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LAL - Final Adjustments

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phil09
phil09

I got the second adjustment this week on my new RxSight Light Adjustable Lens. Here's a report for anyone who may find it useful, or anyone who cares to offer advice or opinions.

  1. Before the second adjustment, refraction was -1.75 D sphere, -1.00 D cylinder.
  2. Vision was tested by the optometrist at 20/70 and J1+ for far and near respectively.
  3. Target refraction for the first adjustment 10 days prior was -1.50 D/0.00 D. So, the adjustment was pretty accurate on sphere, but way off - actually nothing - on cylinder. The optometrist was suprised by this and speculated that because of the large amount of myopia added in the first adjustment, the machine was unable to do any cylinder adjustment last time. (In the first adjustment, she had targed a myopia increase of 2.00 D and the actual myopia increase was measured at 2.25 D, from the pre-adjustment result of +0.50 D hyperopia).

2 likes, 22 replies

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  • phil09
    phil09

    Edited

    1. I suspect the optometrist is correct in her speculation about the reason I got no improvement in astigmatism with the first adjustment. I have heard the LAL process can only handle about 2 D of adjustment in any one session. However, I had asked about this at the time, and she told me the ~3 D adjustment (sph plus cyl) should be no problem. I found this kind of shocking. I would expect the optometrist to know this after hundreds of LAL adjustments, and I would also expect the machine/software/computer to provide immediate feedback.
  • phil09
    phil09

    Posted

    1. Based on my new refraction, the optometrist offered three options:

      a. target -2.25 sph/0.00 cyl in the second adjustment, to correct the astigmatism and maintain my highly satisfactory near vision

      b. target -1.75 sph/0.00 cyl in the second adjustment, correcting astigmatism only

      c. do nothing for now, come back in a week and get another measurement before deciding on next adjustment

    2. I chose option b. My thinking was to keep it simple because I now have reduced confidence in the adjustment process with this optometrist, and also to proceed with caution and avoid wasting my remaining adjustment diopters too early.
    3. I think the second adjustment did correct my remaining astigmatism partially but not completely. My home testing suggests -0.25 to -0.50 cylinder still remains. I figure I am now at about 20/50 distance vision and still better than J1+ for near. I don't really notice the change in distance vision, since my natural eye is still close to 20/20 and takes care of distance vision. I do notice my near vision is a bit worse since the second adjustment, but still excellent, I think, for a cataract patient. My intermediate (computer) distance vision is also improved with the second adjustment.
    4. My optometrist says LAL adjustments need to be for a minimum of 0.50 D. Minimum applies to both sphere and cylinder, I think. So for my third and final adjustment, she would not be able to combine a +0.50 D cylinder adjustment (to cure remaining astigmatism) with a -0.25 D sphere adjustment (to offset the astigmatism correction with spherical equivalent myopia). The -0.25 D is too small, and might be ignored by the light adjustment machine.
    5. So, I'm not sure what I will request for my final adjustment. Depending on the refraction next week, options may include:

      a. Target a final outcome of -2.25 D sphere, 0.00 D cylinder (this would be a change of about 0.5 D for both sphere and cylinder from my current state), or

      b. Just lock it in right here.

      Being a perfectionist, I would prefer to correct the astigmatism completely, but on the other hand I am quite pleased with my current LAL vision - near, intermediate and far. Also, there is some risk in trying to squeeze the last few drops of improvement out of an imperfect adjustment process. And I may not even have enough remaining astigmatism to meet the 0.50 D correction threshold (without targeting an over-correction).

    • RonAKA
      RonAKA phil09

      Posted

      The issue is that you were at -2.25 D SE before this adjustment, and the target is was to bring this to -1.75 D SE. This would be a noticeable loss in near vision. I think I would have targeted -2.00 D sphere and -0.00 cylinder, as I think you wanted to be up in that range, rather than the more standard -1.50 D in the near eye. Water under the bridge now, but I think I questioned the starting point before adjustment. If the objective was -2.0 D sphere and 0.00 D cylinder, I think I would have started at -1.0 to -1.50 D sphere with the IOL basic power selection. This would have given more adjustment room to deal with the significant cylinder correction. The saving grace may be that I see some actually can squeeze in 4 adjustments instead of the promised 3.

    • phil09
      phil09 RonAKA

      Posted

      "The issue is that you were at -2.25 D SE before this adjustment, and the target is was to bring this to -1.75 D SE. This would be a noticeable loss in near vision. I think I would have targeted -2.00 D sphere and -0.00 cylinder..."

      Yes, the loss of near vision was expected due to the change in SE. I actually requested that exact target: -2.00/0.00. But the optometrist advised that going from my current -1.75 to -2.00 sphere could not be done - the change needs to be at least 0.50 D, up or down.

    • RonAKA
      RonAKA phil09

      Posted

      That is interesting. I thought I read at one point that being able to make less than 0.5 D adjustments was one of the advantages...

      .

      One other thought is the axis of the cylinder. If you under correct cylinder typically the axis stays the same but the diopter amount goes down. If you over correct the cylinder the axis "flips" by about 90 degrees. The diopter amount may go down as well. It may be important to determine if they are under correcting or over correcting cylinder. If over correcting it may turn into a chasing your tail exercise.

      .

      Some believe that flipping the cylinder is not a good thing to do, while I have seen arguments that it does not matter, and the objective should be to minimize the diopter amount and not worry about the axis flipping.

    • phil09
      phil09 RonAKA

      Posted

      The manufacturer's website says: "The LAL corrects down to 0.5 diopters of astigmatism, which is the lowest level approved to be treated." I don't know who is disapproving correction of lower levels of astigmatism, nor why they would want to disapprove. Perhaps this also means that LAL will refuse to do cylinder adjustments smaller than 0.5 D, even when treating astigmatism that was initially greater than 0.50 D. Dunno. Maybe others who have LALs can clarify.

