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Why is my distance prescription stronger after cataract surgery?
I’d gradually been developing bilateral cataracts for several years. In Sept. 2014, I was refracted (progressives) as Sphere -.25 right and -1 left, with a reading correction of +2.50. (couldn’t use drugstore readers due to astigmatism). My cataracts were ripening then but not yet causing problems. Then in 2015 I started having poor contrast vision (people & things looked silhouetted when backlit such as through a window) and by June 2016 I had trouble seeing unlit roads at night without my brights on, and needed both a flashlight and magnifying glass to read small print on menus, especially on tinted paper and in dim light. Push came to shove when during a refraction (due to misplacing my glasses), the optometrist not only couldn’t correct my reading beyond 2.50, she couldn’t even visualize my fundi through the cataracts (but I still needed glasses anyway, unfortunately, I don’t have access to that interim Rx). So after that I went to my opthalmologist, and we decided that to avoid glare (and because Medicare is stingy) I would get monovision lenses implanted to correct for distance. Had first the R done in mid-Sept. and then L done in early Nov.; finally got re-refracted a month after the L surgery, just before Thanksgiving. That new prescription is -.75 R and -1.50 L, with reading correction unchanged (+2.50). Only my astigmatism correction (cylinder & access) is stronger on the new prescription.
What gives? I thought that depending on which monovision lens was implanted, it would result in either greatly improved distance or reading acuity—instead, according to my 2014 and post-op 2016 prescriptions, I am now more nearsighted and just as presbyopic. What’s even more confusing is that I perceive improved acuity with & w/o glasses, distance & reading—the DMV removed the “corrective lenses” restriction from my license (though I feel I do see better with my glasses on, especially at night; and because of little-to-no astigmatism now, I can even get by with 1.50 readers or no glasses at all in bright light) compared to my pre-op vision with glasses. Can it be that my distance acuity had significantly worsened between Sept. 2014 and June 2016? Or did my ophtho. (who did my latest refraction) decide to correct me more sharply than before, because my clear new lenses make that possible when the cataracts couldn't? (i.e., was my distance vision previously under-corrected)? If I could dig up my June 2016 prescription, would that explain it, or is something else at play here?
What gives? I thought that depending on which monovision lens was implanted, it would result in either greatly improved distance or reading acuity—instead, according to my 2014 and post-op 2016 prescriptions, I am now more nearsighted and just as presbyopic. What’s even more confusing is that I perceive improved acuity with & w/o glasses, distance & reading—the DMV removed the “corrective lenses” restriction from my license (though I feel I do see better with my glasses on, especially at night; and because of little-to-no astigmatism now, I can even get by with 1.50 readers or no glasses at all in bright light) compared to my pre-op vision with glasses. Can it be that my distance acuity had significantly worsened between Sept. 2014 and June 2016? Or did my ophtho. (who did my latest refraction) decide to correct me more sharply than before, because my clear new lenses make that possible when the cataracts couldn't? (i.e., was my distance vision previously under-corrected)? If I could dig up my June 2016 prescription, would that explain it, or is something else at play here?
The main issue seems to be that your astigmatism wasn't addressed during surgery, though they could deal with it now.
Your post seems to imply that perhaps you expected the cataract surgery to not alter your refraction, or hopefully to at least improve on it if it changed. One thing you might not realize is that the sphere correction before cataract surgery has no bearing on the correction after cataract surgery (other than that those with high prescriptions are more at risk of the lens power choice being inaccurate). They replaced your natural lens with some unknown lens power X with a new lens whose power they needed to take an educated guess at. If you had perfect vision beforehand, they are trying to guess at a power thats essentially comparable to the natural lens you had that will give you the same vision afterwards. If your natural lens power gave you poor vision, they try to chose a lens power that will make it better.
The refractive error afterwards depends on how good a guess they made at the lens power. Although on the surface it looks like yours is off a bit, as I'll get to later, it may actually be a fairly accurate result. The IOL power should be on a card they gave you. Its likely somewhere around 21D or so given your eyes were likely fairly close to using an average power. The problem is there is no way to determine the exact lens power needed, they use a formula based on statistics about eye measurements and lens powers for past patients to take an educated guess. Usually the results are fairly accurate for those with low prescriptions like you had, but not always, some people's eyes just don't match the statistics as well as others. If the lens power is off by 1D for instance, then it is a smaller prescription than someone who had a large one before surgery, but might be a larger prescription for someone who didn't need much correction before surgery.
