The human eye is approximately spherical with a diameter of 2.3 cm
Key Components
👁️ Cornea
Transparent bulge on front surface where most refraction occurs
🟤 Iris
Dark muscular diaphragm that controls pupil size
⚫ Pupil
Regulates amount of light entering the eye
🔍 Crystalline Lens
Provides fine adjustment for focusing at different distances
📺 Retina
Light-sensitive screen with millions of cells
🧠 Optic Nerve
Sends electrical signals to the brain
The human eye works remarkably like a camera
| Camera Part | Eye Part | Function |
|---|---|---|
| Lens | Cornea + Crystalline Lens | Focuses light |
| Aperture | Pupil | Controls light entry |
| Film/Sensor | Retina | Captures image |
| Processor | Brain | Processes image |
Image Formation
The eye lens forms an inverted real image on the retina. The brain interprets and processes this information so we perceive objects as they actually are.
The ability of the eye lens to adjust its focal length
How Accommodation Works
The eye lens is composed of a fibrous, jelly-like material. Ciliary muscles can modify its curvature:
- For Distant Objects - Muscles relaxed, lens thin, focal length increases
- For Near Objects - Muscles contract, lens thick, focal length decreases
The range of clear vision for a normal eye
Near Point (Least Distance of Distinct Vision)
The minimum distance at which objects can be seen most distinctly without strain:
- For a young adult with normal vision: 25 cm
- Below this distance, image becomes blurred
- Eye feels strain when trying to focus closer
Far Point
The farthest point up to which the eye can see objects clearly:
- For a normal eye: Infinity
- Normal eye sees clearly between 25 cm and infinity
Understanding eye parameters and vision quality
Eye Response Times
Accommodation Speed ≈ 0.3 - 0.5 seconds
The time taken by the eye to adjust focus from far to near objects