Conferring The Relationship Between Tonic Accommodatin And Refractive Components

ProposeCompare TA and refractive components in the low myopic group with those in emmetropic group and confer the relationship between tonic accommodation and refractive components.MethodsTo select the patients years from 11 ~ 15 without strabismus 39 cases 75 eyes, which had no amblyopia, abnormal of biocular vision and no other ocular diseases. Based on the refractive error, the patients were -divided into two groups: low myopic group ( experiment group ) and emmetropic group ( control group ) . The physical dimensions from ultrasound and keratometry include cornea refractive power, anterior chamber depth, lens thickness, vitreous length and axis length. The values of TA obtained from DOG target. All these data were used for statistic analysis.ResultCornea refractive power and anterior chamber depth in the low myopic group were larger than those in emmetropic group, but the values of TA were lower than those in emmetropic group. The correlation between cornea refractive power and TA was stronger than the correlation between axis length and TA. The regressive formula for TA and refractive components was TA = 17.065 -0.156 * cornea refractive power - 0.376 * lens thickness - 0.339 * axis length.DiscussionIn the low myopic group pure coroeal origin was found in 20.9% , pure axial origin in 29.2% , and combined origin in 45.8% of the eyes. In the medium and high myopic groups no pure comeal myopia was found, while axial myopia was found in 16.7% and combined myopia in 83.3% of the eyes. These were illustrated that in the low myopic group, the function of cornea refractive power are larger. Axis length in the low myopic group are in normal or extended very little, but cornea refractive power are larger than emmetropia. In this experiment , cornea refractive power in the low myopic group was 43.95 D, larger than 42.64D in emmetropic group and axis length were 23.82mm, 23.56mm respectively, which were no significant difference.iTonic accommodation is the resting position of the accommodative system in the absence of compelling visual stimuli. Some studies were found that intersub-ject variations in tonic levels of accommodation are related to refractive state. In the myopic group TA is the lowest, the hyperopic group is the highest and the emmetropic group is medium. In this study TA in the low myopic group was 0. 79D 0.12D, significantly lower than that in the emmetropic group which was 1.24D 0. 3ID. Perhaps myopia have lower parasympathetic innervation than emmetropia, so the values of TA is lower.TA had correlation with cornea refractive power and axis length. Correction coefficients were -0.799, -0.381 respectively. The regressive formula was TA = 17.065 -0.156 * cornea refractive power - 0.376 * lens thickness -0.339 * axis length, so we can calculate the values of TA by measuring refractive components.Conclusion1. The values of TA in the low myopic group is lower than that in emmetropia.2. The regressive formula was TA = 17.065 -0.156 * cornea refractive pow-er -0.376 * lens thickness -0.339 * axis length, we can calculate the values of TA by measuring refractive components.