Unexplained visual acuity loss or a complaint of intermittent blurred vision experienced by the contact lens corrected aphakic may all too frequently be caused by surfacing imperfections in the front surface optical zone of these high-plus corneal lenses. The lensometer is a highly inadequate instrument for "checking the optics" of a corneal contact lens; yet it is usually the only instrument used for this purpose.
The "radiuscope" can be used to check the "back-surface optics" of a corneal lens; yet it is rarely used to check anything but the radius of the central 3 or 4 mm of the rear surface of the lens. The radiuscope is almost never used to check the peripheral optical portions of the front surface. It can be particularly revealing and useful in front surface checking of the periphery of the lenticular zone of the high-plus corneal lens.
After suspecting flaws in peripheral optical quality
WELSH RC, FALL EE, AHORNER F. Hand Neutralization of Aphakic-Range Corneal Contact LensesA Practical Method of Discovering Surfacing and Power Blemishes in the Periphery of the Refracting Lenticular Zone. Arch Ophthalmol. 1965;73(5):621-622. doi:10.1001/archopht.1965.00970030623005