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EL Francis, K Nipper, G Quinn, DI Flitcroft, G-S Ying, R Rees, X Zhu, G Schmid, RA Stone, M Maguire; Precise Eye Length Measurement in Children Aage 3-12 Years . Invest. Ophthalmol. Vis. Sci. 2002;43(13):358.
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Purpose: Laser Doppler interferometry (LDI) is a non-contact method that employs a short coherence multimode laser diode to measure ocular axial length. The technique detects interference patterns of low coherence light reflected from various layers of the eye. The purpose of this study was to determine if LDI measurement is feasible in young children and to determine the variability and reliability of the measurement. Methods: Sixty-two subjects, mean age 8.5 yrs (range 3.4-12.9), with best corrected visual acuity of 20/40 or better participated. Subjects fixated monocularly on an alignment starburst pattern while their fixation was visually monitored by the experimenter. The alignment beam was replaced by a low coherence measurement beam pattern for the 0.8 sec during which eye length measurements were made. Five sessions of 16 measures each were taken, with short rests between sessions. An average axial length for each of the 5 sessions was calculated using a variation of a novel automated signal processing algorithm that yielded an estimate of the geometric length from the corneal surface to the peak that is thought to correspond to the retinal pigment epithelium (Flitcroft et al., 2002). Results: Mean refractive error was +0.8 D (range –5D to +6D). Within subject variation of axial length was very small with an average Standard Error of Measurement of 8.0 microns for individual subjects across the five sessions. This suggests a 95% CI of +16.0 microns for an axial length measurement by this technique. Neither refractive error nor axial length significantly influenced the reliability of the measurement. Several demographic variables (gender, race and eye color) did affect the reliability. Conclusion: Highly precise eye length measurements can be obtained reproducibly in young children using this non-contact technique. Eye growth can therefore be examined in detail over shorter time intervals than previously possible.
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