Presbyopia

When as the result of age thepower of accommodation has diminislished to such an extent that the eye (corrected for distance,if ametropic) cannot produce sufficient accommodation for the reading distance, the condition is called presbyopia. The average age when this state of affairs is present is 45, and as age advances the accommodation gradually diminishes and the presbyopia correspondingly increases. The amount of presbyopia is represented by the difference between the number of dioptries of comfortable accommodation presentand three dioptries, which must be made good by plus spheres. The presbyope sees well at adistance, providing there is no error of refraction, but has difficulty in maintaining good vision for near work, and the eyes become tired after reading, especially at night.A person has trouble in seeing small objects because has to hold them far away, and consequently get sasmaller visual angle.

Source: Ophthalmic Dictionary including pronunciation, derivation and definition of the words used in Optometry and Ophthalmology by James J. Lewis, Oph. D. Professor of Optometry in the Northern Illinois College of Ophthalmology and Otology, Chicago.