near addition

addition, near (add) 

The difference in spherical power between the distance and near corrections. A common method of arriving at the power of the addition is to measure the patient's working distance and the amplitude of accommodation. The add is obtained as follows
add = (1 metre/working distance in metre) − x(amplitude)
where x is the percentage of the total amplitude of accommodation which is to be used: two-thirds is usually more appropriate for young presbyopes (below about 52 years of age), while one-half is more appropriate for older presbyopes. Thus, this formula allows for a certain amount of the amplitude of accommodation to be left in reserve (usually one-third or one-half). It can also be estimated based on age: +1.0 D to +1.25 D for age 45-50 years; +1.5 to +1.75 D for age 50-55 years; +2.0 D to +2.25 D for age 55-60 years; +2.5 D to +3.0 D for older patients. However these figures may need to be adjusted to take into account the average working distance of the patient. Syn. reading addition. See bracketing; reading distance; presbyopia; cross-cylinder test at near.
Fig. A6 Abduction of the right eye. Adduction of the left eyeenlarge picture
Fig. A6 Abduction of the right eye. Adduction of the left eye
References in periodicals archive ?
Common causes of non-tolerance may result from, for example, an increase to the near addition creating increased jump, shortening of the focal range and reduction of the near vision area with progressive power lenses (PPLs).
While other presbyopic algorithms create undesired aberrations inside the pupil region, SUPRACOR provides the expected near addition without inducing undesired aberrations.
5,6,7) However, the majority of monofocal IOL recipients will require a near addition for everyday tasks.
The trial flame should be used as it allows a more natural investigation of refractive needs, especially when finding the near addition.
Progressive addition lenses of CD design have a periphery providing a near addition of up to +3.
60 depending on the near addition and a near add set 3mm from the geometric centre.
The lens therefore gives centre distance with an intermediate to near addition of up to +2.
00D Near addition Low add N/A Table 2: Outline of all real-world tasks & assessments made during each week of lens wear Timepoint Location Assessment Rating of .