The Schematic Eye is used primarily for teaching or training retinoscopy.

Although the scale at the back of the unit only indicates a range of +3D to -5D, the range may be extended by placing trial lenses as appropriate in the lens wells provided. The back of the unit is slid out to the ‘0’ position on the scale. It should then require a +1.50D trial lens in the lens well or retinoscopy rack to neutralise the retinoscope’s reflex when working at a distance of 2/3 m or 66.7 cm. If a different, more comfortable working distance is required, the neutralising lens must be changed accordingly. For example, for a working distance of 80 cm, a neutralising lens of +1.25D is needed or for a working distance of 57 cms, a lens of +1.75D is required. 

Assuming a +1.5 D lens and a working distance of 66.7 cm, 1.50D is simply subtracted from the power of the lens, or lenses, that are required to neutralise the eye, to determine the actual refractive power of the eye. For example, if it takes a +4.5D lens to achieve a neutral retinoscopy reflex, the actual refractive correction will be +3.0D. If a -4.5D lens is necessary to neutralise the reflex, the refractive correction will be -6.0D. These powers should match with the powers on the scale at the back of the eye. 

To simulate astigmatism, a cylinder trial lens may be placed in the lens well closest to the artificial pupil, with the power concealed. A lens power needs to be obtained for each meridian and an axis determined.