Intraocular Lens Options
Most patients undergoing cataract surgery have options regarding the type of IOL to be implanted in their eyes. The choice may depend largely on which type of vision correction will be most convenient for one’s lifestyle. In other cases, co-existing eye conditions limit the effectiveness of certain IOLs, leaving the patient with one clearly best option.
Monofocal IOLs: Traditional lens implants have a single curvature and focal point, providing best focusing at a particular distance, such as near vision or far vision. Each patient decides whether to be near-sighted or distance-sighted, and the surgeon chooses lens implants accordingly. For patients who receive implants that maximize distance vision, reading glasses will be used for close tasks, including computer work, reading, and sewing. If IOLs are implanted to make a patient nearsighted, he/she would plan to read without glasses but need spectacle correction for distance tasks, such as driving and watching television.
Multifocal IOLs: A number of intraocular lenses with the potential to restore some of the near focusing ability of the eye (accommodation) have been approved by the Food and Drug Administration (FDA,) providing ophthalmologists and their patients with expanded choices for cataract surgery. Depending upon the technological features of the lenses, they are described as “bifocal,” “multifocal,” “accommodating,” “apodized diffractive,” or “presbyopia-correcting.” All of these lenses correct for both distance and some degree of near vision. Your surgeon may determine through the eye examination and a discussion with you that one of these lenses is an appropriate choice for you.
Possible Limitations of Multifocal IOLs: The goal of cataract surgery with a multifocal IOL is to restore some of the near focusing ability of your eye. There is no guarantee that all of the near focusing ability of your eye will be restored. Other factors affect the visual outcome of cataract surgery, including the power of the lens implant, your individual healing response, pre-existing astigmatism, and the function of the ciliary muscles in your eyes. While a multifocal IOL can reduce dependence on glasses, it might result in less sharp vision, which may become worse in dim light or fog. It may also cause some visual side effects such as haloes around lights at night and faint double images when reading. Driving at night may be affected.
Monovision: Another option available to cataract patients is “monovision.” In this method, lenses of different powers are placed in your two eyes. The ophthalmologist deliberately corrects one of your eyes for close vision, which would allow you to read without glasses. The fellow eye would receive a distance lens that would provide better far vision. This technique has been employed successfully in many contact lens and implant patients. Your surgeon or staff may discuss and demonstrate this option.
Astigmatism and Toric IOL’s: Astigmatism is a very common imperfection of the eye and is present when the cornea is not spherical like a basketball. An asymmetrically curved object, such as a football, is said to have a “toric” shape. When a cornea (the front curved surface of the eye) is toric, light rays passing through it do not focus to a single point. The result is “astigmatism” (Greek: not to a point). Glasses and contacts can be made in toric shapes to compensate for the imperfect curvature of the cornea. Likewise, a toric IOL can be implanted instead of spherical one to neutralize astigmatism of the cornea, thereby providing better focusing without glasses than spherical IOLs. In this way, astigmatism can be reduced or eliminated at the time of cataract surgery. If you have a significant degree of astigmatism, this IOL option may be discussed with you.
The use of a toric IOL necessitates additional specific measurements, planning, surgical execution and post-operative considerations not required when implanting traditional spherical IOLs. As Medicare and most other insurance companies do not provide payment for the surgical correction of astigmatism, patients are responsible for payment of these non-covered services. Toric IOLs, like toric eyeglasses, must be oriented correctly within the optical system of the eye to improve astigmatism maximally. It is possible, although unlikely, that a toric IOL may shift in position during the first few weeks following implantation, since it takes some time for the tissue inside the eye to firmly affix an IOL in position. In the case of significant IOL shift and reduction in vision, a second brief procedure to reposition the IOL may be necessary a few weeks after implantation.
