Presbyopia is the term used for the loss of focusing capacity at near distances. The eye has a lens inside about the size of a button that accommodates, or changes shape to add power for reading similar to the way a zoom lens works on a camera. Helmholtz was a noted scientist that proposed the first mechanism for accommodation in 1855. There have been disagreements over the way accommodation works ever since that proposal. Probably multiple changes in the eyes cellular structure and physiology are responsible. The lens is held in place by small fiber like strands called zonules. The zonules are attached to a smooth muscle in the eye called the ciliary muscle. Helmholtz believed the ciliary muscle contracted when we viewed objects up close and released the tension on the lens by the zonules. He hypothesized this caused the lens to change shape and increase its focusing power by becoming more round and increasing the curvature of the lens.
Throughout our lives the lens continues to grow and loses elasticity, both by growth and UV sun induced changes to the lens proteins. Other aging changes occur including forward displacement of the lens, loss of it’s aspherical shape, changes in the light bending capacity of the lens material, and changes in the zonules and the ciliary muscle.
In all likelihood the loss of elasticity from growth is causing most of the diminishing capacity for you to focus on reading material. The lens grows in a forward direction and as the zonules lose some of their tension they can no longer effectively change the shape and focusing power of the lens.
The loss of focusing range is remarkably correlated with age. A 15 year old teenager can clearly focus within several cm of their face but by their early twenties they are already losing these levels of accommodation. Since we have almost no near work done at 3-4 cm there is no awareness of loss. In a fairly linear manner the nearest focal distance recedes until between the ages of 39 to 42 you can only focus to 13-14 inches. Most reading is done at 16 inches (40 cm for the metric folks). When you read, you need to have a small amount of excess focusing capacity in reserve or there will be eyestrain (similar to trying to hold the maximum weight you can lift for a sustained period). Overnight it seems like the eyes have deteriorated but in reality the process is a normal age related change that crosses into the zone where you read in at a predictable age. There are some genetic factors in play also; for instance, the onset of reading problems is several years younger in India. Over the years of practicing in a Fort Collins Eye Doctors office I have seen twp patients out of 40,000+ who had reached their 50’s with no signs of presbyopia (lucky eye genes). I have also seen several patients with complete loss of focusing ranges in their early 30’s. They all reported their mom and other maternal relatives were the same way. However, almost universally the focusing capacity can be predicted by your age. The optometrists job comes in adjusting for variations in how close you read. This is individual and bears some relationship to arm length. Compounding reading ranges issues are computers which typically (not always) are viewed a little farther away (20 inches or 50 cm).
Once your focusing capacity has diminished to the point where you need a near correction in the form of bifocals (typically no line progressive lenses today), you can expect the near strength to need to be adjusted every 18-24 months. At some point by the age of 55-60 you essentially lose all of your focusing capacity (a small residual amount does remains) and become what we refer to as an absolute presbyope. While that sounds bad, the good news is the changes have now stabilized.
Arguments continue over what causes presbyopia. One study by Tos T. J. M. Berendschot, PhD; Wendy M. R. Broekmans, PhD; Ineke A. A. Klöpping-Ketelaars, MD, PhD; Alwine F. M. Kardinaal, PhD; Geert van Poppel, PhD; Dirk van Norren, PhD (2002) concluded that the carotenoids lutein and zeaxanthin may retard the development of cataracts. This could translate into a delaying of the onset of presbyopia to some extent but no studies have been done to test this hypothesis. Lutein and zeaxanthin are present in the lens and lutein is one of the primary supplementation ingredients of formulations that have been shown to slow the progression of certain forms of macular degeneration.
Many different options of lenses and contact lenses are available to address your needs in correcting presbyopia for reading and computer work. There are some evolving options in lens implants after cataract surgery that have become available in recent years also. Don’t delay in diagnosing the care for near vision problems. Most vision insurance including Vision Service Plan (VSP) offer options to help in treating your presbyopia.