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Cataract Surgery: Complex Case Management | Mar 2009

Marking the Axis for a Toric IOL

One complication of a toric IOL's implantation is misalignment of the axis. Briefly, how do you mark your axis in order to ensure the lens' accurate placement during surgery?

I developed the concept of iris "fingerprinting" for the accurate intraoperative orientation of a toric lens several years ago. I realized that the use of a marking pen to identify the major meridians was not very precise, especially when the ink mark would diffuse, fade, or, in some cases, disappear entirely. Initially, I tried to use the limbal vessels but found these difficult to identify after the conjunctiva became injected following the instillation of drops or regional anesthesia. By observing the peripheral iris during the dilated examination in the office, I became aware of just how complex and unique each iris appeared. With the patient's fixation in the primary position, I would draw the peripheral iris landmarks with a horizontal beam and then a vertical beam, each splitting the pupil. The more central iris anatomy was irrelevant, because the pupil would be widely dilated in the OR.

It was remarkable to find so many different types of anatomic landmarks that became even more apparent as I studied more irides—an observation proving a point often made by the late Edward Norton, MD, chairman of the Department of Ophthalmology at the Bascom Palmer Eye Institute in Miami. Dr. Norton would emphasize that we would only see what we are looking for! Brushfield spots, nevi, pigmentary clusters, stromal contours, holes, and crypts were quickly drawn in relation to the narrowed slit beam through the major meridians. Prior to beginning the cataract surgery, I could quickly identify these landmarks in the OR, which would facilitate the accurate and precise location of the steepest meridian along which I intended to orient the toric lens. By using a protractor-like dial, I could use either two ink marks or two dots of point cautery on the conjunctiva that would subsequently become the reference points as I rotated the toric IOL.

I was able to validate this concept first by using intraoperative keratoscopy in eyes with high cylinder. Subsequently, I marked the major meridians in the preoperative area and compared the placement of the ink marks to the major meridians identified by the iris landmarks. It was not uncommon to find a 5° or even a 10° error, which becomes significant since every degree of inaccuracy reduces the amount of cylindrical correction by approximately 3%. Although the ophthalmologist can take some comfort in knowing that a toric lens that is misaligned by 5° or 10° may still have a beneficial effect, it should be the goal of every refractive cataract surgeon to achieve an outcome as close as possible to emmetropia.

I foresee a growing acceptance of toric IOLs, which will become the standard of care in the near future in the same way that every refraction evaluates cylinder as an essential component of the spectacle prescription. Moreover, as the father of astigmatic keratotomy combined with cataract surgery, I am the first to admit that astigmatic keratotomy and limbal relaxing incisions are an art with variable results in contrast to the precision and predictability of toric lenses. Technology designed to improve surgeons' accuracy in orienting toric lenses will evolve from the current method of using insensitive ink marks to methods of comparing intraoperative with preoperative imaging. I plan to introduce this software during my Innovators' Award lecture at the ASCRS annual meeting in April 2009. Eventually, microscope-based intraoperative solutions will allow the surgeon not only to orient the toric lens, but also to confirm the intended refractive error "on the table." Although IOL implantation represents one of medicine's brightest accomplishments, surgeons must continue to seek technology that will allow them to target and achieve spherical and cylindrical emmetropia.

After identifying the intended axis for the toric IOL through a combination of keratometry and topography, I use a disposable felt-tipped pen to mark the horizontal axis while the patient is seated upright in the preoperative holding area. I make freehand limbal dots at both the 3- and 9-o'clock positions. Once in the OR, I use a Dell LRI marker (Rhein Medical Inc., Tampa, FL) to imprint the toric IOL axis while the cornea is still dry. This leaves two additional ink marks that I then darken manually with the pen.

The eye is anesthetized with preservative-free tetracaine, and a wire lid speculum is placed. With the patient sitting in an upright position and fixating on a distant object viewed straight ahead, reference marks are accurately placed at the 3-, 6-, and 9-o'clock positions on the limbus with a pre-inked reference marker or soft felt-tipped marker. These marks may be made freehand or with various reference markers designed for this purpose. I prefer the accuracy of the latter. This procedure can also be performed at the slit lamp for even greater accuracy, but I have found doing so unnecessary and difficult if a slit lamp is not in close proximity to the OR. Marking is the most important step of the procedure, because it establishes the reference point for the final alignment of the IOL and acts as a guide for the incision site.

