Study On Ocular Wavefront Aberration Measurement And Correction

Eyes are the windows of soul. Our quality of lives largely depends on the health ofeyes. However, just like all the other kinds of optical systems in practice, aberrations, nomatter tiny or significant, are almost inevitable in human eyes. Including but not limitedto low order aberrations like defocus, astigmatism and higher order aberrations liketrifoil, quatrefoil as well. For a long period of time, human beings pay most of theirefforts in trying to measuring and correcting low order aberrations while making lessprogress in dealing with higher order ones. Fact of this is partly because that, statisticlyspeaking, low order aberrations impact the majority of people the most. On the otherhand, confined by the technique of lens manufacturing, we are only able to correcte loworder aberrations by using traditional glasses. Nowadays, with the development ofLASIK, corneal operations are being widely used. Unfortunately, post-operationsyndromes that take place in small percentage of patients trouble both doctors andpatients a lot. Part of the reasons result from the incapability of our technology toadequately measure the essential higher order aberrations. Thereby, efforts on studyingand measuring ocular aberrations play very important role in controlling reliability ofcorneal operation and improving patients’ lives.In this article, we discuss in details as to the probable causes of system errorsduring our installment of ocular aberration measurement system and quantitivelyanalyze the impact brought by them. According to the calculation results, we proposenovel approaches to install and adjust optical system, which, is fully based on objectiveinformation. After that, we optimised the design of combined ocular measurementsystem. And we also deduce the algorithm method that could be used to trace back theoriginal aberrations on the condition that exit pupils of measured eyes are expanded tomatch the entrance pupils of HSS. We will begin to introduce our ocular measurementsystem in the following steps.Firstly, we introduced the basic principle of wavefront aberration theory anddiscuss the physical meaning of each Zernike term in details. After that, theHartmann-Shack principle was introduced in details. Secondly, we deduced theequations that could be used to calculate the measureable range of HSS and the limits ofHSS used in our experiments are calculated in accordingly. When it comes to the mostimportant part of this article, the impacts of reference plane to the measurement resultsare given, not only theoretically, but also experimentally. Given as a solution to solve the problem brought by the necessity to acquire highly flat reference plane，weintroduced a series of novel methods to adjust and minimize the system errors duringour setup of optical system and was thereby able to exactly judge the system errors,which, makes our measurement results characterized as convincible, reliable andrepeatable. We also improved pre-adjusted illumination system, which significantlyimprove the SNR performance while at the same time solve the difficulty in coaxialadjustment. Also, we invented a device that could be used to remove the speckles oflaser inlumination and experiments were performed in accordingly. Finally, an ocularmeasurement system which allow the users to take participate into adjustment whiletheir aberrations are being measured was successfully established and a series ofexperiments were performed. We tried several ways to correctify the ocular aberrations,including wearing glasses and using deformable mirror to correctify both high and loworder aberrations in realtime.