| ObjectiveMeasuring the binocular and monocular accommodation reactions of different types of phoria and the rule of changes in direction and magnitude of phoria before and after the reading, the research is aim to discuss the effects and rule of phoria to binocular accommodative response and vergence adaptation. Speculating the factor of phoria on the development of myopia. Speculating the rule of different types of phoria monocular and binocular accommodative response, the research could provide the clinical reference of evaluating abnormal binocular vision by measuring monocular and binocular accommodation response. At the same time, the research could evaluate the effects of different types of phoria on asthenopia by reading on video display terminal and the effects of each type of phoria on asthenopia between reading on video display terminal and papers.MethodsOne hundred and sixteen subjects were enrolled, including undergraduate and graduate students, with a mean age of 20.58 years±2.96(SD)(range 18 to 29 years) from Tianjin Medical University from September to November in 2013. Inclusion criteria: spherical equivalent degree <-6.00D; astigmatism <-1.00D; anisometropia <1.00D; best corrected visual acuity ≥1.0. Subjects with strabismus and taking drugs were excluded. According to the amount of near phoria(NP), subjects were divided into three group: normal group(N group), exophoria group(EXO group) and(EXO group). Normal phoria was defined as-6 to 0 prism degree(Δ). Exophoria was defined as less than-6Δ. Esophoria was defined as more than 0Δ. There were 48 subjects with a mean age of 20.96 years±2.45(SD) and a mean spherical equivalent degree of(-3.63 ± 1.66) D in normal group. There were 42 subjects with a mean age of 21.29 years±2.10(SD) and a mean spherical equivalent degree of(-3.99 ± 1.94) D in exoporia group. There were 26 subjects with a mean age of 19.77 years±1.61(SD) and a mean spherical equivalent degree of(-3.69 ± 1.24) D in esophoria group.Procedures as follows:1.Refraction: Objective refraction measures were performed with phoropter.2.Binocular function measure: Measure the horizontal distance and near phoria with Von Graefe to calculate the accommodation convergence / accommodation(AC/A) ratios. Measure positive relative accommodation(PRA), negative relative accommodation(NRA), amplitude of monocular accommodation(M-AMP) and amplitude of binocular accommodation(B-AMP).3.Accommodative response: The accommodative response(monocular accommodative response and binocular accommodative response)measurements were performed with the open vision automatic infrared refractometer(Shin-Nippon WR-5100 K, Japan).4.Reading: Subjects were required to perform a sustained fixation task consisting of reading unordered words on video display terminal(VDT) at a viewing distance of 0.4 meter for a continuous 20-minute period.5.Evaluating: Subjects were performed to fill the form of evaluating asthenopia.6.Measuring again: Again, the binocular function and monocular and binocular accommodative response measurements were performed after reading.7.Reading: After 24 hours, half of subjects randomly selected with the best correction lens were required to perform a sustained fixation task consisting of reading unordered words on paper, which were the same as words on VDT, at a viewing distance of 0.4 meter for a continuous 20-minute period.8.Evaluating again: Again, subjects were performed to fill the form of evaluating asthenopia after reading.Statistical Analysis: All data were collected in an Excel database(Microsoft Office 2003, Microsoft Corp.). Data analysis was performed using SPSS for Windows(version 17.0, SPSS Inc.). Baseline characteristics were compared between the groups using the two-tailed t-test if normality assumptions were preserved, or Kruskal-Wallis H test or Mann-Whhitney U test for non-normal distribution data, and the χ~2 test for categorical data, using in all cases the same level of significance(P<0.05).Results1. There were statistically significant differences between monocular and binocular accommodative response in each group before reading(P<0.05). The BA were more than the MA in EXO group and N group(t=9.264, P<0.05; t=4.840, P<0.05, respectively). The MA were more than the BA in ESO group(t=-6.064, P<0.05). There were statistically significant differences in the results of BA of three groups by LSD multiple comparisons. The BA of EXO group was more than the BA of ESO group(P<0.05). The BA of EXO group was more than the BA of N group(P<0.05). The BA of N group was more than the BA of ESO group(P<0.05). There were no statistically significant differences in the results of MA of three groups by LSD multiple comparisons.2. There were no statistically significant differences in MA and BA of three groups in pre-reading and post-reading on VDT(MA: χ~2=0.011,P>0.05; BA: χ~2=1.190,P>0.05, respectively). The BA was more than the MA in EXO group and N group. The MA was more than BA in ESO group. The MA and BA in post-reading were more than in pre-reading, but there was no significant difference(P>0.05).3. There were no statistically significant differences in the results of distant phoria between pre-reading and post-reading(χ~2=5.220,P>0.05).4. There were no statistically significant differences in the results of positive relative accommodation(PRA), negative relative accommodation(NRA), amplitude of monocular accommodation(M-AMP) and amplitude of binocular accommodation(B-AMP) between pre-reading and post-reading on VDT(P>0.05).5. There were statistically significant differences in the variation of near phoria and AC/A in three groups(χ~2=44.026,P<0.05; χ~2=6.986,P<0.05, respectively). The phoria degree decreased in ESO group and EXO group. The phoria degree increased in N group. The AC/A ratio decreased in ESO group. The AC/A ratio increased in EXO group. The AC/A ratio unchanged in N group.6. There were no statistically significant differences in evaluating asthenopia of three groups after reading on VDT(χ~2=5.281,P>0.05).7. There were statistically significant differences between half of subjects reading on VDT and half of subjects reading on paper in evaluating asthenopia(U=1320.5,P<0.05).Conclusions1. Different types of phoria have an impact on binocular accommodative response. The binocular accommodative response is more than the monocular accommodative response in exophoria and normal phoria. The monocular accommodative response is more than the binocular accommodative response in esophoria.2. Different types of phoria have no obvious impact on monocular.3. With the compensation of fusional vergence, different types of phoria show up as different directions of vergence adaptation in pre-reading and post-reading on VDT. Exophoria shows up as convergent vergence adaptation. Esophoria and normal phoria show up as divergent vergence adaptation.4. The AC/A ratio could have an impact on vergence adaptation in different types of phoria.5. The esophoria eye had the higher binocular accommodative lag and this may be a factor of development of myopia.6. There is no significant difference between different types of phoria after reading on VDT.7. Reading on VDT is more likely to cause asthenopia than reading on paper. |
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