Is this possible?
My prescription is -4.25 -3.00 x 150.
I know what it means, but I’m wondering, is it possible for someone’s second number to be positive, like -4.25 +3.00 x 150? I know that the astigmatism means the eye is shaped like a football, but if it was positive, what would that mean? Could someone explain this to me?
Yes, -4.25+3.00×150 is equivalent to -1.25 -3.00 x 060, just a different way of writing it. Opththalmologists here are trained to write it the first way, and optometrists learn it the second way. But they mean essentially the same thing and both of those prescriptions would correct the same eye. 
Your prescription could be transcribed to -7.25+3.00×060. And you’re quite welcome
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It is a mathmatical equation optometrist use negative therefore your prescription is -4.25 -3.00 x 150. Ophthalmologist use positive so your prescription translates to -1.25 +3.00 x 60.