Dark-field Swept-source Optical Coherence Tomography For Retinal Imaging

The structure and function of human retina are extremely complex,and their changes are related to ophthalmic diseases and some body diseases.It is possible to realize early disease-diagnosis by high-resolution observation of the retina.Optical coherence tomography(OCT)is a non-contact,nondestructive,rapid and high-resolution imaging technique,that uses low coherence interference to observe the internal structure or function of biological tissues in micron-scale “optical sectioning”.Therefore,OCT technology has become the most suitable technique for retinal observation.A lot of research has been carried out and practical applications have also been demonstrated.However,the existing retinal OCT systems have some problems,including: 1)Due to the influence of human ocular aberrations,the lateral resolution is low,and the cost of using adaptive optics to correct aberrations is too high.2)Due to the inherent contradiction between lateral resolution and depth of focus(DOF),it is difficult to obtain high-resolution images of all retinal tissues in depth direction.3)The currently images have low signal-to-noise ratio and low contrast,which is not conducive to information interpretation.Aiming at the above problems,this work proposes to study the dark-field swept-source(SS-)OCT system for retinal imaging.An axicon is used to form the dark-field illumination,which power distribution is Bessel form.Bessel distribution can improve the lateral resolution,expand the DOF and keep the lateral resolution unchanged in the extended DOF.In addition,dark-field imaging has the characteristics of high signal-to-noise ratio,high contrast,and strong stereo-sense,which makes this work has obvious technical advantages and theoretically possible to solve the above problems.The main contents of this work are as follows:1)The basis of selecting SS-OCT technology in this work was analyzed.The basic principle of SS-OCT technology was introduced briefly,and the main parameters and its influencing factors were also analyzed.2)The use of an axicon to form dark-field Bessel illumination was proposed.The properties of Bessel annular beam formed by the axicon were analyzed,and the expressions of the lateral resolution and the DOF of Bessel distribution field were derived.3)A dark-field SS-OCT experiment system for principle verification using an axicon was designed and built.The design and construction of optical system,timing control,signal acquisition,and data processing,etc.were completed.The correctness of the proposed method is verified by experiments.The longitudinal resolution of ~10.7μm,the lateral resolution of ~22.1μm,and the DOF of ~3.0mm,were obtained experimentally.