Understanding Presbyopia & Near Vision
Reviewed by Marc Michelson, M.D.
Presbyopia is a loss of flexibility of the crystalline lens of your eye that causes a gradual progressive decrease in focusing ability. The loss of focusing ability results in an inability to see near objects and thus blurs your vision for near tasks such as reading, sewing, and knitting, viewing a computer and seeing medicine bottles.
For most people under 40 years old, the crystalline lens is typically crystal clear, soft and flexible. This flexibility permits the crystalline lens to change its shape and alter its curvature so that it can help focus your vision at various distances-from far, to near, to arms length, to far or near again. Thus, it is this flexibility of the crystalline lens that allows you to see things at all distances. As we enter our 40’s, the crystalline lens begins to lose its flexibility, making it more and more difficult for you to change focus and see arms length or close objects or reading material-and thus resulting in Presbyopia.
Presbyopia literally means "old eyes". Presbyopia is a normal and expected part of the aging process. People who are experiencing the start of Presbyopia often notice that their "arms are too short" to read and they have to hold close things further away to see them clearly. Presbyopia typically becomes noticeable between age forty and fifty and progressively worsens through age sixty-five. Presbyopia affects everyone. When Presbyopia begins, people who already wear glasses may need bifocals or trifocals, and those who have never worn glasses may require reading glasses. In addition to bifocals and trifocals, there are a number of eyeglass lenses for Presbyopia called Progressive Addition Lenses, that help people achieve relatively smooth and continuous focusing ability from far to near. Also, there are a number of bifocal contact lenses for Presbyopia. Laser Eye Surgery such as LASIK, may offer near vision correction by using a technique called Monovision LASIK. Recently, thanks to advances in lens replacement surgery techniques and modern intraocular lens implants (IOL), lens replacement surgery has helped many patients restore their normal range of vision without dependence on bifocals and trifocals.
Diagnosis of Presbyopia & Near Vision Problems
Presbyopia is a near vision-focusing problem. It is easily diagnosed during a routine eye examination by testing your near vision and by measuring your amplitude of accommodation. Accommodation is the process by which the increases its power in order provide clear near vision. The necessary near vision testing involves the presentation of various lens combinations and measuring the effect on the clarity of your near vision as increasing and decreasing size print is moved closer and further away.
Eyeglass Lenses for Presbyopia & Near Vision
There are a number of different types of eyeglass lenses that will help your near vision if you have Presbyopia.
Reading Glasses-If you have never worn eyeglasses for correcting your distance vision, and have “normal” clear vision for seeing far away, it is likely that you will have good reading vision by simply using reading glasses. Reading glasses have the advantage of really not requiring any adaptation, but have the disadvantage of not allowing you to see far away while wearing them. Thus, while wearing reading glasses, you will be unable to read and watch television at the same time, or drive and read a map at the same time. This requires the use of bifocals or trifocals. Further, not all reading glasses or readers are the same and you should understand the difference.
Bifocal Lenses- Bifocal eyeglasses are most often prescribed in one of two different styles. The most common style is called a Flat Top Bifocal and is composed of two distinct segments-one for far vision and one for near or up close vision. The near vision segment is available in several sizes to accommodate the width of the near field of vision that you wish to see clearly. Typical designations for Flat Top Bifocals might be FT-25, FT-28, FT-35 or FT-40 with the larger number indicating a wider near field of vision. A second style of bifocal lens is called an Executive Bifocal. Executive Bifocals are bifocal lenses that are also split into two segments, however the division runs the entire width of the lens. Bifocal eyeglass lenses do not allow a continuous range of clear vision and create a somewhat blurry zone of vision for intermediate or arms length vision.
Trifocal Lenses-Trifocal eyeglasses are eyeglass lenses that are divided into three distinct segments-one for far vision, one for near vision and one for intermediate vision. The styles of trifocal lenses are similar to bifocal lenses. Even with the added feature of a segment for intermediate range vision, Trifocal eyeglass lenses do not provide a continuous range of clear vision, but provide "zones of clear vision".
Progressive Addition Lenses (PALs)-Progressive Addition Lenses (PALs) are a very popular way to correct Presbyopia. Progressive Addition Lenses provide patients with a number of significant advantages over either bifocal lenses or trifocal lenses in the correction of Presbyopia. First, Progressive Addition Lenses provide a visual function advantage in that they create a continuous and seamless range of vision, whereas bifocals and trifocals create a “segmented” range of vision with noticeable blur zones. Second, PALs provide a considerable cosmetic advantage as a result of their seamless design. PALs are designed with smooth and continuous changes in curvature across the lens surface making it possible to have a large number of lens designs. In fact there are many manufacturers of PALs producing many different designs. Depending on your specific vision correction needs, the Optometrist or Dispensing Optician assisting you with you eyeglass lens selection will be able to make an appropriate recommendation for you as the optical characteristics of each type of PAL vary widely. It is wise to stick with well-known popular “premium” brands of PALs such as Varilux, as with PALs, you get what you pay for.
