Manual Occluder For Eye Examination

occluder is an opaque disk with one or more small holes through it, used by ophthalmologists, orthoptists and optometrists to test visual acuity.  Because light passes only through the center of the eye's lens, defects in the shape of the lens (errors of refraction) have no effect while the occluder is used. In this way the ophthalmologist, orthoptist or optometrist can estimate the maximum improvement in a patient's vision that can be attained by lenses to correct errors of refraction.^[1] This can be used to distinguish visual defects caused by refractive error, which improve when the occluder is used, from other problems, which do not.^[2] The pinhole occluder can also be used in testing visual acuity in mydriatic patients.