Improving IOL power calculations
An advanced, self-validating method is providing a new approach to IOL power selection, explains Warren E. Hill, MD, FACS.
Take-home message: An advanced, self-validating method is providing a new approach to IOL power selection, explains Warren E. Hill, MD, FACS.
Reviewed by Warren E. Hill, MD, FACS
Mesa, AZ-Every time ophthalmologists implant a multifocal lens, a toric lens, or even a monofocal lens-“where we absolutely positively have to get the power right”-the selection of IOL power is always playing in the background, said Warren E. Hill, MD, FACS.
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The continued emphasis on improving outcomes is to increase patient safety and reduce the many burdens associated with a refractive surprise, said Dr. Hill, in private practice, East Valley Ophthalmology, Mesa, AZ.
“If a patient ends up –4 D, it’s an annoyance for us, but can be a life-changing event for the patient,” he said.
Even with the most advanced metrics and the use of multiple theoretical formulas, there can still be problems with the selection of IOL power, according to Dr. Hill.
The simple fact is that no one gets the calculations right all the time, he noted. Refractive targets within 1 D are usually achieved, but the discrepancy between what was expected and what is reached for ± 0.50-D accuracy remains problematic.
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For more than a decade, Dr. Hill has reviewed physician databases for lens constant optimization from surgeons around the world, totaling now more than 260,000 optical biometry cases. Each physician submits between 200 and 300 cases, which typically represents their best work.
Less than 1% of surgeons have a refractive accuracy of 92% or better within ± 0.5D 92%. Six percent reach that level of accuracy 84% of the time, and the vast majority reaches that level of accuracy only 78% of the time, he noted.
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“If we’re in the business of putting in lens-based refractive IOLs, this is probably not good enough,” he said.
The “mathematical backbone” of all theoretical formulas is basically the same: Lens vergence equals image vergence minus object vergence.
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