The document on this link describes some different ways to diagnose refractive error. What’s not surprising is that retinoscopy is cited as the most accurate, but there are a few other options. “Spherical Endpoint” on p. 11 is an interesting section.
A few things to consider:
When the pirate scope becomes “over-minus-ed,” the image should become darker (not clearer). Can we somehow use a grayed out target to become black to prevent this?
Also, there is some discussion about the use of different colors in a “Bichrome” test.