EyeWorld India September 2019 Issue

EWAP SEPTEMBER 2019 55 REFRACTIVE ADVERTISER LISTING U ntil recently, the popular IOL power calculation formulas were generally based on thin lens vergence formulas. These are simple mathematical formulas that are easy to execute. A simple old-fashioned calculator can easily compute the calculations. It worked well and had served us well. With the increasing accuracy of measuring devices and the enormous scalability of computational power, more can be done. Complex calculations such as multi-thread parallel calculations and expansive iterations are now a possibility. Together with big or mega data, artificial intelligence is now a reality. With these developments and the demand for better refractive outcomes, IOL power calculation is undergoing a revolution. We have been seeing many new and innovative methods of formulating IOL power in the last few years. The generational classification of IOL power calculation formula is confusing. It is historical and can be misleading. As explained in Koch and Weikert’s article, later generations of formulas are perceived to be better but that may not be the case. I have approached and classified these formulas into three broad groups: data-driven, optical, and a combination of both. The classification is based on the concept of the formula. The data-driven group is sub-divided into two groups: regression and artificial intelligence. The optical group is further sub-divided into three groups: simple thin lens vergence, complex thick lens vergence, and ray tracing. The hybrid group stands alone. All together there are six groups (Table 1). Data-Driven Optical Approach Hybrid Regression Artificial Intelligence Simple Thin Lens Vergence Complex Thick Lens Vergence Ray Tracing Combination SRK SRK II Clarke Hill-RBF Binkhorst Colenbrander Holladay 1 Holladay 2 Hoffer Q Hoffer H5 Haigis SRK-T Barrett EVO Olsen- PhacoOptics Okulix FullMonte IOL Kane Ladas Super Formula Table 1. Classification of IOL formulas into three broad groups. Source: Fam Han Bor, MD The above list is not exhaustive. The above classification is similar to that proposed by Koch and Weikert. This formulaic classification gives a better understanding of the mechanisms of the formulas, their strengths and limitations. It is more helpful in clarifying decision making and choosing the appropriate formula to use in the relevant circumstances. The regression method is essentially obsolete and should be avoided. The simple thin lens vergence method is still relevant for its simplicity; it is easy to start a new IOL with. The newer formulas are improving our predicted outcomes in an expanding range of eyes. I agree with Koch and Weikert. A new functional classification is necessary, timely, and more intuitive. Editors’ note: Dr. Fam declared no relevant financial interests. Fam Han Bor, MD Senior Consultant and Head, Cataract & Anterior Segment, NHG Eye Institute, Tan Tock Seng Hospital 11 Jalan Tan Tock Seng dr.fam.eye@gmail.com ASIA-PACIFIC PERSPECTIVES Alcon Page 2, 40-51 www.alcon.com Appasamy Associates Page 15 www.appasamy.com Haag Streit Page 37 www.haag-streit.com Johnson & Johnson Vision Page 5, 80 www.jjvision.com Oculus Page 35 corneal-biomechanics.com VSY Biotechnology Page 12 www.vsybiotechnology.com Zeiss Page 28-31 www.zeiss.com ASCRS Page 56 www.ascrs.org APACRS Page 7, 8, 18, 21 www.apacrs.org