EyeWorld India March 2012 Issue

Hiroko BISSEN-MIYAJIMA, MD, PhD Professor and Department Chair of Ophthalmology Tokyo Dental College Suidobashi Hospital 2-9-18 Misaki-cho, Chiyoda-ku, Tokyo 101-0061 Japan Tel. no. +81-3-5275-1912 Fax no. +81-3-5275-1912 bissen@tdc.ac.jp E very ophthalmologist who has implanted a toric intraocular lens (IOL) has experienced the benefit of correcting astigmatism by seeing the superior visual outcomes and patient’s satisfaction following the implantation. The question is how precise the alignment of the astigmatic axis should be. There are roughly three groups of surgeons. The first group are surgeons who do not use any extra instruments or marking. I believe this works; however, the results could be better by taking into account the cyclotorsion of the eye and further defining by using the axis marker. The second group are surgeons who put the reference mark on the cornea and conjunctiva before the patient lies down in the supine position. The reference mark is usually at the 3 and 9 o’clock positions; however, there is no guarantee that these positions match the exact axis of the cornea. The third group includes a higher level of precision. In this article, everyone belongs to the third group. Iris landmarks which Dr. Osher prefers to use are reliable and successfully used for the tracking system of the excimer laser. The problem is that the recognition of the iris pattern under the operating microscope is not 100% and we may need a back-up technique. The intraoperative corneal topography or wavefront analysis mentioned by Dr. Packer is another attractive tool. The possible influence on the corneal shape by the lid speculum and the dryness of the ocular surface should be considered. The way of importing the pre-op data and overlay on the eye under the operating microscope mentioned by Dr. Weinstock seems to be the most accurate way. These technologies supersede the process of pre-op marking and increase the accuracy of axis alignment which brings superior postoperative vision. However, the surgeon needs to invest a large amount of the money and prepare the space for the extra apparatus. I am sure the price will become more reasonable and the size of the apparatus will be smaller with the rapid development of the technology. We know the toric IOL provides good results without advanced technologies and provides preferable outcome even when the axis of the IOL does not perfectly match the corneal astigmatisms; however, we only see perfect correction when the axis is precisely aligned. The technologies mentioned here are used by a limited number of surgeons now, but will be accepted as a standard method in refractive cataract surgery in the future. Editors’ note: Prof. Bissen-Miyajima has no financial interests related to her comments. incisional correction when the patient is getting a presbyopia- correcting lens “and there is no other way of correcting for cylinder”, he said. Combination toric and presbyopia-correcting lenses, available outside the U.S., are “the best way to correct for presbyopia and astigmatism”, he said. Even in the cataract population, “many surgeons feel that they can correct somewhere around 1.5 D of astigmatism on the cornea with an LRI alone,” Dr. Weinstock said. “Relaxing incisions aren’t even an option with some post- LASIK eyes and are quite limited in cases of previous RK,” said Mark Packer, MD , clinical associate professor of ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, Ore., USA. “In post-RK eyes, if there’s a large enough optical zone and some regular astigmatism within the optical zone, then I’ll use a toric.” Dr. Osher first introduced astigmatic keratotomy in 1983, and “it remains an effective technique that will reduce astigmatism” in conjunction with cataract surgery. But outcomes are variable and rely on patient healing times, he said, and he was quick to embrace toric IOL technology. “I perform astigmatic reduction in over 50% of my routine cataract patients, and 27% of those are torics,” he said. Challenges today Irregular astigmatic patterns and determining the axis of astigmatism remain the two biggest challenges. Occasionally K readings from an IOLMaster (Carl Zeiss Meditec, Dublin, Calif., USA) may not align with topography, Dr. Trattler said. Online calculators such as the LRIcalculator.com (Abbott Medical Optics, AMO, Santa Ana, Calif., USA) can be useful as well, he added. “There’s a lot out there to measure corneal astigmatism but no single instrument that will give you the right answer all the time,” Dr. Lane said. “I can do all the diagnostic tests I want, but I still have to pick a number.” Some surgeons prefer to use a pen to mark the axis pre-op and use it as a reference during surgery. Others prefer to use digital markers because they can provide more accurate data on the true vertical and horizontal meridians, Dr. Weinstock said. Dr. Osher uses iris fingerprinting, noting ink can lead to “huge amounts of inaccuracy” in the correction. “I know from my fingerprinting where the major meridia are, so it’s very easy for me to take a semi- lunar marker and snuggle it right up to the limbus and be very accurate,” he said. “While I also use ink, I don’t rely on it.” Newer diagnostic tools Dr. Osher developed the Micron Imaging Systems (Pegram, Tenn., USA), which can identify the number of degrees for any iris landmark accurately with software applied to a dilated pupil. He believes iris landmarks (pigment, nevi, stromal patterns, vessels, Brushfield spots, etc.) are more reliable “because vascular landmarks can change after dilating drops”. He also developed the Osher Alignment Toric System (Haag- Streit, Koeniz, Switzerland), but does not retain a financial interest in either version. With the TrueVision 3D System (Santa Barbara, Calif., USA), an overlay template gives the “exact location for the lens”, Dr. Weinstock said. “You take a pre-op photo to find the primary meridians. In the OR, I import the data and align it by limbal vessel registration. It eliminates concerns about cyclotorsion on the table.” A major benefit of the system is that surgeons can look through the microscope, but also at a screen with a superimposed reticle on the limbus to track and show where the axis is, he said. The WaveTec ORA (Aliso Viejo, Calif., USA) also uses a March 2012 EW FEATURE 21 continued on page 22