A barrier for use in relation to an eye contacting testing apparatus of the sort having a probe for contacting the eye, comprises a layer of substantially transparent material having dimensions comparable to the surface of the head of the probe and is removably fixable to the probe by means, such as a peelable adhesive, which do not affect the transparency of the material layer. The layer is sterile on the surface which contacts the eye in place of the probe head. Such barriers are disposable and quick and easy to position and replace. Barriers according to the invention can be conveniently provided in sheets comprising multiples of barriers.