A-Scan Resources

uuuImmersion Scanning

uuuA-Scan Tips and Techniques

uuuPost-Refractive A-Scans

uuuTissue Velocity References

uuuTable of IOL Constants for the Holladay Formula

uuuRecommended Training Courses

Immersion Scanning

Primarily due to concerns over corneal compression when performing direct contact A-scans, the immersion technique is increasingly gaining in popularity. The technique involves placing a small scleral shell onto the eye between the lids, filling with BSS, and immersing the probe into the fluid without contacting the cornea. The BSS acts as an ultrasonic coupling media, allowing scans to be taken without compressing the cornea. Click here for more detailed instructions.

Two of the primary benefits for using immersion scanning are:

uuuGreater Accuracy. Since the immersion scanning technique is non-contact, there is no indentation of the
uuuglobe and the measures obtained are more accurate than with direct contact scanning. In fact,
uuudepending upon the user, axial lengths of eyes measured using the immersion technique can measure
uuuupwards of 0.3 mm longer than when measured with direct contact.

uuuGreater Repeatability and Less Operator Bias. The immersion technique will yield more repeatable
uuuresults across different technicians, since the method is not dependent upon how hard the technician
uuuplaces the ultrasound probe onto the eye from scan to scan. For that same reason, biometric results
uuuusing the immersion technique are more repeatable even when taken by the same technician.

For these reasons, immersion A-scan is becoming the standard of care and is provided standard in the Sonomed PacScan and EZ-Scan models. It should be noted that a practice that changes from direct contact to immersion scanning must repersonalize their personal surgeon factors and IOL constants, since the measures will now reflect true lengths rather than the slightly shortened lengths achieved previously through direct contact scanning.