The Screenless Sight Codex

06. Retina

The retina is a layered neural processor. It is not just film at the back of the eye.

Simplified Route

photons
-> rods and cones
-> bipolar, horizontal, and amacrine cells
-> ganglion cells
-> optic nerve

Layers And Functions

Layer Or Cell Type	Function
Rods	High sensitivity, low-light vision.
Cones	Color and high-acuity vision.
Bipolar cells	Relay signals from photoreceptors.
Horizontal cells	Support contrast and lateral interactions.
Amacrine cells	Shape timing, motion, and local signaling.
Ganglion cells	Encode retinal output as spike trains.

Interface Points

Interface Point	What It Tries To Do
Photoreceptor replacement	Restore or mimic damaged light-sensitive cells.
Subretinal implant	Stimulate near the photoreceptor/bipolar layer.
Epiretinal implant	Stimulate near ganglion cells on the retinal surface.
Optogenetic retina	Make remaining cells light responsive.
Retinal projection	Use existing photoreceptors with a synthetic image source.

Why Retina Is Hard

• The retina compresses and transforms information before the brain.
• Many ganglion cell types encode different features.
• Disease changes what tissue remains usable.
• Eye movements alter the relationship between device and world.
• A stimulated spot may produce an elongated, distorted, or moving phosphene.
• The perceptual result is personal and must be calibrated.

Creative Workaround: Retina-Matched Encoding

Instead of driving every electrode as if it were a pixel, a retinal system could preprocess camera data into retina-like signals:

• Contrast changes
• Motion onset
• Edges
• Center-surround patterns
• Coarse object boundaries
• Brightness adaptation

The goal is not to mimic the whole retina perfectly. The goal is to give the remaining circuitry signals it can use more naturally.

Related Entries

• 05. Eye Optics
• 07. Visual Pathway
• 08. Neural Interfaces