After this time since posting I presume you have already found out:
The written entry is sph = 'sphere' abbreviated.
So the rx comprises only spheres (first boxes).
It is a poor way of ensuring no confusion, by causing confusion - but only to non-professionals etc.
Leaving boxes blank is also valid but this could be by omission / error.
Another can be DS = dioptre sphere to confirm this rx is only for sphere powers.
(DC, diopter cyl., is another label but cyl. entries are obvious so 'DC' is unnecessary).
Often the cyl and axes boxes are just stroked through, which is much clearer in showing no values have been entered or prescribed.
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