Heterodyne moiré interferometry for measuring corneal surface profile

• We proposed a measurement technique for reconstructing the corneal surface profile.
• The method uses the Talbot effect, the projection moiré method, and heterodyne interferometry.
• The phase distribution can be obtained using the IEEE 1241 least-square sine fitting algorithm and 2D phase unwrapping.
• The corneal surface profile can be reconstructed by a special derived equation.
• This method has been verified by an experiment with a resolution about 3.5 μm.

This study proposes an accurate method for reconstructing the corneal surface profile. By applying a constant velocity to the projection grating along the grating plane, a series of sampling points of the sinusoidal wave, which behaves in the manner of heterodyne interferometric signals, can be recorded using a CMOS camera. The phase distribution of the moiré fringes can then be obtained using the IEEE 1241 least-square sine fitting algorithm and two-dimensional (2D) phase unwrapping. Finally, the corneal surface profile can be reconstructed by substituting the phase distribution into a specially derived equation. To validate the proposed method, the corneal surface of a pig eyeball was measured. The measurement resolution was approximately 3.5 μm. Because of the introduction of the Talbot effect, the projection moiré method, and heterodyne interferometry, this approach provides the advantages of a simple optical setup, ease of operation, high stability, and high resolution.