The present disclosure discloses a guarding wall mechanism (100) for an optical fiber (101). The mechanism (100) comprises a housing (202) adapted to house the optical fiber (101), wherein the housing (202) defines a space (108) between the optical fiber (101) and a guarding wall of the housing (202). A plurality of suction units (103) disposed in the space (108). Each of the plurality of suction units (103) are configured to selectively exert suction pressure on an examination surface in contact with a free end (109) of the optical fiber (101). The guarding wall mechanism (100) of the present disclosure eliminates leakage of light and reduces Fresnel losses. Also, the mechanism (100) improves comfort to the patient during examination.