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Ideal IOL power calculations achievable
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WAIKOLOA, Hawaii — Manipulation of seven elements can lead, within 5 years, to the perfect IOL calculation, wherein perfection is measured as one-eighth of a diopter of intended outcomes in every patient, according to a speaker here.
According to Jack T. Holladay, MD, MSEE, FACS, speaking at Hawaiian Eye 2013, the seven elements that will make ideal IOL power calculations achievable include the formula, biometers, corneal power, new developments in B-scan, improved precision of femtosecond lasers, intraoperative aberrometry and adjustable IOLs.
Jack T. Holladay
Modern IOL calculation formulations, optical biometry, Scheimpflug corneal power and astigmatism measurements are more accurate, Holladay, OSN Optics Section Editor, said.
Regarding the formula, Holladay said, “Binkhorst was the first in 1981 to size the ELP (effective lens position) based upon the axial length and the lens. Since then, a rash of variables and predictors have been proposed as means to estimate the ELP. The point is, is that [the ELP] does not run along the axial length. The anterior segment is actually only proportional to the axial length about 10% to 20% of the time. Most of the time the anterior segment is normal, irrespective of the axial length. Where it makes the biggest difference is in the short eye.”
Optical biometry is more accurate because it measures to the foveola and includes retinal thickness.
“Measuring the posterior surface is very valuable,” Holladay said. “Scheimpflug instruments that are available today help us measure the back surface … and now we can take into consideration the K readings that help us take into consideration the back surface.”
Ultrasonic B-scan imaging can identify ciliary sulcus, zonules, iris root and equatorial lens locations, which will improve prediction of ELP. Femtosecond lasers have improved precision, and intraoperative aberrometry will become commonplace and eliminate significant refractive surprises in virgin eyes after refractive surgery and toric IOL implantation, according to Holladay.
Furthermore, adjustable IOLs will eliminate spherical, cylindrical and possibly higher-order aberrations.
Disclosure: Holladay is a consultant for AcuFocus, Alcon, AMO, Oculus, Visiometrics, WaveTec and Zeiss.