An optical access apparatus for receiving an endoscope to permit visualization during passage through tissue, which comprises: an access member dimensioned for insertion through body tissue, the access member defining a longitudinal axis ('a') and having a longitudinal opening for receiving an endoscope, the access member having a closed penetrating end adapted to pass through tissue, the closed penetrating end being transparent to permit visualization of tissue with the endoscope; a locking collet coaxially mounted relative to the longitudinal axis ('a') of the access member, the locking collet having internal surfaces defining an internal passage to permit passage of the endoscope; and a manual member mounted adjacent the locking collet and operatively engageable therewith, the manual member adapted for rotational movement about the longitudinal axis ('a') to reduce an internal dimension of the internal passage of the locking collet to cause the internal surfaces of the locking collet to securely engage the endoscope; and characterised in that the locking collet is adapted for both rotational movement relative to the longitudinal axis ('a') and for longitudinal movement relative to the manual member whereby rotational movement of the manual member causes the locking collet to corresponding rotate to define a central aperture for at least partial reception of the locking collet and wherein the locking collet and the manual member include corresponding camming surfaces (122, 128) whereby upon longitudinal movement of the locking collet relative to the manual member the camming surfaces (122, 128) cooperate to reduce the internal dimension of the internal passage of the locking collet, the manual member further comprising cam slot means and the collet further comprising cam pins for traversing the cam slots for effecting longitudinal movement of the locking collet upon rotational movement thereof. an access member dimensioned for insertion through body tissue, the access member defining a longitudinal axis ('a') and having a longitudinal opening for receiving an endoscope, the access member having a closed penetrating end adapted to pass through tissue, the closed penetrating end being transparent to permit visualization of tissue with the endoscope; a locking collet coaxially mounted relative to the longitudinal axis ('a') of the access member, the locking collet having internal surfaces defining an internal passage to permit passage of the endoscope; and a manual member mounted adjacent the locking collet and operatively engageable therewith, the manual member adapted for rotational movement about the longitudinal axis ('a') to reduce an internal dimension of the internal passage of the locking collet to cause the internal surfaces of the locking collet to securely engage the endoscope; and characterised in that the locking collet is adapted for both rotational movement relative to the longitudinal axis ('a') and for longitudinal movement relative to the manual member whereby rotational movement of the manual member causes the locking collet to corresponding rotate to define a central aperture for at least partial reception of the locking collet and wherein the locking collet and the manual member include corresponding camming surfaces (122, 128) whereby upon longitudinal movement of the locking collet relative to the manual member the camming surfaces (122, 128) cooperate to reduce the internal dimension of the internal passage of the locking collet, the manual member further comprising cam slot means and the collet further comprising cam pins for traversing the cam slots for effecting longitudinal movement of the locking collet upon rotational movement thereof.