The Visian ICL (STAAR Surgical, Monrovia, CA) is a collamer phakic IOL.  This lens material is inserted into the front portion of the eye behind the iris but anterior to the natural lens.

There is always concerns over what is the best size fit for each eye.  If the lens is too large it will vault too high and crowd the angles.  If the lens is too small, then it would sit too flat and touch the crystalline lens increasing the potential for cataract formation.

Many methods have been used in the past.  The "white to white" is a gross measurement using the calipers to other instruments to measure the distance from sclera on one side to the other side of the cornea.  This is generally regarded as too gross and not the most accurate.  The measurement also has relatively weak correlation with the true "sulcus to sulcus" space.

I had the pleasure of using the Sonomed VuMax-II Ultrasound Biomicroscope with the 35Mhz probe (Sonomed Inc., Lake Success, NY).  The experience with limited to 2 days and about 10 eyes.  The eyes were prepared with Tetracaine for comfort.  One of the 3 water reservoir wells were chosen based on palpebral fissure and the corneal size.  The well was placed on the eye, with the patient lying in the supine position.  The well was then filled with 10 ml of water.  The probe was inserted into the water bath and adjusted in depth until acceptable image was acquired.  Once the study was done, the probe was removed and the water bath was removed.  Towel was placed around the patients eye to avoid water dripping all over the rest of the head and on the floor.

I have placed an image of the same eye using the VuMax, Pentacam (Oculus GmbH, Germany) and the Visante OCT.

The UBM provides an exquisite image with a size of 18.5 mm by 14 mm deep.  The depth allows for evaluation from the corneal surface to beyond the posterior capsule.  The UBM is able to visualize the angle, the ciliary body, the lens and the zonules.  The is some echo noise as can be seen in this image.  The echos are also a note of reliability of the image as far as how well the probe is positioned.

My overall experience with the UBM, in comparison with Visante Anterior Segment OCT, was not very favorable.  The Visante is a non-contact instrument.  Most of the patients that were examined by the UBM did not "enjoy" the experience and all have mild-moderate discomfort for the next few hours.  My biggest criticism is that I could not by any mean confirm how well centered I was on the eye.  With the Visante there is a video camera that views the eye and allows for the scan to be perfectly centered onto the eye.  This allows for the widest and the truest sulcus to sulcus space.

This is a DARK Chocolate BROWN eye.  I have many examples of light blue eyes that detail the ciliary body much better.  Darker eyes have a more limited view of the ciliary body and the ciliary processes.  The Visante provides significantly more advanced image of the anterior segment.  The cornea is in full detail as well as the angles.  The chamber tools, the rainbow tool, and the multiples of calipers play a tremendous role in pre-operative and post-operative evaluations.  Although the ciliary body and the true sulcus space may not be as visible as UBM, the posterior pigmented iris epithelium's most lateral termination is a great land mark that is readily visible on the Visante and is just as reliably usable for the sulcus to sulcus space measurement. 

The Visante provides multiples of calipers that are very easy to use.  The anterior chamber tool in green is set at the deepest point on the angle to provide the crystalline lens rise as noted by Dr. George Baikoff.  Here it is 320 microns.  The endothelium to anterior lens surface distance is 2.96 mm and the corneal thickness is approximately 390 microns post high myopic iLASIK correction.  The free hand caliper in blue is used to measure the distance from end of posterior pigmented iris epithelium to the other end.

One of the other concerns was the true positioning of the UBM and its effect on the measurements.  I used the Visante OCT to measure the "sulcus-to-sulcus" space in the horizontal meridian, right on center, then 1mm above and 1mm below the central meridian.  It was amazing to me that one could not identify anything to differentiate these images; henceforth, nor could one really tell that the UBM was perfectly on the central horizontal meridian.  The Central horizontal meridian Sulcus-to-Sulcus measured 12.3 mm, but with 1mm up or down, that measurement changed to 12.0 mm.  I believe that is sufficient enough to influence the lens choice for the Visian.  Similarly, what happens if you change the angle of imaging.  I had the same eye measured with superior and inferior gaze, but measuring based on central horizontal meridian of sulcus to sulcus space.  This angle change resulted in minimal anterior chamber depth, but all other parameters remained relatively identical.  So my biggest concern with UBM is how can one know it is truly on the central horizontal meridian? Little above or below the central horizontal meridian can have significant influence. 

This same eye as imaged in the UBM and the Visante also had Scheimpflug imaging done via the Pentacam.  The Pentacam image shows the existence of an IntraLase LASIK flap, but there is really nothing to note of the angles, the ciliary body, and the posterior pigmented iris epithelium.  The white sclera reflects and visible blue light (475 nm) of the Scheimpflug and much "noise" is created.  The Scheimpflug image as seen here does not provided sufficient enough details to allow reasonable assessment for a posterior chamber phakic IOL such as the Visian ICL.