Noun and の adjective
もうまく
網膜とは、カメラのフィルムに似た、眼の奥の膜のことです。
The retina is a membrane inside your eye that resembles a camera’s film.
The nerve netting in the back of your eye is made up of membranes called the retina. It's what lets light in to help you see!
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.