      .

      My doc said 0.5 D is the minimum adjustment for sphere, but I don't see that confirmed anywhere on the internet. 0.5 D is fairly small, but I agree that it would be an advantage for an adjustable lens to allow finer adjustments.

      .

      I can't tell for sure whether my cylinder flipped this week. But I will keep that in mind at my appointment next week. Thanks.

    • RonAKA
      RonAKA phil09

      Posted

      If you plot your before and after cylinder and axis on a polar chart then there will be a vector between the two points that represents the impact of the light adjustment.

    • trilemma
      trilemma RonAKA

      Posted

      If you plot your before and after cylinder and axis on a polar chart then there will be a vector between the two points that represents the impact of the light adjustment.

      Interesting idea. Food for thought. I am thinking that plotting each reading twice might be better -- one at the reciprocal axis... so if 90 degrees for a point, also plot that at 270.

      An obvious case is where one measurement showed a 5 degree axis, and the other showed a 175 degree axis. I am wondering if there would be other cases where the two dots per reading would help.

    • RonAKA
      RonAKA trilemma

      Posted

      Not sure. A point on a polar graph is fully described with a single amplitude and phase angle (axis).

      .

      The interesting one would be for example going from cylinder 1.0 D at 0 deg to 1.0 D at 90 deg. - in other words a full flip. The vector would be well over 1.0 D, but there is potentially no impact on astigmatism visual acuity.

      .

      My only point was that one cannot quantify the impact of the adjustment without considering both magnitude and angle. What looks like nothing, may actually have been a large change.

    • RonAKA
      RonAKA phil09

      Edited

      I re-read some of the articles I had saved on the subject to see if I could figure out where I got the idea that less than 0.5 D adjustments were possible. I found a FDA approval from 2017 that basically said the LAL was approved for adjustments of greater than or equal to 0.75 D cylinder. In the study they used spherical equivalent for measuring effectiveness when prior to surgery cylinder was less than 0.75 D. In this document I found this interesting statement:

      " Eyes implanted with the LAL were targeted to a postoperative MRSE of +0.50 D (to compensate for the expected 0.50 D myopic shift of the required LDD lock-in treatment)"

      P160055: FDA Summary of Safety and Effectiveness Data

      .

      This seems to suggest you have to target on the hyperopic side to allow for the lock in shift. Perhaps that only applies to the early version of the lens. I gather the current one is LAL 2.0.

      .

      I found one other more recent study from 2022 at the link below. It included a significant number of post refractive surgery eyes. This study reports that cylinder was reduced to less than 0.25 D in 80.6% of all eyes in the study that targeted emmetropia. For the post refractive surgery eyes only, it was a little less at 75.0%. It seems to me that it would be hard to hit a target that tight unless one could target changes of less than 0.5 D.

      .

      https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9359783/

    • phil09
      phil09 RonAKA

      Posted

      Thanks, RonAKA. I had not heard of the myopic shift at lock-in. I think/hope you are right that it may no longer apply to the current LAL version 2.0, but I will inquire. I'll also inquire further about the 0.5 D minimum adjustments. I may need to speak with a different doctor to get good answers.

    • trilemma
      trilemma phil09

      Posted

      I'll also inquire further about the 0.5 D minimum adjustments. I may need to speak with a different doctor to get good answers.

      I am confident that no such thing exists.

      I think any such text that leads to that interpretation is text that is saying they don't market the RxLAL for purposes of dealing with astigmatism below a certain magnitude. In earlier lit, the corresponding magnitude was 3/4.

  • phil09
    phil09

    Edited

    It seems item 4 of my report triggered some auto-moderation. I could not find any problem with it, but if I learn more, I will endeavor to post the information in an appropriate way. (Item 4 was manually moderated and is posted now, without any edits as far as I can tell.)

  • trilemma
    trilemma phil09

    Edited

    Vision was tested by the optometrist at 20/70 and J1+ for far and near respectively.

    20/70 is bad.

    Target refraction for the first adjustment 10 days prior was -1.50 D/0.00 D. So, the adjustment was pretty accurate on sphere, but way off - actually nothing - on cylinder.

    I think you are saying that there is a lot of residual astigmatism but there was no change in the astigmatism/cyl. Any reason to not post that number?

    • phil09
      phil09 trilemma

      Posted

      I did post it, above. Cylinder was measured at -1.00 D before the first light treatment, and again at -1.00 D before the second light treatment. No change.

      After the second treatment, I am estimating -0.25 D or maybe a little more. But that's just my own estimate with home lens kit. I'll get a professional measurement in a week or so.

    • phil09
      phil09 trilemma

      Edited

      "20/70 is bad."

      .

      I was very happy with the 20/70. I use monovision, and the LAL eye is my reading eye. LAL is a monofocal lens, so it cannot excel at both near and far distances. With spherical equivalent of -2.25 D, I expected distance vision would be about 20/200, so 20/70 was a pleasant surprise.

      .

      My astigmatism was subsequently partly/mostly corrected in my second light adjustment, and I estimate that I am now closer to 20/50. My reading vision is still better than J1+.

    • trilemma
      trilemma phil09

      Edited

      Good to hear. To turn around an old saying, don't let the very good be the enemy of the excellent.

      My point is to avoid your joy from preventing you from tweaking to more nearly perfect.

    • phil09
      phil09 trilemma

      Posted

      Agreed. I think I have a very good result already, but if I see any opportunity to improve further next week, I will take it. Thanks

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