Simultaneous optical coherence tomography and Scheimpflug imaging using the same incident light

Abstract

For any single anterior chamber cross-sectional (tomographic) imaging method, there is a practical compromise between image size and image resolution. In order to obtain large field-of-view cross-sectional images of the whole anterior chamber and high-resolution cross-sectional images of the fine corneal layers, measurements by multiple devices are currently required. This paper presents a novel raster scanning tomographic imaging device that acquires simultaneous large field-of-view Scheimpflug (12.5 mm image depth, 50 μm axial resolution in air) and high-resolution spectral domain optical coherence tomography (SD-OCT) (2 mm image depth, 3.7μm axial resolution in air) using the same illuminating photons. For the novel raster scanning 3D Scheimpflug imaging, a tunable lens system together with numerical methods for correcting refraction distortion were used. To demonstrate the capability of simultaneous measurement of both fine corneal layers and whole anterior chambers topology, ex vivo measurements on 12 porcine and 12 bovine eyes were carried out. There is a reasonable agreement in the overall central corneal thicknesses (CCT) obtained from the simultaneous SD-OCT and Scheimpflug measurements. In addition, because the same infrared light beam was used to illuminate the sample, both OCT and Scheimpflug images were taken at the exact same location of a sample simultaneously in a single measurement. This provides a unique method for measuring both the thickness and the refractive index of a sample.

Rapid imaging and product screening with low-cost line-field Fourier domain optical coherence tomography

“…5 c,d, a false color scale is used to map the thickness variation encompassing a range from 700 to 760 µm for the whole corneal region and a range from 65 to 71 µm for the corneal epithelium. As a result, the thicknesses of the structures were calculated to be 743.2 ± 13.1 µm (cornea) and 69.2 ± 1.5 µm (corneal epithelium), which are within the range of reported values 35 , 37 – 39 . Notably, the imaged region of interest (ROI) was aligned by manually centering the corneal sample, and it cannot represent the accurate corneal centre.…”

“…The SD-OCT was developed by using a commercial spectrometer (Cobra-S 800, Wasatch Photonics) whose spectral resolution is 0.1 nm (Fig. 4 b) 35 . Specifically, the power used to illuminate the tape sample in the SD-OCT was 1.4 mW, close to the 1.8 mW power used in the LF-FD-OCT.…”

Accuracy of OCT–derived net corneal astigmatism measurement

“…The better accuracy and repeatability of OCT obtained in our study could be due to several factors. The axial resolution of the Avanti SD-OCT system, at 5 μm, is 4 times finer than the 22 μm resolution of the IOLMaster 700's swept-source OCT. From the literature based on optical experiments, the axial resolution of Scheimpflug imaging is of the order of 50 μm, 10 times lower than Avanti OCT. 32 The finer resolution may enable more precise segmentation of anterior and posterior corneal surfaces. The IOLMaster 700 measures the anterior surface using 18 spot illumination (equivalent to 9 meridians) and maps the posterior surface using 6 meridional swept-source OCT scans.…”

Measuring corneal astigmatism using OCT in keratoconus

“…First, the axial resolution of the Avanti OCT is 5 μm, approximately 10 times better than the axial resolution of Scheimpflug imaging reported in the literature. 25 The finer resolution of Avanti OCT may enable more precise segmentation of the anterior and posterior corneal surfaces, resulting in more accurate corneal astigmatism measurements. Second, the Avanti OCT scans the cornea more than 6 times faster than the Pentacam HR performs.…”