Cataract: YES Connect
Fall 2024

by Ellen Stodola
Editorial Co-Director

Cataract surgery in patients with keratoconus presents a challenge in the presurgical, intraoperative, and postoperative stages. Refractive outcomes are notoriously difficult to predict despite careful preoperative planning, and patients with irregular corneas often require postoperative correction with rigid contact lenses for their best visual acuity and quality of vision. Recent developments, such as newer-generation keratoconus-specific IOL formulas and advanced lens technology (including the Light Adjustable Lens and aperture optics), hold promise for improving outcomes for these patients. Yet, significant challenges remain.

For this YES Connect column, we queried two experts regarding how they proceed with cataract surgery in patients with keratoconus and how they leverage the latest technology to maximize outcomes for this unique patient population.

—Eric Weinlander, MD, Guest Editor, YES Connect

When performing cataract surgery in patients with keratoconus, there are considerations for surgical planning, lenses, and techniques that surgeons need to account for to ensure success. In this issue’s YES Connect column, Nandini Venkateswaran, MD, and Neel Pasricha, MD, discussed how they handle these patients, including testing, formulas, and IOL selection.

Potential problems of preexisting keratoconus 

Dr. Venkateswaran shared the major challenges in eyes with keratoconus undergoing cataract surgery. There is always the concern for ongoing keratoconus progression. She said to ensure that the keratoconus is stable prior to proceeding with cataract surgery, as ongoing keratometric changes can lead to refractive changes and blurred vision post-cataract surgery. In addition, given the degree of ectasia and possible corneal scarring, the view for cataract surgery can be difficult, and trypan blue to stain the anterior capsule can be helpful. A suture in the main wound is often needed given corneal elasticity changes. Finally, she shared that IOL calculations are an ongoing challenge. She’ll advise patients of the risk of refractive surprises, even with modern-day formulas. She also advises patients that they will likely need to be in glasses or hard contact lenses after surgery based on the degree of keratoconus/ectasia for best 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.

Nandini Venkateswaran, MD

Dr. Pasricha also discussed several challenges of performing cataract surgery in patients with keratoconus: intraocular lens selection, choosing the correct formula, and surgical technique modification.

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 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 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 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 study¹ 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 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 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 fluctuations,” 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 microscope. 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 corneas, he said, so when you make the incisions, oftentimes you want to aim on the longer end. He has a low threshold to place a suture if the wound is not closing well. “If you’re aware ahead of time and have a severe case, it’s always safer to plan for a scleral tunnel incision because you’ll have less concern about the wound leaking postop,” Dr. Pasricha said. 

Other considerations

While Dr. Venkateswaran and Dr. Pasricha said that cataract surgery will not directly exacerbate keratoconus, there are some things to consider. Dr. Venkateswaran said it’s important to ensure the keratoconus is stable prior to proceeding with cataract surgery. If corneal ectasia or scarring is severe, the patient may need staged penetrating keratoplasty or DALK prior to cataract surgery. Rarely, keratoconus patients can have concomitant Fuchs dystrophy/guttae, and some cases may require an endothelial keratoplasty. Progressive keratoconus that is missed prior to cataract surgery can lead to ongoing refractive shifts and blurred vision, she added. 

The physicians agreed that, if needed, crosslinking should be performed prior to the cataract surgery. Dr. Venkateswaran recommended monitoring the patient for 3–6 months after crosslinking to ensure keratometric stability. 

With the older cataract population, it’s rare to have keratoconus progress, but it’s still important to know if it is progressing, Dr. Pasricha said. You want to crosslink before cataract surgery, he said, because the crosslinking does have some flattening effect to the cornea. You want to get the most accurate biometry measurements that will hopefully be relevant for the remainder of that patient’s life, he said.

Dr. Pasricha said that patients usually heal quite well from cataract surgery. When refitting patients with a history of scleral lenses or rigid gas permeable lenses, you might want to wait longer than a month after surgery to do the final fitting. He usually waits at least 3 months. 

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About the physicians 

Neel Pasricha, MD
Assistant Professor of Ophthalmology
University of California, San Francisco
San Francisco, California

Nandini Venkateswaran, MD
Assistant Professor of Ophthalmology
Harvard Medical School Cornea and Refractive Surgery Service
Massachusetts Eye and Ear, Lexington
Lexington, Massachusetts 

Reference

1. Heath MT, et al. Intraocular lens power calculations in keratoconus eyes comparing keratometry, total keratometry, and newer formulae. Am J Ophthalmol. 2023;253:206–214.

Relevant disclosures

Pasricha: None
Venkateswaran: Glaukos

Contact 

Pasricha: Neel.Pasricha@ucsf.edu
Venkateswaran: nandini.venkat89@gmail.com