Background: Previous studies have indicated that axial length determination is important in strabismic patients for defining the limit for a safe maximum recession of the medial rectus. Also, the response to strabismus surgery may be, in part, a function of axial length. We previously published a formula for predicting axial length based on age and refractive error; however, its accuracy has not been tested in a patient population that is different from the one used to generate the formula. The purpose of this study is to test a formula for estimating axial length, given age and refractive error, in a population that is different from that from which it was generated.
Method: We measured axial length using A-scan ultrasonography in 163 consecutive patients undergoing strabismus surgery. Twenty-nine patients were younger than 18 months of age; 134 patients were between 18 months and 10 years of age. We compared the measured axial length determination with the axial length value estimated by a formula generated from our previous published series.
Results: For patients younger than 18 months of age, the equation estimated axial length within 0.5 mm in 41.4% of patients, within 1.0 mm in 79.3% of patients, and within 1.5 mm in 93.1% of patients. For patients between 18 months and 18 years of age, the formula estimated axial length within 0.5 mm in 37.3% of patients, within 1.0 mm in 73.1% of patients, and within 1.5 mm in 87.3% of patients.
Conclusions: The formula may be useful for the strabismus surgeon in estimating axial length when A-scan ultrasonography is not available in an operating room setting, particularly in congenital esotropes who require larger recessions in small eyes. If, however, A-scan ultrasonography is available, it is preferable to using the formula. The formula is not sufficiently accurate for use for calculating intraocular lens power.