Anterior chamber depth measurement: a-scan versus optical methods.

PURPOSE: To evaluate methods of measuring anterior chamber depth (ACD) before and after cataract surgery.

SETTING

St. Erik's Eye Hospital, Stockholm, Sweden.

METHODS

A-scan (BVI Axis) and Scheimpflug imaging (Nidek EAS-1000) were used to measure ACD preoperatively and 6 and 18 weeks after phacoemulsification with implantation of a poly(methyl methacrylate) (PMMA) intraocular lens (IOL) in 23 patients. Because of a large systematic difference between the 2 methods, measurement with Orbscan (Orbtek) and optical pachymetry (Haag-Streit) were included when measurements were repeated 36 weeks postoperatively. A t test for paired observations was used for statistical analysis.

RESULTS

Preoperatively, the mean A-scan measurements were significantly shorter than the Scheimpflug values: 3.05 mm +/- 0.36 (SD) and 3.37 +/- 0.35 mm, respectively (P < .001). At 6 weeks, the difference was more pronounced: 3.73 +/- 0.26 mm and 4.65 +/- 0.33 mm, respectively (P < .001). At 36 weeks, the A-scan and Scheimpflug values remained unchanged. The results of the Scheimpflug measurements were confirmed with optical pachymetry and Orbscan analysis.

CONCLUSIONS

There was good agreement between results obtained with 3 methods based on optical principles. Considering the basic and simple measurement principle of these instruments, they appear to provide the correct result. The A-scan equipment used in this study is unsuitable for determination of ACD in eyes with PMMA IOLs.