Comparative study of central corneal and midperipheral corneal thickness measurement with specular microscopy, Slit-scanning pachymetry, anterior segment optical coherence tomography and ultrasound pachymetry

Objective To compare corneal thickness (CT) measurements obtained by specular microscopy,Slit-scanning pachymetry,anterior segment optical coherence tomography (AS-OCT) and ultrasound pachymetry,with a focus on central and midpeipheral (3.0 mm) region of cornea. Methods Central CT and CT at four midperipheral points were measured with the specular microscopy (Topcon SP-3000P),Slit-scanning pachymetry (Orbscan),AS-OCT and ultrasound pachymetry. Results In 134 eyes of 134 healthy subjects,the mean central CT was 543.10±32.69μm for ultrasound pachymetry,537.02±32.39 μm for AS-OCT,534.93±34.25μtm for Orbsan Ⅱ and 515.49±32.76μm for specular microscopy.No significant difference was found between AS-OCT measurements and Orbsan Ⅱ (P =0.07).The best agreement was observed in the ultrasound pachymetry and AS-OCT.In 125 eyes,the measurements of mean midperipheral CT obtained by Orbsan Ⅱ were much higher than AS-OCT and specular microscopy at all points. Conclusions Specular microscopy measurements of central CT and midperipheral CT are much thinner than other methods.Central CT measurements obtained by Orbscan Ⅱ and AS-OCT show good agreement,therefore can be used interchangcably; but midperipheral CT measurements cannot be used interchangeably due to the large difference. Key words: Corneal thickness;  Specular microscopy;  Anterior segment OCT;  Orbscan Ⅱ;  Ultrasound pachymetry