The UBM is an ultrasound that allows the doctor to see inside the eye, behind the iris (the colored part of the eye). Just like an ultrasound allows doctors to see inside our bodies for things like evaluating a pregnant woman to make sure a baby is OK, these ultrasounds allow us to look into an eye and make sure there are no abnormalities in the area of the eye where the Visian ICL is placed. It also allows us to accurately measure the space where the Visian ICL is positioned so the correct size can be determined. In my opinion, this has been more accurate than just measuring the width of the cornea. The width of the cornea is variable depending on how the white part of the eye and the cornea developed, or if there has been scarring from contact lens wear, infections, or other inflammatory problems on the surface of the eye. Although it takes a little longer to do the UBM measurements, I feel that it has greatly improved the outcomes with Visian ICL surgery.