![]() ![]() Failing this, the mirror was adjusted and scout images rescanned. A series of scout scans were obtained and examined to check that the subject was looking vertically upward. Each subject was advised to restrict blinking while keeping the eye as still as possible and focused on the LED (46% of eyes wore a best sphere contact lens). The LED was placed approximately 6 m in front of the magnet along the axis of the magnet tunnel and patient table. To ensure minimum eye movement during imaging, participants were scanned while lying supine and looking vertically upward at the image of a 5-mm diameter light emitting diode (LED) reflected in a mirror mounted at an angle 45° to the horizontal inside the bore of the magnet. MRI was performed on a 1.5-T clinical system (Signa Twin Speed GE Medical Systems, Milwaukee, WI) with a 7.5-cm receive-only surface coil positioned over the eye. 8 measured the transverse axial (horizontal) plane using computerized x-ray tomography, finding that emmetropic eyes usually have similar lengths and widths, but that myopic eyes are greater in length than in width and that the dimension differences increases quickly with increase in myopia. ![]() These results suggest that expansion of highly myopic eyes may be predominantly axial rather than global, at least for comparison in the horizontal meridian. Lengths increased at more than three times the rate of increases in width. Eyes were categorized by axial length rather than refractive error, but as 60% of eyes had lengths greater than 27 mm, it can be concluded that most were highly myopic. Vohra and Good 7 measured axial lengths and widths with B-scan echography in both eyes of 50 patients. For most emmetropic eyes, these dimensions were similar, but lengths increased at approximately twice the rate of increases in height and width as myopia increased. 6 used an x-ray technique involving subjective responses from participants to determine lengths, heights (retina to retina), and widths (retina to retina) of eyes. There is a limited number of published studies investigating ocular shape. The small proportions are due primarily to the large variability in the dimensions of emmetropic eyes. Approximately a quarter of the myopic participants fitted each of the global expansion or axial elongation model exclusively. Although there are considerable individual variations, in general myopic eyes are elongated relative to emmetropic eyes, more in length than in height and even less in width. Based on width and length dimensions, 17% and 39% of myopic eyes exclusively fitted the global expansion and axial elongation models, respectively.Ĭonclusions. Based on height and length dimensions, 25% and 29% of myopic eyes exclusively fitted global expansion and axial elongation models, respectively. With an increase in myopic refractive correction, myopic eyes became much larger in all three dimensions, but more so in length (0.35 mm/D, 95% confidence interval 0.28–0.40) than in height (0.19 mm/D, 95% CI 0.09–0.29) and more so in height than in width (0.10 mm/D, 95% CI 0.01–0.20). ![]() Axial (horizontal through middle of eye) and sagittal (vertical through visual axis) sections were taken with a T 1-weighted fast spin-echo sequence. Eye images were acquired with a 7.5-cm receive-only radio frequency surface coil. The fixation target was imaged straight ahead of the subject by an overhead 45° inclined mirror. Participants were positioned supine in a clinical MRI scanner. The internal length (cornea to retina), height and width (both retina to retina) were measured in emmetropic and myopic eyes (up to −12 D) of 88 participants aged 18 to 36 years. To determine axial, vertical, and horizontal eye dimensions in myopic and emmetropic eyes by using magnetic resonance imaging (MRI) and to relate these to different ocular expansion models of myopia development. ![]()
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