LAL depth of focus research
Posted , 5 users are following.
I'm reading an old study from Spain in 2014 on depth of focus in the RxSight (then called Calhoun Vision) Light Adjustable Lens LAL. Some things I found interesting:
.
- Either positive or negative spherical aberration adds depth of focus. The researchers used negative asphericity on the ground that it performs better with anticipated small myopic defocus errors.
- The authors suggest that it is the adjustment for asphericity that causes the LAL to shift toward myopia, rather than the other way around (I had previously thought that adding myopia caused the asphericity as a by-product). It probably doesn't matter either way.
- In the study, the amount of induced myopia (in D) was positively correlated with the amount of spherical aberration (in microns), though less than directly proportional.
- Asphericity was introduced in the second LAL adjustment, not the first. I've seen some statements suggesting the EDOF adjustment must be the first one. That could still be true, if the adjustment parameters have changed over time, or if the Spanish research utilized different/special adjustment capabilities.
- They looked at two different levels of induced spherical aberration. The higher level was associated with nearly -2 D of shift toward myopia on average (near eye only), and showed impressive results for depth of focus.
- The higher-myopia group averaged 20/30 monocular vision or better from about 11 inches to infinity, in the near eye. Binocular vision was better, including about 20/17 acuity at infinity.
- The lower-myopia group averaged 20/30 or better monocular vision from about 15 inches to infinity.
- Monocular acuity for the near eye seemed to top out at about 20/20, maybe a little worse than 20/20 for the higher-myopia group. So it appears there is some tradeoff of peak acuity for the extended depth of focus, as would be expected. The tradeoff seems satisfactory for someone like me who wants to not wear eyeglasses 99.99% of the time.
- The researchers did not measure contrast sensitivity.
.
So far, I am still feeling good about choosing the LAL for my near eye.
1 like, 9 replies
RonAKA phil09
Edited
I find the most useful data that I have seen on spherical aberration and depth of focus is a graph from B+L on the enVista lens. See graph below. the red dot is where I would estimate the Eyhance comes in.
.
.
My thoughts are that only positive spherical aberration of the whole eye considering aberration in the lens and cornea is useful. More positive aberration cause more light to focus closer for better near vision -- at a cost of visual acuity of course because the image is being smeared. However total negative aberration would seem to cause light to focus beyond infinity which is not useful at all.
phil09 RonAKA
Posted
"...total negative aberration would seem to cause light to focus beyond infinity ..."
.
This experiment added negative aberration to the near vision eye and not to the plano eye, so I don't think any light would be lost to infinity. Maybe the sign (positive or negative) of the induced spherical aberration determines the direction of DOF extension? That is, acuity would be improved either beyond the primary focal point or nearer than the primary focal point, with negative or positive asphericity, respectively. Not sure about that, I really have not yet wrapped my head around the whole concept...
RonAKA phil09
Edited
My understanding of it all is very basic. The average cornea has +0.27 um of spherical aberration, but individuals may vary. If you put -0.27 um of aberration in the IOL then you can theoretically correct all aberration to zero, if you have an average cornea.
.
So it is probably only when the IOL peak visual acuity point is set to distance (infinity) that adding more than -0.27 um negativity direct light to beyond infinity or is essentially lost. And, if is done in the near eye then it could increase visual acuity to the distance side of the peak, but at the cost of a loss to the nearer vision side of the peak. There is no free lunch...
jimluck phil09
Edited
My doc said EDOF would be added in the last adjustment and locked . No do-overs on the EDOF .
phil09 jimluck
Posted
Added for both eyes? That's interesting, I have not heard that approach before. I'd want to understand whether the EDOF adjustment is independent of any sphere change.
.
My doctor (optometrist) who does the adjustments knows nothing about any EDOF effects. This surprised me, since the surgeon and technician who worked with me both were well aware.
jimluck phil09
Edited
Don't know whether EDOF is added to both eyes when both have LAL . I assume so. I am only considering LAL for my left The right needs more cyl than LAL can do .
susan03345 jimluck
Edited
I've been hearing about the LAL + having EDOF but it is very new. I'm having trouble finding real patient results. I know of a woman on a cataract surgery support group on Facebook who just had it implanted in her second eye today. I am interested in how her journey turns out.
RonAKA susan03345
Posted
Unfortunately it seems that the outcomes of the LAL and LAL+ with respect to EDOF is all anecdotal. It will be interesting to see if they ever produce a peer reviewed clinical study to back up their claims about EDOF.