Irregular corneas need to be addressed before cataract surgery
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Cataract surgery is one of the most common, successful and safest surgeries in the United States.
Advances in lens design and preoperative refractive calculations have meant good outcomes and happy patients. However, irregular corneas can throw a wrench into the situation and complicate cataract surgery, as well as other vision correction procedures.
Source: Kenneth A. Beckman, MD, FACS
“The big challenges with irregular corneas are the stray light rays that get refracted through them,” OSN Refractive Surgery Section Editor John P. Berdahl, MD, said. “Those rays are going places that we don’t want them to go, and that can lead to blurred vision, glare and halos. ... They’re also hard to predict. Sometimes our technologies aren’t as capable of creating a consistent diagnostic that we can predict from.”
According to Healio/OSN Board Member Kenneth A. Beckman, MD, FACS, irregular corneas generally fall into two categories: obstruction or distortion.
“By obstruction, I mean something like a scar in the visual axis obstructing the patient’s view,” he said. “By distortion, we’re talking about the shape of the cornea.”
Beckman said surgeons first have to determine what kind of irregularity they are dealing with in order to set themselves up for a successful surgery. OSN Cornea/External Disease Board Member Marjan Farid, MD, said the first thing she does is obtain a good mapping of the cornea.
“It has become standard of care to perform a topography or tomography for every patient that comes in for cataract surgery,” she said. “We want to look for irregularity in the cornea because if you don’t have that information going in, it can lead to unhappy patient outcomes postoperatively.”
Whether the patient has regular or irregular astigmatism, that data can help the surgeon determine the reason for the corneal irregularity.
“If you just use astigmatism measurements from your biometry, you might end up putting a toric lens in for a patient who could have significant irregularity,” Farid said. “In that case, you’re going to worsen their higher-order aberrations and visual outcomes.”
OSN Cornea/External Disease Section Editor Preeya K. Gupta, MD, said that irregular astigmatism can be the result of several things, including damage to the cornea.
“It could be anyone who has had a scar or some sort of infectious or inflammatory process that damages the stromal tissue that leads to an irregular shape,” she said. “Even after the inciting event is fixed, patients can be left with an irregular cornea shape. What we have to do is do something to alter that shape or determine what we can do with our lens selection.”
The process of getting a patient with an irregular cornea to the visual correction step of their journey can take a lot of different routes and is determined on an individual basis. But according to OSN Technology Board Member Kendall E. Donaldson, MD, MS, the process should always begin with educating patients and ensuring they understand how their individual situation needs to be treated.
“Every patient these days comes in expecting perfect vision after cataract surgery,” she said. “But it’s not just the cataract we’re treating here. We also have to take this other condition into account. I spend a lot of time showing patients their images because I think that can help them understand that this is a little bit more of a process.”
Common irregularities
There can be many causes for corneal irregularities, but Farid said ocular surface disease is probably the most common, including tear film instability and dry eye disease.
“That shows up as an irregular pattern on topography,” she said. “We look at the map and the mires and can usually see if it’s pretty significant. However, it’s something that, if we see it early, we can start to treat it, manage it and improve it before proceeding with lens power selection and so on.”
Beckman said ocular surface disease is common in these patients because it can also result from any other kind of surface irregularity.
“Any time there’s a surface irregularity, you’re always at risk to have a tear film issue,” he said. “Even if you’re producing tears normally, they might not be able to spread normally.”
Some patients may not understand how their dry eye could ultimately affect their refractive outcome, but Beckman helps educate them by using terms that almost anyone is likely to understand.
“The tear film is the most important refractive surface of the eye,” he said. “When there’s an issue there, it’s like when there’s a smudge on a car’s windshield or the windshield wipers aren’t working right. When you turn the wipers on and you get dry and wet patches, it significantly distorts your vision. Right off the bat, you need to have good tear film.”
Donaldson said as a corneal specialist, other common causes of irregular corneas she sees are keratoconus, anterior basement membrane dystrophy and Salzmann’s nodular degeneration. For any of these conditions, she needs to see improvement on topography before moving forward with lens selection and surgery.
“I do about four or five superficial keratectomies every week to prepare these patients for cataract surgery,” she said. “It all comes down to distinguishing how much of their astigmatism is regular vs. irregular because irregular astigmatism can’t be corrected at the time of cataract surgery and may benefit from treatment prior to cataract surgery.”
Addressing the issues
For patients with regular astigmatism, Donaldson said the solution can be as easy as picking out a toric lens, but that is not an option for a lot of patients with underlying corneal disease.
