Extended-depth Spectral Domain Optical Coherence Tomography And Its Application In Imaging Accommodation Of The Eye

Precise and rapid in vivo imaging and measurement of ocular dimensions is extremely valuable for ophthalmological research and clinical diagnosis. Compared with other conventional ophthalmic imaging methods, the state-of-the-art optical coherence tomography(OCT) can provide real-time high-resolution two/three-dimensional(2D/3D) imaging with non-contact and non-invasiveness. Nevertheless, due to the limited imaging depth, OCT is unable to image the whole anterior segment, let along the whole eye segment, which confines its applications in ophthalmology. Hence, the emphasis of my doctoral issue is focused on improving the penetration depth of spectral-domain OCT(SD-OCT) to provide more detailed and abundant information for ophthalmological research and clinical examination. By combining dual channel dual focus and full range complex(FRC) methods, we developed and optimized long imaging range SD-OCT system for the whole eye segment imaging and ocular biometry, and applied it to image the accommodation of eye. The research work can be summarized as follows:Firstly, a dual channel dual focus SD-OCT was built to image the whole eye anterior segments simultaneously with higher lateral resolution. Based on the composited OCT image, we were able to calculate the dimensions of eye anterior segment. This experimental system was then applied to image the changes in ocular dimensions among the relaxed and different accommodated states. The results not only supported the Helmholtz theory, but also demonstrated this dual channel SD-OCT system was feasible for noninvasive measurement of ocular dimensions and studying accommodation.Secondly, in order to further improve the imaging depth, a dual channel dual focus SD-OCT system with FRC method was built for imaging the whole anterior segment and retina simultaneously. The ocular dimensions can be calculated from the composited whole eye segment image. The results demonstrated this dual channel SD-OCT system had good reproducibility for ocular biometry. Furthermore, this improved imaging system also had high correlation and agreement with IOLMaster for measurements of anterior chamber depth and axial length. Hence, it will be an effective imaging tool for ophthalmological clinical examination and basic research.Thirdly, since the retinal stretching or distortion with accommodation may be associated with accommodation-dependent perceptual phenomena, a high-resolution imaging measurement tool is able to provide direct and accurate quantitative analysis for accommodation-induced morphological changes in human retina. In this study, a modified dual channel dual focus SD-OCT system was built to realize simultaneously 3D imaging of central cornea and retina in relaxed and maximally accommodated states. Based on the volumetric data, the retinal thickness, retinal volume and axial length were calculated. The results indicated that there was a significant and quadrant-independent retinal thinning in 4-mm2 macular area centered at fovea. This was the first report to demonstrate accommodation-induced retinal stretching or distortion in human eye from the perspective of the change in retinal thickness.Lastly, in order to solve the problem of limited scanning range of retina imaging and further improve the imaging quality, a dual band dual focus SD-OCT centered at 1050 nm and 840 nm with FRC method was built to image the whole eye anterior segment and retina simultaneously with large scanning range. Taking advantages of the special optical design of the sample arm, we not only solved the problem of signal attenuation caused by beam splitter in our previous system, but also separated the scanning paths of the two beams to ensure the optimal tradeoff among resolution, focus of view and scanning range for each imaging channel(especially the retina imaging). This system was then used to measure the ocular dimensions in relaxed and +6D accommodated states. Most results were well documented. And the result on the increase of axial length induced by accommodation may be associated with near-work induced transient myopia(NITM). Hence, this novel imaging system is not only suitable for ophthalmological examination, but also can provide powerful technical supports for the studies in visual optics, such as accommodation and ametropia.The research successfully solved the technical difficulty for long-depth imaging of SD-OCT with large-scaled scanning range, and realized high-resolution whole eye segment imaging as well as high-accuracy ocular biometry simultaneously. Using these home-made SD-OCT, we investigated the accommodation-induced changes in ocular dimensions, the results provided direct evidences for eye elongation and retinal stretching or distortion during accommodation. Therefore, this research not only provides powerful imaging tools for the objective assessments of ophthalmological investigation and clinical diagnosis, but also contributes to the in-depth accommodation study.