Monovision (Blended Vision)
As people approach the age of 40 – 50, they experience an aging change in which they begin to lose the ability to change their visual focus from far to near. This causes a decrease in the ability to see clearly at near, when the eyes are adjusted for distance. Thus, if you naturally have clear distance vision, then you will begin to need “magnifying glasses” for clear close-up vision when you approach 40 – 50 years of age.
If your vision at distance is clear with glasses or contact lenses and you are 40-50 years of age, you will not see clearly at near with your glasses or contacts on unless they are bifocals, or unless one eye is purposefully under-adjusted. You will generally need to wear bifocal glasses for near vision, although some people can remove their distance glasses and see well at near.
For people approaching or in this age group, we must decide how to best adjust your eyes given this aging change. People who have already begun to use bifocals, reading glasses, or who need to remove their distance glasses for clear near vision usually understand this, though people who have not yet crossed this threshold sometimes find this confusing.
People often refer to this condition mistakenly as “farsightedness”. To be accurate, it is not “farsightedness” at all. The medical term is “presbyopia”, which comes from Greek and means “old eyes” (Since Dr. Caster is in this age group, we prefer to call it “middle-age eyes”!). This is the aging condition of the eye that makes near vision difficult, whereas “farsightedness” is an inherent (not aging) difficulty with close-up vision. Unfortunately, there is no word in English other than “presbyopia” that describes this condition.
If you are nearsighted, farsighted, or have astigmatism and are developing presbyopia, you will probably need bifocal or trifocal glasses. The upper lenses of the bifocals are for distance vision; the lower are for close-up vision. Some people prefer trifocals, in which there are three pairs of lenses—an upper pair for distance, a middle pair for middle distances (about three to six feet), and a bottom pair for objects one to three feet away. Progressive lenses also have distance vision on the top and near vision at the bottom, but the tell-tale line between the different sections is eliminated.
Bifocal contact lenses are available but generally do not provide sharp vision for both distance and near.
For those of you approaching or in this age group, you and your doctor must decide how best to correct your vision when you develop presbyopia. This decision must be made regardless of how you choose to correct your refractive error—either surgically or with glasses or contact lenses. People who have already begun to use bifocals, trifocals, or reading glasses understand this, but people who have not yet crossed this threshold or who simply remove their glasses when they read usually find this confusing.
You have three choices regarding your presbyopia. None of these options cure the presbyopia, so no option is ideal. Each has pros and cons. The key is to select the option that is most suitable for you.
1. Adjust for distance. Both eyes can be fully adjusted for clear distance vision. The patient will need to wear reading glasses (“magnifying glasses”) for good close vision, usually beginning sometime between the ages of forty and fifty. This might be referred to as the “normal” situation, because most people start to need reading glasses at about that age.
2. Blended vision. Blended vision, also known as monovision, is when one eye is adjusted for distance vision and one eye for near vision. Blended vision is often created with contact lenses for people over forty-five years old and can be replicated with laser vision correction. In blended vision, one eye is primarily used at a time for ideal focus. The “distance” eye is primarily used to see far-off objects, while the “close-up” eye is mainly used to see near will still use glasses in particular situations where they require excellent vision out of both eyes. Some, but not all, blended vision patients will use glasses when driving a car (especially at night) or doing extensive reading. Other blended vision patients will almost never use glasses.Blended vision is achieved by purposefully leaving one eye somewhat nearsighted, either with contact lenses or when having laser treatment. Usually, this is the non- dominant eye (often but not always the left eye in a right-handed person or the right eye in a left-handed person). If a patient chooses blended vision and for some reason does not like it afterward, the “near” eye can usually be corrected for distance in a second laser procedure. This will eliminate the remaining nearsightedness.
A person with both eyes corrected for distance can typically go back at a later date and have one eye readjusted for blended vision. Getting completely used to blended vision generally takes several weeks but may take several months, because you are breaking very well-established ways of using your eyes. People rarely ask to have blended vision eliminated after they get adjusted to it, but this certainly can be accomplished with an enhancement procedure.
3. Mild Blended vision. This is a compromise between full distance vision in each eye and full blended vision. In mild blended vision, one eye is left with only a small amount of nearsightedness. This will cause only a small decrease in distance vision in that eye, but will aid somewhat in midrange and close-up vision. For many patients forty-five or older, this mild blended vision is a reasonable solution to the problem of poor distance vision combined with the loss of near vision that comes with middle age. The degree of mild blended vision is adjustable, based on the patient’s age and visual demands, and can be further adjusted as the person ages.
How can you determine if full blended vision or mild blended vision might be right for you? During your consultation, Dr. Caster will show you blended vision using test glasses or contact lenses. Most people can immediately tell whether they like blended vision or not. If you desire, you can have a special pair of blended vision glasses or contact lenses made in order to test for a longer period of time at home or work.
A small number of people over forty with nearsightedness do not wear bifocal, trifocal, or progressive glasses, but merely take off their distance glasses when they want to read close-up. The key question you must ask yourself is: Can you read up close with your distance glasses on? If you must take off your distance glasses to read up close, then you have presbyopia. People with presbyopia who get both eyes fully corrected for distance vision will then need to use reading glasses to see clearly close-up. If you currently simply take off your glasses to read up close, then you should carefully consider whether or not you really want to have laser treatment to eliminate completely your distance glasses prescription.