A surgical device, comprising: a base having a track formed therein and a proximal-facing surface in which a plurality of recesses (30a-f) are formed; a plurality of retractor blades (16a-f), each of the retractor blades having a proximal portion seated in one of the recesses and a distal portion extending distally from the base to contact and retract tissue, the retractor blades being configured to move radially relative to one another between a collapsed position and an expanded position in which the retractor blades define a working channel for receiving an instrument therethrough and in which a diameter of the working channel is greater than the diameter of the working channel when the retractor blades are in the collapsed position; an actuator seated in the track, the actuator being rotatable within the track relative to the base, a distal-facing surface of the actuator including a thread formed thereon, rotation of the actuator relative to the base causing the retractor blades to move between the collapsed and expanded positions; in which the proximal portions of the retractor blades are sandwiched between the distal-facing surface of the actuator and the proximal-facing surface of the base, the proximal portions including a plurality of teeth (42a-d) protruding proximally from surfaces of the retractor blades for engaging the thread of the actuator; and in which rotation of the actuator in a first direction slides the thread of the actuator between the teeth of the retractor blades to move the retractor blades radially inwardly to the collapsed position, and rotation of the actuator in a second direction, opposite to the first direction, slides the thread of the actuator between the teeth of the retractor blades to move the retractor blades radially outwardly to the expanded position. a base having a track formed therein and a proximal-facing surface in which a plurality of recesses (30a-f) are formed; a plurality of retractor blades (16a-f), each of the retractor blades having a proximal portion seated in one of the recesses and a distal portion extending distally from the base to contact and retract tissue, the retractor blades being configured to move radially relative to one another between a collapsed position and an expanded position in which the retractor blades define a working channel for receiving an instrument therethrough and in which a diameter of the working channel is greater than the diameter of the working channel when the retractor blades are in the collapsed position; an actuator seated in the track, the actuator being rotatable within the track relative to the base, a distal-facing surface of the actuator including a thread formed thereon, rotation of the actuator relative to the base causing the retractor blades to move between the collapsed and expanded positions; in which the proximal portions of the retractor blades are sandwiched between the distal-facing surface of the actuator and the proximal-facing surface of the base, the proximal portions including a plurality of teeth (42a-d) protruding proximally from surfaces of the retractor blades for engaging the thread of the actuator; and in which rotation of the actuator in a first direction slides the thread of the actuator between the teeth of the retractor blades to move the retractor blades radially inwardly to the collapsed position, and rotation of the actuator in a second direction, opposite to the first direction, slides the thread of the actuator between the teeth of the retractor blades to move the retractor blades radially outwardly to the expanded position.