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Presbyopia is the hardening of the [[lens]] in the [[eyeballs]] such that it becomes difficult to see [[near work]]. This is common in older adults and is commonly treated with [[reading glasses]] or [[bifocals]]. | Presbyopia is the hardening of the [[lens]] in the [[eyeballs]] such that it becomes difficult to see [[near work]]. This is common in older adults and is commonly treated with [[reading glasses]] or [[bifocals]]. | ||
== Measuring == | |||
To determine your '''power of accommodation''', you need to measure your '''far power''' and '''near power'''. | |||
Your '''far power''' is straightforward, and it’s the [[cm measurement]]s you normally do: 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. | |||
* 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. | |||
Your '''near power''' is the same, but you 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. | |||
* It might be useful to use a big minus lens to measure young people (don’t look through it for too long!). In the example above, you expect to see as close as 50 cm with a -8 lens, which is 1/(50 cm) - (-8 D) = 2 D + 8 D = 10 D. | |||
The '''power of accommodation''' is (near power) - (far power). With the first example in each of the above, it would be 10 D - 1.5 D = 8.5 D. | |||
===Caveats=== | |||
I’m not entirely sure how cylinder affects this measurement, so you’ll have to refine the technique if you have cylinder. | |||
The cornea and lens actually have more power because the total power has to focus the image on your retina, but they cancel out in the subtraction step, so it’s easier to ignore them. | |||
== Videos == | |||
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{{#ev:youtube|QvmOkVjwPyI||inline}} | {{#ev:youtube|QvmOkVjwPyI||inline}} | ||
== | == Resources == | ||
* Here is a resource that may be of interest to people with presbyopia that was found in the Discord chat. The resource is used for training convergence. http://www.i-see.org/rizzi_charts_readvertical.pdf | |||
[[Category:Articles]] | [[Category:Articles]] | ||
[[Category:Eye conditions]] | [[Category:Eye conditions]] | ||