Q & A With the Experts
Our expert panel answers frequently asked questions about elective IOLs.
How many degrees of lens decentration can
patients tolerate with toric IOLs?
Dr. Donnenfeld: Optimally, you want to be within 5° of the cylinder. Being off by 30° neutralizes the cylinder and negates the toric correction.
Dr. Holland: You will not induce astigmatism until there is 30° or more of decentration. You have to be significantly off axis to induce higher cylinder postoperatively compared to what there was preoperatively. One degree of decentration reduces the effect by 3.3% (slightly more so if the degree of astigmatism is large). The AcrySof IQ Toric lens has been shown in studies to have excellent rotational stability. Decentration is not an issue with this lens.
What do you do if the preoperative astigmatism
measurements do not match up? What if the
keratometer does not match up with the optical
biometer, the topographer, or the refraction?
Dr. Holland: First, determine if there is a problem with the ocular surface. Does the patient have dry eye or blepharitis, or does he wear contact lenses (contact lenses can throw off these measurements)? If so, keep the patient out of contact lenses longer before doing the testing. Although it is rare, if there is a large discrepancy between the measurements that you cannot reconcile, the safest option is not to implant an IOL.
Dr. Solomon: I am going to quote Warren Hill, MD, who is an expert with IOL calculations. Dr. Hill addresses this issue very simply: A sim K is just that, a simulated keratometry reading. The Ks on the IOLMaster are sim Ks. If you are measuring an eye and getting perhaps 0.25 D of difference between the various measurements, Dr. Hill says to go with manual Ks. The most reliable manual keratometer is the Javal-Schiotz (Haag- Streit AG, Koeniz, Switzerland). Use the manual Ks for the magnitude of astigmatism you’re going to correct. Use the average Ks off of the 5.4 version of the IOLMaster for your IOL calculation, and use the topographer to create a straight line directly through the middle of the steep axis to pinpoint the axis of the astigmatism.
Does the panel have any tips or new techniques for marking the eye preoperatively?
Dr. Holland: Have the patient sitting up instead of lying flat when you mark him. I place corneal marks at 3-, 9-, and 6 o’clock. Also, many patients have corneas that are wider at the horizontal axis, between 3- and 9 o’clock.
Dr. Solomon: You can mark patients at a slit lamp. Mastel Precision, Inc. (Rapid City, SD) and ASICO LLC (Westmont, IL) have weighted markers that help keep the eye level while you mark.
When operating on an eye with a small amount
of astigmatism, and you make the incision in the
steep meridian (the axis of the astigmatism),
what is the size of your incision? Do you vary the
length or the location of your incision?
Dr. Donnenfeld: I do. When I make a 2.2-mm incision, I induce about 0.30 D of cylinder. When I make a 3-mm incision, I get about 0.50 of cylinder. If the cylinder is 0.50 D and is directly in the axis of my incision, I will extend my incision slightly, and that solves the problem.
Dr. Solomon: If you want to use a 3-mm incision to address astigmatism, do it at the end of the case. If you begin cataract surgery with a 3-mm incision, a lot of fluid will leak through it. Make your phaco incision 2.2- or 2.4 mm to fit the phaco sleeve, and then widen the incision at the end of the case.
Now that we have both the AcrySof IQ ReSTOR
IOL +3.0 D and +4.0 D, are there any instances
for which you’d use an optic with a +4.0 D add?
Dr. Holland:I no longer use the +4.0 D add much at all; the +3.0 D add has great reading vision and better intermediate vision.
Dr. Solomon: I do not use the +4.0 D add much, either. Patients may say they want close-range vision (ie, to read the stock pages), but if you tell them that the +4.0 D add can give them that vision, but it will sacrifice a normal range of vision for reading or looking at a computer screen, most patients will prefer to have the +3.0 D add and use glasses for reading the stock pages.
We know that a significant number of people
switch their axis of astigmatism (from with-therule
to against-the-rule) with age. How do we
know when that effect takes place and becomes
stable? When is it safe to implant a toric IOL so
that it will stay at that axis and the patient’s
corneal cylinder won’t move?
Dr. Holland: Say you have a 55-year-old patient with astigmatism at 90º. His astigmatism might change over the next 25 years of his life, but not by 1.50 D. I would still recommend a toric IOL so that this patient has 15 to 20 years of good uncorrected vision. The change with age is very slow, and I do not factor it into my decision.
Dr. Donnenfeld: The rate of change with axis of astigmatism is probably in the order of 0.02 D per decade. Remember that it always changes from with-the-rule to against-the-rule, so in choosing whether to leave patients either a little with or a little against, I always try to leave them a little with-the-rule cylinder.
What is your approach with presbyopia-correcting lenses in post-RK eyes?
Dr. Solomon: I would implant an aspheric monofocal lens.
Dr. Donnenfeld: Agreed. My go-to lens for these patients is an aspheric monofocal IOL.
I am an ocular surgeon and have had 20/20 UCVA
all my life. I now hava a cataract and 1.00 D of
astigmatism. I want to preserve my ability to use
the operating microscope. Am I better off with a
regular lens or a refractive IOL?
Dr. Donnenfeld: I would probably put a toric aspheric IOL in your eye for 1.00 D of cylinder. If you are willing to forgo treating the astigmatism with an IOL, then I think the AcrySof IQ ReSTOR IOL +3.0 D is a very reasonable option. I have implanted this lens in several ophthalmologists who are thrilled with it.
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