Parts of Human Eye: Structure, Function, and How We See

Parts of Human Eye: Structure, Function, and How We See

Image Credit – Smart Biology

The human eye is an extraordinary organ that allows us to perceive the world around us. Every part of the eye plays a critical role in vision, working together to focus light and send signals to the brain.

Eye Lid
The eyelids protect the eyes from dust, debris, and bright light while helping to spread tears over the surface to keep it moist.

Lacrimal Caruncle and Tear Duct
The lacrimal caruncle is a small pink mound at the corner of the eye. The tear duct drains tears into the nose, keeping the eye moist and removing waste.

Pupil and Iris
Light enters the eye through the pupil, whose size changes depending on the light intensity. The iris, the colored part of the eye, controls this size adjustment to regulate the amount of light entering.

Sclera and Cornea
The sclera is the white, protective outer layer of the eye. The cornea is the transparent front part of the eye that allows light to pass through and helps focus it on the retina.

Lens, Anterior, and Posterior Chambers
The lens changes shape to focus images onto the retina. It is protected and supported by the aqueous humour in the anterior chamber and positioned behind the cornea in the posterior chamber.

Suspensory Ligaments and Ciliary Body
Suspensory ligaments connect the lens to the ciliary body. The ciliary body and its muscles adjust the lens shape to focus on objects at different distances.

Muscles of the Eye
Muscles like the lateral and medial rectus hold the eyeball in place and control eye movements, allowing us to track objects.

Retina and Photoreceptor Cells
The retina lines the back of the eye and contains photoreceptor cells called rods and cones. Rods, approximately 125 million in number, detect light and dark, while cones, around 7 million, distinguish colors such as red, green, and blue. The central pit of the retina provides the sharpest vision.

Choroid and Hyaloid Canal
The choroid is a layer of blood vessels that nourishes the retina. The hyaloid canal runs through the vitreous body, though it is largely vestigial in adults.

Optic Nerve and Retinal Blood Vessels
The optic nerve transmits electrical signals from the retina to the brain. Retinal blood vessels supply oxygen and nutrients to the retina.

Vitreous and Aqueous Humour
The vitreous body is a jelly-like substance filling the eyeball, maintaining its shape. The aqueous humour protects the lens and keeps the eye healthy.

Conjunctiva
A thin layer of tissue called the conjunctiva lubricates and protects the eye from infections.

How We See

1. Light reflects off an object onto the lens.
2. The lens focuses the image onto the retina.
3. An upside-down image forms on the retina.
4. Rods and cones convert the image into electrical signals.
5. These signals travel through the optic nerve to the brain.
6. The brain decodes the signals, allowing us to perceive the object right-side up.

The human eye is capable of seeing objects both near and extremely far away, making it one of the most remarkable organs in the body. Its intricate design of muscles, chambers, photoreceptors, and nerves enables us to experience the world in vivid detail.