You mention that they gave you "monovision lenses", by which I assume you meant monofocal lenses, i.e. lenses that focus at only one distance (unlike a multifocal). However since you use the term "monovision", although you the lenses were meant to "correct for distance", I'm wondering if they talked about doing monovision for you. Perhaps they intended to correct at least one eye for "monovision" which is making it a little bit myopic to give you some reading vision. So Its possible they targeted distance, aiming for 0D, but its also possible they targeted at least one eye to be slightly myopic. I've seen some surgeons comment on targeting even the distance eye for -.025 rather than 0D to reduce the risk that if there is an error, that the eye will be hyperopic (since that reduces near vision, while not providing any benefit in exchange). An error of -0.25D tends to not reduce distance vision much, though it depends on the person how much (I have at least 20/15 vision in an eye with -0.25D sphere, -0.25D cylinder).
Unless they explicitly tried to correct astigmatism, usually that will remain after surgery. They can either correct it via toric IOLs that correct astigmatism, or via using an incision that causes the eye to reshape to reduce astigmatism, or a combination of the two methods. The incisions used to replace the lens also cause the eye to reshape, they call it "surgically induced astigmatism". Where they locate the incisions, and how large they are impacts whether the astigmatism is in the same direction as your current astigmatism and makes it worse, or if its opposite it and makes it better . These days the incisions are small enough its not much of a factor if they don't wish it to be, but good surgeons try to plan the incisions so they cause the existing astigmatism to be reduced, rather than adding to it. It looks like your surgeon managed to at least reduce your astigmatism a bit.
Before surgery you were on average slightly hyperopic in one eye and myopic in the other. Astigmatism means that the lens power in one direction is different than in another, and the cylinder power is the difference between the two. So prior to surgery the power OD went from -0.25 in one direction to (-0.25 + 1.75)=1.5D in the other direction. That means the average power was (-0.25+1.5D)/2 = +0.625D . For OS it was from -1D to (-1 + 1.5) = 0.5D for an average power of (-1 + 0.5) / 2 = -0.25D. The average power, the spherical equivalent, can be calculated directly as sphere +cylinder/2.
Unfortunately astigmatism reduces visual clarity overall, though it can also extend the visual range a bit over the range the eye's power varies.
After surgery your spherical equivalent is myopic in both eyes: OD=-0.25D, OS= -1D, with the astigmatism unfortunately reducing clarity. They can usually use an incision after cataract surgery to correct astigmatism, which doesn't change the spherical equivalent. (though a surgeon would need to be sure this would work for you, that there isn't something atypical about your situation). Its a minor procedure some surgeons do at a slit lamp since it is only on the surface of the eye and doesn't require entering the eye like cataract surgery does. If they corrected the astigmatism via incision, those spherical equivalents would give you fairly good distance vision in the -0.25D eye, with the other eye giving you a bit better intermediate or some farther out near. Unfortunately the correction of astigmatism via incision is something that relies on statistics also, since not every eye reshapes the same in response to an incision, but it'd likely make a difference. That would leave you needing readers for near, but perhaps having decent distance&intermediate without correction.
Your post seems to imply that perhaps you expected the cataract surgery to not alter your refraction, or hopefully to at least improve on it if it changed. One thing you might not realize is that the sphere correction before cataract surgery has no bearing on the correction after cataract surgery (other than that those with high prescriptions are more at risk of the lens power choice being inaccurate). They replaced your natural lens with some unknown lens power X with a new lens whose power they needed to take an educated guess at. If you had perfect vision beforehand, they are trying to guess at a power thats essentially comparable to the natural lens you had that will give you the same vision afterwards. If your natural lens power gave you poor vision, they try to chose a lens power that will make it better.
The refractive error afterwards depends on how good a guess they made at the lens power. Although on the surface it looks like yours is off a bit, as I'll get to later, it may actually be a fairly accurate result. The IOL power should be on a card they gave you. Its likely somewhere around 21D or so given your eyes were likely fairly close to using an average power. The problem is there is no way to determine the exact lens power needed, they use a formula based on statistics about eye measurements and lens powers for past patients to take an educated guess. Usually the results are fairly accurate for those with low prescriptions like you had, but not always, some people's eyes just don't match the statistics as well as others. If the lens power is off by 1D for instance, then it is a smaller prescription than someone who had a large one before surgery, but might be a larger prescription for someone who didn't need much correction before surgery.
You mention that they gave you "monovision lenses", by which I assume you meant monofocal lenses, i.e. lenses that focus at only one distance (unlike a multifocal). However since you use the term "monovision", although you the lenses were meant to "correct for distance", I'm wondering if they talked about doing monovision for you. Perhaps they intended to correct at least one eye for "monovision" which is making it a little bit myopic to give you some reading vision. So Its possible they targeted distance, aiming for 0D, but its also possible they targeted at least one eye to be slightly myopic. I've seen some surgeons comment on targeting even the distance eye for -.025 rather than 0D to reduce the risk that if there is an error, that the eye will be hyperopic (since that reduces near vision, while not providing any benefit in exchange). An error of -0.25D tends to not reduce distance vision much, though it depends on the person how much (I have at least 20/15 vision in an eye with -0.25D sphere, -0.25D cylinder).