Contact Lenses for Presbyopia & Near Vision
Just as with eyeglass lenses, contact lenses cannot restore the natural focusing ability of the eye, or accommodation that is decreased as you age. However, just as with bifocals, trifocals and PALS, near vision contact lenses for Presbyopia are available and offer a vision correction option for many patients.
Alternating Vision Bifocal Contact Lenses-Alternating Vision Bifocal Contact Lenses are similar to bifocal eyeglass lenses in that they have two distinct segments-one for the correction of distance vision and one for the correction of near vision. The zones can be upper and lower segments such as with bifocal eyeglass lenses or can be concentric with the near segment being constructed in a peripheral ring. As you look down to read, the bifocal contact lens moves up, or “translates so as to place the near vision segment into your line of sight. Alternating Vision Bifocal Contact Lenses are available in both soft contact lenses and rigid oxygen permeable contact lenses, but the majority prescribed are rigid oxygen permeable designs. Often patients who wear these types of lenses complain of discomfort, glare or haloes.
Progressive Bifocal Contact Lenses-Progressive Bifocal Contact Lenses correct the distance vision in the center of the contact lens and the intermediate and near vision in the more peripheral zones of the lens. Progressive Bifocal Contact Lenses are also available as both soft contact lenses as well as rigid oxygen permeable contact lenses. In order to appreciate the different zones of intermediate and near vision, your brain must learn to “select” certain images and “suppress” other images depending on what you are trying to see. This requires some level of adaptation for most patients.
Monovision Contact Lenses-With Monovision Contact Lens fitting for Presbyopia, one eye-usually the dominant eye-is corrected for distance vision and the other eye is corrected for near vision. Depending on the distance you are trying to see, your brain will again “select” the in focus image and provide you with an approximation of continuous seamless vision. Some patients experience a loss of depth perception, which can be disturbing. In most cases, patients adapt to Monovision Contact Lenses for Presbyopia easily and quickly. Monovision has proven to be a successful near vision correction option for Presbyopia for approximately 65-75% of patients who try it.
Surgery for Presbyopia & Near Vision
Currently there are three main types of surgery to correct Presbyopia and near vision: Corneal Laser Eye Surgery, Multifocal & Accommodative Intraocular Lens Implants and Surgical Reversal of Presbyopia
Corneal Laser Eye Surgery - Laser Eye Surgery for the correction of Presbyopia and near vision is often performed using Monovision LASIK. It is also possible to perform Monovision PRK, Monovision Epi-LASIK and Monovision LASEK, depending on which procedure your LASIK Surgeon feels will give you the best result.
Multifocal & Accommodative Intraocular Lens Implants (IOL) for Presbyopia - Since Presbyopia is a condition in which the crystalline lens loses its focusing power, it seems logical that the best possible solutions for Presbyopia may in fact be achieved through the replacement of the crystalline lens itself. Removal and replacement of the crystalline lens is an easy decision for those Presbyopes who have a loss of transparency of the crystalline lens, or cataract formation. In these cases it is obvious that in order to achieve clear vision, the crystalline lens must be removed-and to achieve concurrent far and near vision, it is most beneficial to replace the natural lens with a presbyopia correcting multifocal intraocular lens or accommodative intraocular lens. If however, the patient is a younger Presbyope, with a clear crystalline lens that has simply lost its focusing ability, the decision becomes a bit more complex and must be carefully evaluated in terms of risks and benefits by both the patient and the cataract surgeon. Presbyopia correcting multifocal intraocular lens implants include the ReZoom Lens Implant and the ReSTOR Lens Implant, which provide far and near vision concurrently through the use of refractive and diffractive optics respectively. Accommodative Intraocular Lens Implants include Crystalens, which achieves its focusing power by slightly altering its position in the eye in order to change its power.
Surgical Reversal of Presbyopia - Surgical Reversal of Presbyopia is currently under investigation. There is considerable research and a number of clinical trials underway to gather data to support the safety, efficacy and predictability of Scleral Expansion Bands. Anterior Ciliary Sclerotomy and Laser Reversal of Presbyopia. At the present time the data is not yet conclusive on any of these methods and none have been approved by the Food and Drug Administration (FDA) for use in a non research setting (http://www.fda.gov).
While the correction of Presbyopia initially seems like a rather simple task, as you can see from the information provided, it can be quite complex as each Presbyope needs to be carefully evaluated as to their individual needs, vision requirements and desire to achieve near, far and intermediate vision with-or without eyeglasses or contacts.
It is important to seek examination and consultation from eye care professionals and eye care practices that can offer the full range of Presbyopic correction including bifocal eyeglasses and progressive lenses for presbyopia and near vision, bifocal contact lenses for presbyopia and near vision, laser eye surgery for presbyopia and near vision and presbyopia correcting multifocal and accommodative lens implants for presbyopia and near vision.