Agreement between A-mode and B-mode ultrasonography in the measurement of ocular distances

It is generally accepted that A-mode ultrasonography is more accurate than B-mode in measuring intraocular dimensions. Consequently, A-mode ultrasonography is the procedure of choice in ocular biometry while B-mode ultrasonography is used principally for diagnostic purposes. In this study, we investigated the agreement between measurement of intraocular distances using A- and B-mode ultrasonography on freshly enucleated camel eyes. Our results suggest that relative to average A-mode values, B-mode overestimates corneal thickness (bias = 0.06 mm) and anterior chamber depth (bias = 0.03 mm), while it underestimates lens thickness (bias = -0.11 mm), vitreous chamber depth (bias = -0.32 mm) and axial length (bias = -0.40 mm). In general, difference between A- and B-mode values is larger for deeper intraocular dimensions. This implies that the two methods are more likely to give different readings for measurements of lens thickness, vitreous chamber depth and axial length.