Input/Output Current from OP amp
The output current from the op-amp (as depicted in the picture in the question) is that current needed to keep the inverting input at ground potential.

So, with 1V at R1 (left hand side), there has to be -1V at the output to make the inverting input zero volts.

This means the current is -1V/100R = -10 mA.

If R2 were (say) double the value (200 ohms), the voltage at the output is -2V but the current remains the same.

In fact the current flowing in R2 is that current flowing thru R1 due to the input voltage. Remember the op-amp forces the inverting node always equal the non-inverting node and, if the non-inverting node is 0V then R1's current is simply input volts/R1. This is what is meant by a virtual earth amplifier.