Close Focus and Reading
If you look through a single lens reflex camera, the barrel of the lens rotates to adjust its focus. If you focus at a distance, things close up are blurry, and vice versa. The human eye works in similar fashion. The optically ideal eye sees distant objects easily. To look at something up close, focus is adjusted by a process called accommodation. A circular muscle behind the iris contracts and moves forward slightly. This muscle is connected to the lens by tiny fibers called zonules. The change in tone and position of the ciliary muscle changes the tension of the zonules on the lens. This "tug" causes the lens to change curvature, increasing focusing power.
In our youth, the lens is flexible and accommodates easily. As we mature, layers of protein are deposited causing the lens to become thicker, denser, and less flexible. At a certain age, close focusing becomes difficult, and we need magnifying glasses to see near objects without eyestrain. This condition, called presbyopia, usually begins in our mid-40s and gets progressively worse for about 15 years.
I want LASIK. Why do I care about Presbyopia?
If you are in your mid-forties and have mild myopia (up to -3.00), you have discovered that it is more comfortable to focus up close and read by TAKING OFF your glasses. But if you have LASIK, your distance vision will be corrected so you'll need to PUT ON reading glasses! This is because no vision correction surgery can eliminate or reverse presbyopia. Laser treatment can permanently reduce or eliminate myopia, hyperopia and astigmatism; but it cannot reverse, reduce, or eliminate presbyopia.
For People who Desire Near and Distance Vision
Monovision is an acceptable option for many (but not all!) individuals who desire to avoid reading and distance glasses for as long as possible.
Monovision, like reading glasses and bifocals, is not a perfect solution to the optical challenges of presbyopia. It is a compromise, and it is not for everybody. If a group of people are given a chance to try monovision correction with soft contact lenses, roughly a third will like it. About a third will find it uncomfortable, unbalanced or otherwise unacceptable, and will prefer having both eyes corrected for distance. The remaining third will have difficulty making a decision one way or the other, and delay proceeding with laser vision correction.
The best way to know if you will like monovision correction by laser treatment is to experience it first in contact lenses. If you wear monovision correction in contact lenses, you already know the answer. At LA Sight, we demonstrate monovision correction (via soft contact lenses) to all individuals over 40. We find that satisfaction with laser treatment is extremely high if people understand the limits of presbyopia and participate in the process of choosing whether or not to have monovision-style treatment.
Until very recently, artificial lenses implanted at the time of cataract surgery were all single-focus or fixed-focus lenses. However, many patients who contemplate cataract surgery want to enjoy clear distance vision, clear reading vision, and clarity everywhere in between, without glasses. There are now several lens implant options that deliver a fuller range of vision, regardless of age.
Clear Lens Replacement (Refractive Lens Exchange) refers to removing the natural lens of the eye, replacing it with a lens implant. New lens implant designs hold the promise of possibly being able to adjust their focus. The interest in these lens implant options is enormous.
 Crystalens: Position of the lens is slightly forward in the eye when viewing a near object, (left) and further back in the eye when viewing a distant object (right). |
In May, '03 the FDA approved a new design of lens implant called the Crystalens™. The initial model afforded some accommodation for close focus, so represented a revolution in design and function of intraocular lenses. This lens was not a "perfect" replacement for the eye's natural lens; it could accommodate or adjust focus by about 1.0 diopter where the normal young eye has an accommodative capacity of 3.0 to 5.0 diopters. However, it did allow improved distance, intermediate and near vision compared to previous lens designs. Crystalens introduced their AT-50 and HD-500 models in subsequent years. In January 2010 the Crystalens AO (for aspheric optic) was introduced; this lens seems to have improved performance vs. prior models. Reading glasses may still be necessary for sustained reading of small print. For further information about the Crystalens and other surgical methods of reading recovery, please browse the Restoring Reading Vision section of our site.
Dr. David Wallace is an experienced lens implant surgeon who offers the highest quality cataract surgery in Los Angeles and surrounding areas. Lens implantation surgery can also be used to provide monovision treatment. To learn more about cataract and lens implant care, clear lens replacement, premium IOLs and other options, call us at 310 828-2020, or Contact Us online with any questions you may have.