Cataract monofocal IOL far or near?

Hi softwaredev,

Oh boy, I'll try to understand, is that what dr will use to put on IOL? I have seen my friends IOL cards from 19 to 21 D. Is that how it is measured? not using eye glasses prescription? like -2.75 for my left eye, use -2D for IOL?

I cannot read at 16" without glasses but can read at about 6"-7".

I want to be able to read at computer distance, do gardening, cooking, play card table games, watch tv read closed captioned.

I like to read but have readers glasses if I can get used to it? or wear progressive lens for intermediate and reading.

If I want to be able to see far far infinity then I will loose near upclose at 5"

If I chose near then I will loose far far infinity not as sharp clear as I would like is that true? and will I be able to see upclose at 5" if I chose near? choices I have to make.

I replied to at201 with my concerns about my RX being not update, IOL power will be using my old rx, that is not accurate.

I am not sure what I want, afraid of wrong choice and will not be happy with it. I'm just learning.

Dr will be using Tecnis 3-piece IOL is that good compare to 1 piece IOL? why 3 piece?

Thank you

The number of pieces of a lens doesn't have anything to do with the optical quality. Usually they use 1 piece lenses inside the capsular bag (the bag where your natural lens was that they try to put the replacement lens in), or a 3 piece outside the capsular bag (if the bag tears when removing the natural lens for instance).

The Tecnis lenses tend to be high quality, though typically they'd use a 1 piece IOL for placement inside the capsular bag. I don't know why they are using a 3 piece in your case, if they think there is some problem with the capsular bag which means it might be placed outside the bag perhaps.

They measure the power of a lens, how strong it is, in units of diopters, which is the "D" that is in the IOL power or is used for glasses or contacts.

Your natural eye acts like a lens, but it actually has 2 major parts you might think of as seperate lenses. Lets call  lens   "A"  the actual natural lens in your eye which has a cataract, and lens   "B"  the rest of the eye. If someone is nearsighted like they are, it means those lenses aren't the right power, and someone gets a prescription for glasses or contacts for a third lens, "C".  Since you have a cataract, they need to replace lens "A" with an IOL.

If you had perfect vision now and didn't need glasses, that would have meant lenses  A and B were the right power (that you didn't need the third lens, C). So if they are going to replace A, with a new lens, they would want the IOL to have the same power as A. The typical power of a natural lens is about 22D (D=diopters), but each person varies.  You can't determine the power of A from the power of your glasses C. If someone has good vision without glasses, their prescription C is 0, but their lens power A is still something like 22D or so. 

 If you wear glasses now, then as long as they are replacing lens A, rather than giving you the same power as A, they can   change its power to give you good vision without glasses. Its sort of like combing the power of A and C into the power of the IOL. The problem is determing what your actual natural lens power is, determining how much of the eye's focusing power is in A and how much is in B. They can't do that with a regular eye test. The way they do that is by taking different measurements of the size of the inside of your eye. They compare it to the measurements of people who had surgery before, and the lens power that worked for them.Your eye measurements won't be exactly the same as anyone elses, but  using statistics they can take a good guess about what power replacement lens would work for you.

So they don't use your current glasses prescription for anything.  The week of surgery they will give you a pre-operative exam some day before the operation and will take measurements of the inside of your eye to try to calculate the right lens power. The question for you is what distance you want the lens to focus at. When people are talking about getting a lens set for say "-1D", they  mean to focus where a slightly nearsighted person would see, which is 1 meter. The actual IOL power is not -1D (it might be perhaps 21D), its merely an indication of how nearsighted you want that eye to be. 

If you don't mind wearing glasses, then there is no wrong choice since you can always wear them afterwards. In general terms there are three general distance ranges: distance, intermediate and near, and the IOL is only good for one of them, and maybe a little bit in another. If you get an IOL set for distance, then intermediate will be a bit blurry and you likely won't be able to see much of anything up close. If you have it set for intermediate, then distance will be blurry but you may see some, and near will be blurry. If you get it set for near, then you may have some blurry intermediate, but likely not see much at distance.  When I say "blurry", how much depends on the person, and the exact distance. You can always wear glasses for the other distances. 

