GENDER AND BIOMETRY

Wider adoption of the Haigis and similar IOL calculation formulas will improve the predictability of refractive outcomes in cataract surgery and eliminate the gender differences in biometry prediction error, said Anders Behndig MD, Umea, Sweden, at the 18th ESCRS Winter meeting in Ljubljana.

Dr Behndig presented an analysis of data from cataract procedures included in the Swedish National Cataract Register during the period from 2008 to 2013. It showed that the mean biometry prediction error decreased from around 0.5 D in 2004 to around 0.4 D in 2013, although there was considerable variation among the different clinics.

The analysis also showed that, whereas in 2005 the mean biometry prediction error was greater by about one-third of a dioptre in women than it was in men, by 2013 the mean biometry prediction error in men and women was roughly equal, though still slightly higher in women. However, an analysis of biometry prediction errors with correct signs showed that there remained a much larger myopic shift in women than in men.

Reduction in gender disparity

He noted that data from 2013, when the National Cataract Register (NCR) first included the IOL calculation formula and axial length, indicate that a shift in recent years to the Haigis and similar formulas may account for the reduction in the gender disparity.

The data showed that the gender difference in biometry prediction error remained in cases where the SRK-T formula was used for IOL calculation, but not where the Haigis formula was used.

“When we look at women and men in large population studies, it turns out that women have steeper corneas and shorter eyes, whereas men have flatter corneas and longer eyes. These two variables are linked. A person with steep corneas will generally have shorter eyes and a person with flat corneas will generally have longer eyes.

“The SRK-T formula renders a myopic error in patients with steep corneas and short axial lengths. These features are predominant in women, which explains the gender difference in biometry prediction between men and women. An increased preference for the Haigis formula over the SRK-T formula have likely diminished the historical gender differences,” Dr Behndig explained.

He also noted that, when he and his associates divided the patients in the registry study into quintiles according to the steepness of their corneas and the shortness of their eyes, it showed that men with short eyes and sharp corneas had the same mean prediction error with the SRK-T formula as did women with similar ocular dimensions.

“Using the Haigis formula or other similar formulas to a greater extent can improve biometry prediction in cataract surgery and also eliminate the prediction error difference between men and women,” Dr Behndig concluded.

Anders Behndig: anders.behndig@ophthal.umu.se