August 2019

CATARACT

Device Focus
Getting the most out of toric lenses


by Rich Daly EyeWorld Contributing Writer


Image of against-the-rule astigmatism in which the
total corneal astigmatism of 0.84 D is higher than the anterior corneal astigmatism of 0.63 D and warrants
a toric IOL over a relaxing incision
Source: Tal Raviv, MD

 

An increasing number of patients are presenting for cataract surgery evaluation with the expectation that modern refractive surgery will decrease their dependence on glasses. Surgeons say that has increased the importance of treating astigmatism to provide excellent uncorrected visual results.
Tal Raviv, MD, noted that in studies comparing corneal relaxing incisions to toric IOLs, toric IOLs have consistently been more accurate and reliable.
The three monofocal toric IOLs available to U.S. surgeons are the AcrySof IQ Toric (Alcon), Tecnis Toric (Johnson & Johnson Vision), and enVista Toric (Bausch + Lomb). The three presbyopic toric options are the Symfony Toric IOL (Johnson & Johnson Vision), Trulign (Bausch + Lomb), and the ReSTOR Toric (Alcon).
The lowest toric IOL astigmatic power available to U.S. surgeons is the enVista Toric IOL, which corrects down to 0.7–0.8 D of total corneal astigmatism, said Elizabeth Yeu, MD.
“This is great because now I can use a toric IOL for those with about 1.0 D of anterior with-the-rule corneal astigmatism and about 0.5 D anterior against-the-rule astigmatism,” Dr. Yeu said.

Lens uses

The minimal amount of astigmatism Michael Patterson, DO, would correct with an IOL is 0.75 D, while the maximum is 4–5 D.
Preeya Gupta, MD, said the threshold for toric IOL use depends on whether the astigmatism is with-the-rule or against-the-rule.
“With-the-rule astigmatism is often corrected with a toric intraocular lens when it is greater than 1.5 D,” Dr. Gupta said. “Against-the-rule astigmatism, however, is corrected with a toric intraocular lens when there is greater than 0.9 D of astigmatism.”
Dr. Raviv noted that when a surgeon takes into account posterior surgical astigmatism and targets about 0.25 D of with-the-rule astigmatism (to allow for future with-the-rule to against-the-rule drift), it is not uncommon to place a toric IOL for 0.3 D of keratometric against-the-rule cylinder.
“The highest powers of monofocal IOLs treat about 4.0 D of corneal cylinder, but I’ll use them in higher amounts, such as post-PK, explaining to the patient that we are debulking their astigmatism and cannot fully eliminate it with an IOL alone,” Dr. Raviv said.

