A phakic eye was measured using an incorrect sound velocity of 1641 m/sec rather than the correct aphakic velocity of 1532 m/sec. The erroneous axial length reading obtained was 23.0 mm. Use the velocity conversion equation to determine the correct axial length measurement.

A-scan biometry, also referred to as A-scan, utilizes an ultrasound device for diagnostic testing. This device can determine the length of the eye and can be useful in diagnosing common sight disorders. A-scans are also extremely beneficial in cataract surgeries, as they enable the ophthalmologist to determine the power of the intraocular lens (IOL) needed for the artificial implant.

Ocular biometry refers to measurement of anatomic dimensions of the eye, which include corneal curvature (keratometry), axial length, and anterior chamber depth. These measurements are primarily used to calculate the appropriate power of the IOL to be implanted during cataract surgery. Given technological advances in cataract surgery and the introduction of premium IOL implants, patient expectations continue to rise, and refractive error following cataract surgery is no longer tolerated. Therefore, it is of utmost importance to obtain accurate biometric readings to optimize postoperative refractive outcomes. [1]

In addition to axial length, ultrasound biometry can measure anterior chamber depth and lens thickness. Ultrasound biometry does not provide keratometry measurements, so corneal power must be measured with a keratometer or a topographer for calculation of IOL power. [1]