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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]] (reduced minus for myopes), progressive lenses, or [[bifocals]]. | ||
==Correction== | |||
As you age, the lens in your eye becomes less flexible. This makes [[accommodation]] more difficult and brings on "arms are not long enough to read" symptoms. Someone may be both [[myopic]] and presbyopic, and have deficits in both near and far vision. Your [[Prescription]] will have an "Add" section specifying bifocals or multifocals if you have diagnosed presbyopia, or if your doctor thinks it best to reduce eye strain. | |||
===Two glasses=== | |||
It is an option to have two pairs of glasses, one for close-up, and one for distance, instead of trying to combine both near and far corrections in one pair of glasses. | |||
===Bifocals=== | |||
Glasses with a lower section that is specifically for close work. | |||
===Progressive lenses=== | |||
Glasses with a gradient from zero to near plus addition spherical power from top to bottom. | |||
===Multifocals=== | |||
Contacts that have sections for near and far work, which the [[visual cortex]] will selectively use when looking at different distances. | |||
== Measuring == | |||
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. | |||
* 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. | |||
* 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. | |||
A person is generally considered to have presbyopia [[wikipedia:if and only if | iff]] his power of accommodation is less than 2.5 D. | |||
===Caveats=== | |||
This technique might need to be refined for cylinder, if spherical equivalent is not used. | |||
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 == | |||
{{#ev:vimeo|284921410||inline}}<br/> | {{#ev:vimeo|284921410||inline}}<br/> | ||
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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]] | ||