December 2020

REFRACTIVE

The many considerations of astigmatism management


by Liz Hillman Editorial Co-Director




A recent patient of Dr. Ristvedt’s presented for cataract evaluation wanting a trifocal IOL. Blurred Placido images indicated dryness, which was then treated before she returned for repeat measurements. The power and orientation of the patient’s astigmatism changed after treating the dry eye.
Source: Deborah Ristvedt, DO

Managing astigmatism at the time of cataract surgery is a weighty topic with many variables. What technology to measure astigmatism—power and axis? How many measurements to take for reliability? How to ensure accuracy and consistency of measurements? What course of correction to take?
EyeWorld spoke with five doctors—John Berdahl, MD, Bryan Lee, MD, JD, Deborah Ristvedt, DO, Russell Swan, MD, and William Wiley, MD—to get their take on these questions and more, finding that, for the most part, they have similar approaches.

Measurements

The doctors EyeWorld spoke with use a range of technologies to obtain astigmatic measurements. One thing they all had in common was the use of multiple devices.
Dr. Swan said he obtains a Placido-based topography (Nidek OPD) and Scheimpflug topography (Pentacam, Oculus) as well as an optical biometry (Lenstar, Haag-Streit) measurement. Through these technologies he also is able to obtain a higher order aberration profile, a Placido disc image to assess the mires, and a whole corneal thickness map. These technologies can help identify corneal aberrations, ocular surface disease, and irregular vs. regular astigmatism.
Dr. Wiley uses the IOLMaster 700 (Carl Zeiss Meditec) and Pentacam, which he said allow him to understand the role of the total cornea—front and back—in the patient’s astigmatism and a standard topography to assess the quality of the astigmatism.
Dr. Lee also gets three sets of measurements—automated Ks, IOLMaster 700, and iTrace (Tracey Technologies) topography and aberrometry. He also said it’s helpful to know the patient’s old glasses prescription to estimate posterior corneal astigmatism.
“You always are looking for consistency among the numbers to give you confidence in your IOL selection,” he said.
Dr. Ristvedt also said a glasses prescription is important to identify what a patient is used to wearing and if lens extraction will uncover more astigmatism.
“I get picky on the Lenstar Ks to make sure the axis is within 3 degrees as we take multiple Ks,” she said, adding later that, because “astigmatism can be from the cornea and the lens itself, it’s nice to compare multiple technologies.”
While all of the doctors mentioned getting corneal topography as part of the astigmatism assessment process, Dr. Berdahl said he doesn’t think it’s standard of care per se.
“But I do think it’s a good idea and almost necessary for premium IOLs. There can be subtleties on a corneal topography that indicate higher order aberrations that originate from the cornea, irregular astigmatism, or even keratoconus. As we’re trying to determine if a lens is going to be able to correct those problems, we need to understand if those problems exist in the first place,” he said.

The role of the ocular surface

Several of the measurement and mapping technologies mentioned above can indicate an ocular surface issue for investigation, but Dr. Ristvedt discussed the importance of dry eye testing overall to ensure accuracy of astigmatic measurements.
“We do tear osmolarity and InflammaDry [Quidel] and put it together with our slit lamp examination,” she said. “We look at our topography to see if the astigmatism is regular or irregular and on the topographer there is a Placido disc. That gives us so much information.”
One of Dr. Ristvedt’s recent patients came in wanting a PanOptix trifocal IOL (Alcon), but some things on her measurements were not adding up and Placido showed blurred rings.
“We treated her dryness and had her come back for repeat measurements. Not only did the power of astigmatism change but also its orientation,” she said. “If I would have gone ahead with a premium lens, we would have been in trouble postop.”
Dr. Lee discussed how pterygium, anterior basement membrane dystrophy, and Salzmann’s nodular degeneration could also impact astigmatic measurements.
“[I]deal astigmatism correction will address those underlying conditions before phaco. If the irregularity is mild or peripheral, I tell [patients] they can proceed without superficial keratectomy or PTK if they are willing to make that compromise,” he said.
Dr. Wiley takes the patient’s outcome goals into consideration at this point.
“If their goals are to see without glasses and have their astigmatism corrected, I urge them to get PTK first to regularize the cornea so we know what we’re treating at the time of cataract surgery. If their goal is more of a basic cataract surgery, maybe I’ll hold off on the PTK,” he said, explaining that the procedure could be done later to regularize the basement membrane disorder, if needed. “Consider what’s important to the patient. Sometimes the patient is not motivated to treat their astigmatism. If that’s the case, we make note of it and go with the basic cataract surgery. But if they’re motivated, we want to make sure we’re measuring properly and make sure we’re not measuring something that’s a dynamic process. … We want to make sure their dry eye disease is stable before we do a treatment plan.”

