Is this equation solvable for $y$?
$$x = y + e^{-1.9 + 3.9 \tanh\left(\frac{-(y - 121)}{14}\right)} (z - 4)^{1.9 + 1.4 \tanh\left(\frac{-(y-121)}{14}\right)}$$
This equation partly describes the nerve fibres that make up our eye, where y is an angle around the optic disc and z is some distance away from the optic disc. x is the angle around the optic disc that the fibre is at that distance (z) and from a particular starting angle (y). What I want is to take an arbitrary angle (x) and distance (z) from the optic disc and see where it started from (y).
Here is the main research paper I am working from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2848177/
Thanks for the help everyone!