Several design changes have been made to Improve the sensitivity of the existing experimental Badal type photoretinoscope apparatus to make the instrumentation more practical as a screening device. The design changes include the use of: aspheric lenses; a narrow pass light filter; a decreased exit pupil diameter; and a single luminous object used with a coincidence (vernier) Scheiner system implemented with a pair of vertically oriented pinhole apertures to test the vertical meridian of the test eye. The resolution of the apparatus (using an emmetropic human eye analogue) was well under 1.0 D. Further modifications contemplated for the future include: a second pair of pinholes, horizontally oriented, to test the horizontal meridian, and the ability to axially rotate the pinholes along with the doubling prisms so as to sample oblique meridians, if necessary. Finally, the entire apparatus will need to be miniaturized and lightened to make it portable for field use (screening).
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