Great advances have been made in cataract surgery. It’s one of the safest, most successful procedures performed today. Cataract surgery involves removing a clouded natural lens from inside the eye and replacing it with a plastic one called an intraocular lens implant or IOL. Traditionally, IOL implants were spherical (meaning the front surface is uniformly curved) and monofocal in power (allowing us to see well at one distance only). New developments in IOL technology are striving to improve both the quality of our vision and reduce our dependency on glasses after the procedure.
Spherical aberration is an optical focusing error inherent to most optical systems, including the eye. It causes slight imperfections to the image we see, affecting its sharpness. Aspheric IOLs are shaped differently than traditional spheric IOLs, being slightly flatter at the peripheral edges of the lens, which can reduce the spherical aberration in many patients’ eyes. Aspheric IOLs have been shown to provide improved functional vision and enhanced contrast sensitivity compared to spherical IOLs. This can improve the ability to see in varying light conditions such as rain, snow, fog, twilight and nighttime darkness.
For patients with astigmatism, there is a new option to treat their refractive error. Traditionally, surgeons have relied on ‘limbal relaxing incisions’ (curved incisions in the peripheral cornea made during cataract surgery) to correct small amounts of astigmatism. Larger amounts of astigmatism required the use of glasses or laser refractive surgery after the cataracts were removed. Toric IOLs are a monofocal lens that have been altered to correct astigmatism and can be an excellent option to correct moderate to large amounts of this. There is a small risk that they will rotate out of position, which may require further surgery to reposition or replace the lens.
While the above two types of IOL implants strive to improve vision at one distance, there are two other types of IOLs available that attempt to improve our focus at varying distances (far, intermediate & near).
Like bifocals or progressive lenses used in glasses, these IOLs include different areas designed for distance, intermediate, and near vision. But unlike the lenses in glasses, the areas are organized in concentric circles, rather than from top to bottom. The brain and eye figure out which part of the lens to use. Because a multifocal optical system does not naturally occur in the human eye, there is a neurological adaptation period to the lens. It takes about 12 weeks for patients to fully experience the maximum benefits of this technology and adapt to the visual side effects that they may experience. The most common problem with multifocal IOLs is difficulty in seeing well at night due to the perception of glare and halos, especially early in the postoperative period. Although it is rarely debilitating, it is noticeable, but it does diminish over time. Some people will also continue to need eyeglasses.
When you switch from gazing at something far away to something nearby (or vice versa), the tiny ciliary muscles in your eye tug on your lenses so they change shape ever so slightly, enabling you to focus near, far, or in-between. This capability, called accommodation, diminishes as the natural lens stiffens with age. But the ciliary muscles retain their ability to contract and relax. Accommodating IOLs have hinges on the sides, enabling them to change focus, just like the lens in a younger eye. Overall, these IOLs offer excellent distance and middle vision, but aren’t as reliable for near vision. The patient must be motivated, as the ultimate success of the lens depends on the patients’ willingness to do eye exercises to strengthen the accommodative system. About half of people who receive them still end up needing reading glasses for certain activities. The subjective quality of vision is usually very good, free of the glare and halos that can be seen with multifocal lens designs.
Not everyone is a good candidate for premium IOLs, and there is an extra cost associated with them. For more information, talk to your optometrist or ophthalmologist.