Prescription leeway for monofocal iols and laser adjustment

Eye care
1

After my cataract op last October my left eye has come out: Sphere: +0.5, Cylinder -0.75 x 10.  I am wondering whether a laser adjustment could reduce the prescription to 0 or -0.5, and whether it could also cure the astigmatism.  But first need to know the margin of error to see whether such an adjustment might take the prescription down further.  I think the surgeon and the optician both consider I am chasing perfection and that the adjustment would be best made by glasses - and I don't mind wearing them !

NB My original prescription was -15 sphere, and I think this may affect the degree of accuracy or a laser adjustment.

2

Based on my excellent experience with LASIK on both of my eyes with similar required changes in prescription, I would say that you should definitely have the LASIK enhancement. If you need glasses to get the vision you want, you are not chasing perfection, you are just trying to get the vision you should have had.

i would try to use an experienced LASIK surgeon who uses the latest equipment, including using a laser to make the flap in the cornea. Every LASIK surgeon may not have that. Also, most of the better LASIK surgeons offer free consulation. So, you should definitely take advantage of it. Also, the better LASIK surgeons do a second minor enhancement, if needed, free of charge, if the first one does not meet the desired goal

The fact that your original prescription was -15 sphere should not have any impact on the feasibility of having LASIK since most of that correction has been taken care of by the new monofocal lens. In other words, the LASIK is not trying to modify your cornea to make a change of 15 D, it is just trying to make a small change.

You can expect to have the astigmatism corrected to 0 or 0.25 as a result of the LASIK treatment. Should also probably aim to end up with the spherical correction in the -0.25 to 0 range. Any amount of farsightedness (a positive needed spherical correction), as you have now, does not serve any useful purpose: it just reduces the distance range in which you have good vision.

3

The surgeon originally offered near, mid or distance vision, but said he didn't recommend mid as he said I would still need to wear glasses for near and distance. I opted for distance, as I didn't think near or mid would necessarily be the right distance for: reading, smartphone, laptop or conducting and playing music (arms length).  When I saw the surgeon after the op he said I shouldn't need glasses for distance when my right eye has been done.  He didn't recommend laser as he said it might reduce the prescription too much, then I would be back again for a further adjustment.

Testing my left eye, it seems good for driving, but I noticed the astigmatism when being tested at the opticians.

The cataract was done under the UK NHS, and I am not certain whether the NHS would cover a laser adjustment, although there is a laser clinic at the hospital and I could pay privately.  I would prefer to have any laser adjustment done by the surgeon's team at the hospital, as my cornea is thin due to high myopia.  I wouldn't risk a high street laser clinic.  

I have a follow-up appointment with the surgeon early next month.

Perhaps I should mention the left eye has come out over-corrected, (although the cylinder minus prescription presumably compensates)? and ask what adjustment could be done. Last time he said a laser adjustment might take the prescription too low, then I would be back for a further adjustment, and so he didn't recommend it. I am not sure I really need full distance correction - or maybe only for night driving.

4

If the right eye is still to be operated on, then it is better to wait to see what that comes out to be before you do any LASIk enhancement to the left eye.

The best step forward at that time will depend on where your vision ends up for the right eye. For example, If it comes out perfect for distance, then the best adjustment for the left eye may be to make it good for mid distance. However, no use doing detailed planning for that right now.

My recommendation for getting LASIK done to better vision in the eye assumed that doing that is not a financial burden on you. If the finances are a factor, then you are in the best position to make the appropriate choice.

5

Thank you.  I could afford the financial cost of a LASIK adjustment - but the first decision is what prescription to request for the right eye. (Basically for distance to balance the left eye, but whether to request -0.5, bearing in mind that if it actually comes out at -1, would that be too weak for night driving, reading train station indicator boards etc)?  If so, requesting 0 would be safer.

 

6

It seems like we have had a discussion on this topic before.

Any way, my suggestion at this time will be to aim for the best distance vision for the right eye at this time (0 to -0.25 spherical correction and no astigmatism) without worrying about balancing the left eye. Just use the glasses shot-term, as needed. After you know exactly where you end up with the right eye, then it will be a better time to make the decisions about the next steps for both eyes, if needed

7

Usually insurance or government plans don't cover laser correction since they feel its an elective since someone can wear glasses/contacts.  Unfortunately there aren't many   studies on the results of small laser corrections, most are on the sort of large corrections people usually come for when younger.

The results vary with the laser, ideally you'd hunt for the one with the latest. I just watched a short video on Eyetube which you can find by googling:

Robert Maloney, MD Wavefront versus topography-guided LASIK 

which reports on the results of the Alcon Contoura system and others: "Sherman W. Reeves, MD, MPH, identifies topography-guided ablation as the next big thing in refractive surgery. The main reason for his selection, he says, is because topography uses 22,000 data points to measure the cornea, including the peripheral cornea. In comparison, at most 1,000 data points from only the central cornea are taken during wavefront. In his talk, Dr. Reeves also reviews results of the FDA clinical trials on the three topography-guided platforms available in the United States."

