Difference between revisions of Presbyopia
Jump to navigation
Jump to search
m
Reverted edits by Ninebalasan (talk) to last revision by User
m (Reverted edits by Ninebalasan (talk) to last revision by User) Tag: Rollback |
|||
| (6 intermediate revisions by 2 users not shown) | |||
| Line 1: | Line 1: | ||
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 == | == Measuring == | ||
| Line 15: | Line 30: | ||
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. | 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=== | ===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. | 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. | ||