“In more advanced keratoconus patients, they aren’t going to be corrected with a toric lens,” she said. “They have to understand that they may need to wear a contact lens again after their cataract surgery, but we can potentially debulk some of their prescription.”
In eyes with irregular astigmatism, the best option can often be limited to a scleral lens.
“The gold standard for noninvasive treatment is to send the patient to a scleral lens fitter,” Gupta said. “I like to work with specialized optometrists in my community to see if a scleral lens can rehabilitate the vision, as this may avoid surgical options for the patient.”
In addition to traditional hard scleral lenses, there are hybrid scleral lenses with a hard and soft component, as well as newer options such as the Prose device (BostonSight), which can be customized to each patient’s ocular surface.
“The scleral lens corrects for that irregular shape and can significantly improve vision,” Beckman said. “Even if there’s a scar in the visual axis, you may still get improved vision.”
That makes scleral lenses an enticing option for patients because Beckman said the alternative to treating a scar in the visual axis is a transplant.
For patients with keratoconus, Gupta said a lamellar transplant such as deep anterior lamellar keratoplasty can structurally improve the shape of the eye. In patients with less severe cases of irregular corneal shape or perhaps vision loss due to anterior stromal scar, she said she often turns to phototherapeutic keratectomy (PTK).
“PTK involves removing corneal tissue to reshape the cornea to a more normal curvature,” she said. “It’s a laser procedure that can be done in the office. Patients with superficial scarring or light irregularity might be more amenable to that treatment.”
Corneal cross-linking is a recent addition to the treatment of irregular corneas and has the potential to help patients with progressive keratoconus, Farid said.
“It helps if patients are caught early on or at a point when they’re continuing to see change in their cornea,” she said. “For patients with keratoconus or corneal ectasia post-LASIK, they may need therapeutic cross-linking to stabilize their cornea and prevent further irregularity or destabilization.”
While cross-linking is generally performed in younger patients who still might be progressing, Donaldson said there are still rare cases in which people older than age 50 or 60 years might be getting worse.
“We used to think of keratoconus as only being progressive in patients under the age of 40,” she said. “It’s more of a recent change of practice to look more carefully for signs of progression in older patients since we now have an effective method to treat progression with cross-linking. The other factor is that people are having cataract surgery at younger ages than they used to.”
For patients with progressive keratoconus, Donaldson said they should be cross-linked before cataract surgery. However, changes to the cornea may still occur for up to a year, so it is best to wait to follow through with the cataract surgery.
Other treatments for corneal issues also need a little lead time before a patient is ready to move on to cataract surgery. If a patient shows signs of dry eye disease at preoperative screening, Farid starts them on aggressive treatment to turn around the disease quickly.
“We start them on lubrications, topical anti-inflammatory drops and even steroids, which are very useful in this setting because they work faster and get the tear film turned around quickly,” she said. “I usually see these patients back in about 4 to 6 weeks to repeat the exam and topography to look for regularity.”
If there is no improvement, she goes to even more aggressive treatments such as autologous serum, thermal pulsation or amniotic membrane to normalize the tear composition.
“I have a staged approach, but we want to be aggressive in these patients,” Farid said. “If we can make improvement quickly, we’re able to give them the best outcomes possible with cataract surgery.”
For patients who have a distorted cornea, lens selection is not as straightforward as it is with other patients. Beckman said some IOLs simply do not work.
“You have to be very careful with what lens you’re going to put in the eye,” he said. “I’m very hesitant to use a multifocal or even an extended depth of focus lens in someone who has a distorted cornea when we’re doing cataract surgery.”
One type of lens that has been beneficial in these cases is the Light Adjustable Lens (RxSight). Berdahl said surgeons can tailor refraction after the lens is already in the eye.
“If you’re not exactly sure where the astigmatism might be, you can use a Light Adjustable Lens in that patient with irregular astigmatism,” he said. “After they heal up from surgery, at least your manifest refraction will help dictate it.”
A game changer in the world of cataract surgery for patients with irregular corneas is the IC-8 small-aperture IOL (AcuFocus). The IC-8 received an approvable letter from the FDA in December 2021 and should be on the market soon.
Berdahl said because of the small aperture, the IC-8 allows only straight light rays to come through the center of the cornea.
“There is an opaque mask with a center pinhole that prevents some of the stray light rays from reaching the retina,” he said. “It can prevent the blur and glare that can come from that stray light, as well.”
