Could you please let all of us know the background and describe the purpose of your circuit?
The diode is for free wheeling.
The output from DAC drives a current thru R and generates a voltage.
Another voltage is generated across the 3.3 ohms Rsense by the current (Isink) passing thru the voice coil.
The OP Amp generates a difference voltage (error voltage) based on these two voltages, and amplifies it (I guess, many other components are involved, including some energy storage elements, to provide optimal settling time for the difference), which, in turn, drives the MOSFET.
If R and Rsense change their values, the two voltages across them will change. This will generate an error voltage even though the current passing thru these resistors may be same.
However, if both change values by almost same amount, the differenece between two voltages will remain almost same.
Thats the reason these two restors are created like this to ensure that if their values change, both change in same direction, leading to ultimately same value resistors.
I hope this clarifies.