Information about calculating the power of the intraocular lens
Prior to surgery, a number of measurements are done, called biometry, to calculate the power of the intraocular lens that will be implanted in the eye. While the methods used to calculate the power of the IOL implant are very accurate in the vast majority of patients, some inaccuracy may occasionally occur. As the eye heals, the implant can shift very slightly toward the front or back of the eye before a stable position is reached. The amount of this shift is not the same in everyone, and may cause you to see differently from what may have been predicted by the measurements taken before surgery. Patients who are highly nearsighted or highly farsighted have the greatest risk of inaccuracies. Patients who have had LASIK, PRK, or Radial Keratotomy (RK) are especially difficult to calculate precisely. Residual refractive error after surgery may be amenable to correction with eyeglasses, contact lenses, refractive surgery, or repositioning or replacement of the IOL itself.
At the time of surgery, your ophthalmologist may decide not to implant an intraocular lens at all even though you have given prior permission to do so. Additionally, a monofocal IOL may need to be placed in your eye instead of a multifocal one, or a spherical one instead of a toric one.
Financial Implications of a Multifocal or Toric IOL
If you have Medicare coverage for this cataract surgery, the “presbyopia-correcting,” multifocal IOL or toric IOL devices and associated services for fitting these lenses are considered partially covered. You are responsible for payment for that portion of the services that exceeds the charge for insertion of a conventional IOL during cataract surgery. Your ophthalmologist and staff will inform you about the coverage, deductible, and co-payment amounts if a private insurance company is paying for this procedure. Financing is available for applicable charges for these premium IOLs.
Complications of cataract surgery and IOL implantation
As a result of surgery, it is possible that your vision could be made worse. Complications of removing a cataract may include hemorrhage (bleeding), perforation of the eye, loss of corneal clarity, retained pieces of cataract in the eye, infection, detachment of the retina, uncomfortable or painful eye, droopy eyelid, glaucoma, double vision, and/or temporary or persistent swelling of the retina (macular edema). These and other complications may occur whether or not a lens is implanted and may result in poor vision, total loss of vision, or even loss of the eye in rare situations.
- Visual effects associated with an intraocular lens may include increased night glare and/or halo, double or ghost images, and dislocation of the lens. Multifocal lenses may increase the likelihood of these problems. In some instances, corrective lenses or surgical replacement of the intraocular lens may be necessary for adequate visual function following cataract surgery.
- If an intraocular lens is implanted, it is done by a surgical method. It is intended that the small plastic, silicone, or acrylic lens will be left in your eye permanently.
At the time of surgery, your doctor may decide not to implant an intraocular lens in your eye even though you may have given prior permission to do so.
- The results of surgery in your case cannot be guaranteed. Additional treatment and/or surgery may be necessary. You may need “YAG” laser surgery to correct clouding of vision months to years later. This is due to a secondary haze of the eye’s natural lens capsule, left in place during cataract surgery to support the IOL. At some future time, the lens implanted in your eye may have to be repositioned, removed surgically, or exchanged for another lens implant.
- The calculation for an intraocular lens implant is not “an exact science,” as explained above. You accept that you might need to wear glasses or contact lenses subsequent to surgery to obtain best possible vision. Even patients that see 20/20 without glasses after surgery can be improved with spectacles. There is a good possibility that subsequent surgeries such as IOL exchange, placement of an additional lens, or refractive laser surgery may prove valuable if you are not satisfied with your vision after cataract removal.
Additional risks related to individual eye characteristics
If you have myopia (nearsightedness) and the size of your eye is somewhat larger than average, you are at increased risk for the development of a retinal detachment in your lifetime. This is due to the extra stretch put on the retina which lines the inside wall of the eye. Having the natural lens of the eye removed slightly increases the risk of retinal detachment in all eyes, whether or not the end result of cataract surgery is nearsightedness or farsightedness. The correction of nearsightedness through the replacement of a natural lens with an IOL does not change the size of the eye; therefore, the “nearsighted” risk of a detachment is not alleviated. Retinal detachments usually require surgical intervention and can lead to vision loss.
Patients with diabetes are at particular risk for development of leaky capillaries in the retina, with resultant tissue swelling and decreased vision. Laser treatments are commonly performed by retina specialists for this condition. Retinal swelling should be controlled prior to cataract surgery, if possible, to minimize these problems. Most adults have “floaters” in their vision, caused by particles in the vitreous gel that fills the eye. After cataract surgery, floaters may be more noticeable.