DESC: Features:Allows for efficient testing for both heterophorias (latent strabismus) and heterotropias (manifest strabismus) at the same time.User can view the movement of covered and uncovered eyes simultaneously.Its halogen light increases the ambient light on the patient's side and aids visualization by the practitioner.Educational teaching tool that offers a clear visual explanation to parents or medical students.Fits all Welch Allyn 3.5v power sources.Product Information:See Strabismus in a whole new light with the Welch Allyn Strabismoscope Unidirectional Occluder, Only (Model 12400). Testing for Strabismus (ocular misalignment) should be a routine part of any child's healthcare program. With the StrabismoScope the testing just became easier. By simply turning on the StrabismoScope and placing it over the patient's eye, the examiner is able to observe the occluded eye directly, but the patient cannot see out. As a result, the examiner is able to detect the often subtle eye movements