If we accommodate too little, we are farsighted and we need a convex lens. The retina, the rear lining of the eye, has 130 million photoreceptors. The retina s cross-section includes receptors, horizontals, bipolars, amacrines, and ganglion cells, which go to the optic disc, and out towards the brain. A single ganglion cell can receive signals from one, a few or many photoreceptors. Rods respond to dim light.
Cones respond to bright light and distinguish colours.
The fovea, a pit in the center of the eye, has only cones. Cones generally connect to one ganglion cell, and serves acute vision. This uses a molecule derived from Vitamin A, plus a protein molecule, forming a photopigment. There are 3 photopigments for cones and one for rods. For all four, when light photons contact them, the photopigment breaks into its two constituents.