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Alexander Vu, Amanda Chi, Jennifer Nguyen, Quan V Hoang; Gaze-Induced Axial Length Changes in Emmetropic Eyes as Gauged by Magnetic Resonance Imaging. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):5913.
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© ARVO (1962-2015); The Authors (2016-present)
Our group previously reported that in highly myopic eyes with staphyloma, a reversible, instantaneous axial length elongation occurs in downgaze. Here we determine if axial length changes occur in emmetropic eyes undergoing the stress and strain of normal eye movement.
A prospective imaging study was performed on 12 eyes of 6 emmetropic patients (with uncorrected visual acuity of 20/20 or better). 3-D MRI scans were acquired while subjects gazed in 5 directions (primary, nasal, temporal, superior and inferior). Volume renderings were manually reoriented so that the plane of the limbus (the cornea-sclera interface) was normal to the plane of the screen. Four axial length measurements were taken at 90 degree rotations around the central axis and averaged for each eye in every gaze. Eye axial lengths at each eccentric gaze were compared to the axial length in primary gaze using a fixed effects regression allowing for person-specific and eye-specific effects.
The mean change in axial length was near-zero and not statistically significant when comparing the primary gaze to the nasal gaze (p = 0.619), temporal gaze (p = 0.406) or up gaze (p = 0.340). Axial lengths lengthened when changing from primary gaze to downgaze by +0.117 mm (p = 0.001, 95% CI 0.051 to 0.183).
A reversible, instantaneous axial length elongation appears to occur in downgaze, not only in highly myopic patients with staphyloma, but also in emmetropic patients without staphyloma. This is of interest given past clinical studies suggesting an association between excessive near work and myopia development and progression.
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