The overhead projector can be used as a simple optical system to simulate the optics of the human eye. The illuminated platform can be considered the far point plane of the eye, and the screen (its optical conjugate), the retina. The space between the screen and the optical components represents the vitreous and in this space the focal line images of simple myopic astigmatism can be imaged. The projector enables the procedures of subjective refraction such as fan and block and cross cylinder methods to be demonstrated. Using a stand magnifier, the vergenee properties of low vision aids can be shown together with the effects of changes in eye-to-lens distance on magnification and field of view. The projector is used to demonstrate nystagmus and regional changes in retinal sensitivity. Other functions such as retinoscopy and duochrome techniques can also be demonstrated.