Eyeworld

38 | EYEWORLD | FALL 2024 ATARACT C Contact Pasricha: Neel.Pasricha@ucsf.edu Venkateswaran: nandini.venkat89@gmail.com Reference 1. Heath MT, et al. Intraocular lens power calculations in keratoconus eyes comparing keratometry, total keratometry, and newer formulae. Am J Oph- thalmol. 2023;253:206–214. Relevant disclosures Pasricha: None Venkateswaran: Glaukos 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 hyperopia." Intraoperative considerations Dr. Venkateswaran said that excellent wound construction is critical, as corneal elasticity in ectatic eyes can affect wound healing. She said to place a suture if the wound does not seal or if there are any concerns about wound closure. Trypan blue can be used to stain the anterior capsule to improve visualization. "Often, these eyes can have deeper anterior chambers; use low flow settings to reduce chamber fluctua- tions," she said. While Dr. Pasricha said that cataract surgery in these patients is generally standard, there are a couple of things that may occur. First, it's possible that the ectasia is so severe that it will distort the intraoperative view through the mi- croscope. Putting a layer of viscoelastic on the cornea can help with this. It smooths it out and gives better optics, he said. A lot of these patients, in addition to having a thin cone, have a thin periphery of their cor- neas, he said, so when you make the incisions, 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 cor- neas 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 lon- ger. The classic teaching is you want them out of their hard contact lenses for 1 week extra for every 10 years they've worn the lenses. "I start with 3 weeks and see how the biometry and topography look, and if it looks reasonable, go with that," he said. Dr. Venkateswaran agreed that avoiding toric IOLs in hard contact lens wearers 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 di- ameter," 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 hard contact lens dependent, 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 study 1 that compared keratoconus-specific 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 astig- matism' and plug in the corneal values that you get from your biometry," Dr. Pasricha said. "That continued from page 37 continued on page 40 "I advise that if patients are hard contact lens dependent, they should expect to obtain the highest image quality with hard lenses after cataract surgery." —Nandini Venkateswaran, MD

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