High-contrast Imaging Of Retinal Blood Vessels Based On Liquid Crystal Adaptive Optics

Fundus examination is a necessary step to diagnos many diseases, for that themorphology of retinal vessels can early represent many endocrine diseases.However, due to the existence of ocular aberrations, the resolution of the traditionalophthalmoscope is not so high to observe changes of vascular subtle timely.Adaptive optics is a novel technology to compensate aberrations of human eye forretinal imaging, which can reach close to the diffraction limit. This research grouphas been employed a liquid crystal adaptive optics system successfully for highresolution imaging of retinal photoreceptor cells. However, there are still someproblems on human vascular imaging, including accurate positioning of microvascular difficulties, not specifically for vascular imaging adaptive optics system, theimage contrast is difficult to achieve the clinical application. In this paper, combinedwith the optical properties of the eye, several measures would be taken on theinnovation design a series of optical system.For non-paralysis eye, a target was employed for eyes staring. According tohuman focal depth, the eye accommodation error, visual acuity and color sensitivity,the visual target location, shape, illumination wavelength were identified anddesigned. The distance of1D target from the human pupil met the accuracyrequirements of the system. The design of Malta cross target shape, regulating arm can meet different visual acuity eyes stare. The most sensitive wavelength is greenlighting. Even if a faint green light was illuminated to the target, the human eye canalso clearly distinguish details, which is beneficial to improve the ability to stare.Based on retinal structures, the location method was determined to divide into threesteps:1） selecting foveal most center positioning reference,2） lateral positioning,in accordance with the system magnification, the imaging camera axial displacement,focusing in the inner layers of the retina blood vessel; this is a process of axial.3）Find the vessel position, along the vascular trend conscious control of lateralpositioning, in order to find the location of the lesion, splicing and processing alsohas the benefit of late vascular.An adaptive optical imaging system with micro vascular searching and locatingwas designed. According to the distribution characteristics of vessels, a stare systemcan realize large range for searching vessels. According to the optical characteristicsof retinal blood vessels, the illumination system contains two sources, includingdetection and imaging light source. In order to achieve good imaging results, thelinkage of light source and camera should be realized. With the analyzed statistics ofthe human eye axis data and calculated axial magnification, the movement of sourceand camera can be confirmed accurately.Specific ways to improve images contrast had been theoretical calculated anddiscussed. Using the difference polarization characteristics between blood and othertissues, a polarization liquid crystal adaptive optics system had been designed. Withthe help of polarized light imaging of micro blood vessels, the imaging contrast canbe improved to0.25, which was increased by about1.2times and basically reachedthe requirements for clinical use. In view of the actual optical path due to theprocessing and optical devices installed in the resolution limit error adjustment, asfar from the ideal design value, design of simple adaptive optical system, greatlyreduce the number of optical components used in the. Based on obtained retinalvascular images, a variety of image processing methods were used for improvingcontrast. Image registration was employed for noise elimination to improve contrast. In accordance with the blood flow, the vascular morphology was reconstructed,which made the obtained images with higher clinical value.