Abstract: A unitary transparent eyepiece has a planar outer rim and a planar inner viewing zone, the plane of the inner viewing zone being inclined at an angle to the plane of the outer rim.The angle between the, preferably circular, inner viewing zone and the, preferably circular, outer rim of the eyepiece is chosed such that when the planar outer rim is fitted into the planar socket of a face-piece in a protective device, the inner viewing zone is orthogonal to the line of forward vision of the wearer. In this way the face piece conforms to the shape of the wearer's head, an efficient planar and circular seal is obtained between the eyepiece and its socket, and optical aberrations (associated with curved eyepieces) are minimized.The position of the inner viewing zone relative to the outer rim may be varied according to the clearance required between the eyepiece and the wearer's eye and the type of face piece employed.