EyeWorld India September 2018 Issue

46 EWAP REFRACTIVE September 2018 High patient expectations necessitate enhancement plans P remium IOLs have greatly improved patient outcomes af- ter cataract surgery. With these improved out- comes have come higher patient expectations, so it is important for surgeons to have an enhancement plan for every patient. “The ability to predict the in- traocular lens power has improved over the years; we and our patients appreciate the value of hitting the refractive target,” said Steven Schallhorn, MD, chief medical officer, Carl Zeiss Meditec. “Years ago, being within 1 D of the post- operative target was acceptable. Today, there is a growing need to understand how we can get closer to the target. In some patients, being even 0.5 D off is not accept- able.” Dr. Schallhorn noted that careful preoperative planning can Premium implant cataract surgery by Michelle Stephenson EyeWorld Contributing Writer minimize the number of patients requiring an enhancement. “The majority of today’s patients are within 0.5 D of predicted,” he said. “Accurate biometry remains the single most important measure- ment for calculating the correct lens power. This is followed by the power calculation that utilizes the biometry data. However, there are other variables that we do not currently take into account, such as the variability in the posterior corneal curvature and a more accu- rate method to predict the position of the IOL in the eye (effective lens position).” Douglas Koch, MD, Houston, agreed. He thinks that minimizing the number of enhancements relies primarily on being able to do a bet- ter job of predicting the effective lens position. “Until we get to that point, we’re still going to be bat- ting, at the very best, 90% within ±0.5 D. Errors in corneal power measurement are the other major cause of refractive misses. Being off by more than 0.5 D often compro- mises quality of vision in patients with presbyopia-correcting IOLs and is something we as surgeons must be prepared to acknowledge and address,” he said. Daniel Chang, MD, Bakersfield, California, said there are several additional factors that prevent surgeons from hitting the target every time. “Variability in keratometry can be a factor. If there is dry eye or fluctuation in the tear film, a one-time measure- ment may give you good numbers, but it may not represent the typical refractive state of the eye. Addi- tionally, keratometry is only an approximation of the true corneal curvature. Keratometry provides three numbers that approximate the three-dimensional shape of the cornea, and describing the refrac- tive state of that cornea with a ker- atometry model is a simplification. Most of our current formulas are based on vergence formulas created from that model, and sometimes the models are off. Ideally, if we can ray trace the entire cornea and measure stability over time, we can better calculate what patients need,” Dr. Chang said. Even with careful preoperative planning and meticulous intraoperative technique, it is important to have a good strategy for possible postoperative enhancement. Source: Daniel Chang, MD