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S. M. Delgado, D. Falk, K. Ehrmann, A. Ho, P. Sankaridurg; On and Off-Axis Ocular Length Measurements Using the IOLMaster. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3950.
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Measure on and off-axis ocular length using the IOLMaster (Carl Zeiss Meditec AG, Germany) while maintaining an open-field of view.
An IOLMaster was modified to allow for presentation of real-space fixation targets. Five subjects (aged 25-29 years) were assessed in a feasibility study using the modified set-up. Only the left eyes (OS) were measured; OS spherical equivalent refractive errors (RE) ranged from -4.81D to +0.06D with cylinder <1.00D. The axial length (AL) was determined for all subjects during a) distance vision under dilated conditions using 1% tropicamide and b) while subjects fixated on a 5D accommodative demand near target. Off-axis dimensions were measured at 5°, 10°, 20°, 25° and 30° in the nasal and temporal visual fields under dilated conditions. Measurements were repeated until at least 3 values with a signal-to-noise ratio (SNR) of ≥2.0 and standard deviation ≤0.03 mm were realized.
The accuracy and precision of the modified set-up was assessed for on-axis conditions using the IOLMaster calibration eye (labelled AL of 20.77±0.05 mm versus measured AL of 20.79±0.01 mm using either the standard or modified set-up). The standard and modified set-up yielded respective SNR values of >37.0 and >11.0. The change in measured AL during accommodation was 0.00±0.04 mm for 5 eyes. The graph shows the results for on and off-axis length for 3 eyes that achieved the SNR criteria for off-axis measurements, and includes a calculation for a schematic eye, all with tilt and asymmetry data.
It is feasible to measure on and off-axis ocular length using an open-field IOLMaster; this method provides a non-invasive option for measuring eye contour during fixation on real-space targets. Our results do not account for the possible change in the eye’s group refractive index as a function of off-axis fixation angle or accommodation. A correction factor is being investigated.
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