Eyes

**1. Cornea:**

The cornea is the eye's outermost layer, responsible for refracting light and protecting the eye from dust, germs, and other harmful particles.

It is composed of specialized cells and proteins arranged in layers, allowing it to maintain transparency while providing structural integrity.

The cornea's shape and curvature play a crucial role in determining the eye's focusing ability, contributing to conditions like nearsightedness (myopia), farsightedness (hyperopia), and astigmatism.

**2. Iris:**

The iris is a pigmented, circular structure located behind the cornea.

Its main function is to regulate the amount of light entering the eye by adjusting the size of the pupil. In bright light, the iris contracts to constrict the pupil, reducing the amount of light entering the eye. In dim light, the iris dilates to enlarge the pupil, allowing more light to enter.

The color of the iris is determined by the amount and distribution of melanin pigment within its layers, resulting in a spectrum of eye colors ranging from blue to brown.

**3. Pupil:**

The pupil is the black circular opening at the center of the iris.

It acts like a camera aperture, controlling the amount of light that reaches the retina.

The size of the pupil is regulated by the iris muscles in response to changes in lighting conditions and the brain's visual processing.

**4. Lens:**

The lens is a transparent, flexible structure located behind the iris and pupil.

Its primary function is to focus light onto the retina, adjusting its shape through a process called accommodation to allow for clear vision at different distances.

With age, the lens may become less flexible, leading to a condition known as presbyopia, where near vision becomes progressively blurry.

**5. Retina:**

The retina is a complex layer of neural tissue lining the back of the eye.

It contains millions of photoreceptor cells called rods and cones, which convert light energy into electrical signals that are transmitted to the brain via the optic nerve.

Rods are sensitive to low light levels and are responsible for peripheral and night vision, while cones are responsible for color vision and visual acuity in bright light.

The macula, located near the center of the retina, contains a high concentration of cones and is responsible for detailed central vision.

**6. Optic Nerve:**

The optic nerve is a bundle of approximately 1.2 million nerve fibers that transmit visual information from the retina to the brain.

It exits the back of the eye at the optic disc (blind spot), where there are no photoreceptor cells.

Visual signals are processed and interpreted in the brain's visual cortex, allowing us to perceive images and make sense of our surroundings.

**7. Sclera:**

The sclera, also known as the white of the eye, is a tough, fibrous outer layer that provides structural support and protection for the eye.

It helps maintain the eye's shape and integrity, serving as an attachment site for the eye's muscles and tendons.

**8. Vitreous Humor:**

The vitreous humor is a clear, gel-like substance that fills the space between the lens and the retina.

It helps maintain the eye's shape and optical properties, providing support for the retina and helping to transmit light to the photoreceptor cells.

With age, the vitreous humor may undergo changes that contribute to the development of conditions such as floaters or posterior vitreous detachment.

**9. Aqueous Humor:**

The aqueous humor is a clear fluid that fills the space between the cornea and the lens.

It nourishes and oxygenates the avascular structures of the anterior eye, including the cornea and lens, and helps maintain intraocular pressure to support the shape of the eye.

Proper drainage of aqueous humor is essential for maintaining normal intraocular pressure and preventing conditions such as glaucoma.

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