Repeat Biometry Measurements

Ocular biometry in adults changes little time over time. Roibeard Ó hÉineacháin reports

Axial length (AL) and average keratotomy (KER) measurements appear to change very little over time, suggesting ophthalmologists may not need to repeat ocular measurements prior to cataract surgery as frequently as previously presumed, said Nicholas K Chan MD at the ARVO 2021 Annual Meeting.

“These results suggest repeating biometry at one- to two-year intervals during surgical workup may not be a necessity. Rather, the measurements can be used selectively, like in high myopes, for example,” said Dr Chan, Northwestern University Feinberg School of Medicine, Chicago, Illinois, USA.

In the retrospective study, Dr Chan and his associates analysed sequential biometry data in 402 eyes of 201 patients obtained with the IOLMaster® 700 (ZEISS) from January 1, 2016, to September 15, 2020, at the Northwestern Memorial Hospital in Chicago. To be included in the study, patients had to have two biometry measurements over six months apart and be more than 35 years of age. Patients were excluded if they had any other intraocular surgery other than cataract.

SMALL, TIME-INDEPENDENT CHANGE IN BIOMETRY PARAMETERS The study included 119 women and 88 men with an average age of 73 years. The average time between biometry measurements was 21.5 months, average AL was 24.08mm, and the average KER was 43.73D. The mean change in AL between measurements was 0.04mm, and the mean change in KER was 0.10D (p=0.33).

Dr Chan noted an analysis using a linear regression model showed no correlation between the length of time between measurements and change in AL or KER. The mean change in AL was 0.04mm among eyes with an interval between measurements of six months to one year, 0.05mm in eyes with a two- to three-year interval, and 0.04mm in eyes with a three- to four-year interval.

Eyes with high myopia showed the greatest mean change in axial length (0.07mm), but this was still a small change and not significantly greater than the AL change in eyes with hyperopia (0.04mm), average length eyes (0.04mm), and eyes with moderate myopia (0.03mm).

“Axial length and keratotomy changed minimally over time between biometry measurements. The amount of change did not significantly increase with the length of time between measurements, even at large intervals like three to four years, and myopic eyes did not have a significantly greater change in axial length than shorter eyes,” Dr Chan summarised.