Difference between revisions of Presbyopia
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== Measuring == | == Measuring == | ||
To determine | To determine '''power of accommodation''', also sometimes called '''amplitude of accommodation''', measure '''far power''' and '''near power'''. | ||
'''Far power''' is straightforward, and it’s the typical [[cm measurement]]: just measure the furthest distance you can see clearly without blur, with a lens to adjust as needed. The far power is ''1/(distance to blur) - (lens power)''. | |||
* For example, 80 cm with a -0.25 lens is calculated as 1/(80 cm) - (-0.25 D) = 1.25 D + 0.25 D = 1.5 D. | * For example, 80 cm with a -0.25 lens is calculated as 1/(80 cm) - (-0.25 D) = 1.25 D + 0.25 D = 1.5 D. | ||
* It might be useful to use a plus lens to measure low myopia. For example, 80 cm with a +0.75 lens is calculated as 1/(80 cm) - (+0.75 D) = 0.5 D. | * It might be useful to use a plus lens to measure low myopia. For example, 80 cm with a +0.75 lens is calculated as 1/(80 cm) - (+0.75 D) = 0.5 D. | ||
'''Near power''' is the same, but measure the '''closest''' distance you can see clearly without blur. | |||
* For example, if the closest you can see is 10 cm without lenses, it’s calculated as 1/(10 cm) - 0 = 10 D. | * For example, if the closest you can see is 10 cm without lenses, it’s calculated as 1/(10 cm) - 0 = 10 D. | ||