Possible Clues:

• Back surface of eye
• Is 'e in the train smash? That's not all my eye
• It's not all my eye, but it's near about it
• Eye part
• Sensory tissue that lines the back of the eye
• Membrane of the inner eye
• It contains 15-Across
• One behind the lens
• Artist captures alien in part one needs to see!
• Holder of many cones