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Advisory Committee Chair

Thomas T Norton

Advisory Committee Members

Robert Angus

Siegwart T John

Document Type

Thesis

Date of Award

2013

Degree Name by School

Master of Science (MS) College of Arts and Sciences

Abstract

The purpose of this study was to compare ocular component dimensions and treated minus control eye differences measured with the Lenstar optical biometer to those measured with A-scan ultrasound in the tree shrew model of refractive development and induced myopia. A-scan ultrasonographic measures (A-scan) were taken with a 15 MHz focused pulser/receiver and compared with measures made with the Lenstar LS900 optical biometer (Haag-Streit, Basel, Switzerland). Anterior segment depth (ASD), lens thickness (LT), vitreous chamber depth (VCD), and axial length (AL) were measured in treated eyes (30), fellow control eyes (30), and normal eyes (86) in tree shrews (n=146), between 10 days after eye opening (days of visual experience [DVE]) and 1973 DVE. Lenstar VCD analyses were made using the retinal cursors. Treated vs. control eye differences were measured (n=60) in eyes made hyperopic or myopic by treatment with a monocular lens or by form deprivation. The A-scan measures and Lenstar measures were generally comparable (3.5% smaller) when the Lenstar was compared to the A-scan excluding vitreous chamber, which was substantially smaller (23%). If either the lens cursors or the retinal cursors (international software version) were used to measure vitreous chamber depth, Lenstar values were very similar (3.4% smaller than A-scan). All components (ASD, LT, VCD, and AL) were found to be highly correlated with a consistent offset (t-test; p < 0.05). Comparing treated vs. control eye differences of myopic (elongated) and hyperopic (shorter) eyes after monocular treatment showed a significant difference in VCD and AL (t-test; p < 0.05). The difference in vitreous chamber depth per diopter difference was 27.2 µm/D for A-scan and 26.1 µm/D for Lenstar. The correlation coefficients were consistently larger for the Lenstar than the A-scan. The slopes between the two systems were not significantly different. Using the standard cursors, the Lenstar substantially underestimates vitreous chamber depth in tree shrews compared with A-scan. Using the retinal (or lens) cursors to measure the vitreous chamber gives comparable results. The treated vs. control eye vitreous chamber differences (retinal cursors) in monocularly treated animals are very similar. In tree shrews, the Lenstar LS900 can be used in place of A-scan ultrasonography and has the advantage that it can be used in awake animals.

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