FEATURE 8 EWAP JUNE 2022 With good biometry and modern IOL power calculation formulas, we can expect 80% of our postoperative cataract patients to achieve 80% or better within 0.5 D. However, about 5% and 1% of patients may still end up with more than 0.75 D and 1.0 D outside the targeted refraction, respectively. -verker in his 2008 paper identified postoperative E P as the biggest source of errors. Since then, with newer formulas, the variability of E P has been narrowed significantly. Here is my approach to refractive surprises. 1. Examine the eye with the pupil dilated. a. Exclude wound leakage, tight sutures, and shallow anterior chamber as these would distort the natural anatomy of the eye. b. Ascertain that the position of the IOL is well-placed within an intact capsular bag and that the bag is intact. c. For cylindrical power misses, exclude rotated and misaligned toric IOLs. 2. Review the biometry calculation sheet and the patient case record. a. Ensure the correct IOL model and power are being implanted in the correct eye of the right patient. Reaffirm that the IO constant is correct. Establish that the appropriate formulas are used to determine the IOL power and calculated for the intended refraction. Recalculate with other formulas for comparison. Newer updated formulas are available online (www.apacrs.org, ascrs.org/tools, evoiolcalculator.com) and are useful tools for comparison. b. An infrequent error is that the refractive history is overlooked during calculation. Using normal formulas for eyes with a history of corneal refractive surgery will results in IOL power misses. 3. Re-refract the patient. As pointed out by Sverker Norrby in his paper, postoperative refraction is the second commonest source of error. Hopefully, the initial refraction is amiss. {. inally, after having gone through the above and failing to find any plausible reason for the surprise, re-measure the eye again to rule out inaccurate preoperative axial lengths or keratometry. Incorrect keratometry or wound-induced keratometric changes can be a factor, especially in toric misses. If the patient is happy with his vision despite the refractive error, no further treatment is necessary. Various options are available to treat residual refractive errors. For residual cylindrical power, a simple realignment may be adequate. Spectacles are a simple and noninvasive option. Refractive surgery, IOL exchange, or supplemental IOL are other options available. It is best to discuss this with the patients. A good biometer and taking the proper steps in biometry preoperatively reduce these misses. Editors’ note: Dr. Fam is a consultant for Alcon, Carl Zeiss Meditec, Nidek, and Johnson & Johnson. Fam Han Bor, MD Senior Consultant & Head, Cataract and Anterior Segment Service The Eye Institute @ Tan Tock Seng Hospital 11, Jalan Tan Tock Seng famhb@singnet.com.sg ASIA-PACIFIC PERSPECTIVES power IOL due to human error,” he said, adding, “The most common cause is an error in axial length measurement. These errors are often seen in long or short eyes, especially if the eyes present with advanced cataracts that could not be measured by optical biometry; the technician will resort to measuring these eyes with ultrasound, with a greater possibility of error measurements.” What options for ‘treatment’ First and foremost, Dr. Shammas said to identify the source of postoperative error. • Recheck the power of the IOL against the calculated power to rule out human error. Dr. Shammas recommended the surgeon personally check the IOL power prior to implantation. • Remeasure both eyes to rule out error in axial length measurement. • Recalculate corneal power to rule out postoperative steepening of the cornea. Dr. Shammas said tight sutures can occasionally cause steepening. • Assess the IOL’s position to rule out forward placement with or without tilt. How to treat the eye with residual refractive error depends on the patient’s level of unhappiness, Dr. Salz said. If the refraction isn’t perfect but the patient is happy with the overall quality of vision, Dr. Salz said there is no reason to subject them to another procedure. Dr. Shammas said patients are more likely to complain if the error is in their dominant eye with an unexpected anisometropia and/ or aniseikonia. Dr. Salz said most patients with some residual refractive error are corrected with glasses. However, if a patient does not want glasses, there are other options. “We’ll say, ‘The effective lens position ended up –0.5 in the other eye; I need to take that into account for the selection of the IOL power for the second eye,’” he explained. Dr. Salz said he’s making this second eye adjustment in 5–10% of cases, though it’s not necessarily because the patient is unhappy. It’s because “I think I can get their other eye even better.” Dr. Shammas said his practice follows a protocol based on a comprehensive study that found patients who had refractive error eÝceeding 0.5 D in their first eye could benefit from modifying the IOL power in the second eye.1 Dr. Shammas said this protocol can correct up to 50% of the error in the first eye. A study published earlier found
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