Treating regular astigmatism

Toric IOLs are an obvious choice for regular astigmatism, but Dr. Swan pointed out that, at least in the U.S., low-add toric powers are not available.
“Below a diopter becomes hard,” he said.
For astigmatism that is less than a diopter, he said he’ll occasionally use an LRI, but over LRIs and torics, Dr. Swan is turning more to the Light Adjustable Lens (RxSight).
“In a patient with regular astigmatism, the results when you look at the FDA trial for the Light Adjustable Lens vs. the FDA trials for many of the other standard toric lenses that we use, the percentage of patients who got to 20/20 with the Light Adjustable Lens is almost twice as high as the PMMA studies looking at the other lenses. I think the accuracy of the Light Adjustable Lens is fantastic. For post-refractive it is a wonderful technology … but even for a primary astigmatic patient with a naive cornea, it is still a nice option.”
If the patient is contraindicated for the Light Adjustable Lens—if they have poor dilation, concerns with compliance of the UV blocking glasses required until treatment is locked in, etc.—toric lenses remain a fantastic option, Dr. Swan said.
Dr. Lee said he’s had good results with toric lenses in patients with prior laser vision correction, even if their cornea isn’t completely regular. However, he mentions preoperatively that toric IOLs are not labeled to correct irregular astigmatism.
“Post-RK toric results are pretty good, but measuring those corneas is even more difficult than post-LASIK eyes. I will occasionally do an LRI in someone who had LASIK or PRK if the topography looks good and the cylinder is too low for a toric. I think the best option for essentially all post-refractive patients is the Light Adjustable Lens,” Dr. Lee said, pointing out that the Light Adjustable Lens needs at least 0.75 D of cylinder to correct, otherwise it’s only correcting spherical adjustments.
Dr. Ristvedt also called the Light Adjustable Lens a “game changer” for both post-corneal refractive surgery patients and those with naive corneas.
“By having an IOL where you can correct the lens itself and you don’t have to fine tune the cornea, it gives me more confidence that we can hit the refractive target despite lens positioning, corneal healing, and preoperative measurement variations,” she said.
Dr. Wiley emphasized the importance of taking the patient’s perception of their current astigmatism into account and setting appropriate postop expectations. He said it’s important to diagnose all areas of astigmatism preop and relate to the patient. Intraoperative aberrometry can be helpful as well.
“I tell patients even though you might not be showing astigmatism now, you don’t know what the final astigmatism is going to be until after the cataract is removed, after I make my incisions for cataract surgery and the eye is in a new state. If you want to see well without glasses, we need to manage your astigmatism, and it may be something that appears during surgery or even after surgery, but we should be prepared for that,” he said.
In terms of the different options for astigmatic correction in cataract surgery, Dr. Wiley talks to his patients in percentages.
“I’ll tell them that with basic technology we can often reduce the prescription somewhere between 50–100%; even with basic we can get lucky and hit 100%, and that’s great. Advanced technologies, like a toric lens, can reduce it to 90–100%, better than basic and quite good but even that means some margin of error. If you want 98–100%, I’ll say the Light Adjustable Lens,” Dr. Wiley said.

