The eyes are sensory organs that allow us to see the world around us. They detect light, color, and movement, and send signals to the brain to process visual information.
Humans have two eyes, located in sockets (orbits) of the skull, and each eye works together with the brain to create a single, 3D image.
🧬 Main Functions of the Eye
| Function | Description |
|---|---|
| Vision | Detects light and sends visual signals to the brain |
| Focus | Adjusts to see objects near and far (accommodation) |
| Depth perception | With two eyes, allows us to judge distance (binocular vision) |
| Color perception | Differentiates millions of colors using cone cells |
🧩 Parts of the Eye and Their Functions
| Part | Function |
|---|---|
| Cornea | Transparent outer layer; bends (refracts) light entering the eye |
| Pupil | Dark opening in the center of the eye; controls how much light enters |
| Iris | Colored part of the eye; adjusts the size of the pupil |
| Lens | Focuses light onto the retina by changing shape |
| Retina | Inner layer at the back of the eye; contains light-sensitive cells |
| Rods | Retinal cells that detect light and dark (night vision) |
| Cones | Retinal cells that detect color (day vision) |
| Optic nerve | Carries visual information from the eye to the brain |
| Macula | Central part of the retina; provides sharp, detailed vision |
| Vitreous humor | Gel-like fluid that fills the eye and maintains its shape |
| Sclera | White part of the eye; protects and maintains shape |
| Choroid | Middle layer; provides blood supply to the eye |
⚙️ How Vision Works – Step by Step
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Light enters through the cornea and pupil.
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The lens focuses the light onto the retina.
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Photoreceptor cells (rods and cones) convert light into electrical signals.
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These signals are sent via the optic nerve to the visual cortex in the brain.
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The brain processes the information and forms an image.
🧠 Fun Facts About the Eye
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The human eye can distinguish 10 million colors.
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Rods are more sensitive to light but cannot detect color.
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Cones detect color and work best in bright light.
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The blind spot is where the optic nerve exits the retina — it contains no photoreceptors.
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Each eye has over 100 million photoreceptor cells.
🩺 Common Eye Conditions
| Condition | Description |
|---|---|
| Myopia (nearsightedness) | Can’t see distant objects clearly |
| Hyperopia (farsightedness) | Can’t see nearby objects clearly |
| Astigmatism | Blurry vision due to irregular cornea shape |
| Presbyopia | Age-related loss of near focus |
| Cataract | Clouding of the lens |
| Glaucoma | Increased eye pressure damages the optic nerve |
| Macular degeneration | Central vision loss in older adults |
| Conjunctivitis (pink eye) | Inflammation of the eye’s surface membrane |
🧪 Eye Tests and Exams
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Visual acuity test (eye chart)
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Refraction test (for glasses or contact lens prescription)
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Tonometry (measures eye pressure)
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Ophthalmoscopy (examines retina and optic nerve)
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Color blindness test
✅ Summary
| Component | Function |
|---|---|
| Cornea & Lens | Focus light |
| Iris & Pupil | Regulate light entry |
| Retina | Detects light and color |
| Optic nerve | Sends signals to the brain |
| Brain (Visual Cortex) | Processes visual information |