Design And Fabrication Of New Type Of Fundus Camera

The eye fundus examination is significant not only for diagnoses of eye diseases(such as cataract, glaucoma etc.)，but also for very early clinic diagnoses of diseasesthat influence the retina (such as hypertension, diabetes, nephropathy etc.). It hasbecome a hot study of clinical medicine and modern science. However, there are threemain factors influencing the imaging quality, the eye’s aberrations, the undesirablescatter light and central ghost, and the complicated optical system. Based on theidea of the modular design, a new style of fundus with cubic imaging optical systemto aid for the eye’s aberrations is designed and developed in this thesis. For theundesirable scatter light and the complicated optical system, two new optical systemsof fundus camera are designed. Spectral domain OCT equipment is designed anddeveloped to expand on tomography function of fundus.1. In the optimization of the imaging system, a new eye model with varyingdefocus revised from Gullstrand-Le Grand standard eye model was introduced toeliminate the negative effect of eye’s aberrations as well as to accommodate the eyewith different refractive error.2. To improve the effectiveness of the correction of eye’s aberration in theimaging optical path and to keep the independence of each part of the imaging opticalsystem, we choose the way of step-by-step and modular optical aberrationcompensation mode. Aperture of the system is compressed to reduce the system’sdifficulty in design and alignment. The cubic relay image system can meet therequirement of different magnification and complete switch of the spectral domainOCT function module. The backreflections of the cornea and ophthalmic lens can be avoided in the way of the annular illumination and the black pot. The location anddiopter compensation of eye are completed by the double optical wedge positioningsystem and the focus target projection optical system. Based on the idea of themodular design, a new style of fundus camara with cubic imaging optical system isdesigned and developed, with the field of view of45°, the free working distance of40mm, the accommodation range between-10D and+6D, the resolution at the objectplane of10~15μm across the entire field of view and the maximum distortion lessthan6.5%.3. In order to eliminate the undesirable stray light such as scatter light and centralghost in a classical fundus camera, the optical system of a catadioptric fundus camerawith an off-axial reflecting free-form-surface ophthalmic lens was designed, which iswith a large field of view and a large working distance. The off-axial reflectingophthalmic lens is introduced to avoid backreflections of refractive ophthalmic lenswithout black pot in the illumination pathways. Two free-form-surfaces wereintroduced in the imaging objective system to correct the residual off-axial aberrationsof the reflective ophthalmic lens. Three adjacent illumination rings were introduced inthe illumination part to avoid the undesirable stray light reflected by the eye’s opticalsystem.4. A new type of portable fundus camera was designed to make the optical systemsimpler and more compact as compared with the classical system. The photographingsystem and the focus target projection optical system are with a common focusinglens, so that the focus target projection optical system can be arranged completely inthe illumination system. In the focus target projection system a special illuminationsystem is not required any longer. In addition, a focus link mechanism between theprojective target and the focusing lens is not required. The position of the focusinglens makes the space of the photographing system. Taking the advantage of narrowbandwidth of LED light source, the observation system and the photographing systemare with a common camera.5. In view of the current development trend of fundus imaging check, the spectraldomain OCT equipment is designed and developed. SD-OCT system is built by use ofall-fiber Michelson interferometer structure. The spectral interference signal iscollected by a fast spectrometer; the reconstruction of depth information is completed by the signal processing method of cubic spline interpolation, the data fitting andFourier transform, and the signal-to-noise ratio of OCT image is improved by theaverage spectrum method. Finally, the OCT images of biological tissue and scatteringsamples of pearl, fresh fruit and human skin have been obtained.