After the patient has been prepped and draped, I ensure that the reference marks are clearly visible and darken them if necessary. The 2.4-mm cataract incision is centered over the temporal ink mark. Following the removal of the cataract and instillation of the ophthalmic viscosurgical device in preparation for the toric IOL's implantation, I orient a Dell marker or Mendez gauge along the reference marks while making sure that the 180° meridian of the marker overlaps the reference ink marks (temporally and nasally) and the 6-o'clock ink mark aligns with the 90° mark. The application of ink on the Dell marker, when properly set, allows easy and accurate marking of the steep axis so the IOL can be accurately oriented. Similarly, the surgeon can mark the steep axis using a felt-tipped sterile marker and the degree marks on the Mendez gauge.

In the future, devices such as the ORange intraoperative wavefront aberrometer (not available in the United States; WaveTec Vision, Aliso Viejo, CA) will make the placement of toric IOLs easier and more accurate. For now, I find the technique I have described very successful.

I (or more likely my technician) mark the paralimbal conjunctiva of the seated patient in the OR at the 3-, 6-, and 9-o'clock positions. I rely on the 6-o'clock mark when I align the corneal marking ring to indicate the steep axis.

In the FDA clinical trials of the AcrySof Toric IOL (Alcon Laboratories, Inc., Fort Worth, TX), premarking was performed with a marking pen while the patient was sitting up to prevent the cyclotorsion that can occur when the patient is supine. The results were impressive, with 97% of recipients of the toric lens completely free of spectacles for distance. I have therefore continued using this method for premarking the horizontal and vertical meridians.

I use the intraoperative axis marking system from Mastel Precision, Inc. (Rapid City, SD). It helps to ensure that the marks will be centered through the center of the cornea so that the IOL can be positioned directly in line with the marks. With other intraoperative marking systems, I have found that marks may be in the proper axis yet not aligned through the center of the cornea. In this instance, it is necessary to position the IOL parallel to the marks instead of directly on the marks. After removing the viscoelastic, I perform the final alignment by turning the aspiration port posteriorly to contact the anterior surface of the IOL's optic in the midperiphery. Vacuum builds to engage the optic and allow me to rotate it to the desired orientation. I learned this technique from my partner Joshua Sands, MD.

Section editor Michael E. Snyder, MD, is a cataract specialist at the Cincinnati Eye Institute in Ohio. Robert J. Cionni, MD, is the medical director of The Eye Institute of Utah in Salt Lake City. Robert H. Osher, MD, is a professor of ophthalmology for the University of Cincinnati College of Medicine, and he is medical director emeritus at the Cincinnati Eye Institute. Dr. Cionni is a consultant to and speaker for Alcon Laboratories, Inc. Dr. Osher is a consultant to Alcon Laboratories, Inc. They may be reached at (513) 984-5133; rhosher@cincinnatieye.com.

David F. Chang, MD, is a clinical professor at the University of California, San Francisco, and is in private practice in Los Altos, California. His consulting fees for Advanced Medical Optics, Inc., and Alcon Laboratories, Inc., are donated to the Himalayan Cataract Project. Dr. Chang may be reached at (650) 948-9123; dceye@earthlink.net.

Stephen S. Lane, MD, is a managing partner of Associated Eye Care in St. Paul, Minnesota, and is an adjunct clinical professor for the University of Minnesota in Minneapolis. He is a consultant to Alcon Laboratories, Inc., Bausch & Lomb, and WaveTec Vision but stated that he holds no proprietary interest in the products mentioned herein. Dr. Lane may be reached at (651) 275-3000; sslane@associatedeyecare.com.

Richard J. Mackool, MD, is the director of the Mackool Eye Institute and Laser Center in Astoria, New York. He is a consultant to Alcon Laboratories, Inc. Dr. Mackool may be reached at (718) 728-3400 ext. 256; mackooleye@aol.com.

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