R_Bibb_Medical_Modelling_The_Application_of_Adv.pdf

Case studies 197
Establishing the correct depth and location of the eyeball is considered
one of the most diffi cult processes in ocular prostheses design and is vital
to achieving a realistic result (10). The tools available within FreeForm ®
made this signifi cantly simpler and more accurate since the work could be
viewed from angles that would be impossible in a clinic situation (Fig. 6.61).
The prosthesis was positioned using planes in the three-dimensional environment
as guides to locate key anatomical features, such as pupil depth
(Fig. 6.61) in relation to each other. Once the pattern was correctly located,
discrepancies in the fi t between the anatomy and prosthesis became apparent.
This was due to signifi cant facial asymmetry caused by reduced growth
following radiotherapy treatment on the patient’s left orbit.
Design
In order to compensate for the poor fi t surrounding the prosthesis pattern,
clay was built up until it overlapped fully with the un-editable buck anatomy.
It was then combined into the anatomy for shaping and blending to create
a seamless edge. A protective mask was ‘painted’ on to the prosthesis clay
where the features were required to match the unaffected side, then ‘carve’,
‘smooth’, ‘tug’ and ‘smudge’ tools were used to manipulate the clay and
feather the fi tting edges to the surrounding anatomical contours, recreating
a natural appearance. Figure 6.62 shows the aesthetically pleasing result
that took less than an hour to achieve.
6.61 Positioning the prosthesis using a guide plane.