In para 3.5.1 Inspection/Test Personnel sub para d states the following:
Personnel designated as inspectors whose duties reqruie visual acuity, shall
be required to take an eye examination on an annual basis as a minimum.  the
examination shall be adequate to assure that the individual has natural or
corrected near-distance acuity in at least one eye such that the individual
is capable of reading a minimum of 8 letters (0.58mm X 0.58mm)  at a distance
of not less than 30.5 cm on a standard Tom Nearpoint Card.

It goes on to give the exact dimensions if you want to set up your own
in-house eye chart.

Hope that helps

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