Eyeworld

6 | SUPPLEMENT TO EYEWORLD | NOVEMBER 2019 toric toolbox: Building skills and strategies to surgically manage astigmatism He carefully aligns the lens on his axis marks and seals the eye, rechecking the lens position and wound seal. Managing residual astigmatism An important part of surgi- cally correcting astigmatism is knowing how to manage postoperative astigmatism. "First, you rule out med- ical problems from the front to the back. Then, you see if they are correctable to 20/20 and happy with that vision. If they are, then you figure out how to correct the refractive error," he said. Targeting sources of error Dr. Al-Mohtaseb explained that surgeons need to rule out corneal pathology that can cause pseudo-astigma- tism or irregular astigmatism. She reviews corneal topog- raphy printouts for irregular mires and performs a clinical examination at the slit lamp, looking for epithelial base- ment membrane dystrophy and ocular surface disease, which she explained should be treated before surgery. "It is important to look at the quality parameters of the topographers, tomographers, and biometers used in practice to measure preoperatively," Dr. Al-Mohtaseb said. She uses two different topographers and at least one biometer for measurements. "I also look at patients' old glasses prescriptions, which might point to underlying pos- terior astigmatism," she said. She prefers the magnitude of astigmatism to be within 0.5 D between devices and the axis within 10 degrees. "If not, I check the quality of the scans, quality of the ocular surface, and then repeat mea- surements," she said. "If they still do not agree, I consider not treating the astigmatism, especially if it is low, and also have a longer discussion with the patient about the potential for postoperative laser refrac- tive surgery or IOL exchange, if needed." Maximizing accuracy Accurate IOL power calcula- tions depend on the accuracy of the preoperative biometric data and IOL calculations. She noted that the following are the most common sources of error (in order, and excluding manifest refraction): • Postoperative IOL position (or true effective lens posi- tion [ELP]) • Axial length measurement • Corneal power measure- ment She explained that formulas are less accurate with short eyes, long eyes, eyes with vari- able anterior chamber depth (ACD), and eyes that have had refractive surgery. "It's important to look even more closely at measurements in those eyes," she said. Dr. Al-Mohtaseb ex- plained that vergence and ray-tracing formulas attempt to estimate ELP, but artificial intelligence-based formulas select IOL power without directly predicting the ELP. "The differences in accuracy between various multiple-vari- able vergence formulas might result from the difference in the method of pseudophakic ACD estimation," she said. Obtaining excellent outcomes Dr. Al-Mohtaseb recommend- ed the following to optimize toric IOL outcomes: • Preoperatively, look at multiple preoperative data points for magni- tude and alignment and do not forget about poste- rior corneal astigmatism. She explained that she uses a manufacturer's calculator that incorporates Barrett's calculator, which accounts for posterior astigmatism. It is important to choose the correct IOL power and toricity, and intraoperative aberrometry can be helpful in confirming the preop- erative measurements and choices, she said. • Properly align the IOL. Errors can occur at the reference axis, alignment axis mark, and final IOL alignment. Preoperative and intraoperative marking can be performed manually or with a digital marking system. Aberrometry-based alignment methods can measure corneal astigma- tism intraoperatively and can also guide surgeons in correctly aligning the toric IOL. It is especially useful in patients who have had refractive surgery or have a high magnitude of astigma- tism. Using the Sinskey hook, she aligns the IOL approximately 10 degrees shy of the me- ridian. She uses bimanual irrigation and aspiration to remove the OVD, and uses irrigation to stabilize the lens and prevent rotation. "I also like to go underneath the lens with the aspirator. Once done, I keep the irrigator in the eye, remove the aspirator, and hydrate the paracentesis as I remove the irrigator. This prevents sudden flattening of the eye and keeps the lens in place," she said. Postoperative concerns If the patient is unhappy after surgery, she recommended ensuring that the refraction is stable and accurate after heal- ing, determining the patient's goals, and identifying residual astigmatism. She explained that astigmatismfix.com is helpful to see whether IOL rotation will correct astigma- tism. "Based on the ocular surface and level of astigma- tism, we can decide if LASIK or PRK, corneal relaxing incisions, or IOL exchange are the answer." n continued from page 5 continued on page 7

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