Presbyopia

1. Presbyopia 15thlectture Dr. Mohammad Shehadeh

2. Presbyopia • The amplitude of accommodation declines steadily with age. • This is due mainly to sclerosis of the fibresof the crystalline lens and changes in its capsule which reduce the spontaneous steepening of its surfaces when the ciliary muscle contracts. • Also it may be that the ciliary muscle itself becomes less efficient with advancing age (after 40 years).

3. Definition of presbiopia • A person experiencing such difficulty and discomfort for near vision due to reduced amplitude of accommodation is said to be presbyopic. • A supplementary convex lens is used to enable the patient to achieve comfortable near vision. • The lens is called a presbyopic correction and the age related inadequacy of accommodation is called presbyopia.

4. In infancy the eye is capable of 14 D of accommodation, • but by the age of 45 years this has fallen to about 4 D. • After the age of 60 years only 1 D or less remains • (A patient with no accommodation will have 0.25 D depth of field, enabling him to see clearly from 4 metres to infinity.)

5. Onset of presbyopia • In order to focus on an object at a reading distance of 25 cm, the emmetropic eye must accommodate by 4 D • However, for comfortable near vision one-third of the available accommodation must be kept in reserve. • Therefore, the patient will begin to experience difficulty or discomfort for near vision at 25 cm when his accommodation has decayed to 6 D • This usually occurs between 40 and 45 years of age.

6. Calculation of Presbyopic Correction • the remaining amplitude of accommodation is determined (from his near point) and the desired working distance is specified • For example, an emmetropic patient has a remaining amplitude of accommodation of 3D (near point 33 cm). In order to achieve comfortable near vision he must keep one third of this in reserve. • Therefore, he must use only 2D of his 3D of accommodation. If he wishes to see clearly at 25 cm he needs 4 D of accommodation. Thus he requires a presbyopic correction of 2D.

7. In practice the refractionist learns by experience to anticipate the approximate presbyopic correction from the patient's age • This is then confirmed by subjective refraction. • In ametropiathe presbyopic correction is added to the patient's distance correction

9. The onset of presbyopia occurs earlier in uncorrected hypermetropia than in emmetropia, • because the patient with hypermetropia must accommodate more to achieve near vision. For example, a patient with 3 D of hypermetropia needs to exert 3D of accommodation to see clearly at infinity. • Therefore, to see clearly at 25 cm 7D of accommodation are needed (3D + 4D) • conversely a patient with 3D of myopia has a far point at 33 cm. • Thus to focus at 25 cm only 1D of accommodation is used.

10. Amplitude of accommodation necessary to achieve clear vision at 25 cm in different refractive states.

12. Beware of prescribing too great a reading addition • The most frequent reason that patients seek a retest is that too strong a near addition has been prescribed. • In normal circumstances not more than +2.50 DS addition should be given. However, pseudophakic patients often prefer a +3.00 DS addition. • Record the near acuity for each eye alone and binocularly.