Midi input that doubles as gate voltage input
There are special low-capacitance TVS diodes, but they are designed for transients, not for continuous current.

HP's Optoelectronics Application Manual suggests to limit the current with a constant-current source in front of the optocoupler (section 3.6.1.2):



However, with MIDI, there is not enough voltage for this to work. (The 220 Ω resistor in the standard circuit drops about 1.1 V.)
So what you have to do instead is to shunt the surplus current:



This is the equivalent of a Zener; you still need another resistor to limit the overall current.