Behavior of biometric parameters during clinical hours

Purpose: To evaluate and quantify variation of biometric parameters - axial length (AL), anterior chamber depth (ACD), central corneal thickness (CCT) and white-to-white (WTW). Methods: A population-based retrospective cohort study was performed on patients who underwent a biometry test prior to cataract surgery using the IOL Master 700 (Carl Zeiss Meditec, Jena, Germany) between the years 2017–2021. Differences in these parameters were evaluated between scans executed at different times of the day. Results: 21,975 examinations of 8611 patients were included. Mean age was 70.50 ± 12.56 years. The mean time of the biometry exams was 10:52 ± 1:23 AM. Measurements of AL, ACD, CCT and WTW were tested hourly and grouped between 7:00–9:00 AM and 12:00–03:00 PM. All the parameters showed a diurnal increase with a significance of P < 0.001 (AL from 23.64 ± 1.5 to 24.01 ± 1.76 mm; ACD from 3.29 ± 0.67 to 3.35 ± 0.64 mm; CCT from 0.52 ± 0.04 to 0.53 ± 0.04 μm and WTW from11.83 ± 0.46 to 11.90 ± 0.51 mm). The most significant change was seen in AL. The difference between time groups remained significant in a generalized linear mixed model (P < 0.001). Conclusions: There are fluctuations in AL, ACD, CCT, WTW measurements during office hours. These results raise questions about the significance of timing of the biometry exam and the effect on the ELP calculation.