It doesn't say how close they came to hitting the target, its talking about those targeting 0D, but they only give the acuity results rather than how close they were to the target. These are results for the typical sorts of corrections (not just small tweaks) shown in one chart for the Alcon Contoura:

93% 20/20 or better, 65% 20/16 or better, 34% 20/12.5 or better, 16% 20/10 or better.

 

Another page indicates:

"Contoura has produced the best results of any laser we have used or any study in which we have participated. The FDA results found nearly 69 percent of patients achieved uncorrected vision of 20/16 or better.1 Additionally, at 12 months, slightly over 31 percent of patients gained one line of uncorrected vision over their previous best corrected vision."

  i.e. with 31% their vision after the laser treatment showed better vision without correction than they had with correction beforehand.  Another article notes for one laser:

"Table 24 below shows that nearly one-third of the eyes treated for myopia with Topoguided (T-CAT) LASIK (78/247, 31.6%) achieved a distance UCVA of 20/12.5 or better, and over two-thirds of the eyes (170/247; 68.8%) were seeing 20/16 or better without correction at 3 months postoperatively. Furthermore, a total of 92.7% of the Topo-guided (T-CAT) LASIK eyes had a UCVA of 20/20 or better at 3 and 12 months postoperatively, with slight shifts toward continuing improvement in the proportion of these eyes that attained UCVA of 20/16, 20/12.5, and 20/10 through 12 months after Topo-guided (TCAT) LASIK."

 I just saw data from the Wavelight system showing that even with large tweaks, 95% were within +-0.5D. That had a little bit of data for small tweaks. For  those seeking correction of  to 0 with preop spherical equivalents from   0 to -1, 100% hit within +-0.5D (though I think it was only 8 patients seeking that small a tweak), and   those from -1.01 to -2.0, 97.3% were within +-0.5D (though also a fairly small number of patients). That was for myopic correction, I don't know if the stats are the same going the other direction, and that was just one study of one laser.

 

8

FYI,I should add that that was just an example, it depends on the patient and IOL whether wavefront or topographic is the better way to go.

 

9

Agree that the choice of wavefront versus topographic depends on the patient. My understanding is that topographic is better if most of the needed correction is in the cornea, specially if  there is some irregular astigmatism due to imperfect cornea. However, unlike wavefront LASIK, it does not compensate for other sources of astigatism (such as in the lens). Thus, for example, if one has a toric IOL lens, which does not have the right power or has rotated from the desired position, then wavefront LASIK will be a better choice.

10

A basic question is: can a cataract op with a monofocal iol inserted cure a small amount of astigmatism?    Or does it only address the spherical correction ?

11

re: "if one has a toric IOL lens"

I seemed to recall that this poster didn't have a toric lens, just a regular monofocal.  I've seen comments in the past about wavefront technology not always working right with diffractive IOLs, though I don't know the current status of it since perhaps that has been fixed, and whether that differs for the Symfony or if its just multifocals.

I just ran into one article from 2010 (so results now with improved technology and software should be better) on laser correction after cataract surgery:

"In a study of 85 eyes of 59 patients who underwent LASIK to correct residual refractive errors after implantation of an apodized diffractive multifocal IOL (AcrySof Restor, Alcon Laboratories, Inc., Fort Worth, Texas) at University of Texas Southwestern Medical Center at Dallas, we found excellent refractive results; 99% of eyes were within ±1.00 D, and 96% of eyes within ±0.50 D of emmetropia at last follow-up. The predictability of astigmatic correction was good, with 98% of eyes within ±1.00 D of cylinder. Overall, these patients had good concurrent uncorrected distance and near visual acuity, with 86% of eyes having distance UCVA of 20/25 or better and near UCVA of J1 or better concurrently.5"

12

I assume you are talking about a regular spherical monofocal, there are also toric monofocal IOLs that correct for astigmatism via the IOL itself.

Incisions can be used to reduce astigmatism, they cause the eye to reshape itself. They are usually called LRIs (limbal relaxing incisions) though they sometimes use incisions on other parts of the eye. Its not an exact process since each eye heals differently, but they have statistics from past patients that let them make a good estimate. 

They need to make incisions to remove the natural lens and insert the IOL. A few decades ago those used to be fairly large incisions which caused "surgically induced astigmatism" themselves. Now the incisions are very tiny "microincisions" since they use lenses that are folded up to fit through smaller openings so there isn't much impact on astigmatism. However  good surgeons try to plan even those incisions if possible to try to counteract any existing astigmatism, rather than add to it. So in the case of a tiny amount of astigmatism, the surgery itself might correct it even without a seperate LRI or other incision meant purely to correct astigmatism.

