An obturator (1) comprises an elongate shaft extending between a proximal end and a distal end, the elongate shaft (3) having an opening at the proximal end and defining an elongate cavity which is sized and shaped to receive an optical instrument (35). The obturator is provided with an axially extending finger (17) which is arranged for radial movement inwardly so as to engage the outer surface of said optical instrument located within said cavity. The finger may be a latch member (45) provided with a latch element (52) and movable between a first position in which the latch element is located relatively radially inward and a second position in which the latch element is located relatively radially outward. With the obturator located within a cannula body, an instrument inserted into the obturator causes the latch element of the latch member to engage with the cannula to prevent relative axial movement therebetween.