The IC-8 is not the only way to get a pinhole effect and reduce issues caused by stray light rays coming through an irregular cornea. Gupta said pharmacologic interventions such as off-label use of Vuity (pilocarpine hydrochloride ophthalmic solution 1.25%, Allergan) may provide the benefit of pupil constriction with lower risk.
“Distracting rays of light are removed, and it increases the depth of focus,” she said. “Patients are able to increase their near vision, but modulating the pupil is another potential way to compensate for aberrations and irregularities in the cornea.”
Gupta said she has used Vuity in her practice to reduce glare and halos after LASIK surgery in the rare patient who has excessive symptoms or to improve nighttime vision in patients with multifocal lenses. This approach could also be considered in patients with mild keratoconus and irregular corneal shape.
“It’s exciting because it’s not a surgical procedure, and it’s reversible,” Gupta said. “We need more data and to see it in more patient types, but it’s a low-risk proposition.”
What can be done better?
Lenses such as the IC-8 have a lot of potential for irregular corneas, and Donaldson said patients are already taking notice.
“I have a waiting list of patients that have learned about it themselves,” she said. “I’ve been telling them, ‘It’s coming, it’s coming.’ They’re pretty excited, and so are we. It’s a great time to be giving patients another option.”
In the future, Donaldson is looking forward to having more options to adjust IOLs postoperatively. In addition to the Light Adjustable Lens, she said newer lenses could feature exchangeable components or even refractive indexing that will allow surgeons to change a prescription postoperatively.
One of the biggest barriers to care for patients with irregular corneas is diagnosis. Berdahl said tests such as gas permeable lens over-refraction and epithelial mapping are underutilized. Both provide a better understanding of what is going on with the cornea, he said.
“Epithelial mapping has a made a huge difference for us to understand the source of the corneal irregularity,” he said. “If it’s the epithelium or the stroma, removing the epithelium and coaxing it to grow back more regular might be a good answer to some of these problems.”
Berdahl said transepithelial topography-guided approaches to LASIK and PRK represent an important area for improved treatment.
“If we could have a situation to ablate the epithelium along with the stroma, then our surface map will be reflected in the refraction, and we will get better outcomes,” he said. “Everybody is working on these different topo-guided approaches.”
Because it may be the most common cause of irregular corneas, Beckman said there needs to be a better understanding of dry eye in general. He said surgeons need to look for it and ask the right questions.
“It’s easy for doctors to just ignore the tear film in general,” he said. “You need to pay attention to these surface conditions and really try to figure out what the problem is. Getting a good topography or tomography can show you irregular astigmatism. From there, you can determine if that astigmatism is from something like keratoconus or a tear film issue. It tells you what to focus on.”
Gupta agreed that diagnostics are one of the biggest hurdles to overcome to better care for these patients. However, she said procedures that have less downtime and faster recovery are also needed.
“Things like the FDA-approved cross-linking protocol or partial corneal transplant take a lot of time to heal from,” she said, adding that simplicity in new therapies would be welcomed by most complex patients.
To make patients happier, Farid said surgeons need to be better at educating them. If patients do not have a good understanding of their underlying condition and its management, there is a better chance of dissatisfaction.
“The most important thing is early detection and diagnosis and then patient education,” she said. “Most patients will understand and take that additional month or two that it takes to give themselves a chance for the best outcome.”
- Reference:
- AcuFocus receives approvable letters from the U.S. FDA for the IC-8 small aperture intraocular lens. https://acufocus.com/press/acufocus-receives-approvable-letter-from-the-u-s-fda-for-the-ic-8-small-aperture-intraocular-lens/. Published Dec. 7, 2021. Accessed May 5, 2022.
- For more information:
- Kenneth A. Beckman, MD, FACS, can be reached at Comprehensive EyeCare of Central Ohio, 450 Alkyre Run Drive #100, Westerville, OH 43082; email: kenbeckman22@aol.com.
- John P. Berdahl, MD, can be reached at Vance Thompson Vision, 3101 W. 57th St., Sioux Falls, SD 57108; email: john.berdahl@vancethompsonvision.com.
- Kendall E. Donaldson, MD, MS, can be reached at Bascom Palmer Eye Institute, 8100 SW 10th St., Building 3, Plantation, FL 33324; email: kdonaldson@med.miami.edu.
- Marjan Farid, MD, can be reached at University of California, Irvine, 850 Health Sciences Road, Irvine, CA 92617; email: mfarid@uci.edu.
- Preeya K. Gupta, MD, can be reached at Triangle Eye Associates, 2075 Renaissance Park Place, Cary, NC 27513; email: preeyakgupta@gmail.com.
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