Visual Evoked Potential Measurements System Based On Adaptive Optics

The formation of visual perception was governed by optics,retina and visual pathway.Any visual pathology or disorders at different levels can cause loss of visual function and bring great inconvenience to people’s daily life.For diagnosis of visual pathway disorders,the methods of visual function assessment are mainly divided into two types: subjective and objective.The subjective test based on psychophysiological method is easy to be influenced by the subjective judgement or cognitive ability of the subject.As a result,the test cannot be applied to some special occasions.The technique of visual evoked potential(VEP)measurement is a kind of objective visual function examination method,especially suitable for infants,mental y disabled,no-verbal patients,hysteria,and malingering.VEP has become one of important means of clinical ophthalmology examination.It is well known that,during the VEP measurement,the projection of a stimulus onto the retina is inevitably affected by the refractive errors or ocular aberrations.However,low-order aberrations(LOAs)of the errors can only be corrected by wearing trial lenses in a traditional VEP.However,in addition to LOAs,there are many higher-order aberrations(HOAs)with more complex shapes.They are also the optical components that influence the further improvement of retinal image quality or visual performance,which would also affect the VEP measurements.However,no relevant studies of using AO to bypass the optical limits in VEP measurement have been reported up to now.Based on this background,this paper develops a VEP measurement system based on adaptive optics(AO)technology,and preliminarily studies the influence of ocular aberrations on the VEP measurements.The main contents are summarized as follows.First,the process of measurement and extraction of VEP was simulated and analyzed.By establishing a mathematical model for extracting VEP,we used the synchronized signals to mark the turning time of stimulus pattern.It was found that the synchronization signal bias would decrese the amplitudes and prolong the latencies of VEP waveform gradually.As a result,the accuracy of measurement was seriously affected.In order to obtain the accurate VPE measurement,the accuracy of the synchronous signal must be strictly guaranteed.In this way,the simulation would provide guidance for the development of VEP measurement system.Also,the influence of ocular aberration on the retinal image quality was simulated and analyzed.A numerical method based on the root mean square error(RMSE)and correlation coefficient(CC)was proposed to directly and quantitatively evaluate the retinal image quality.Through this evaluation,the effect of ocular aberration on the process of stimulus pattern projection onto the retina during the VEP measurements could be directly reflected.Furthermore,the VEP measurement system based on an AO technology was designed and developed.In order to further improve the performance of this system and reduce the requirements of subject cooperation and manual intervention,the system size was minimized and integrated with a subsystem of pupil position and active eye tracking.In the system,the stimulus pattern was displayed by an OLED(organic lightemitting diode)displayer after a stimulus processor.Meanwhile,the processor output a synchronous signal to accurately mark the time of the stimulus presentation.The stimulus pattern on the OLED was final y projected onto the retina through the AO system.As a result,the VEP measurements could be performed without and wtih HOA correction or under different correction strategies.Compared the characteristic waveforms of VEP between these different strategies,the influence of ocular aberrations on VEP would become clear.The system will provide a platform for the accurate VEP measurements and further improve its clinical value.Finally,through comparing the VEP waveform between the field sizes of 15° and 2°,it was verified that the effective and reliable VEP waveforms could also be recorded with 2°.Thus,we used the developed system to study the effects of aberration on VEP through the AO aberration regulation technique.The result shown that the VPE characteristic amplitudes were increased with statistical significance(p < 0.05)when using AO to improve the retinal image quality,but it did not have a significant effect on the latencies.Therefore,based on an AO technology,we can connect the retinal image quality or subjective visual perception together with VEP to accurate measurement of the VEP.It would provide the necessary technical and equipment support for future researches on visual function.