Intraocular lenses (IOLs) are medical devices that are implanted inside the eye to replace the eye's natural lens after it has been removed during a procedure. IOLs have been available since the early 1980s. Before the use of intraocular lenses, if you had cataracts removed, you had to wear very thick eyeglasses or special contact lenses in order to see after cataract surgery, since no device was implanted in the eye to replace the focusing power of the natural lens.

Traditional intraocular lenses have a spherical optical design, meaning the front surface is uniformly curved from the center of the lens to its periphery. Though a spherical IOL is relatively easy to manufacture, this design does not mimic the shape of the natural lens inside the eye, which varies in curvature from center to periphery. In other words, the eye's natural lens is aspheric ("not spherical"). A spherical intraocular lens can induce minor optical imperfections called higher-order aberrations (HOAs), which can affect quality of vision, particularly in low-light conditions such as driving at night. Premium aspheric IOLs, on the other hand, match more closely the shape and optical quality of the eye's natural lens, and thereby can provide sharper vision — especially in low light conditions and for people with large pupils.

Toric IOLs are premium intraocular lenses that correct astigmatism as well as nearsightedness or farsightedness. Toric IOLs can correct these conditions because they have different powers in different meridians of the lens. They also have alignment markings on the peripheral part of the lens that enable the surgeon to adjust the orientation of the IOL inside the eye for optimal correction. Prior to the development of toric IOLs, cataract surgeons had to perform a procedure call limbal relaxing incisions (LRI) to correct astigmatism during or after cataract surgery. There are a few procedures that can correct astigmatism after cataract surgery, but toric IOLs decrease the likelihood of needing these additional surgical procedures.

Conventional spherical IOLs are monofocal lenses, meaning they are designed to provide clear vision at a single focal point (usually far away for good driving vision, for example). With conventional IOLs, typically you must wear eyeglasses or contact lenses in order to use a computer, read or perform other close-up tasks within arm's length. Accommodating IOLs are premium intraocular lenses that expand the range of clear vision with both an aspheric design and flexible "haptics" — the supporting legs that hold the IOL in place inside the eye. These flexible legs allow the accommodating IOL to move forward slightly when you look at near objects, which increases the focusing power of the eye enough to provide better near vision than a conventional monofocal lens. Accommodating IOLs may not provide the same level of magnification for near vision that a multifocal IOL does. But many people find these premium IOLs greatly reduce their need for reading glasses or computer glasses after cataract surgery, while providing exceptionally clear distance vision similar to that offered by a monofocal IOL.

Multifocal IOLs are another category of presbyopia-correcting IOLs that can decrease your need for reading glasses or computer glasses. These premium IOLs contain added magnification in different parts of the lens to expand your range of vision so you can see objects clearly at all distances without glasses or contact lenses. Some studies have shown multifocal IOLs tend to provide better near vision than accommodating IOLs, but they also are more likely to cause glare or mildly blurred distance vision as a tradeoff.

An alternative to accommodating and multifocal IOLs for correcting presbyopia is monovision. There is no such thing as a "monovision IOL." Monovision is the technique of fully correcting the refractive error of one eye and intentionally making the other eye mildly nearsighted. In this scenario, the fully corrected eye sees distant objects clearly (but cannot see very well up close without glasses), and the mildly nearsighted eye sees very well up close without glasses (but not so clearly far away). Any combination of premium IOLs can be used for monovision cataract surgery. Monovision may sound odd the first time you hear about it, but this technique has been used very successfully with contact lenses for many years. And it is now being used frequently with cataract surgery to decrease a person's dependency on reading glasses and computer glasses after surgery.

Sometimes the best visual outcome after cataract surgery is achieved by using a different type of premium IOL in each eye. For example, you may have more astigmatism in one eye than the other. If this is the case, your cataract surgeon may recommend a toric IOL in that eye, and perhaps an accommodating IOL in the other eye to also decrease your need for computer glasses. Another scenario is for your cataract surgeon to recommend one brand of multifocal lens for one eye and a different brand for the other. This is because one brand may provide better computer vision and the other may provide sharper vision at a closer distance, for reading and other close-up tasks.