Human Eye

Human eyes are one of the classic five sense organs i.e. eyes, nose, ears, tongue, and skin of the human body. Human Eyes are specialized sense organs that react to light and allows vision. It regulates the sense of vision which allows humans to interpret shapes, size, the color of any object, dimensions of their surroundings by processing the amount of light they reflect or emit.

Structure of the eye:

• Pupil: The central dark part of the front eyeball surrounded by iris which regulates the amount of light entering it.
• Cornea: The cornea is a front and transparent layer of the eyeball. It acts as the eye's outermost lens. It's a dome-shaped clear surface, covers the iris, the pupil, and the fluid-filled anterior chamber of the eyeball. It contains no blood vessels, receives nutrients from tears and aqueous humor. It protects the eye as an outer covering, acts as a barrier against germs, dirt, and other particles that can infect or damage the eyes. It also protects against harmful ultraviolet rays from the sun. It's another important function is that it allows light to enter the eye and responsible for approximately 65-75 percent of the eye's total focusing power. The cornea with the lens focuses the light on the retina. Its main function is to refract or bend the light.
• Limbus: Limbus is a border between the cornea and the sclera. It's a site, a ring border, of surgical incisions for glaucoma and cataract.
• Iris: It's a colored part of the eyes covered by the cornea. It regulates the size of the pupil thereby controlling the amount of light.
• Sclera: the white part of the human eye which surrounds the cornea. It's the tough, fibrous, opaque outer layer of the human eye, provides protection and structural integrity.
• Conjunctiva: It's an important structure on the surface of the eye that is not easily noticed. It's a tissue, semi-transparent layer, that lines the inner surface of the eyelids, covers the white part i.e sclera of the eye.

• Lens: It's a transparent, biconvex flexible disc, located behind the pupil. It acts like a camera lens, focuses light onto the natural screen i.e. retina of the eye.
• Retina: A part of the human eye where light is focused and object is seen i.e a natural screen where images are formed. Retina senses light and creates impulses that travel through the optic nerve to the brain. Furthermore, it contains photoreceptor cells called rods and cones, the macula—an important area in the center responsible for sharp, clear, and straight-ahead vision.

Rods and cones :

1. Rods and Cones are the color-sensitive cells of the eyes.
2. Rods respond at a very low-level of light. They do not help in color vision. The human eye has more than 100 million rod cells. Rods are concentrated on the edges of the retina. They have low visual acuity i.e. can't register detail. They register only black and white.
3. Cones help in color vision. They are concentrated in the middle of the retina, require a high amount of light to enable them to respond. Cones help the eyes see the color and fine details of any image. Human eyes have three types of cones - red, blue, and green. A human eye has about 6 million cones. Most of these cells are present in the fovea, a small pit located in the macula of the retina.

• Optic nerve: The optic nerve connects the eye to the brain. It is located in the back of the eye, transfers visual information from the retina to the vision center of the brain. Then the brain interprets the image.

• Aqueous humor: A fluid in the eye that fills in space between cornea and iris i.e. anterior chamber, and iris and lens i.e. posterior chamber. It gives the eye its shape. It nourishes the eye and keeps inflated (Albert & Gamm, n.d.).
• Vitreous humor: It is present in the vitreous chamber, positioned at the back of the eyeball. The vitreous chamber is the largest chamber of the human eye and takes up around 80 percent of the eye. Vitreous humor is a clear transparent fluid that fills the space between the lens and the retina. It consists of 99% of water but it has a jelly-like consistency. It helps the eyes maintaining a spherical shape.

The above information is about the basic components of the human eye I have mentioned, I hope you would like it.

References:

1. Albert, D. M. and Gamm, . David M. (2007, November 1). aqueous humour. Encyclopedia Britannica. https://www.britannica.com/science/aqueous-humor