EyeWorld Asia-Pacific September 2015 Issue

September 2015 12 EWAP FEATURE Blowing out the candles on toric surprise by Maxine Lipner EyeWorld Senior Contributing Writer AT A GLANCE • More than 0.5 D of residual astigmatism can be an unwelcome surprise for toric IOL patients. • Cumulative small errors may contribute to a signi cant toric surprise. • Toric surprise patients who cannot be corrected by a simple IOL rotation may have to undergo laser vision correction or an IOL exchange. Patient’s right eye after dry eye disease treatment Source (all): Elizabeth Yeu, MD Patient’s right eye before treatment for dry eye disease Dealing with rotation, power problems, and more I t happens with no fanfare in about one out of every 20 to 25 cases—toric IOL surprise, according to Elizabeth Yeu, MD , assistant professor of ophthalmology, Eastern Virginia Medical School, Norfolk, Va. But unlike some surprises, under- or overcorrection of astigmatism is definitely an unwelcome one for both patients and practitioners. “I don’t like a 4–5% surprise rate that results in more than 0.25 D of postoperative astigmatism,” Dr. Yeu said. Here is a closer look at what causes such errors and what can be done to keep patients happy. Dr. Yeu finds that any rotation that is going to lead to more than 0.5 D of residual astigmatism is going to be visually significant for patients. This means that the more astigmatism that is being corrected, the less margin there is for error. For example, if a patient needs just 1 D of astigmatism correction, as long as about half of that is corrected, the patient will likely not have complaints. However, by contrast, if you are correcting 3 D of astigmatism, at least 2.5 D needs to be successfully treated, Dr. Yeu noted, adding that not too much rotation of the toric lens can be tolerated as that will leave residual uncorrected astigmatism. Donald N. Serafano, MD , associate clinical professor, Department of Ophthalmology, University of Southern California, and Eye Physicians of Long Beach, Long Beach, Calif., agreed that the amount of toric lens rotation tolerated by patients is small. “I think you will do well if they’re (within) + or –4 degrees from the mathematical calculated axis,” he said. If the lens is off axis by more than this, he finds that two things will occur. Not only will the patient lose the effect of the toric IOL, but also in vector analysis there will be resulting astigmatism at another axis. “It’s not just a matter of a doctor saying, ‘I was off and I didn’t get as much effect as I thought I would,’” Dr. Serafano said. “You actually have produced an astigmatism somewhere else.” This can be frustrating to the patient who now has some refractive astigmatism at some oblique axis, which is not comfortable. “Now you’re prescribing glasses in someone who thought they had bought an IOL to avoid glasses,” he said. The only other options are to go back to the OR and rotate the lens or to do a secondary intervention with laser vision correction. Common causes Dr. Serafano finds that the most common cause of postoperative error is the result of small cumulative misses. “You give up 2 or 3 degrees on cyclotorsion, you give up a couple of degrees on your marking, and maybe when you put the IOL in, you remove the viscoelastic and you got a little movement of the lens and don’t get it reoriented correctly,” he said, adding that soon the surgeon is 8 or 10 degrees from where he or she would be in the mathematical calculations. Dr. Yeu said that another huge source for such errors is the “unknown” factor. “There is more to astigmatism correction than what we see on the anterior corneal surface,” she said. “So it’s managing the total corneal astigmatism.” This is still not as accurate as measurements of the anterior