When we are young, the natural lens inside of our eye is both clear and flexible. Normal, natural, age-related changes result in the lens becoming both less flexible and less clear. This decreased flexibility interferes with the ability of the eye to change focus from distance to near, and is the reason most people will need reading glasses or bifocals by their early to mid 40s. This is called presbyopia. The decrease in the clarity of the lens is what we refer to as a cataract. This can be seen in most patients by their 60s, and in some patients even younger. The yellowing and clouding of the lens (cataract) may cause blurred vision, dulled vision, sensitivity to light and glare, and/or ghost images. Early on glasses may be able to help correct vision even with a cataract present. Eventually the cataract will progress so that even with the best possible glasses the vision is not adequate.
Decreased flexibility of natural lens = Presbyopia
Decreased clarity of natural lens = Cataract
When the cataract changes vision so that even with the best possible glasses your daily activities are affected, the cataract would need to be removed in order to allow for improved vision. Because the visual needs of different people are very different, this timing can vary widely. If your vision can be corrected with glasses, but you would prefer to have surgery in order to decrease the need for glasses, this is considered elective / refractive surgery that is not medically necessary and would not be covered by insurance. Surgery is the only way to remove a cataract. You can decide not to have the cataract removed, but without surgery, your vision loss from the cataract will continue to get worse. We are unable to predict how quickly or slowly that this may occur.
In standard cataract surgery, the primary goal is to remove the cloudy, opacified natural lens and replace it with a clear artificial lens implant (intraocular lens - IOL), so that with proper correction (glasses, contact lenses) the patient is able to see more clearly. Because we are able to choose the power of IOL to implant, we also have some control over what type of glasses prescription a patient will have after surgery. Two important factors to consider regarding expectations for vision after cataract surgery are the level of astigmatism and the desire for better vision at distance, near, or both without glasses. These will be discussed further below in relation to lens implant options for astigmatism and presbyopia. It is also important to realize that cataract surgery will not correct other causes of decreased vision, such as glaucoma, diabetes, corneal irregularities, or age-related macular degeneration. Although the technology for IOLs is continuing to improve, there is no lens implant option that is able to replicate the clarity and range of focus of the healthy natural lens in a young person.
The power of the lens implant for an individual patient is determined based on several different measurements made before surgery. Calculations are then performed to estimate the power of the IOL needed. Fractions of a millimeter difference in the healing response can have a significant effect on the glasses prescription needed after surgery. Even with the best possible measurements and calculations there is no guarantee of the final result equaling the estimation, and a different glasses prescription may be needed than what was desired. Dry eyes, contact lens wear, or corneal irregularities can make the measurements difficult or inaccurate. Contact lenses must be left out for a period of time before these measurements – make sure your doctor knows if you wear contacts and discuss how long to leave them out. Patients who are highly nearsighted or highly farsighted have the greatest risk of differences between planned and actual outcomes. Patients who have had LASIK or other refractive surgeries are also especially difficult to measure precisely.
Astigmatism is related to the shape of the cornea. Ideally the corneal surface is perfectly round (like a basketball) and focuses light into a sharp point. In many people, the cornea is steeper in one axis than another (more like a football). This shape can keep the eye from being able to focus light clearly. Glasses or contacts are in most cases able to easily account for astigmatism in the prescription to allow a clear focus. Patients with astigmatism now have options to be able to help correct the astigmatism at the time of cataract surgery to decrease the need for glasses after surgery. The options for astigmatism treatment are:
1) Glasses - The basic option would be implantation of a standard IOL to correct for nearsightedness or farsightedness, and continuing to wear glasses or contacts postoperatively to correct for the astigmatism. Depending on the level of astigmatism, patients will likely need glasses for most daily activities at all distances. This option would not result in extra out-of-pocket expense.
2) Corneal Relaxing Incisions - For low to moderate levels of astigmatism, small incisions in the cornea can be made to induce a change in its shape to reduce or eliminate the astigmatism. This can be performed with a laser or a diamond blade at the time of cataract surgery. The benefit is reducing dependency on glasses after surgery. When performed with a standard IOL, glasses would still likely be needed for either distance or near, but not both. These can also be used with multifocal or accommodating IOLs to improve both distance and near vision without glasses. Insurance does not cover the expense of any surgical correction of astigmatism, which results in additional out of pocket costs.
3) Toric IOL - For moderate to high levels of astigmatism, special toric IOLs can be used which account for and offset the eye’s natural astigmatism, allowing for improved vision without glasses after surgery. These can be an excellent option for patients with significant astigmatism. Again, insurance does not cover the expense of any surgical correction of astigmatism, and the extra costs associated with the use of a toric IOL are paid by the patient.
As discussed above, presbyopia is the natural loss of our eyes’ ability to change focus associated with stiffening of the lens. This begins to affect everyone by their early to mid 40s, and is the reason we need reading glasses or bifocals. Because the natural lens is removed at the time of cataract surgery, it does not matter whether someone needed reading glasses before surgery, whether they were nearsighted or farsighted, or even their age. The ability to see clearly at different distances after surgery is determined entirely by the type and prescription of the IOL implanted. A standard, monofocal IOL is not able to change focus, and cannot provide clear vision at both distance and near without glasses. For all of the options listed below, the level of astigmatism also affects the clarity of vision without glasses (see section above on astigmatism).
1. Glasses - You can choose to have a monofocal (single focus) IOL implanted and plan to wear glasses (or possibly contact lenses). The prescription of the IOL can be targeted for distance vision so that glasses are needed more for near, or targeted for near vision and needing glasses more for distance.
2. Monovision - This involves using IOLs with two different powers, one for near vision in one eye, and one for distance vision in the other eye. This combination of a distance eye and a reading eye is called monovision. It can allow you to read and see at a distance without glasses. Many patients who wear contacts or who have had refractive surgery have monovision and are happy with it. This option does have some limitations, and not all patients are good candidates for this approach.
3. Multifocal IOL - This type of IOL can correct for both distance and near vision in the same eye. Because multifocal IOLs are very sensitive to any problems in other parts of the eye, not everyone is a good candidate for multifocal IOLs. The benefit of multifocal IOLs is deceased dependency on glasses after surgery. Choosing this option will lead to higher out-of-pocket expenses since insurance companies only pay for a monofocal (single focus) lens. Multifocal IOLs will decrease one’s dependency on glasses for many tasks, but not necessarily for all tasks in all situations. These lenses may also have some increased risks of glare and/or halos, especially at night.
4. Accommodative IOL - This is a different type of IOL that is able to provide clear distance vision, as well as an improved range of focus for intermediate and near vision by utilizing the eye’s natural focusing mechanism. Intermediate vision is typically good without glasses, and near vision is better than with a monofocal IOL, although low power reading glasses may still be needed for small or prolonged near tasks. Accommodating IOLs are less sensitive to other eye problems than multifocal IOLs, so many patients who would not be good candidates for a multifocal would still be able to have an accommodative lens. As with multifocal IOLs, the extra cost associated with the accommodative IOL is not covered by insurance.