The Standard Multiple Pinhole Occluder works by restricting the light reaching the patient's eye, which eliminates the effects of refractive error, and improves visual acuity. If there is no improvement in acuity through the pinhole occluder, it may indicate a more serious problem for the doctor to investigate. The Multiple Pinhole Occluder is designed to cover one eye at a time during testing. The WO-221 Pinhole Occluder is a standard long-handle size of 9-5/8" (25cm) in length, with seventeen 1.3mm diameter pin holes. The durable ABS black plastic with polished finish is easily cleaned.