AIM:To compare the accuracy of conventional contact A-scan and IOL Master in measuring axial length and anterior chamber depth, and to evaluate the characteristics of these two different methods.

METHODS:Totally 145 cases(189 eyes)who underwent phacoemulsification and intraocular lens implantation in our hospital from January 2015 to December 2016 were observed prospectively. They were divided into five groups according to ocular axial length measured by IOL Master(Group A: AL≤22mm, Group B:22mm28mm). The axial length and anterior chamber depth were measured by A-scan and IOL Master respectively before operation, corneal curvature was measured by IOL Master. AL≤22mm using Hoffer Q formula to calculate the crystal degree, AL>22mm using Haigis formula to calculate the crystal degree. Analysis of axial length, anterior chamber depth and mean absolute refractive error at 3mo after surgery.

RESULTS:The axial length measured by A-scan and IOL-master: Group A were 21.48±0.41mm and 21.46±0.40mm(P>0.05); Group B were 23.13±0.62mm and 23.14±0.63mm(P>0.05); Group C were 25.24±0.56mm and 25.27±0.59mm(P>0.05); Group D were 26.97±0.59mm and 27.03±0.64mm(P>0.05); Group E were 30.76±1.40mm and 31.01±1.53mm(P<0.05). Mean absolute refractive error(MAE)at 3mo after surgery by A-scan and IOL Master: Group A were 0.50±0.30D and 0.43±0.27D(P>0.05); Group B were 0.48±0.34D and 0.45±0.32D(P>0.05); Group C were 0.56±0.32D and 0.49±0.40D(P>0.05); Group D were 0.64±0.16D and 0.50±0.22D(P>0.05); Group E were 0.91±0.47D and 0.62±0.29D(P<0.05), MAE≤±0.50D were 38.7% and 65%(P<0.05), MAE≤±1.00D were 69.2% and 83.3%(P>0.05). Anterior chamber depth measured by A-scan and IOL Master:Group A were 2.81±0.35mm and 2.82±0.41mm(P>0.05); Group B were 3.04±0.50mm and3.10±0.47mm(P>0.05); Group C were 3.55±0.62mm and 3.60±0.52mm(P>0.05); Group D were 3.42±0.24mm and 3.51±0.30mm(P>0.05); Group E were 3.50±0.28mm and 3.61±0.34mm(P>0.05).

CONCLUSION:IOL Master and contact A-scan have a high degree of consistency in the biological measurement, IOL Master has higher accuracy for patients with high myopia and long axis. It is a simple, accurate, good-repeatable and non-contact measurement tool.