Unless they explicitly tried to correct astigmatism, usually that will remain after surgery. They can either correct it via toric IOLs that correct astigmatism, or via using an incision that causes the eye to reshape to reduce astigmatism, or a combination of the two methods. The incisions used to replace the lens also cause the eye to reshape, they call it "surgically induced astigmatism". Where they locate the incisions, and how large they are impacts whether the astigmatism is in the same direction as your current astigmatism and makes it worse, or if its opposite it and makes it better . These days the incisions are small enough its not much of a factor if they don't wish it to be, but good surgeons try to plan the incisions so they cause the existing astigmatism to be reduced, rather than adding to it. It looks like your surgeon managed to at least reduce your astigmatism a bit.
Before surgery you were on average slightly hyperopic in one eye and myopic in the other. Astigmatism means that the lens power in one direction is different than in another, and the cylinder power is the difference between the two. So prior to surgery the power OD went from -0.25 in one direction to (-0.25 + 1.75)=1.5D in the other direction. That means the average power was (-0.25+1.5D)/2 = +0.625D . For OS it was from -1D to (-1 + 1.5) = 0.5D for an average power of (-1 + 0.5) / 2 = -0.25D. The average power, the spherical equivalent, can be calculated directly as sphere +cylinder/2.
Unfortunately astigmatism reduces visual clarity overall, though it can also extend the visual range a bit over the range the eye's power varies.
After surgery your spherical equivalent is myopic in both eyes: OD=-0.25D, OS= -1D, with the astigmatism unfortunately reducing clarity. They can usually use an incision after cataract surgery to correct astigmatism, which doesn't change the spherical equivalent. (though a surgeon would need to be sure this would work for you, that there isn't something atypical about your situation). Its a minor procedure some surgeons do at a slit lamp since it is only on the surface of the eye and doesn't require entering the eye like cataract surgery does. If they corrected the astigmatism via incision, those spherical equivalents would give you fairly good distance vision in the -0.25D eye, with the other eye giving you a bit better intermediate or some farther out near. Unfortunately the correction of astigmatism via incision is something that relies on statistics also, since not every eye reshapes the same in response to an incision, but it'd likely make a difference. That would leave you needing readers for near, but perhaps having decent distance&intermediate without correction.
2 Comments
I should mention that if the near eye is at -1D, that is a best focal distance of 1 meter = 39.37 inches. You see inwards from that a ways, so it improves near compared to an eye focused at distance, but for most people with a monofocal IOL they will still need readers . People's depth of focus (/depth of field), how far in they see from their best focal point, varies with the person. Some lucky minority with a monofocal set for distance can do some reading due to their eye's larger than average depth of focus, but that isn't typical and shouldn't be expected.
What I need to answer your question is your complete glasses RX sphere, cylinder and axis for both eyes before surgery with your best corrected vision and your complete glasses RX post surgery with sphere cylinder and axis. Be sure to include the plus or minus signs before sphere and cylinder.
5 Comments
(Sorry for the duplicate post—could not find any way to edit the title of the first post for grammar or syntax).
Certainly, Dr. Hagan. Here are the exact measurements for both prescriptions:
Sept. 4, 2014: Sphere OD -.25, OS -1.00; Cyl +1.75 OD, +1.50; Axis OD 170, OS 175; Add. (reading) +2.50 both eyes.
Nov. 17, 2016: Sphere OD -.75, OS -1.50; Cyl both eyes +1.00; Axis OD 170, OS 020; Add. (reading) +2.50 both eyes.
At neither refractions was pupillary distance measured (that was a matter for whichever optician I were to choose)
I will clarify that both these prescriptions were written by the same ophthalmologist (who also performed my cataract surgeries). As for June 2016, the optometrist at an optical chain reminded me this evening that she did not issue me a new prescription, but instead recommended both using the Sept. 2014 prescription to replace the glasses I’d lost and starting the ball rolling with my ophthalmologist for cataract surgeries. (I decided to attempt being refracted in June 2016, rather than just getting new duplicate glasses, because I had noticed considerable deterioration of my visual acuity; and since my lost frames had been discontinued, I needed new ones—which came with a free optometric exam).
