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Viswanathan G. Ramasubramanian, Adrian Glasser; Can Ultrasound Biomicroscopy (UBM) Be Used To Measure Accommodation Accurately?. Invest. Ophthalmol. Vis. Sci. 2012;53(14):1355.
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Techniques to measure accommodative intraocular changes objectively are of interest to understand accommodation and for evaluating corrective options for presbyopia. Ultrasound biomicroscopy (UBM) is a clinical instrument widely used to image the anterior segment of the eye. The goal of this study was to establish the accuracy of UBM in measuring accommodation.
Static accommodative responses (AR) to 0D to 6D stimuli in 1D steps were measured with infra-red photorefraction (PR) and a Grand-Seiko (GS) autorefractor (WR-5100K) in 25 human subjects aged 24 to 36 years (mean ± standard deviation (SD) : 24.44 ± 2.74 years). For PR, three 8 second videos were captured at 30Hz and for GS, 3 measurements were recorded for each amplitude. A 35 MHz UBM (Sonomed Escalon VuMAX) was used to perform biometric imaging in the subjects’ left eye, while their right eye viewed the accommodative stimuli. Three sequences of 50 images each were acquired over 8 seconds for each stimulus amplitude, as the subjects viewed thetargets. An automated Matlab image analysis program was developed to measure the ocular biometry parameters from the UBM images.
A Bland-Altman plot between PR and GS showed the mean difference of -0.519 ± 0.87D with a 95% confidence interval of ± 1.70D, with GS underestimating the PR at higher amplitudes. During accommodation, anterior chamber depth (ACD) decreased by 38.7µm/D, lens thickness (LT) increased by 51.2 µm/D, anterior and posterior lens radii of curvature (ALRC & PLRC) steepened by 680 µm/D and 202 µm/D respectively, anterior and posterior lens surface (ALM & PLM) moved anteriorly and posteriorly by 38.6 µm/D and 17 µm/D respectively. All parameters except PLM were significantly linearly correlated with the PR measured AR for all individual subjects and when the data from all subjects was considered together (p<0.0001). The SD of measured biometry parameters for all subjects was consistent across the range of AR. The mean SD ± SD of the measurements for all subjects for all amplitudes were: ACD: 18.4 ± 4.2 µm, LT: 32.7 ± 17.1 µm, ALRC: 398 ± 180 µm, PLRC: 195 ± 32 µm, ALM: 29.8 ± 16.3 µm and PLM: 58 ± 30.2 µm. This equates to a calculated SD of AR in diopters from the measured biometry of: ACD: 0.12 D, LT: 0.43 D, ALRC: 0.23 D, PLRC: 0.18 D, ALM: 0.48 D and PLM:1.39 D.
Per-diopter biometry changes in the current study are comparable with prior Scheimpflug studies. UBM parameters (except for PLM) can, on average, determine AR with a SD of less than 0.50D as compared to the mean SD of 0.20D for PR. Despite UBM having relatively low axial resolution (68 µm), this study demonstrates that UBM is a useful and accurate objective technique for measuring accommodation in young phakic eyes.
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