Vision and Light: How we see the world

👁️ The Biophysics of Vision

Vision begins the moment light enters our eyes through the cornea and pupil. Here, our eyes act like cameras forming a clear image.

A clear, curved, and flexible structure behind the iris (the colored part) called the lens focuses light onto the retina at the back of the eye — this is the optics stage.

The photoreceptors in the retina — rods and cones — then convert light into electrical signals:

• Rods: Enable vision in dim light.
• Cones: Detect color and detail.

These signals travel via the optic nerve to the brain, where they are interpreted as shapes, motion, depth, and color.

Our eyes constantly adapt to changing light conditions — called light adaptation. For example:

• In darkness, pupils dilate and rods become more sensitive.
• In bright light, pupils shrink and cones dominate vision.

🔬 Build a Model Eye: DIY Experiment

Materials:

• Clear plastic bottle or glass jar
• Water
• Clear plastic wrap or plastic bag
• Rubber bands
• Convex lens (e.g., from a magnifying glass)
• White screen or paper

Instructions:

1. Fill the bottle with water to mimic the vitreous humor (the gel inside the eye).
2. Stretch plastic wrap over one end of the bottle as a cornea, and seal with a rubber band.
3. Place a convex lens in front of the bottle to simulate the eye’s adjustable lens.
4. Shine light from an object (like a flashlight shining on a paper shape) toward the lens.
5. Adjust the lens distance to focus a clear image on the paper screen behind the bottle.

🔎 Analysis of the Experiment

This model simulates the eye’s structure and shows how changing lens position or curvature helps focus images — a hands-on demonstration of accommodation in vision.