Does astigmatism mean it's irons or bust?

It is possible to have astigmatism in only one eye. Since you are myopic, and at 64,most likely presbyopic, your Spectacle Rx might read something like this, (X replacing all numbers):

OD (R) -X.XX Sph. (or 0)
OS (L) -X.XX - (or +) X.XX at XXX deg.
Reading Add X.XX OU (both)

Your spotting scope has a dioptric focus on it with a range of @3-4 diopters of power.
It sounds like your Dr. prescribed monovision contacts. It wouldn't make sense to wear only one unless the other eye's add power and distance power were opposite ( i.e. -2.50 sph with a +2.50 add), with very low or no astigmatism, effectively turning that eye into a near vision only eye uncorrected.
The eye with astigmatism would have to have a low power to the astigmatism in order for it to be the one that can see through the spotting scope better.
 
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