28 EyeWorld Asia-Pacific | December 2024 CATARACT Dr. Pasricha said you want to look at the central corneal astigmatism of these patients, which can be broken down to regular or irregular. If it’s regular, there are different options. “You could consider doing a standard monofocal toric in some cases. Most people, including myself, would opt for a non-toric monofocal,” he said. “If you have the LAL [Light Adjustable Lens, RxSight] available, that’s a great option for those patients.” He noted that the LAL FDA label states it can correct up to 2.75 D of astigmatism but in the real world can achieve more. You ideally want to use a monofocal lens that will treat the negative spherical aberration that the keratoconus induces, Dr. Pasricha said. Keratoconus is similar to hyperopic LASIK in that it causes a central steepening ectasia effect, and that causes negative spherical aberration, he said. The lens you want to go with is either a zero spherical aberration, like the EnVista platform (Bausch + Lomb), or an older one that has positive spherical aberration, like the SA60AT (Alcon). If the central corneal astigmatism is irregular, with the classic inferior steepening, you want to find out if the patient wears hard contact lenses, he said. Many of these patients are wearing a scleral lens or rigid gas permeable lens ahead of time. “That’s great because it does an amazing job of correcting their irregular astigmatism,” he said. “If they do wear a hard contact lens, I like to counsel them that after surgery, they’ll need to wear the hard contact lens for their best vision, but the prescription is going to need to be changed.” If they don’t wear scleral lenses or rigid gas permeable lenses, and they’re not planning to after surgery, you can think of things like the IC-8 Apthera (Bausch + Lomb), which does a nice job of correcting some of the irregular corneas with its pinhole optics, he said. For those patients who already wear hard contact lenses, Dr. Pasricha said they will need to be out of that lens for a minimum of 3 weeks before they get their biometry, sometimes longer. The classic teaching is you want them out of their hard contact lenses for 1 week extra for every 10 years that they’ve been wearing their lenses. “I start with 3 weeks and see how the biometry and topography look, and if it looks reasonable, I go with that,” he said. Dr. Venkateswaran agreed that avoiding toric IOLs in wearers of hard contact lenses is a good choice, as placing a toric IOL makes new contact lens fittings more challenging. She said you can consider toric IOLs if patients are used to wearing high astigmatism in spectacles and can tolerate this degree of correction. Dr. Venkateswaran will obtain biometry, topography, and tomography prior to surgery. She said that comparing maps on tomographic images to assess for keratoconus stability or progression is critical. “If keratometric values are very variable, the EKR65 printout in the Pentacam [Oculus] is helpful to understand predominant K values in the 4.5-mm pupil diameter,” Dr. Venkateswaran said. She added that online calculators that use the Barrett and Kane formulas are often preferred when performing IOL calculations. “I tend to aim more myopic with IOLs to avoid hyperopic surprise,” she said. “Patients with keratoconus often are used to having multifocal-type corneas and good near vision. I advise that if patients are dependent on hard contact lenses, they should expect to obtain the highest image quality with hard lenses after cataract surgery.” There are keratoconus-specific formulas, Dr. Pasricha said, noting a recent study1 that compared keratoconusspecific IOL formulas for patients. The winner was the Barrett True-K formula for keratoconus with the measured posterior corneal astigmatism, he said. “You go to the Barrett True-K formula website, click keratoconus, plug in details from your biometry machine, and it will run a predicted posterior corneal astigmatism by default. Instead, you want to select ‘measured posterior corneal astigmatism’ and plug in the corneal values that you get from your biometry,” Dr. Pasricha said. “That will give you the most accurate formula.” Even with the options currently available in formulas, around 50% of patients end up within 0.5 D of target and 75% end up within 1 D of target. He said that’s “still not great,” so it’s important to warn patients about this. “This is another reason the LAL is so great. If not using the LAL, I’m generally targeting more myopia to make sure I don’t have a hyperopic surprise. It’s easier to correct myopia with scleral lenses than it is to correct hyperopia.”
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