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Givago S Souza, Iraquitan Cordeiro Filho, Lorena Botelho Vergara, Alexandre Rosa, Hideraldo Cabeça, Schubert Carvalho; Method to detect visual field loss using multifocal visual evoked potential. Invest. Ophthalmol. Vis. Sci. 2014;55(13):5127. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To develop a supervised learning model with decision trees to act as a decision support system in the task to identify visual field losses by using multifocal visual evoked cortical potential (mfVECP).
We studied mfVECP data from 22 eyes of healthy subjects, 23 eyes of subjects with neuromyelitis optica (NMO), and 16 eyes from subjects with multiple sclerosis (MS). Dartboards with 60 checkboard sectors were used as stimuli. The SNR from the waveforms of the 60 sectors was used as input into a decision tree. A combination of two-sample t-test feature selection and forward sequential feature selection was used to obtain the best representative features or sectors that sorted out the three subject classes. With these selected features, decision tree models were fitted and cross-validated using leave-one-out technique. For evaluation criteria, we used the classification of accuracy and Cohen’s Kappa coefficient. The following comparisons were analyzed: healthy subjects versus NMO subjects; healthy subjects versus MS subjects; NMO subjects versus MS subjects; healthy subjects versus subjects suffering for both illnesses.
We found a number of visual field sectors that better differentiate mfVEP data for each comparison: 12 sectors (healthy subjects vs NMO subjects); 24 sectors (healthy subjects vs MS subjects); 21 sectors (healthy subjects vs both illnesses); none sector (NMO subjects vs MS subjects). With the selected features, decision trees were fitted following the same combinations of the feature selection process. For each combination, two decision trees were fitted, one without the feature selection process and another with the selected features. In the healthy vs NMO dataset the results after cross-validation shows that the accuracy of the decision tree and the Kappa value were 80% and 0.6002, respectively; for this same dataset after the feature selection the results were 84% and 0.6884, respectively. For healthy vs MS dataset, the accuracy and Kappa value were 71.05% and 0.4011, respectively (no feature selection), and after feature selection the results were 76% and 0.5100, respectively. For healthy vs both illnesses as one class, the accuracy and Kappa value were 68.85% and 0.3039, respectively, after feature selection the results were 68.85% and 0.3178, respectively.
In general, the use of feature selection improved classification accuracy.
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