Comparison of lens thickness measurements in pediatric eyes using ultrasound biomicroscopy and A-scan biometry

Abstract

Purpose : Accurate lens thickness (LT) measurement is imperative when monitoring myopia progression, tracking lens growth, and calculating intraocular lens power. Immersion A-scan biometry is the current gold standard for measuring LT. However, operator error can cause misalignment of the probe with the optical axis, particularly with pediatric patients who may not be able to fixate on a target while A-scan is performed. The correlation between A-scan and intraocular imaging modalities, such as ultrasound biomicroscopy (UBM), has not been thoroughly examined. Using a prospective cohort of pediatric subjects, we tested the hypothesis that A-scan overestimates LT compared to UBM due to oblique placement of the A-scan probe.

Methods : Twenty-eight UBM images and 28 A-scan measurements were collected from 28 eyes (23 eyes with congenital cataracts, 3 eyes with traumatic cataract, and 2 healthy control eyes) of 16 subjects (mean age 2.9+/-2.6 yr, median 2.3 yr, range 0.1-8.3 yr). Immersion A-scan and UBM were performed using the 50-MHz Aviso Ultrasound Platform. Immersion A-scan LT measurements were based on an average of 10 consecutive automatic values derived from axial length. Two observers measured LT in each UBM image using ImageJ software and the values were averaged. In a sample of UBM images (n=10), LT was measured from A-scan cross vector (CV) overlay using ImageJ.

Results : LT measured using immersion A-scan (3.5+/-0.73 mm) was significantly greater (p<0.001) compared to LT measured directly from UBM (3.01+/-0.65 mm). UBM and immersion A-scan measurements were moderately positively correlated (r=0.69, p<0.001). UBM and A-scan CV measurements were strongly positively correlated (r=0.97, p<0.001) and there was no significant difference in mean LT (p=0.46). Regression analysis demonstrated a stronger linear relationship between UBM and A-scan CV (R²=0.93, p<0.001) than UBM and immersion A-scan (R²=0.64, p<0.001).

Conclusions : LT determined using immersion A-scan was significantly greater than LT measured directly from UBM, while A-scan CV and UBM LT measurements were strongly correlated. UBM may provide a suitable alternative for accurate LT measurement in pediatric patients due to the ability to confirm proper alignment of the probe with the pupil.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.

 

LT measured from A-scan CV (red), immersion A-scan (blue), and UBM (yellow).

 

Linear regression plots of immersion A-scan and CV compared to UBM.