Measurement of eye length and eye shape by optical low coherence reflectometry

The precise and rapid measurement of eye length and eye shape is essential for investigating eye growth regulation and myopia. For this purpose, we developed an optical low coherence reflectometer (OLCR) and present preliminary measurements.

The OLCR includes a super luminescent diode (wavelength: 845 nm, coherence length: approximately 30 microm) and rotating glass cube to produce longitudinal scans at a velocity of 0.42 m/s and a repetition rate of approximately 13 scans/s. Heterodyne detection of light reflected from the anterior cornea and the posterior retina permits to measure axial eye length and eye shape (off-axis eye length). Each measurement consists of five consecutive scans. Reproducibility and precision were determined in one volunteer by measuring axial eye length five consecutive times, each time repositioning the eye. Eye shapes were determined in right eyes of four volunteers by measuring eye length every 3.3 degrees from 10 degrees nasally to 10 degrees temporally.

Axial eye length measured repeatedly in one volunteer did not differ between or within the measurements (one-factor ANOVA). The average standard deviation was 11 microm. Eye shapes (a) varied substantially among subjects and (b) differed considerably from the corresponding shapes of spherical model eyes with identical axial eye lengths.

The newly developed OLCR permits the precise and rapid measurement of eye length and eye shape. Such measurements, especially in children, may provide important information about mechanisms of eye growth regulation and the development of myopia.