Considering irregular astigmatism

Ocular surface conditions causing irregular astigmatism, such as ABMD, Salzmann’s nodular degeneration, and pterygium, are very treatable. Dr. Swan said he’ll treat these conditions and wait 3 months before retaking measurements for cataract surgery.
Causes of irregular astigmatism that are untreatable are keratoconus, post-refractive ectasia, and pellucid marginal degeneration. Dr. Swan said some stable keratoconus or pellucid marginal degeneration that has non-skewed astigmatism in the central 6-mm zone could still respond well to a toric lens. It goes without saying that a limbal relaxing incision would not be appropriate for these patients, he added.
“The defining questions to ask are 1) is it stable and 2) have they gotten good vision in glasses, historically, or did they need to be in a scleral lens or a rigid gas permeable lens. If they had to be in a hard contact lens, your likelihood of success with a toric is very low,” Dr. Swan said.
He added that while the IC-8 pinhole IOL (AcuFocus) is not yet FDA approved, there is hope for its use in patients with irregular astigmatism.
If there is significant irregularity, Dr. Lee said he mentions the possibility of wearing a rigid gas permeable contact lens during the preop consultation.
“I explain that no IOL can correct an irregular cornea perfectly and that choosing a toric or adjustable lens means closing the door on a rigid gas permeable lens, practically speaking,” he said.

About the doctors

John Berdahl, MD
Vance Thompson Vision
Sioux Falls, South Dakota

Bryan Lee, MD, JD
Altos Eye Physicians
Los Altos, California

Deborah Ristvedt, DO
Vance Thompson Vision
Alexandria, Minnesota

Russell Swan, MD
Vance Thompson Vision
Bozeman, Montana

William Wiley, MD
Cleveland Eye Clinic
Division of Midwest Vision Partners
Cleveland, Ohio

Relevant disclosures

Berdahl: Alcon, Bausch + Lomb, Johnson & Johnson Vision, RxSight
Lee: Carl Zeiss Meditec
Ristvedt: None
Swan: None
Wiley: Alcon, Johnson & Johnson Vision, RxSight, Carl Zeiss Meditec

Contact

Berdahl: john.berdahl@vancethompsonvision.com
Lee: bryan@bryanlee.pro
Ristvedt: deborah.ristvedt@vancethompsonvision.com
Swan: russell.swan@vancethompsonvision.com
Wiley: wiley@cle2020.com
 

Treating low corneal astigmatism with femto

Gary Wortz, MD, et al. recently published a paper in Clinical Ophthalmology that shared real-world outcomes of treating low corneal astigmatism of less than 1 D with a novel formula for femtosecond laser arcuate incisions. The outcomes of this were compared to basic cataract surgery without surgical management for low levels of astigmatism. According to the paper, the Wortz-Gupta Formula calculated arcuate parameters for 224 patients with less than 1 D of astigmatism; the Barrett Universal II formula was used for IOL calculations. Average preoperative cylinder was similar in the femtosecond group vs. the conventional cataract surgery group (0.61 D [n=124] and 0.57 D [n=100], respectively). More patients had more than 0.5 D of astigmatism in the femtosecond group compared to the conventional group. The investigators found that the mean postop refractive astigmatism was significantly higher in the conventional cataract surgery group. More patients achieved UCDVA 20/20 or better in the femtosecond group (62%) vs. the conventional group (48%). The study authors concluded that “[u]sing femtosecond laser for arcuate incisions in combination with a novel nomogram can provide excellent anatomic and refractive outcomes in patients with lower levels of preoperative astigmatism at the time of cataract surgery.”

Reference

Wortz G, et al. Outcomes of femtosecond laser arcuate incisions in the treatment of low corneal astigmatism. Clin Ophthalmol. 2020;14:2229–2236.

The many considerations of astigmatism management The many considerations of astigmatism management
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