Research On Intraocular Distance Measurement System Utilizing Low Coherence Interferometry

Eye is an important visual organ,with which we can perceive external things in the world directly.As with other organs,there are some abnormalities in the eye that often more or less influence the quality of our life.Cataract is just a common eye disease caused by blindness.In the early stages of illness,cataract patients feel vague when he or she is seeing things and patients would be blind when the crystalline lens became opaque in the late stages.At present.there is no complete cure for cataract,and the only effective way is to remove the opaque lens by surgery and then implant the intraocular lens.Such surgery requires preoperative accurate measurement of intraocular distances;only in that way might the patients get optimal refractive results.Diagnosis and treatment of cataract and other diseases are closely related with the intraocular distances as well.Therefore,accurate and effective measurement of intraocular distances plays a significant role in the diagnosis and treatment of these diseases related to intraocular distances.When it comes to the measurement of the intraocular distances,our system utilizes the main principle of low coherence optical interference(LCI,low coherence interferometry).LCI is an accurate photoelectric detection technology,which shows non-contact,high-speed,high sensitivity and many other advantages.Time-domain LCI(TD-LCI)is an early low-coherence optical interference technique.Compared with other detection techniques,TD-LCI has great obvious advantages.However,it also has many ignorable shortcomings meanwhile.Firstly,TD-LCI,due to its unique detection method,has a humble sensitivity.For example,under low light conditions,effective signal could not even be detected with the application of the TD-LCI methods.Secondly,it is necessary to move the reference arm back and forth to cooperatively detect interference signals at different depths in the sample,and in this way the detection speed of the TD method is badly limited,which is not suitable for detection of intraocular distances in vivo.When it comes to the advantages of detection technology and its convenience,Fourier domain LCI(FD-LCI)related technologies are quite suitable for the detection of the intraocular distances.In the laboratory,a set of intraocular distances measurement system utilizing FD-LCI is set up.Compared with the existing devices,this system has three innovations as follows:(1)Aiming at the problem that the detection rate of the intraocular measurement devices is low,the system uses the focused light to detect the position of the intraocular lens to ensure the intensity of the interfering signal,thus ensuring the detection rate of the system.(2)Aiming at the problem that the frequency domain method could not distinguish the positive and negative frequency of the interference signal,a quadratic measurement method is proposed and applied to ensure the reliability of the detection results of the visual axis parameters.(3)Aiming at the problem that the detection range of the frequency domain method is so humble,the system establishes four reference arms corresponding to the detection arms of the different intraocular positions,and acquire a measurement range covering the whole eyes from the cornea to the retina.Several experiments have been carried out,including the measurement of the thickness of the glass sample and the measurement of intraocular distances in vivo.The results show excellent performance and indicate that the system has great development potential and practical application in the ophthalmology.