Objective　To investigate the relationship between muscular asthenopia post photorefractive keratectomy (PRK) and eccentric ablation. Methods　16 eyes of 8 myopia cases whose muscular asthenopia was corrected by subjectively accepted triangular prism after PRK with vision more than 0.8 were followed up for 6-14 months. On the basis of data provided by the pre-PRK, post-PRK and their difference corneal topography, we calculated the real corrected corneal diopter (D) with the Holladay formula and measured the ablating eccentricity (h) and its direction. According to the formula δ≈Dh, the prism effective value (δ) caused by the eccentric ablation was computed and compared with objectively accepted triangular prism. Results　The subjectively accepted prism was similar to values calculated from the formula. Their mean difference is 0.10±0.25. The direction of the subjectively accepted prism was in the direction of ablation deviation. Conclusions　Eccentric ablation was the chief cause of post-PRK muscular visual asthenopia. The triangular prism effective value from eccentric ablation may be estimated by the formula δ≈Dh. We must pay attention to the diagnosis, treatment and prevention of post-PRK muscular asthenopia.

Objective To compare the diagnostic value of 18F-fluorodeoxyglucose(18F-FDG)positron emission tomography(PET)/CT and MR whole body diffusion weighted imaging(WB-DWI)in malignant tumor bone metastasis.Methods A total of 100 patients with suspected malignant tumor bone metastasis admitted were selected as the research objects.All patients underwent 18F-FDG PET/CT and WB-DWI before treatment.Pathological examination and follow-up results were used as the gold standard,the diagnostic value of the two examination modalities in malignant tumor bone metastasis was analyzed.Results There were 93 patients with bone metastasis diagnosed by gold standard,with a total of 232 lesions.The detection rate of 18F-FDG PET/CT was 92.67％,which was not significantly different from that of WB-DWI(89.66％)(P＞0.05).The sensitivity,positive predictive value and diag-nostic coincidence rate in malignant tumor bone metastasis of 18F-FDG PET/CT were 92.67％,98.62％and 98.71％,respectively,which were significantly higher than 89.66％,97.65％and 94.83％of WB-DWI,but the difference was not significant(P＞0.05).The specificity and negative predictive value of 18F-FDG PET/CT were 82.35％and 45.16％,respectively,which were significantly higher than 70.59％and 33.33％of WB-DWI(P＜0.05).The maximum standardized uptake value(SUVmax)of patients with bone metastasis was significantly higher than that of patients with benign lesions,and the apparent diffusion coefficient(ADC)value was significantly lower than that of patients with benign lesions(P＜0.05).Receiver operating characteristic(ROC)curve showed that the diagnostic value of SUVmax combined with ADC[area under the curve(AUC)=0.912,P＜0.05]was higher than that of single examination.Conclusion 18F-FDG PET/CT is more effective than WB-DWI in the diagnosis of malignant tumor bone metastasis,he combination of the two examinations can improve the diagnostic efficacy for malignant tumor bone metastasis.