Handheld keratoscopes are not a new idea.  The Maloney and original Mastel keratoscope have been used by thousands of surgeons to qualitatively define astigmatism through the projection of mires on the eye using surgical scope lighting. Similarly the Mastel Neuhann Keratsoscope uses available light. However, this tool is smaller and can actually rest on the surface of the eye for hands-free operation.  The diameter is ideal for identifying corneal astigmatism and ensuring the proper orientation before performing AK or aligning a toric lense.

For more detail: http://www.mastel.com/neuhann_keratoscope.html