| Visual field testing is of great significance for the early diagnosis,prevention and management of chronic eye diseases such as glaucoma.Other diseases such as epilepsy may also affect the visual field and require visual field testing.The traditional visual field detection method is greatly influenced by the subjective factors of the subjects.Therefore,in the past two decades,a method of objectively detecting the visual field with multifocal visual evoked potential(mfVEP)has been gradually developed.In mfVEP technology,the visual stimuli of various patterns determined by orthogonal pseudo-random sequences are presented simultaneously in multiple visual field areas of the subjects,and the visual response of each visual field is obtained from the EEG signals recorded in the occipital region(primary visual region)by a decoding process similar to the code division multiple access(CDMA)wireless communication,so as to determine the visual acuity of each visual field of the subjects.Although mfVEP provides an objective measure of the visual field,it has not been widely used in clinical practice,mainly because the uncomfortable long period of black and white alternation stimulation makes it difficult for subjects to successfully complete the test.This thesis proposes to use an equal-brightness color stimulation to improve the comfort of the mfVEP technology.The corresponding color mfVEP visual field test system is designed and implemented.The performance of the proposed color mfVEP is evaluated and compared to the traditional mfVEP through a study of a group of normal subjects.According to the theory of visual color collocation,the thesis chooses red and green of equal brightness as the color of the checkerboard blocks used in the visual stimulation to replace the black and white pair in the traditional mfVEP.According to the questionnaire survey,the equal-brightness red-green stimulus designed in this paper makes the users feel much more comfortables as compared to the black and white stimulus of the traditional mfVEP.A platform for visual field testing is designed and implemented,including both hardware and software.The platform implements a variety of functions such as the presentation of stimuli flexible visual field partition,automatic calculation of optimal pseudo-random m sequence,first and second-order nonlinear kernel decoding,noise removal and electrode fusion based on principal component analysis(PCA),visual field estimation and result presentation.Based on the proposed red-green equal-brightness mfVEP platform,visual field testing was performed on 10 subjects using the novel color mfVEP and another 10 subjects using the traditional mfVEP,and performance was compared for the two methods.Among the 36 locations in the visual field covered in the experiment,8 locations showed significant difference between color and traditional mfVEP,and color mfVEP always performed better.The results for the remaining 28 locations showed no significant difference between the two mfVEP techniques.Further more,visual field loss was simulated by blocking visual stimulation in specific locations.The experiment results show that color mfVEP can effectively detect the visual field loss.The experimental results show that the mfVEP technology with equal-brightness red-green stimuli proposed in the thesis not only solves the key problem of the comfort of the subjects brought by the traditional black and white stimuli,enabling the subjects to use the mfVEP technique which is an advanced objective method of visual field testing,but also its performance is obviously better than the traditional mfVEP.The use of equal-brightness red-green stimulation may play a key role in the clinical promotion of mfVEP for objective visual field testing.In order to achieve this goal,the usability and performance of the proposed color mfVEP technology still need to be extensively tested in clinical applications. |
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