Through the natural aging process, changes occur in the lens of the eye which interferes with our ability to see clearly. The first changes begin when the lens of the eye swells and begins to lose its elasticity. As this develops the lens of the eye slowly loses its ability to change shape and focus properly on near object, near or reading vision begins to deteriorate.
This effective loss in ability to accommodate focus changes from distant objects to near objects is called presbyopia. Early in their 40’s, people find they have to start holding reading materials further from their eyes to see clearly. Eventually reading glasses, bifocals or refractive surgery is required.
Optics of the eye and vision
With normal vision light passes through the cornea and the lens of the eye and is focused onto the retina. The retina then transmits the image to the brain via the optic nerve.
The curve of the cornea provides most of the focusing for the eye. The lens of the eye fine tunes vision to adjust focus between near and far objects.
When light passes through the curved cornea the rays are bent (refracted). The greater the curve of the cornea, the greater the bending or refraction of light rays and the shorter the focal length.
The focusing lens adjusts vision for near or distant vision. By increasing or decreasing the curve of the lens the eye can shorten or lengthen the focal point and bring either near or distant objects into focus.
The lens continually changes shape to focus objects which are various distances from the eye. The shape of the lens is controlled by the zonules and ciliary body, which are thin fibers and muscles that hold the lens in place. Through contraction or relaxation the size and shape of the lens is controlled. When we look at something close up, the lens becomes more round. When we gaze into the distance, the lens becomes flatter to bring the distant image into focus.
How does Presbyopia affect vision?
At birth the lens is soft and flexible, and its shape is easily controlled by the zonules. As we age however, swelling and hardening of the lens reduces its ability to change shape. Since the older lens cannot change shape as easily, the eye has increasing difficulty changing focus from far to near objects. This loss in focusing ability, or presbyopia, results in blurred or distorted vision when looking at close objects.
Who gets presbyopia?
Presbyopia is a natural result of the aging process. Everyone will eventually experience some degree of presbyopia, beginning about the age of forty. In fact, presbyopia is one of the most predictable, routine age changes that occur in the human body.
What are the symptoms of presbyopia?
- Blurred vision of near objects
- Difficulty reading or doing close work
- Eye fatigue or headache after doing close work
- Difficulty changing focus from near to far vision
The most common symptoms of presbyopia are blurred vision of near objects and difficulty doing close work. Many people find reading difficult and hold the material further away in an attempt to see more clearly. It may be noticed that it starts taking longer to focus sharply when switching attention from near objects to distant objects (and vice versa). Eye fatigue and headache, after close work like reading, are also symptoms of presbyopia. In addition, farsighted people will usually notice the symptoms of presbyopia sooner than those who are nearsighted, because nearsighted persons can simply remove their glasses to see close objects more clearly.
Dr. Keith Liang offers this eye procedure called The Raindrop Near Vision Inlay which is a tiny, contact lens shaped corneal inlay designed to correct presbyopia.
How is presbyopia treated?
Unfortunately, there is no treatment such as medication, diet or exercise that will slow the progression of presbyopia. However, corrective lenses, refractive surgery (or a new corrective lens prescription) can be used to bring things back into focus. In many cases, a new prescription is required about every two years to overcome blurred vision caused by presbyopia and the progressive loss of accommodation.
Bifocal, Multifocal, Progressive and Reading Eyeglasses
Reading glasses can be worn when doing close work; distant objects become blurry however, when viewed through reading glasses. Consequently, some people choose bifocal or multifocal lenses which offer good distance vision through the top and clear reading vision through the bottom (multifocal also give good intermediate vision). People who have good distance vision without glasses may use half glasses to correct presbyopia. Progressive lenses or no line bifocals allow continuous correction from distance, to intermediate, to reading vision and are also a popular choice.
Bifocal, Multifocal, Progressive Contact Lenses
Contact lenses have become a popular alternative for many people who have deployed presbyopia. They come in many styles and designs to satisfy a wide range of needs including bifocal and progressive disposable soft lenses. After an adjustment period, the eye learns to automatically look through the correct area of the lens depending on whether sharp near vision or sharp distance vision is needed.
Monovision is a technique (used for people with presbyopia) that corrects vision in one eye for distance and adjusts the other eye (usually the non-dominant eye) for reading vision. Contact lenses and, in some cases, refractive surgery are used for patients who choose monovision. Like bifocal contact lenses, monovision add the convenience of always having good distance and reading vision at the same time.
If you are experiencing difficulty with reading and close work or have other vision problems, you should obtain a complete eye examination.