You can set both eyes to focus at different distances, but they can't be *too* different or your brain has trouble combining the two. 

Unfortunately the closer in you set an eye, the smaller the range of good vision. e.g. someone set to have good distance vision might see well from 6 feet to infinitiy, but someone who gets an IOL set to focus well at say 10" might only get 1.5" of good vision. That is a result of the math (which I know many people don't like to deal with).  The point of best focus is distance_in_centimeters = - (100/ lens_power_in_diopters)

So getting set to focus at -0.5D would be -(100 / -0.5) = 200 cm, or getting to focus at -2D would be -(100/ -2) = 50cm.  The reverse calculation to find the diopters for a particular distance is then lens_power = - (100 / distance_in_cm). 

You might have a range of good vision of perhaps 0.5D from the best focal distance (however it depends on the IOL and the person, it might be more like 0.75D for some) . So a lens focused at -2D would give some good vision at -2.5D (or -1.5D going the other way, though there is usually less of a range of vision going outwards than going inwards). 

Thank you, it helps, getting better understanding it, I learn alot, math is hard part, i'm getting there.

I had eye exam they measured few weeks ago, they used Keratometry, Pachymetry and axial length.

Surgery K's 43 and 44 both eyes axial length: od 24.06 mm os 23.93 mm

He did the external exam, (pupil bright 3mm) (last year was 5mm bright, dim 6mm) Slit lamp exam and Fundus exam.

That is what is on my report paper include eye pressure, visual acuity

that was all, hopefully that is what they need to measure my eyes.

Still haven't decide which to go for near or distance, will ask dr to change to -2.25--2.50 for near from -2.50 to -2.75 for computer distance.

OR

go for distance set at ?? for some intermediate vison, and wear glasses for reading, maybe some intermediate? and have a good distance vision, no glasses.

I did not get the # D for IOL from the dr yet.

Thank you for your help.

The diopter power of the IOL itself won't tell us much of use. The issue is how myopic its targeted to leave you.

The average axial length for eyes is about 23mm, with higher axial lengths on average for those who are nearsighted.The axial length is usually what they consider in terms of the potential accuracy of IOl power choice.  Although its possible for lens power calculations to be off for anyone, for low myopes its less of a concern. They tend to have more of a concern for the accuracy of lens power calculation for those who are 25mm or higher, though moreso when it gets up around 27mm or so. One of my eyes  was 25.69 mm and the power was on target, the other was 26.9mm and it was off target +0.5D.

The K's by themselves aren't of much use, the more important issue is the level of corneal  astigmatism in terms of whether or how much correction you need. (you presumably need it, since most astigmatism is corneal, but some is on the natural lens which goes away when the natural lens is removed). I deally they got that  through measuring total corneal astigmatism including  posterior astigmatism in addition to the usual anterior astigmatism. Usually they used to just measure astigmatism from the scan of the front of the cornea, assuming other astigmatism was always too little to worry about. They discovered that sometimes they were left with more astigmatism postop than they expected, and that the issue was they needed to measure posterior astigmatism. Not all surgeons do this yet since not all equipment is up to date to provide accurate measues of that. 

oops, typo.not that it matters but the eye on target was 25.96, not 25.69.

what is it called when they measure corneal astigmatism did I have it done?

maybe I can look for it in my report.

Your doctor should have obtained the values for your astigmatism during keratometry.

Finally, even if you get a toric lens, please be prepared for needing some  spherical or cylinderical corrections required after surgery. The posterior capsule also can introduce some astigmatism (can't be measured beforehand). The cut made to the cornea to insert the lens can introduce another source of astigmatism (takes a few months for that to settle down). For example, in my case, I got a toric lens, but had to have LASIK enhancement to correct the residual astigmatism and the slight error in the desired spherical correction. Fortunately, my surgeon provides the LASIK enhancement at no additional cost if one gets a toric lens. However, most of them don't. So, you may want to check whether your surgeon provides that extra benefit.

ok i see Merid and Delta ks is that measure astigmatism?

That is correct. The values of the meridian and the delta ks indicate the required astigmatism correction due to cornea.

ok Here it is:

       Merid            Delta Ks

OD    083              1.49

         173

OS    096               0.89

         006

what is my astigmatism?

