What are intraocular lenses? And how can they restore sight for patients with cataracts?

Each year, more than 30 million people globally receive surgery to correct cataracts. As many people age, the crystalline lenses in their eyes become cloudy and obstruct their vision, but a simple and safe form of surgery where the crystalline lens is replaced with an artificial lens—known as an intraocular lens—can restore clarity and lead to a vast improvement in quality of life.

Recent advancements in optics, ophthalmology, artificial intelligence, and biomedical engineering have led to rapid improvements in the types of intraocular lenses available and the methods patients and their doctors use to select the right fit. Susana Marcos, the David R. Williams Director of the Center for Visual Science, the Nicholas George Professor in Optics, and a professor of ophthalmology at the University of Rochester, served as the lead guest editor of a special issue of the journals of Biomedical Optics Express and Optics Express (published by Optica Publishing Group) that explores the state of the technology.

Why do people need intraocular lenses?

When people turn about 45 years old, their crystalline lenses typically lose the ability to accommodate, or adjust, between looking at near and far objects. Further into the aging process, crystalline lenses develop cataracts and become opaque, leading to blurry vision.

“The first intraocular lenses were intended to remove this opacity,” says Marcos. “Now, not only do they restore the transparency, but the appropriate lens selection allows to optimally project focus on the retina, so it’s also a refractive procedure. Furthermore, some lens designs also give functional vision at near distances, so that patients may not need glasses to compensate their refractive errors and presbyopia.”

As a result, some patients now opt to have intraocular lens surgery earlier in life even before cataracts develop to correct their eyes’ loss of abilities to accommodate. Intraocular lenses have evolved to mimic some of the properties of the natural human lens. For example, Marcos says that in the young eye, both the cornea and the crystalline lens have imperfections that balance out one another, and now more advanced monofocal intraocular lenses can balance the aberrations in the cornea.

How is an intraocular lens implanted?

When a person is diagnosed with a cataract and a doctor determines the crystalline lens needs to be replaced, a surgeon will take noninvasive biometric measurements to determine features such as the length of the eye and the curvature of the cornea. The surgeon will have a conversation with the patient about the right type of lens and use formulas to determine characteristics such as the power of the lens.

During surgery, a small 2- to 3-millimeter incision is made in the eye, the crystalline lens is broken into pieces and removed, and a folded up intraocular lens is inserted and released, unfolding into place.

“These days, there are no sutures, and truly a patient can see clearly again just minutes after the surgery,” says Marcos.

What are the different types of intraocular lenses?

“There’s a large variety of designs that aim at first to try to restore transparency and second, to produce the best optical quality possible, at least for distance vision,” says Marcos.

Intraocular lenses essentially fall into two categories: monofocal lenses and presbyopia-correcting lenses.

Monofocal intraocular lenses have a fixed focus for one distance at a near, mid, or far range. Most commonly, monofocal intraocular lenses are designed to help the eyes focus on distant objects, and patients can then use reading glasses to see up close.

Presbyopia-correcting lenses, by contrast, are designed to work at multiple distances, correcting the refractive error that causes a decline in up-close vision. Presbyopia-correcting intraocular lenses can have multifocal or extended depth-of-focus designs.

Multifocal intraocular lenses, with designs mimicking the Fresnel lenses used in lighthouses, have two or more focal points. Extended depth-of-focus designs provide an elongated focal point, allowing the eye to focus on multiple distances. But Marcos notes that the presbyopia-correcting lenses have their downsides.

“The drawback of these lenses is that they split the energy in more than one focus, so that the image from afar is not as crisp as you have with a monofocal lens,” she says. “You gain at near range, but you lose contrast, you lose a little bit of quality at far range.”

Both monofocal and presbyopia-correcting lenses can have a toric design—instead of the typically spherical shape of a lens, it is shaped like a slice of a doughnut—which corrects astigmatism of the cornea.

What innovations are emerging in intraocular lens technology?

Marcos says the complexity of intraocular lens designs is rapidly evolving, as are simulations to test new designs and identify the right fit for patients.

“The advanced quantification of three-dimensional geometry using high resolution imaging techniques like anterior segment optical coherence tomography, and the creation of custom models based on eye powered by artificial intelligence have put us in a different paradigm of selecting the intraocular lenses,” says Marcos. She says these simulation techniques are a boon to manufacturers, who can test different iterations of designs more quickly.

“Many are advocating for the use of digital twin eyes, or simulations that are very accurate to help select the best lens to be implanted, but also for accurate predictions of optical outcomes, helping for example to reduce the number of patients for a clinical trial,” says Marcos. “If you can accelerate the clinical trial, making it less costly or requiring fewer patients, and if the regulatory bodies accept these simulations as part of the evidence gathering process, it will be very helpful in bringing new products to the market.”

But patients and surgeons can be understandably wary of becoming early adopters of technology when vision has such a profound impact on people’s everyday lives. To help address this apprehension, Marcos’s team has developed visual simulators, which use adaptive optics (a technique borrowed from telescope) and tunable lenses to give patients the experience of vision through different intraocular lenses. Marcos helped develop a commercial headset version of the instrumentation called SimVis Gekko that allows patients to see the world around them as if they had the surgery.

“We see this as a way to reassure the patient and the surgeon, but also as a way to increase dissemination of these really well-designed lenses,” says Marcos. “It’s unknown how they will work if a patient doesn’t try them first, and you cannot do that with an intraocular lens the same way you would with a pair of glasses.”

How Rochester is driving innovation in intraocular lenses

Faculty, students, and alumni from the University of Rochester’s Institute of Optics, Center for Visual Science, and Flaum Eye Institute have led advancements in intraocular lenses for decades. For example, Marcos and her colleagues dedicated the special issue of Biomedical Optics Express and Optics Express to the late Jim Schwiegerling ’90, ’91 (MS), an optics alumnus who pioneered a trifocal intraocular lens design commercialized by Alcon that had been implanted in more than one million eyes by 2022.

In addition to her work developing visual simulations for evaluating intraocular lenses, Marcos has led numerous innovations in lens design and AI applications. Together with David Fernandez, a research engineer at the Center for Visual Science, they invented Isofocal technology that created the Isopure extended depth-of-focus intraocular lens that was licensed to PhysIOL/BVI and has been in implanted in thousands of patients across dozens of countries. Marcos’ team, in collaboration with researchers the Flaum Eye Institute and Goergen Institute for Data Science and Artificial Intelligence, have also developed novel strategies for predicting the intraocular lens position after surgery, which is key to selecting the lens with the best refractive outcomes.

Research to improve intraocular lenses

A special issue, “Improving Vision through Intraocular Lenses: A tribute to Jim Schwiegerling,” published by the Optica Publishing Group collects 20 papers with recent research on how to make artificial lenses for cataract surgery work better, including two review papers coauthored by Rochester researcher Susana Marcos. Discover how she and her fellow scientists are using advanced optical tools and new paradigms to improve vision.

Access the issue