As my co-editor Daniel H. Chang, MD, stated in our introduction to this column in the last edition, we would like to challenge ophthalmologists’ perspective on presbyopia, discuss current treatments, and highlight the promise of new therapies. Perhaps the day will come when Daniel and I discover the solution to remove over-the-counter readers from all shelves, or perhaps one of the bright superstars reading this column will discover the means to halt the loss of accommodation for billions of people. However, before we delve into the current surgical treatments, it is important to understand the proposed theories on the mechanism of the disease as well as the history of presbyopia and its management during the last couple of millennia.
Whether you prefer to use the term presbyopia or the now in vogue dysfunctional lens syndrome, the meaning is the same. From the Greek words presbys or old man, and ops, meaning “eye,” the disease was well known to the ancient Greeks with mention by Aristotle and Cicero. The earliest documented reference to presbyopia in texts can be traced back to 100 AD when Plutarch provided several explanations for the cause of presbyopia. The use of younger colleagues to read to elders was likely employed through the end of the first millennium when the understanding of convex lenses for reading finally offered a more practical solution. It would take yet another millennium replete with philosophers and scientists offering various theories on the mechanism of the disease in order to move us towards the surgical corrections of the past decades.
The 16th and 17th centuries marked the understanding of an accommodative mechanism and spawned numerous theories related to the cause of presbyopia. Throughout the centuries there would be many postulated theories on accommodation: from elongation of the eye, to changes in the shape of the cornea, to axial movement of the lens, and even proposed changes in the refractive index of lens fibers. Many of these theories never gained acceptance with the exception of earlier work by René Descartes, who proposed in 1677 that accommodation was due to changes in the shape of the crystalline lens. Although the mechanism for such changes in the shape of the lens was unclear, the discovery of the ciliary body in 1847 would lead to the prevailing theories by which presbyopia occurs.
In 1855, the German physician and physicist, Hermann von Helmholtz proposed the most widely accepted theory on accommodation in which the lens becomes increasingly convex as a result of ciliary muscle contraction, allowing the lens to exhibit its own natural elasticity. Presbyopia, according to von Helmholtz, was therefore the loss in elasticity of the lens, which occurred as a result of sclerotic changes with aging. Recently, however, another theory has been proposed by ophthalmologist and physicist Ronald A. Schachar. According to this theory, accommodation is the result of increased tension applied to equatorial zonules with opposing relaxation of the anterior and posterior zonules. Presbyopia is therefore caused by the increase in the equatorial diameter of the lens that occurs with aging. The subsequent decrease in the effective distance from the ciliary muscle to the lens equator does not allow for sufficient contraction and accommodative amplitude. The understanding of these and other theories on accommodation, and the resulting means by which presbyopia occurs, has driven the current concepts behind treatment with the use of corneal, lens, and scleral modifications.
It was in 1784 when Benjamin Franklin commissioned the first pair of bifocals. Since that time, and likely since the time of Aristotle, the treatment of presbyopia has primarily involved compensating for the loss of accommodation, rather than a true medical or surgical treatment of the disease. It is mindboggling to think that in all this time there have been minimal advances in our ability to reverse or prevent this disease process. Perhaps due to the oversimplification that the use of glasses offers a “simple and safe” means of treatment. Perhaps it is time for what the next millennium will offer.