Preop preparation

Dr. Yeu said online calculators that incorporate the Barrett Toric algorithm for toric IOLs are extremely accurate. Dr. Yeu uses Veracity Surgical (Carl Zeiss Meditec) for her IOL planning, which incorporates the Barrett Toric Calculator and the effects of posterior corneal astigmatism, effective lens position, and likely IOL tilt into the toric IOL recommendation. The Alcon Toric Calculator utilizes the Barrett Toric algorithm, and the Johnson & Johnson Vision Toric Calculator can also account for posterior corneal astigmatism in its toric IOL selection using a proprietary in-house nomogram.
Dr. Patterson uses the Barrett Toric Calculator and Ladas Super formula. To account for posterior corneal astigmatism, Dr. Patterson has used total K on the IOLMaster 700 (Carl Zeiss Meditec).
“But I don’t think this PCA measurement is knowledgeable enough yet in formulas, and therefore I am not using it currently in my toric calculations,” Dr. Patterson said.
Dr. Raviv said the Barrett Toric Calculator, which estimates the posterior corneal astigmatism, has been shown to be more accurate than current direct measurement devices and is his formula of choice. Additionally, he uses a color LED topographer, which measures the posterior cornea and intraoperative aberrometry to give insight into the total corneal astigmatism.
“I am carefully following the other posterior corneal measuring instruments such as Scheimpflug and swept source OCT for continued improvement,” Dr. Raviv said. “When using a formula that estimates for posterior cornea, it is important to use the anterior Ks, not the ‘total K,’ which would lead to a double accounting of posterior astigmatism.”
Among preop testing, Dr. Gupta said it is very important to assess whether or not the corneal astigmatism is regular or irregular.
“Caution should be exhibited in anyone with irregular astigmatism with respect to using a toric IOL,” Dr. Gupta said. “It is also critical to look for corneal pathology that may be inducing astigmatism, such as pterygium, anterior basement membrane dystrophy, and dry eye. These conditions should be treated prior to cataract surgery as they may alleviate astigmatism.”
Dr. Yeu uses the LENSTAR (Haag-Streit) for quantity and meridian of astigmatism and checks against Placido topography (Atlas [Carl Zeiss Meditec] or OPD-Scan III [Nidek]) for quality and quantity of astigmatism. She evaluates the anterior and posterior cornea directly with an LED topographer (Cassini [Cassini Technologies]).
“I make certain that among the diagnostics, the magnitude of astigmatism is within 0.25 D, the meridian within 5 degrees, and the average K values are within 0.2 D of each other,” Dr. Yeu said. “If these are inconsistent among devices, I carefully review the placido keratoscopic images and perform a close ocular surface examination. These patients often have ocular surface disease (i.e., corneal staining, anterior basement membrane dystrophy, rapid tear breakup time). Such patients are started on dry eye treatment and return for repeat measurements, especially if the patient opts to have their corneal astigmatism surgically corrected at the time of cataract surgery.”

Patients to avoid

Dr. Raviv avoids using toric lenses in patients with ocular surface disease, epithelial basement membrane dystrophy, Salzmann’s nodular degeneration, and pterygium.
“In these cases, it is best to optimize or operate on the proximate cause of the astigmatism, rather than placing a toric IOL,” Dr. Raviv said.
Dr. Raviv uses three to four preop measurements of the corneal Ks. If he finds significant discrepancies among the tests, even after ocular surface optimization, he will not proceed with toric lens use.
Additionally, patients who wear rigid gas permeable contact lenses and plan to continue their use are viewed as a relative contraindication to use of a toric IOL, Dr. Raviv said.
Dr. Yeu avoids toric lenses in severe dry eye patients whose measurements are inconsistent; patients with pterygium; patients with anterior basement membrane dystrophy; and those with Salzmann’s nodular degeneration, who are not willing to undergo either pterygium repair or a superficial keratectomy prior to cataract surgery. Also avoided are those with irregular astigmatism such as seen post-RK or in severe ectasia patients.
“I will use toric IOLs off-label in patients with irregular astigmatism that is consistent in amount and meridian between the MRx as well as the diagnostics,” Dr. Yeu said.

About the doctors

Preeya Gupta, MD
Associate professor of ophthalmology
Duke University Eye Center
Durham, North Carolina

Michael Patterson, DO
Eye Centers of Tennessee
Crossville, Tennessee

Tal Raviv, MD
Associate clinical professor
of ophthalmology
Icahn School of Medicine
at Mount Sinai
New York

Elizabeth Yeu, MD
Assistant professor of
ophthalmology
Eastern Virginia Medical School
Virginia Eye Consultants
Norfolk, Virginia

Contact information

Gupta
: preeyakgupta@gmail.com
Patterson: michaelp@ecotn.com
Raviv: tal.raviv.md@gmail.com
Yeu: eyeulin@gmail.com

Financial interests

Gupta: Johnson & Johnson Vision, Alcon
Patterson: None
Raviv: Johnson & Johnson Vision, Cassini Technologies
Yeu: Johnson & Johnson Vision, Alcon, Bausch + Lomb, iOptics

Getting the most out of toric lenses Getting the most out of toric lenses
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2019-07-29T15:06:45Z
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