Institute of Optics (CSIC), Madrid, Spain.
Acta Ophthalmol. 2014 Jun;92(4):394-9. doi: 10.1111/aos.12196. Epub 2013 Jun 15.
Presbyopia, understood as the age-related loss of ability to clearly see near objects, was known to ancient Greeks. However, few references to it can be found in ancient manuscripts. A relevant discussion on presbyopia appears in a book called Symposiacs written by Lucius Mestrius Plutarchus around 100 A.C. In this work, Plutarch provided four explanations of presbyopia, associated with different theories of vision. One of the explanations is particularly interesting as it is based on a binocular theory of vision. In this theory, vision is produced when visual rays, emanating from the eyes, form visual cones that impinge on the objects to be seen. Visual rays coming from old people's eyes, it was supposed, are weaker than those from younger people's eyes; so the theory, to be logically coherent, implies that this effect is compensated by the increase in light intensity due to the overlapping, at a certain distance, of the visual cones coming from both eyes. Thus, it benefits the reader to move the reading text further away from the eyes in order to increase the fusion area of both visual cones. The historical hypothesis taking into consideration that the astronomer Hipparchus of Nicaea was the source of Plutarch's explanation of the theory is discussed.
老花眼，即随着年龄的增长而逐渐丧失清晰地看近物的能力，这一现象为古希腊人所了解。然而，在古代文献中几乎找不到与之相关的记载。公元 100 年左右，卢修斯·梅斯特里乌斯·普卢塔克所著的《论老年》一书中，有一个关于老花眼的相关论述。在这部作品中，普卢塔克提出了四种与不同视觉理论相关的老花眼解释。其中一种解释特别有趣，因为它基于一种视觉的双眼理论。在这种理论中，视觉是由从眼睛发出的视觉光线形成视觉锥体而产生的，视觉锥体撞击到要看到的物体上。据推测，老年人的视觉光线比年轻人的弱；因此，为了使理论在逻辑上一致，这意味着这种效果可以通过来自双眼的视觉锥体在一定距离处的重叠而增加光强度来补偿。因此，读者为了增加两个视觉锥体的融合区域，将阅读文本移得更远，这样对他们来说是有益的。文中还讨论了一个历史假设，即尼西亚的天文学家希帕恰斯是普卢塔克对该理论解释的来源。