My vision was examined at that first pre-op opthalmologist appointment in July 2016 but I was never issued a written prescription (because it would have shortly been rendered obsolete)—we simply scheduled my surgeries after taking the necessary measurements and discussing what type of lenses to implant, which component of my vision (distance vs. reading) to correct, that my astigmatism would be corrected as much as possible, and pre-op preparations & precautions to undertake.
I wonder if should contact my ophthalmologist to find out if there is a written record of his findings when he refracted me in July 2016 at the surgical-planning visit. But would you be able to come up with an answer to my question in the interim, or if it turns out there was no written record of the results of that pre-op refraction?
Certainly, Dr. Hagan. Here are the exact measurements for both prescriptions:
Sept. 4, 2014: Sphere OD -.25, OS -1.00; Cyl +1.75 OD, +1.50; Axis OD 170, OS 175; Add. (reading) +2.50 both eyes.
Nov. 17, 2016: Sphere OD -.75, OS -1.50; Cyl both eyes +1.00; Axis OD 170, OS 020; Add. (reading) +2.50 both eyes.
At neither refractions was pupillary distance measured (that was a matter for whichever optician I were to choose)
I will clarify that both these prescriptions were written by the same ophthalmologist (who also performed my cataract surgeries). As for June 2016, the optometrist at an optical chain reminded me this evening that she did not issue me a new prescription, but instead recommended both using the Sept. 2014 prescription to replace the glasses I’d lost and starting the ball rolling with my ophthalmologist for cataract surgeries. (I decided to attempt being refracted in June 2016, rather than just getting new duplicate glasses, because I had noticed considerable deterioration of my visual acuity; and since my lost frames had been discontinued, I needed new ones—which came with a free optometric exam).
My vision was examined at that first pre-op opthalmologist appointment in July 2016 but I was never issued a written prescription (because it would have shortly been rendered obsolete)—we simply scheduled my surgeries after taking the necessary measurements and discussing what type of lenses to implant, which component of my vision (distance vs. reading) to correct, that my astigmatism would be corrected as much as possible, and pre-op preparations & precautions to undertake.
I wonder if should contact my ophthalmologist to find out if there is a written record of his findings when he refracted me in July 2016 at the surgical-planning visit. But would you be able to come up with an answer to my question in the interim, or if it turns out there was no written record of the results of that pre-op refraction?
First of all important information is still absent. Cataract surgery is done when the vision is not correctable with glasses to a level that meets a persons need for things then need to do and want to do. So at our surgicenter tomorrow in Kansas City there will be about 20 people having cataract surgery. Their cataracts are different sizes, their vision with glasses is different, their complaints are different. Some have very tiny cataracts but have jobs like truck driver and airline pilots. Some people are at home with big cataracts but don't need surgery because they don't need much vision to function satisfactory. Example would be a 87 year old man with dementia.
So what you've posted tells us nothing about your vision before surgery and says nothing about your vision after surgery. Presumably your vision WITH and WITHOUT glasses is better than before surgery. The amount of astigmatism you have is LESS after surgery by .75 diopters RE and .50 diopters LE. You are more myopic. That is generally done intentionally so that after surgery without glasses you can see yourself in the mirror, put on make up, sometimes read or use a computer without glasses. You have monofocal IOLs not toric so you would not expect all your astigmatism to be gone. Assuming you see well with your new glasses, have better color vision, less glare and also see better without glasses you would belong in the "Good Result" column.
So what you've posted tells us nothing about your vision before surgery and says nothing about your vision after surgery. Presumably your vision WITH and WITHOUT glasses is better than before surgery. The amount of astigmatism you have is LESS after surgery by .75 diopters RE and .50 diopters LE. You are more myopic. That is generally done intentionally so that after surgery without glasses you can see yourself in the mirror, put on make up, sometimes read or use a computer without glasses. You have monofocal IOLs not toric so you would not expect all your astigmatism to be gone. Assuming you see well with your new glasses, have better color vision, less glare and also see better without glasses you would belong in the "Good Result" column.
Thanks, Dr. Hagan. Push came to shove for me when I couldn’t read fine print, yet the optometrist told me my near vision acuity hadn’t changed in two years and going up any more diopters wouldn’t have helped. The other factor (besides that she couldn’t see my fundi with the slitlamp) was that anything even slightly backlit looked like silhouettes. I was at an outdoor festival on a tented stage with no overhead light, but was facing a moderately sunny sky. I couldn’t make out any audience members’ faces, even those close to the stage. I looked down at my guitar neck and realized I couldn’t see the fret markers along the side of the neck, and that led to some very strange chords (and I play folk music, not jazz). You’re right—that I can see much more clearly and brightly now far outweighs the numbers written on my prescription.
That is a "Eureka Moment"
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