Unfortunately  insurers and government plans usually only pay for basic treatment of a cataract, considering any astigmatism correction to be optional since someone can always wear glasses/contacts. So if any extra incisions are done purely to correct astigmatism, it might be an out of pocket expense, though likely low cost even in the US (and its possible some surgeons might just throw it in without charge, I hadn't checked, I just know I'd heard of at least some that charge, I don't know if any don't).

 

13

A cataract surgery with a monofocal will modify the astigmatism (amount and axis) slightly, but the change is unpredicatable. That is, your astigmatism may be slightly worse or slightly better.

My wife's experience with Limbal Relaxing Incision was not positive. Even though her astigmatism was small to start with, it did not go away.

So, my suggestion will be to not pay anything  extra to reduce astigmatism at the time of the cataract surgery (unless your astigmatism is high enough to require toric lens). After your vision settles down following cataract surgery, then you will know the amount of the spherical and cylinderical correction which you may need. You can then decide on whether to have LASIK to correct  it or just use glasses, when needed.

14

The astigmatism in my right eye is low - it is in the range 0.25 - 0.75 axis 25 or 172, 6/6+ (taken from two different optician apointments).

I will see the surgeon for a consultation next month.  Requesting 0 to -0.25 spherical correction, and no astigmatism, for the right eye seems a safe idea.  

On the one hand, I would prefer not to be over-corrected for distance (as that would have no advantages) but on the other I am concerned that an outcome of, say, -1 might feel rather too myopic, which one would then regret !  

He did offer to set the right eye for close vision, but that didn't seem a good idea, as a) I might not get used to it, and b) it wouldn't cover all the mid distance activities including reading music about an arms length laptop, shopping, general indoor activities etc., c) there might be halos or fringes around headlamps and signposts when night-driving.

15

If that is your eye with the natural lens, you can't tell how much astigmatism needst to be corrected from just the prescription, a refraction. It needs to be determined by a scan, since part of the astigmatism may be in the natural lens, which goes away during surger, while the rest is in the cornea. Perhaps that is what you were referring to in your first post in this thread, that the actual operation might reduce astigmatism if the astigmatism is in the natural lens.

Cataracts can sometimes cause astigmatism in the natural lens, so if your astigmatism was lower in the past that would be a good indication the astigmatism is from the cataract.

Both of my eyes had much less corneal astigmatism shown in a scan than they had in the refraction. One of those had a problem cataract, but the other only had barely a noticeable one, it was 20/20, but still had a lot of the astigamtism in the lens. 

If that is the amount of astigmatism, its in the range that they recommend correcting since its > 0.5D e.g. search:

"pablo artal" "What is the minimum amount of astigmatism that has to be corrected?"

 

16

I am seeing the surgeon in a couple of weeks:  I will request 0 to -0.25 spherical correction in the right eye and discuss with him if aiming at 0 cylinder is feasible.  (The current cylinder is 0.75 x 172 6/6+).  If an astigmatism correction is not available on the UK NHS it is probably worth paying the extra cost.    I did wonder whether I should have requested near vision in both eyes as most of my work is at close range and I was previously very myopic, but I think monovision iols would still have been very fixed focus, and so (eg) only set (at a distance decided by the surgeon), probably for reading, and not other activities such as playing the piano or organ(armslength), laptop, teaching, shopping, reading the car satnav etc.  

So I would have been just as dependent on progressive glasses or mini-monovision glasses as I am/will be with the iols set on distance ?  

17

I am seeing the surgeon in a couple of weeks:  I plan to request 0 to -0.25 spherical correction in the right eye, so as to be able to see distance without glasses, and to balance with my left eye (currently +0.5 sphere, -0.25 - 0.75 cylinder) but without the risk of being over-corrected as in the left eye, and will  discuss with him if aiming at 0 cylinder is feasible.  (The current cylinder is 0.75 x 172 6/6+).  If an astigmatism correction is not available on the UK NHS it is probably worth paying the extra cost.    

However, I still wonder if I should have requested near vision for both eyes, to make reading, using the smartphone and laptop, and playing the organ (armslength) easier, or would I still have had as limited a range of focus as with distance iols + glasses for near and intermediate ?

18

Best wishes for a successful surgery.

19

Just spotted a typo - last sentence should have read: So would I have been just as dependent on progressive glasses or mini-monovision glasses as I am/will be with the iols set on distance ?  

20

Would there be a problem with using my post cataract operation non dominant left eye for full distance, and my dominant right eye, still -15 on 60cm distance using a contact lens, or should they be set up the other way round? I also need to drive with a right hand drive car (UK)

I can have a cataract operation in my right eye but not essential as the cataract isn't very advanced at the moment.