There are a variety of instruments that measure corneal astigmatism.  Again however, not all measure total corneal astigmatism, including  posterior corneal astigmatism, rather than just the anterior corneal astigmatism.  It may or may not have been something measured by what gave the keratometry values.  Most corneal scans for uses other than cataract surgery didn't need to measure it, they only scanned the front surface of the cornea and its only the last few years that they have started doing so, and not all instruments measure it accurately, so the doctor may or may not have up to date equipment. It likely doesn't matter too much, but personally I'd prefer a doctor with up to date equipment if I had a choice and had astigmatism worth correcting.  (I was fortunate enough not to have much astigmatism).

The figures you show listing "Delta Ks" appear to be  just for  the anterior corneal astigmatism, and those deltas are the level of your astigmatism, e.g. 1.49D and 0.89D. Astigmatism is the difference in lens power in different directions of your eye, which is due to the eye being not full spherical but somewhat like an American football shape. The keratometry is measuring the surface curvature of the cornea in different directions  (the merid is the meridian, the angle) and the corresponding lens power resulting from that, and in this case the difference between the lens power at different angles, the delta ks.

As the other poster noted, often with astigmatism correction there is a need to fine tune the results of cataract surgery. A figure I'd seen recently was a meta-study (analysis of multiple studies) suggesting perhaps 29% of people have > +0.5D of astigmatism that is useful to correct afterwards via laser enhancement. 

This means that you have 1.49 diopter cylinderical correction needed for the right eye and 0.89 diopter cylinderical correction required for the left eye (based on the cornea only). Right now, a significant part of the astigmatism correction needed by you may be because of the natural lens. After you have the cataract surgery and get an IOL, the astigmatism correction needed due to the natural lens disappears.

no tori iol needed? but correction glasses needed after surgery, mild astigmatism? my old rx was -2.00 on both eyes was -2.50 and it went down year befoe that. so that has changed?

16"- 18" is -2.25 to -2.50 and 26" would be what?

16" to 18" is 40.64 cm to 45.72 cm =   -2.46D to  -2.19 D, rounding to nearest 0.25 makes that  -2.5 to -2.25. Then 26" is 66.04 cm = -1.51D

   

Though the result of the lens formulas won't be rounded to the nearest 0.25 so the exact targets can be mentioned. The formulas generate a list of IOL powers and what refraction they would leave you at, e.g there was a printout of fomulas for my right eye saying that one said a 13.5D IOL would leave me at  -0.15D, a 14D IOL would have left me -.5D , a 14.5D IOL would have left me at -0.84, a 15D IOL would have left me at -1.19D, etc.  They would then choose what IOL power is nearest the target refraction.  

Both eyes have astigmatism that needs to be corrected for the best quality vision. That costs extra to do during surgery, but if its not done then glasses or contacts are usually required afterwards if it isn't (unless its corrected afterwards via incision or laser).

 

Astigmatism can be corrected  during surgery using an incision, or a toric lens, and it partly depends on the amount of astigmatism which they go for. Different surgeons have different cutoff points for when they prefer to use a toric lens. *If* you gave the total corneal astigmatism, then  the lower amount of astigmatism, 0.89, is in the range often corrected via incision,but some surgeons would use a lens. The 1.49 amount is typically corrected using a toric lens, but some surgeons would still prefer to use an incision. 

 

Unfortunately we can't tell how much astigmatism you need to correct from the information you have given. Astigmatism can be in 3 different places: the natural lens, the anterior cornea or the posterior cornea. Together the astigmatism from all 3 sources produce the astigmatism that is in your prescription for glasses that needs to be corrected.  Any astigmatism in the natural lens goes away when the lens is removed during cataract surgery, so the only astigmatism that needs to be corrected is in the cornea. 

Unfortunately its likely the astigmatism figure you gave was just the anterior corneal astigmatism. Since it doesn't match your prescription, its likely there is astigmatism either in the lens or posterior corneal astigmatism. Usually the natural lens doesn't have much astigmatism, but sometimes it does, especially since cataracts can induce astigmatism in the cornea.  

 

well very explained, softwaredev