the astigmatic effect is popular with some patients, treating it at the source by decreasing the corneal astigmatism remains an important option.
Generally performed with diamond knife incisions in the cornea, AK treats the astigmatism on the cornea itself by flattening the steep meridian so that the cornea becomes more spherical.
“The corneal power in that meridian is slightly weakened by creating partial depth incisions either with a blade or a laser,” said Uday Devgan, MD, clinical professor of ophthalmology, Jules Stein Eye Institute, University of California, Los Angeles.
The classic AK is placed from the surface of the cornea to 80–90% depth, noted Eric Donnenfeld, MD, clinical professor of ophthalmology, New York University, New York.
Dr. Donnenfeld said intrastromal incisions may be placed in the stroma and not penetrate through to the epithelium with a femtosecond laser and penetrating incisions can be made with a keratome.
Incisions placed in the peripheral cornea—astigmatic keratotomies—are different than corneal incisions placed closer to the limbus, which are often referred to as limbal relaxing incisions (LRIs).
Surgeons should consider using AKs in eyes with corneas that have a modest amount of astigmatism but are otherwise normal, Dr. Devgan said. They are usually done at the time of cataract surgery and tend to work well to treat 0.5–1.0 D of corneal astigmatism.
Dr. Donnenfeld noted that AKs also can be performed as standalone procedures.
The incisions can be used for higher degrees—up to 2.0 D—but they tend not to be as accurate at that level of astigmatism, Dr. Devgan said.
“I favor LRIs for 0.5–1.0 D of astigmatism and toric IOLs for 1.5 D or more of astigmatism,” Dr. Devgan said.

Femto option

Femtosecond laser astigmatic incisions used to reduce astigmatism provide more precision than a manual diamond knife incision, Dr. Donnenfeld said.
“They are done with OCT guidance so the depth of the incision is more precise as well as their centration on the visual axis,” Dr. Donnenfeld said. “Femtosecond laser astigmatic incisions can be titrated by manually opening them during the postop period based on the refraction.”
Dr. Devgan agreed that femtosecond AKs have the benefit of laser precision so that the depth of the AK can be made exactly at 80% or another level for the entire length of the incision.
“Since the femto incision does not automatically open like a diamond blade incision would, we can use that to titrate the AK effect by opening it in stages,” Dr. Devgan said. “So the femto AKs can be better than the manual LRIs but this is only up to 1.0 D of astigmatism. After that, the toric IOLs are far better than femto AKs.”
Dr. Donnenfeld noted that intrastromal incisions performed with a femtosecond laser are not painful and do not require postop antibiotics.
Dr. Devgan avoids using AKs if the cornea is thin or irregular. He also avoids them with eyes that have asymmetric astigmatism.
Dr. Donnenfeld urged caution in using AKs in patients with irregular astigmatism, as well as those with ectasia or dry eye disease.

Effective treatment range

The degree of astigmatism AKs can correct include high levels of astigmatism, but in such eyes, the incisions also induce irregular astigmatism and dry eye, Dr. Donnenfeld said.
“In the past, it was routine to correct 3 D of cylinder or more with an AK,” Dr. Donnenfeld said. “Today, toric IOLs and excimer laser ablation are better options for high levels of astigmatism, and we generally perform astigmatic keratotomies for 1.5 D or less of cylinder.”
Dr. Devgan has found about 0.5–1.0 D to be the ideal treatment range for AKs.
“More can be done but it is less accurate and less predictable,” Dr. Devgan said.
Normal healing time for AKs include epithelial closure within 48 hours, but stromal remodeling may take several months, Dr. Donnenfeld said.
Dr. Devgan has also found the epithelium closes within a day or two for both AKs and LRIs.
“The effect starts immediately but may take a week or two to stabilize,” Dr. Devgan said.

Regression possible?

In general, astigmatic incisions do not regress, Dr. Donnenfeld said.
“In fact, they may progress over time,” Dr. Donnenfeld said. “Progression is much more common with larger incisions, and for incisions of 1.5 D or less, it is generally minimal.”
Dr. Devgan has found that at larger attempted corrections, regression is more common. “But at 1.0 D or less, it is fairly stable over years,” Dr. Devgan said.

Editors’ note: Dr. Devgan has financial interests with LensGen (Irvine, California), IOLcalc.com, and CataractCoach.com. Dr. Donnenfeld has financial interests with Alcon (Fort Worth, Texas), Johnson & Johnson Vision (Santa Ana, California), Katena (Denville, New Jersey), and Bausch + Lomb (Bridgewater, New Jersey).

Contact information

Devgan
: devgan@gmail.com
Donnenfeld: ericdonnenfeld@gmail.com

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