A compact optical device for eye-length measurement

Signal and Resolution Enhancements in Dual Beam Optical Coherence Tomography of the Human Eye

“…Wavefront matching with the use of a special lens with a hole in its optical center was reported by Chen et al 38 Half of the illuminating beam is focused on the cornea by the special lens, the other part passes through the hole in the center and is focused by the lens of the eye onto the retina. Both of the beams reflected at the cornea and the retina are recollimated by the special lens and the eye lens, respectively, so that all the optical power reflected by the eye may be collected by the photodetector.…”

“…By using a single diffractive optical element, we were able to improve the S/N by about 20 to 25 dB in in vivo measurements. Compared with the rather complex spatial filtering method used by Chen et al 38 our solution has the advantage of consisting of a single, lightweight optical element. The lens with the central hole, 38 on the other hand, has the drawback that only a narrow parallel beam can pass through the hole, which restricts the possible resolution on the retina because of the small aperture angle and consequently the rather large diameter of the diffraction-limited probing beam on the retina.…”

Resolution-improved dual-beam and standard optical coherence tomography: a comparison

“…3,4). The triplicate band structure observed at the posterior side of the retina in foveal tomograms is not visible in the Humphrey OCT images (see Figs.…”

“…Compared to previous OCT images recorded with this technique [9,15], the signal-tonoise ratio is considerably improved by the wave front matching accomplished with the diffractive optical element. Compared to other wave front matching techniques [4,31], the diffractive optical element is lightweight, cheap, easier to align, and does not restrict the aperture of the retinal beam, which would increase the beam focus diameter on the retina and therefore might degrade the transverse resolution. From the viewpoint of the signal-to-noise ratio, the dual-beam OCT images are now comparable to those of the Humphrey OCT instrument; however, it should be mentioned that we used signal averaging only with the dual-beam technique.…”

Rapid and Precise In Vivo Measurement of Human Corneal Thickness with Optical Low-Coherence Reflectometry in Normal Human Eyes

“…Optical low-coherence reflectometry (OLCR) has been reported to be a highly sensitive technique for measuring optical powers in the sub-fW range. [1][2][3] It has been used to investigate optical properties of industrial [4][5][6][7][8][9] and biological samples. [10][11][12][13][14][15][16] In diffusive media the longitudinal resolution of this technique is limited to the coherence length of the broadband source.…”