Objective  To evaluate the accuracy of three methods which use to calculated the length of foreign scleral materials.
Methods Posterior Scleral Reinforcement (PSR) after Thompson was performed on 62 patients（65 eyes）with high myopia from 7 to 66 years of age. The main indication criteria for surgery during the period 2008-12 /2010-02 included: severe myopia more than -9 diopt and the increase in refraction more than -1 D per year. Two formulas were designed to calculate the length of sclera material (LSM) with data of refraction, corneal curvature, anterior chamber depth and axial length (AL). The third method was to build regression equation to calculate the predictable length of sclera material. Results of three methods were compared to the actual length of Scleral material of PSR.
Results The mean of cornea refractive power, anterior chamber depth, sypheris equivalent, axial length and the actual length of sclera material was 7.60±0.29mm, 3.630±0.445mm, -19.3±6.9D, 30.14±2.65mm, 47.8±4.0mm. The regression equation of the relation between the length of sclera material and the length of axis was as followed: LSM=9.576+1.271×AL. Mean length of three methods was method 1：58.7±8.0mm，methods 2 ：58.6±8.0mm, methods 3：47.8±3.3mm. All three methods were highly correlated with actual SLM: method 3（r=0.835, P﹤0.001）﹥method 2（r=0.829, P﹤0.001）﹥method 1(r=0.822, P﹤0.001).
 Conclusions The regression equation can predict the SLM more accurately than the other
two methods.