| IntroductionThe identification of clinical forensic medicine often includes the determination of visual function. It is important to find an objective way in determining visual function because people undergoing identification sometimes tend to exaggerate the visual disturbance or pretend to be incomplete in visual function ( blandness ). Visual evoked potential. (VEP) is an objective method to determine visual function. According to the difference of stimulation lights, the VEP is classified as flash visual evoked potential ( F - VEP) and pattern visual evoked potential ( P - VEP). In P - VEP wave group, the P100, also known as P, ,is usually used in the identification in forensic medicine. However , the amplitude of vibration and latent period of the P100 are affected by many factors. Among these factors, the refraction state is usually easy to be neglected, which results in false positive reaction. Therefore , the real visual function of people undergoing identification cannot be determined correctly.Present studies in effects of ametropia on VEP mainly focus on the changes of absolute values of amplitude of wave and latent period, and limit the stimulation with single spatial frequency. There is no definite report on effects of ametropia on VEP with stimulations of different space frequencies.Our experiment examined the VEP with stimulations of different space frequencies after different refraction loads in 80 eyes of 40 people. We discussed the effects of ametropia on VEP and its applicationin the identification of forensic medicine through the comparison of variation rate of the amplitude of wave and the comparison of the latent period.Materials and methodsForty undergraduates aging from 20 to 25 at China Medical University were included in our experiment. The results of ocular examination of these students were normal. All of these students had no ocular diseases except myopia, the corrected visual acuity of all 80 eyes was 1.0.The examined eye stared at the center of screen, and we covered the other eye. Three kinds of tessellated stimulation of different spatial frequencies (8x8, 16x16, and 32 x32) were used. We recorded the optimum corrected visual acuity of 1.0 with relative refraction load of OD. At the same time, the shapes of P - VEP wave with different refraction loads of + 2.00D, + 4.00D, + 6.00D, and + 8.00D were also recorded. The relative refraction load of OD was as control, and the other refraction loads were as experiment groups. The changes of amplitude of P100 and latent period were calculated and compared between control and experiment groups.Results1. The decrease rates of amplitude of P100 induced by the stimulations of 3 space frequencies (8x8, 16 x 16, and 32 x 32) all increased with the increase of diopter of convex lens. The correlation coefficients were 0.999, 0.992, and 0.957, respectively. That means the decrease rate of amplitude of P100 has a positive correlation with the diopter of convex lens. With the same refraction rate, the decreaserate of the amplitude of P100 increased with the increase of the spatial frequency of stimulation.2. The dispersion coefficients of the decrease rate of amplitude of P100 with different refraction loads and space frequencies were significandy lower than the dispersion coefficients of the absolute values (Pairedt test, t = -15.026, P<0.001).3. In the 80 eyes of these 40 students, no difference was found between the latent period of the control and that of stimulation of 8 x 8 spatial frequency with + 2.00D refraction load ( P > 0. 05 ). In other experiment groups with stimulation of same spatial frequency, the e-longation of latent period of P100 increased significandy with the increase of the refraction load. And with the same refraction load, the e-longation of latent period of P100 also increased significandy with the increase of the spatial frequency of the stimulation.Discussion1. Effects of ametropia on amplitude of P100Our experiment determined the VEP of different refraction loads in 40 st...
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