My Doc disagrees with IOL masster

[fidlhead]

I have a cataract in right eye, left eye is 20/20, no health problems or eye health problems otherwise.  Right eye has lenticular astigmatism, doc says a standard (no astig correction) IOL will fix.  The problem:  Doc used an IOL master to measure my eye (this is good) but when setting the "target reference" (post-op perscription he is aiming to obtain?), he set this to -0.5 whereas I think it should have been Plano.  A previous Doc (their fees were too expensive) set her "target reference" to plano.  My doc says that implanting the -0.5 IOL recommended by the IOL master software will actually result in plano vision.  My fear is that he is using seat of the pants, anecdotal incidents from his practice to override the judgement of the IOL manufacturer.  Should I trust his judgement as more comprehensive than that of the people who wrote the formulae used my the IOL master software?  My fear is that he is really doing this so that the results will be more correctable via future laser surgury.  But, I am self insured and cannot afford such corrections.  I am afraid I will end up with  Plano, -0.5 or -1.0 (-0.5 most likely) where I should be ending up with 0.5 plano or -0.5 (plano most likely).  I do understand that hitting dead on the desired perscription is not guaranteed, and that most patients hit "close enough".  I just want to maximize my chances of 20/20 in the right eye since I have 20/20 in the left.  I am worried because for me, (financially) this is a one shot deal.  I will have to live with the post op prescription and will not be able to afford a lasik "tweak" to give me the desired 20/20 in both eyes (distance vision).  I expect to use glasses for reading, computers etc.

[JakeMooreMD]

I typically target -0.25 to -0.50 D with my cataract surgeries for a number of reasons, and I am using a regression based surgeon customized A constant for my IOL master calculations.  The first is the best surgeons in the nation are reaching a 0.25 Diopter standard deviation in their IOL power calculations meaning there will be some people who fall on either side of the bullseye.  There is no margin in leaving a patient hyperopic whereas falling even a Diopter nearsighted is a respectable outcome.  The second is that most people have a small amount of corneal astigmatism (maybe not enough to mention).  If the spherical equilavent is slightly nearsighted than the conoid of strum or interval between far and near focal points will give the greatest amount of useful uncorrected vision.  Finally recognize the concept from photography of the "hyperfocal point."  That is for a given F number there is a focal point closer than infinity, where the far end of the depth of field falls on infinity.  This is the point that will give the widest depth of in-focus vision.  My estimates put the hyperfocal point of the eye between -0.25 and -0.5 D depending on pupil size.  All this adds up to the fact that there is no margin in leaving a patient farsighted.

FWIW I am -0.75 in both eyes and in good light see 20/20 uncorrected at distance monocular and 20/15 binocular.  I sometimes wear glasses at night.

[Michael J Kutryb, MD]

The a-constant will be something like 118.7 or 118.3 or 119.1 and you also need to look at what implant is being used (LI61AO, SA60AT, SI40NB are common examples.)  Never worry about pestering your doctor if you have legitimate questions.

MJK MD

[fidlhead]

Thanks very much for the quick (and to the point) response.  Mainly, I was looking for reassurance that there are possible legitimate reasons to "aim for" a prescription other than plano (within the IOL Master software/printout) when you are in fact actually trying to achieve plano.  I did look at the IOL master printouts, and the only thing that looks like it might be an "A-constant" is a number on the printout that is labeled "ACD".   But it looks to me like some sort of raw measurment data, not something the doc selects.  The first doctor's printout has my "ACD" value at 3.92mm, and a month later, my current doctors printout has an ACD value of  3.98mm.  Both docs used the Holladay formula, and both had my AL (axial length of the eyeball?) at very similar lengths, first doc at 24.60mm, current doc at 24.65mm.  I am fairly sure those length differences are not significant.  At any rate, this is enough over my head so that I am probably wasting my time trying to understand it fully.  More than anything else, it is a "trust" issue.  Threre really is no way for a patient to "know" whether to trust a doctor, so we have to make a leap of faith.  This is most easily done when we do what we can to make sure that obvious blunders, such as sawing off the wrong leg, are caught by the simple expedient of the patient being willing to ask questions.  This forum is great, since it allows me to ask my questions (and allay my fears) without having to take the risk of possibly insulting or annoying my own doctor by being persistent.  My doc, who seems perfectly competent to me, is basically just saying "trust me", and I needed something just a little bit more concrete than that.  So, again, many thanks for the reply, and there is no need to reply further, unless the info in this post tells you something I might need to know.

[JodieJ]

It sounds like you are very careful and through.  If I lived in your area and needed cataract surgery, you'd definitely be on my list.

[Michael J Kutryb, MD]

It all depends on what A-constant he uses.  If he uses the modified A-constant then might go more for plano.  If he uses standard a-constant then would need to overshoot a little to around -0.5.  Look at the a-constant on the iol master printout between the two surgeons.  One may differ from the other.  Also what formula is dr using.  I typically use 3 and each formula will give a slightly different predicted implant.  Sometimes there is an adjustment factor depending on how first eye responded or  perhaps your Keratometry readings are fluctuating.  Basically this is way more complicated than you can understand.  Only your surgeon knows the best IOL to pick for your case.

In the end just talk to  your surgeon.  He has your best interest in mind.  Let him know what your concerns are.  If nothing else if you call and ask questions - it might stir them to double and triple check your readings and that's not a bad thing,  Finally, either you trust your surgeon or not.  If you do then let him do the surgery.  If you don't then get another surgeon.  I think you'er going to do great.  Good Luck.

MJK MD