What is the mass of a human retina?
I did some research and I found this site : https://www.covance.com/content/dam/covance/assetLibrary/posters/StrubleEVER14.pdf

It has the weight for ocular tissues for different kinds of animals ( rabbit , human  etc. ).

I also found that the area of a retina is 1094 mm² and the thickness is 0,12 mm , so if you can find the density you can find the mass.

(found on this site https://faculty.washington.edu/chudler/facts.html#sensory )