Presbyopia is Blurred Vision at Near due to Aging
Introduction to Presbyopia
Presbyopia is the loss of ability to focus on close objects caused by a hardening of the crystalline lens inside the eye. The crystalline lens starts out soft and flexible early in life. By the early to mid 40’s the crystalline lens hardens as part of the natural aging process. That makes it increasingly difficult for the lens to change shape and therefore difficult to change one’s focal point from far to near and vice versa.
It is impossible to prevent presbyopia, as it is a normal change that occurs with age.
Symptoms of Presbyopia
- Blurred near vision
- Moving near objects and reading material farther away helps to bring the object into focus
- Reading light seems too dim
- Not able to focus quickly when changing focal distance from far to near and vice versa
- Occasional headaches after prolonged reading or near work
- Blur at near occurs more with your contacts on than when using your glasses.
The crystalline lens is the second refracting surface of the eye which means it is the second surface that light must pass through to get to the retina. In order for us to see a perfectly clear image, light must be focused directly on the retina.
Crystalline lens of the Eye Shown in a side view
Some people, when they are younger, do not need glasses for either distance or near vision. This is known as emmetropia and means that light coming into the eye is focused directly onto the retina. People that are emmetropic will not need to have any vision correction until they are in their 40's and become presbyopic. At that point they will need glasses in order to see up close.
Other people need vision correction for distance and this is known as myopia (nearsighted). This means that light coming into the eye is focused before it reaches the retina creating a blurred distance image. These people must wear either glasses or contact lenses in order to see small objects which are far away. However, depending on the amount of myopia some myopic people are able to see up close with or without their glasses. When these same people become presbyopic, they will be able to see up close without their glasses on but will not be able to see up close if they are wearing their glasses or contact lenses.
Some people are considered farsighted and this is called hyperopia. This means that light coming into the eye is focused behind the retina. They may or may not need glasses depending on the magnitude of hyperopia. These people will definitely need reading glasses when they reach presbyopia and they may start to notice blurred vision at distance depending on the amount of hyperopia they have.
Now that we know the different types of refractive errors we can talk more about the cause of presbyopia.
Causes of Presbyopia
In order for us to see anything up close our eyes must accommodate. Accommodation is the process of changing focus from distance to near and involves changing the shape of the crystalline lens inside the eye. In people under the average age of 40, the human eye performs accommodation automatically when viewing anything up close. When we're young our lens is very flexible and therefore can be manipulated in order to change focal distances. When we reach age 40 or soon thereafter, the lens hardens and gradually becomes less pliable until it is so stiff that it is unable to change focus.
Treatment for Presbyopia
Eyeglasses with Bifocals, Trifocals or Progressive Lenses
The first option is getting bifocals, trifocals or progressive lenses in your glasses. Bifocals have a line and the lens above the line is focused for distance while the area below the line is focused for reading. Progressives do not have a line and gradually change from the top of the lens to the bottom. The top is focused for distance, the middle for intermediate (computer) and the bottom is for reading small print. The advantage of progressives is that there is no line on the lens, which can be distracting, and that they have an intermediate focus for objects just out of reading range but not far in the distance. The disadvantage is that they are more expensive than bifocals.
If you would rather not try bifocals or progressives, you could always go with a pair of glasses for reading. This works best if no prescription is needed for distance so you could just take the glasses off to see far away or look over them. If separate glasses are needed for distance, it may be a hassle to constantly switch back and forth.
Contact lenses are another option for correcting presbyopia. You could choose a multifocal contact lens or a monovision fit or simply where contact lenses for far vision and use reading glasses in conjunction with the distance only contacts.
Multifocal contact lenses come in many different brands and each is designed a little differently. Soft lenses continuously move and rotate on the eye, so the design is not like a traditional bifocal with distance on top and near at the bottom. Instead, the lenses are made so that you are looking through both distance and near at the same time. Since you are looking through a lens with two different focal lengths, it will not produce a perfectly clear image at first. The near portion will blur the distance vision slightly and the distance portion will blur near a little. You have to try them for a few weeks in order to adapt and your brain will eventually learn to compensate for the blurred image. Many people quit too early because they expect their vision to be equally as clear as it was with bifocal glasses. The contacts may never be equally as clear as glasses but with time and patience the majority of people are able to function throughout the day without problems.
Monovision refers to the method of correcting one eye for distance and the other for near vision. Usually a person's dominant eye is corrected for distance and tests can be done in office to determine which eye is the dominant one. There are several advantages and disadvantages to this method of correction.
A major advantage is that you are not forced to choose from a limited list of lenses. You can choose any type or brand of contact lens you want and if you already wear contact lenses, you can stay with the same brand that has always worked for you. If you suffer from problems such as dry eye, allergies, or contact lens discomfort then monovision could make it easier to find a lens that works well for you. Another advantage is that if you have astigmatism you will not be forced to purchase a very expensive, customized, toric multi-focal lens. You can use a regular disposable toric lens which will be much more affordable. Along the same lines, you can do a monovision fit with a lens which is less expensive than a multi-focal lens would be.
A disadvantage to monovision is that it will decrease depth perception. This may make night driving difficult and if you have any hobbies or a job that requires depth perception, it is not a good option for you.
Similar to the multi-focal lenses, monovision takes about 2 to 3 weeks to adapt to. Your brain is used to using your dominant eye more at both distance and near so it has to get used to switching eyes based on where you are focusing. You may notice objects or print having a shadow image at first but with time that will go away. It is very important to give monovision a chance for at least a week or two before giving up...even if it is very hard at first.
Surgery to Correct Presbyopia
Unfortunately there is no cure for presbyopia except a surgical procedure of implanting an accommodative or multifocal intraocular lens (IOL). An intraocular lens is a synthetic lens made to replace the crystalline lens. They have been used for years to replace crystalline lenses with cataracts and can be customized to make distance vision much better. There are new intraocular lens designs out which are able to correct both distance and near vision. The first of these accommodative IOL's (the original Crystalens) was FDA approved in late 2003. Several multifocal IOL's (brand names of Crystalens HD, Restore, Rezoom and Tecnis to name a few) are now FDA approved and have proven to be quite successful in providing patients freedom from eyeglasses for both far and near vision. There are more new accommodative and multifocal IOL's in development and in FDA approval stages that will become available in the future. Like most technological advancements these IOL's will probably continue to improve.
Will LASIK correct presbyopia?
LASIK can be done to correct presbyopia, but it is a monovision correction. It is the exact same thing as monovision contact lenses except that it is permanent. You would definitely want to simulate the monovision LASIK with contacts before having the procedure done. Researchers are working on something called Presby-Lasik, which would be more like a bifocal correction but it is still in the experimental phase right now.