Human Eye

The human eye is a complex sensory organ responsible for vision. It perceives light, colours, depth, and distance, functioning similarly to a camera. Light enters through the eye, undergoes refraction, and forms an image on the retina, which is processed by the brain to create a clear visual experience. The human eye is a spherical structure with a diameter of about 2.3 cm. It consists of various parts, each with a specific function.

1. External Parts of the Eye

• Sclera: Tough, white outer covering that protects the eye.
• Conjunctiva: A Transparent membrane covering the eye for protection.
• Cornea: The Transparent, curved front part of the sclera that allows light to enter and performs most of the refraction.
• Iris: Coloured muscular structure behind the cornea that controls the size of the pupil.
• Pupil: A small, adjustable opening in the iris that controls the amount of light entering the eye.

2. Internal Parts of the Eye

• Lens: Transparent, convex structure that adjusts its curvature using ciliary muscles to focus light on the retina.
• Ciliary Muscles: Control the lens’s shape to adjust focus for near and far objects (accommodation).
• Retina: Light-sensitive inner layer containing rod and cone photoreceptor cells, which convert light into electrical signals.
• Optic Nerve: Transmits electrical signals from the retina to the brain for image processing.
• Blind Spot: The point where the optic nerve leaves the eye with no photoreceptors, resulting in no vision at that point.
• Aqueous Humour: A clear fluid between the cornea and lens that maintains eye pressure and provides nutrients.
• Vitreous Humour: A gel-like substance between the lens and retina that helps maintain the eye's shape.

Construction of human eye

Photoreceptor Cells in the Retina:

• Cones: sensitive to bright light and responsible for detecting colours.
• Rods: sensitive to dim light and essential for night vision.

Muscles Controlling Eye Movement:

The human eye has six muscles that provide tension and torque for controlling movement:

1. Medial Rectus
2. Lateral Rectus
3. Superior Rectus
4. Inferior Rectus
5. Inferior Oblique
6. Superior Oblique

These muscles work together to allow the eye to move in different directions.