Biology Stack Exchange is a question and answer site for biology researchers, academics, and students. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

The section of retina shows a layered arrangement of the various retinal cells. Starting from the inside (where the light strikes first) is the nerve fibre layer, ganglionic layer, amacrine cell layer, bipolar cell layer, horizontal cell layer and finally rods and cones (and that too in inverted position, i.e. the actual receptor portions are farther inwards).

Why is this stratification inverted? If the receptors would have been the innermost cells, they could have received the maximum quantity of unaltered light. Does this "inverted" arrangement, i.e. arrangement with the receptor cell behind a screen of several other layers not hinder the process of photoreception by blocking a lot of incident light and hence the formed image? What is, if any, advantage of this reverse arrangement?

enter image description here

share|improve this question
up vote 4 down vote accepted

I don't have an other explanation than pointing to evolution. It was obviously not a problem to evolve the way it did. One article I found (see "The Inverted Retina: Maladaptation or Pre-adaptation?") called it a sign of pre-adaptation, where forms exist before they get their final function. Another pretty comprehensive review can be found here: "Evolution of Phototransduction, Vertebrate Photoreceptors and Retina."

share|improve this answer
Thank you. And great references, as usual. – Satwik Pasani Dec 25 '13 at 10:04

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.