Posted on September 06 2015
Whether farsightedness, nearsightedness or astigmatism, all of the vision problems we have discussed thus far are conditions caused by the shape or size of the eyeball. However, there are other vision problems that are simply a part of aging. One of the most common age-related vision conditions is called presbyopia. The roots of this word come from Greek and essentially mean “old eyes.”
So when does presbyopia begin? What are its symptoms? On average, people will start to see the effects of presbyopia in their early to mid-forties. The main symptom of presbyopia is that it becomes hard to clearly focus on close objects. This may make reading or other detail-oriented tasks more difficult. Often, this causes those with presbyopia to hold reading material at an arm's length in order to see clearly. At first, the symptoms may sound similar to farsightedness. However, there are different causes, and someone with farsightedness will develop their symptoms relatively early in life while presbyopia will start in middle age.
With the normally-functioning eye, the crystalline lens of the eye bends to refract light waves from close objects directly onto the photoreceptors in the retina. In presbyopia, the crystalline lens cannot bend as well to focus the light waves from close objects. Although the exact cause is not definitively known, many believe that presbyopia stems from a loss of elasticity in the crystalline lens. With age, the lens gradually gets harder and less able to flexibly bend to refract light waves from close objects. Another cause may be that the ciliary muscles, which are the muscles in the eye that help pull and bend the crystalline lens when we are trying to focus on a close object, become weaker. Much like how the muscles in someone's knee or shoulder may weaken as they age, the ciliary muscles in the eye can lose strength. If those muscles cannot bend the crystalline lens as well, the light waves from close objects will not be properly focused on the retina.
Presbyopia is an inevitable part of aging that eventually affects everyone to a degree. There are, however, treatments that will generally allow people to continue to see all distances as they age. In most cases, glasses or contact lenses will compensate for the loss in strength of the crystalline lens and allow for clear close-up vision. If you have presbyopia and have never had any vision problems, you may only need glasses for tasks like reading. For those who have other vision issues, such as nearsightedness or astigmatism, an eye-care professional may prescribe lenses with multiple focusing areas. One version of these glasses is bifocals, which have one area of the lens for distance vision and another section (at the bottom) for near sight. There is also a type of lens called progressive addition lenses. Like bifocals, progressive lenses have different sections for distance and near vision, but the sections are more seamlessly blended throughout the lens than bifocals.