Research And Implementation Of Axial Length Measurement System Based On Low Coherence Optical Interference Technology

Cataract surgery has gradually changed from traditional rehabilitation surgery to better refractive surgery with the continuous development of science and technology.Accurate ocular tissue biological length measurement is more and more important before surgery.The accuracy of axial length measurement will closely affect the postoperative refractive error.The axial length has a positive correlation with the degree of myopia,which is an important basis for distinguishing between true and false myopia.The existing method for measuring the axial length is divided into two types:an ultrasonic measuring method and an optical measuring method according to different techniques.Ultrasonic measurement methods require ocular anesthesia before measurement.The pressure of the probe to contact the cornea affects the measurement results,and the measurement results are easily affected by the operator.Relatively speaking,the optical measurement method has higher measurement accuracy and axial resolution.At the same time,it avoids some limitations in the ultrasonic measurement method,which brings great convenience for the measurement of the axial length.However,for some eye diseases that affect the transparency of refractive medium,such as cataracts,traditional ultrasonic measurement methods are still more suitable,which is also a shortcoming of existing optical biometric methods.In this thesis,a set of eye axis length measurement system is designed and built based on low-coherence light interference technology.In view of the shortcomings of the existing light source penetration,combined with the light absorption characteristics of the eye tissue,a super luminescent diode(SLD)of 1060 nm is selected as a system light source,theoretically improved the penetration ability of the light source.In order to better obtain the signal inside the eye tissue,this paper studies a focus synchronization technology,which uses stepping motors to separately control the reference arm optical path compensation mirror and the sample arm for focus synchronization to adjust the focus lens,and start scan motion at the set scanning speed simultaneously,and the measurement scanning beam is simultaneously focused on different interfaces of the eye tissue during the measurement process,thereby improving the signal strength of the measurement signal and the signal-to-noise ratio of the measurement result.In this paper,the optical path and measurement control system of the axial length measurement system are introduced in detail,and the implementation of the focus synchronization technology is emphasized.At the same time,the paper also introduces the development of measurement control software used in conjunction with the measurement system and the preliminary signal processing method.In this thesis,the designed axial length measurement system is verified by experiments,including plane target experiment,self-test module measurement experiment and human eye measurement experiment,and the measurement results are compared with the ultrasonic measurement instrument.The experimental results show that the eye axis length measurement system designed by this paper uses the focus synchronization technology to obtain the coherent signals of each interface in the eye tissue,and has high measurement accuracy.At the same time,the measurement results are consistent with the ultrasonic measurement results.The axial length measurement system designed in this paper has many areas for improvement in practical applications,and there is still great potential for development.