Purpose: To compare the accuracy of biometry using conventional A-scan ultras onography and partial coherence interferometry, and to improve the accuracy of b iometry by sequential audit of postoperative refractive er...Purpose: To compare the accuracy of biometry using conventional A-scan ultras onography and partial coherence interferometry, and to improve the accuracy of b iometry by sequential audit of postoperative refractive error. Methods: The stud y was performed in three phases. In phase 1, 20 consecutive patients undergoing routine phacoemulsification underwent biometry using bothA-scan ultrasonography and the Zeiss IOLMaster (ZIOLM).Asingle experienced optometrist refracted all p atients 2 weeks after surgery. The errors between expected and achieved refracti on were calculated and compared between the two methods. In phases 2 and 3, a fu rther 22 and 20 patients, respectively, were recruited and only the ZIOLM was us ed for biometry. The manufacturer’s suggested A-constant was refined and the e rror between expected and achieved refraction was calculated. Results: In phase 1, the median unexpected error for the ZIOLM was +0.63 (interquartile range +0 .368 to +1.015) and for A-scan biometry was 0.24 (interqu artile range-1.335 to +0.802). In phase 1 65%of patients’- postoperative refractions were found to be within 1.0 D of emmetropia using th e ZIOLM (55%using A-scan biometry). Refinements to the A-constant improved th is to 95%by phase 3. Conclusion: An error was identified in IOL power estimatio n with the ZIOLM, when using the manufacturer’s recommended A-constant (recomm ended and previously optimized ultrasound A-constant 118.0; ZIOLMoptimized A-c onstant 118.6). Serial modifications to the A-constant were successful in reduc ing the unexpected error towellwithin the tolerance limits of published internat ional standards.展开更多
文摘Purpose: To compare the accuracy of biometry using conventional A-scan ultras onography and partial coherence interferometry, and to improve the accuracy of b iometry by sequential audit of postoperative refractive error. Methods: The stud y was performed in three phases. In phase 1, 20 consecutive patients undergoing routine phacoemulsification underwent biometry using bothA-scan ultrasonography and the Zeiss IOLMaster (ZIOLM).Asingle experienced optometrist refracted all p atients 2 weeks after surgery. The errors between expected and achieved refracti on were calculated and compared between the two methods. In phases 2 and 3, a fu rther 22 and 20 patients, respectively, were recruited and only the ZIOLM was us ed for biometry. The manufacturer’s suggested A-constant was refined and the e rror between expected and achieved refraction was calculated. Results: In phase 1, the median unexpected error for the ZIOLM was +0.63 (interquartile range +0 .368 to +1.015) and for A-scan biometry was 0.24 (interqu artile range-1.335 to +0.802). In phase 1 65%of patients’- postoperative refractions were found to be within 1.0 D of emmetropia using th e ZIOLM (55%using A-scan biometry). Refinements to the A-constant improved th is to 95%by phase 3. Conclusion: An error was identified in IOL power estimatio n with the ZIOLM, when using the manufacturer’s recommended A-constant (recomm ended and previously optimized ultrasound A-constant 118.0; ZIOLMoptimized A-c onstant 118.6). Serial modifications to the A-constant were successful in reduc ing the unexpected error towellwithin the tolerance limits of published internat ional standards.
