Patent ID: 8534848

Claim:
A marker ( 10 , 10 ′) for a navigation system configured to determine the position in space of a surgical instrument, the marker comprising: a spherical retroreflecting surface ( 13 , 13 ′) in the form of a retroreflecting sphere ( 12 , 12 ′); and a dimensionally stable translucent shell ( 14 ) that protects the retroreflecting surface in such a way that a reflecting image is substantially uninfluenced by the shell in respect of contour and barycentre location, wherein the shell ( 14 ″) includes a hood ( 16 ″) placed over the retroreflecting surface ( 13 ″), wherein the hood ( 16 ″) includes a spherical hood portion ( 25 ″) and an aspherical hood portion adiacent thereto, and wherein the hood ( 16 ″) terminates in a vertically extending asphere ( 26 ″).