Certified Ophthalmic Technician (COT) Test 2025 – 400 Free Practice Questions to Pass the Exam

The feature that enhances the accuracy of immersion A-scan compared to contact A-scan is the elimination of corneal compression. In a contact A-scan, the transducer is placed directly on the cornea, which can lead to a flattening effect caused by the pressure applied. This compression may alter the true axial length measurement of the eye by artificially reducing the distance between the anterior surface of the cornea and the retinal surface.

In contrast, immersion A-scan uses a coupling medium, typically a saline solution, in which the eye is submerged. This method avoids direct contact with the cornea, thereby preventing any deformation due to applied pressure. As a result, the immersion technique provides a more accurate representation of the true optical path length of the eye. Thus, the measurements taken in this way are more reliable, leading to enhanced precision in calculating parameters like axial length, which is critical for determining proper intraocular lens power in cataract surgery and other ocular procedures.