near addition

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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 ?
The higherthe reading addition, the smaller the reading area will become.
esba To rectify it, your optometrist will add a reading addition to your prescription.
To rectify it, you need a reading addition to your prescription to help your eyes focus at close distances.
Bifocals or varifocals, with a reading addition, may help young patients with significant esophoria at near.
The IP/RP ratio informs the dispenser as to what percentage of the reading addition is required for intermediate vision, and can be calculated from: IP/RP ratio = Intermediate Add/reading Add x 100.
PPLs offer a greater working distance range than trifocal and bifocal lenses, but the intermediate and reading areas become narrower in size as the reading addition increases.
In the consulting room, the optometrist can place the reading addition in the trial frame and gain affirmation from the patient that their need is present.
Optometrists will commonly assess a near reading addition power but often overlook the available range of clear vision (accommodative flexibility; af), which can actually be reduced due to the visual field and affects on the magno-cellular (kinetic or awareness) pathway.
When the desired near visual acuity is met, the magnification of the high reading addition thus demonstrated will give the practitioner a starting point magnification with which to demonstrate the device of choice, such as a hand magnifier
In all cases, the distance over-refraction should be confirmed before checking the required reading addition.
These results are understandable because these were asymptomatic (at near) subjects with no or very low reading addition.
High reading additions can easily be demonstrated in a trial frame and no extra equipment is required to do this.

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