Comparison of ocular anterior segment parameters measured by three kinds of biometric measuring methods in myopic eyes

Abstract

Background It is essential to measure and assess the parameters of ocular anterior segment for refractive surgery in myopic eyes.Some different imaging devices can be used for biometric measurement of ocular anterior segment,but which is more accurate and convenient is still under investigation.Objective This study was to compare the anterior segment parameters in myopic eyes measured by anterior segment optical coherence tomography (AS-OCT),Orbscan topography and ultrasonic pachymetry (US).Methods One hundred and forty eyes of 70 myopic subjects with the diopter of-0.75 to-10.25 D,who intended to receive corneal refractive surgery in the Second Affiliated Hospital of Zhejiang University School of Medicine from November 2011 to May 2012,were retrospectively analyzed.Central corneal thickness (CCT) was measured using AS-OCT,Orbscan Ⅱ and US,respectively,and anterior chamber depth (ACD) was measured by AS-OCT and Orbscan Ⅱ,and the angle to angle (ATA) distance and corneal white-to-white corneal distance (WTW) were measured by AS-OCT and Orbscan Ⅱ,respectively.The parameters from different apparatuses were statistically compared.Results The mean CCT were (516.57±30.25) μm in AS-OCT,(523.68±31.87) μm in US and (514.69±38.40) μm in Orbscan Ⅱ,without significant difference among them (F =2.775,P =0.063).Then the patients were divided into three groups based on the US measurement of CCT (＜500 μm group,500-569 μm group,and ≥ 570 μm group).In the ＜500 μm group,there was a significant difference in the CCT among the three methods (F =22.236,P =0.000),significant differences were found between AS-OCT and Orbscan Ⅱ,or Orbscan Ⅱ and US(both at P＜0.05).In the 500-569 μm group,there was no significant difference in the CCT among the three methods (F =3.011,P =0.051).In the ≥ 570 μm group,there was a significant difference in the CCT among the three methods (F =4.133,P =0.021),a significant difference was found between AS-OCT and US(P＜0.05),but there was no significant difference between AS-OCT and Orbscan Ⅱ (P＞0.05).The ACD values measured by AS-OCT was (3.83±0.21) mm,which was higher than (3.75 ± 0.21) mm by Orbscan Ⅱ,with a significant difference between them (t =-8.520,P =0.000).In addition,the ATA value by AS-OCT (12.43 mm±0.74 mm) was higher than the WTW value (11.42 mm±0.33 mm) by OrbscanⅡ,with a significant difference between them(t=-18.088,P=0.000).Conclusions AS-OCT,US and Orbscan Ⅱ can offer accurate CCT value,and they can provide references to one another before refractive surgery.However,the ACD,ATA and WTW values by AS-OCT and Orbscan]Ⅱ have large differences. Key words: Anterior segment optical coherence tomography; Orbscan topography; Ultrasonic pachymetry; Central corneal thickness; Anterior chamber depth; White to white corneal distance; Angle to angle distance