This all started in the Refractors forum (https://www.cloudyni...s/#entry9463348). I wanted to comment, but didn't want to hijack poor starcruiser's thread, so here's a new post.
Copied from TOMDEY's posts:
Hi, starcruiser; Great question and ostensible concern!
We DO have significant, traditional Longitudinal Chromatic Aberration. My recollection is that it's about 1/6 Diopter, "undercorrected".
OK... OK... I just computed it from 1st principles, assuming that the human eye has a 1-inch focal length and is made of water and I get 0.29 Diopter (@450-650nm)... reasonably in the ballpark of my recollection... especially considering that there is more stuff in there and different dimensions. Optometrists generally refract eyes to about a quarter of a diopter accuracy... but a really scrupulous patient (like me) can discriminate differences of about a tenth of a diopter. So, the chromatic of our eye is just enough to be pretty annoying... depending on how picky you are.
Our eyes also have traditional (Seidel lateral cubic) Spherical Aberration. And that is quite substantial for dilated pupil. Lens Implants and/or Lasik/PRK actually correct the ~natural~ spherical aberration of the human eye! I had those surgeries done and actually do enjoy the hyper-acuity consequent of those improvements. 20/12.5 each and both eyes... even with dilated pupils. And that makes it really nice for enjoying things like star clusters. I just don't need as much magnification as my companions, to see all the detail. Worth considering, as an additional motivation to get one's eyes done. I've commented before that when I look out at the yard (post improvements)... that every blade of grass, tree twig, etc. looks razor sharp. I'm not kidding --- the improvement is that dramatic! Tom
Hi, Kerry! Ophthalmologist Surgeons now offer ~True Astronomical Infinity~ correction, both eyes, dark-adapted open pupils, rather than the usual default of closer in, constricted pupils, not quite able to focus out to the stars. Our local guy here, at the teaching hospital, includes that option right in his marketing literature! Keep in mind that you entirely lose focus accommodation when your old cloudy yellow bio-lenses are replaced with pristine clear prosthetics. The implants also correct your astigmatism and even the ~natural~ spherical aberration of the human eye! Your vision will become laser sharp day and night true infinity. If there is any small (typically tiny) residual focus and/or astig remaining... PRK and/or very mild "no line" glasses will take care of that. My final correction, after the surgeries and settling-in time... came out perfect 20/12.5 Dark Adapted in one eye and the other also measures 20/12.5, but has tiny remaining astigmatism... tiny. So the stars look like miniscule bright dots.
I have progressive eyeglass lenses so I can read thru the bottoms and see infinity through the tops... plus that little astig correction on one side. With the glasses off, I can't read! Getting one eye far and one close is a pretty debilitating compromise. Even worse are surgeries that focus near with one zone of the lens and far with the other --- so you can resolve both but never again see anything very well focused! My surgeon strongly suggests against those... will only do that if the patient demands them and signs off on vision quality.
Regarding congenital/progressive nature of eye lens degradation. We all have a combination. The congenital component, you can be lucky or unfortunate, but never immune... we all have human genes; progressive, we all suffer that too. A lot of sun can accelerate the degradation, but it's as inexorable as wrinkly skin. And... just like wrinkly skin... gets quite noticeable around age thirty-five. That from my optometrist... he said he looks in there and can tell a person's age quite accurately... the eyes' interior don't lie! He then commented that people would opt for the surgeries at 35, if cost were no object; I got mine done at 65 and WOW! But, optometrists are not going to tell you that unless you press the issue. Just like your Primary Care doctor won't tell you that your skin is getting wrinkly. And friends won't tell a 35-year-old that she looks 35... they'll politely "guess" twenty.
Most of us (even astronomers) are very tomophobic... throwback to mom cautioning, "Don't poke your eye out!" That puts us in a state of denial, "Oh, my eyes are still perfect... Ehhh... perfect!" Yeah... and I'm 35, going on 72!
Results may vary.
I can second TOMDEY's comments about Lasik. I had Lasik before I was thirty (the date excapes me). Unfortunately, sometime in my 40s I "outgrew" Lasik (OK, my eyes continued to evolve and my prescription changed) and my astigmatism came back. I approached the ophthalmologist who performed my Lasik something like sixteen years previously about doing it again. He didn't recommend two Lasik procedures, the second attempt doesn't heal properly in something like 1 out of 5 procedures. Those odds were too poor for me. He then did an LRI (limbal relaxing incision), a single cut in the cornea, similar to radial keratotomy. I enjoyed super-human clarity like TOMDEY describes for about three days. Then my cornea healed and scarred and I went back to what I had prior to the LRI. Too bad for me. My ophthalmologist says I need PRK (kind of like Lasik without the "flap"), but with a laser that isn't FDA approved yet. So I either wait, or I take a trip to his clinic in Monterrey, Mexico. Sigh.
Edited by macdonjh, 28 June 2019 - 12:44 PM.