Page 11 - Practical-Refraction-English

Supplement The Optical Principle of the Correction of Presbyopia 1 The effect of prescribing a near addition is to restore to point Rl; the image of the near vision far point Pp seen the presbyopic eye the ability to see near objects clear- through the addition is the distance vision near point Pl. ly. Its purpose is to produce an image of a near object Since Rl is located at infinity (that is, at the corrected far at a further distance from the eye which lies within the point of the ametropic eye or the real far point remaining range of accommodation. The apparent range of the emmetropic eye), it follows that Rp always lies in of near vision which results has the optical property of the focal plane of the addition (Figure 10). being the object conjugate of the distance vision accom- modation range. The image of the near vision far point Rp seen through the addition is the distance vision far Acc=0 Acc=max Practical Refraction R 8 l P l L R p P p Add Fadd R 8 l © Essilor International Acc=0 Acc=max Figure 10: The Principle of Correction of the Presbyopic Eye Real and Virtual Optical Spaces Two optical spaces can be distinguished in the ametro- Any optical space extends really or virtually to infinity; pic eye corrected by a spectacle lens: that is, the apparent optical space extends in front of - the apparent or corrected optical space, which is and behind the lens and the real optical space extends restored to the ametropic eye by its refractive correction in front of and behind the eye. The corrective lens acts and in which exist the physical objects that it sees. This as a creator of apparent optical space. The image of this is the object space of the lens. space is formed, through the lens, in the optical space - the real optical space, which is the optical image perceived clearly by the ametropic eye. This is why it is space for the lens and the object space for the eye, in a little improper to speak of optical correction by spec- which exist the optical images of the objects formed by tacle lenses as the lens does not really correct the ame- the corrective lens. These are the images which are seen tropia. It would be more appropriate to speak of the by the ametropic eye and which are formed on its retina. optical compensation of ametropia by spectacle lenses. 11 Copyright © 2008 ESSILOR ACADEMY EUROPE, 13 rue Moreau, 75012 Paris, France - All rights reserved – Do not copy or distribute.