Specific embodiments of the invention are directed to improved 
phacoemulsification procedures involving the use of processed non-visual three-dimensional data (i.e. 
diagnostic scan data) to provide a surgeon with additional guidance (i.e. more than that generally obtained from 
visual observation of the working area) concerning the distance separating a working end of a 
phacoemulsification instrument and the posterior portion of the 
capsule of the eye during 
surgical procedures involving the removal of the crystalline lens of an eye (e.g. a cataract 
removal procedure). Such separation (i.e. distance or gap) information may be used to aid the surgeon in 
cutting or scoring the lens to a desired depth while minimizing the risk of penetrating the posterior portion of the 
capsule with the working end of the instrument. Some embodiments provide for the visual and / or auditory conveyance of distance information to the surgeon wherein visual information may be conveyed by overlaying it with real visual images of actual surface features viewed by the surgeon. Additional embodiments provide for overlaying visual representations of selected three-dimensional structure information (e.g. depths of troughs 
cut into the lens) with the real surface feature images viewed by the surgeon.