Axial length measurement and its relation to intraocular lens power calculations

The axial length was measured in five hundred consecutive cases using the Kretz 7200 MA ultrasound unit and an immersion technique. The reproducibility of the measurements was within +/- 0.2 mm when performed manually, and within +/- 0.05 mm when performed electronically. Intraocular lens power calculations were performed using a modification of Colenbrander's formula. We predicted within + 1 diopter in 78.8% of the cases. The accuracy was up to 83% when the axial length ranged between 23.0 and 25.0 mm. Stronger power lenses were implanted in shorter eyes and weaker power lenses in longer eyes, necessitating the use of a fudge factor. Surgeons using an immersion technique for axial length measurements should use formulas yielding stronger power lenses, such as Binkhorst's formula or our modification of Colenbrander's formula, with a fudge factor for short and long eyes.