The Human Eye

• Main parts: cornea, iris, pupil, lens, retina, optic nerve.
• How we see objects; blind spot; persistence of vision.
• Common defects: myopia (near-sighted) and hypermetropia (far-sighted) — corrected with lenses.
• Braille system; care of eyes.

1. Cornea & lens — refract light to focus image on retina.
2. Iris & pupil — control amount of light entering (pupil dilates in dim light).
3. Retina — contains rods and cones; sends signals via optic nerve to brain.
4. Blind spot — where optic nerve leaves; no vision there.
5. Persistence of vision — images persist ~1/16 s (movies, animation).
6. Defects — myopia (distant blur, concave lens); hypermetropia (near blur, convex lens).
7. Real world — Braille for visually impaired; avoid reading in dim light; don't stare at Sun.

Why movies appear continuous (persistence of vision)

Step 1 — Projector shows 24+ frames per second.
Step 2 — Each image persists on retina briefly.
Step 3 — Brain merges frames into smooth motion.
Step 4 — Same principle in flip-book animation.

• Thinking image forms on cornea (focused on retina).
• Misconception: myopia corrected with convex lens (needs concave).
• Ignoring vitamin A for healthy eyes (NCERT nutrition link).
• Confusing blind spot with eyelid closure.

• Name four parts of the human eye and their functions.
• What is persistence of vision?
• Which lens corrects hypermetropia?

Open the Practice tab for graded questions on The Human Eye.