Why do some people get more depth of field than others from the same IOL?
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Fascinating article on natural depth of focus: https://jov.arvojournals.org/article.aspx?articleid=2713946. " "Impact of higher Order Aberrations on Depth of Field."
The conclusion: Natural higher order aberrations of the cornea, which differ from one person to another confering different amounts of natural extended depth of focus, explain some of the variability in depth of focus across persons, but differences in neural processing are a bigger factor. Some people's brains are better at coping with blur and filtering it out than others and this is a more important source of variation in depth of field across persons. (This is apart from accomodation.)
My obvservation: The fact that people's corneas and people's brains differ so much from one person to another, resulting in great variation in depth of field perceived with the same lens, makes the outcome of cataract surgery very hard to predict. The IOL is only one component of a very complex system.
4 likes, 6 replies
RonAKA jimluck
Edited
One study I saw found that being more myopic prior to surgery and having a smaller pupil was associated with a larger depth of focus. I translate that to mean an older myopic person with smaller pupils will be more likely to get better depth of focus.
Lynda111 jimluck
Posted
Well said. After surgery your cataract will be gone., but how well you will see will vary from person to person
Guest jimluck
Edited
I didn't read the article (are we allowed to post external links now by the way? seems like it) but I think pupil size is a big factor too. And astigmatism too. I have glasses that only correct my -0.75 astigmatism (sphere is 0) and they really crisp up my distance vision but they also really ruin my near vision.
trilemma Guest
Edited
Interesting! Thanks for that observation.
Jim: I suspect lenticular astigmatism would be one of those higher order aberrations.
Another way to write that prescription is -0.375 sph +0.75 cyl with the axis changed by 90 degrees -- if I did that right.
Ophthalmologists typically write prescriptions with positive cyl numbers, and optometrists typically use negative cyl. What occurs to me, as a weird consequence, is that maybe an Ophthalmologist would not write that prescription for, since it has the sph in eighths and they normally only deal with quarter D as their granularity. This doesn't seem as it should be right. Where is the flaw in my suspicion? There must be a flaw.
RonAKA trilemma
Edited
Ophthalmologists typically do not write prescriptions for eyeglasses. The eyeglass trade uses negative cylinder, so a negative cylinder prescription ensures the optical dispensary does not make a translation error from one convention to the other. Eyeglasses come in 0.25 D steps so all prescriptions I have seen are in 1/4 D steps.
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I agree that some astigmatism can help with near vision, but at a price of sharpness of focus.
Lynda111 RonAKA
Edited
Here in the USA, in my state, ophthalmologists do write eyeglasses prescriptions. Their optical technicians do the refraction, but the ophthalmologist goes over it and signs their name to the refraction numbers the techs have written. It was even done that way at a university medical center in my state.