Eye anatomy

The eye is one of the important structures present in the human body. The eye is present amongst the five senses. A study in which the survey was made about the five senses of the body shows that most people say that their eyesight is a mode of perception they value. The eye anatomy is very simple. The eyes are slightly asymmetrical globes and each is about an inch in diameter. The part of the eye that you see in the mirror includes the iris, cornea, pupil, Sclera, and conjunctiva.

Behind the pupil lens is present. The inner side of the eye is lined by special light-sensing cells called the retina. The function of the lens is to focus light while the function of the retina is to convert the light signals into electrical signals. The macula is an area present in the retina that gives you central vision. The optic nerves carry the signals from the eye to the brain.

Parts of eye anatomy

In the eye many structures are present. These structures are choroid, ciliary body, cornea, fovea, iris, lens, macula, optic nerve, pupil, retina, sclera, and vitreous humor.

eye anatomy

eye anatomy

 

1. Choroid

The choroid is a vascular layer that contains connective tissues. It lies between the sclera and the retina. This structure is thick in it’s far extreme and is the outlying areas. The functions of the choroid are to provide oxygen and nourishment to the outer retina layers. The uveal tract is a structure that is formed by the ciliary body, iris, and the choroid. Anatomists divide the choroids into four layers.

a). Haller’s layer.   the outermost layer that contains large diameter blood vessels.
b). Sattler’s layer.    Medium diameter blood vessels are present in this layer.
c). Choriocappilaries.  This layer contains capillaries.
d). Bruch’s membrane. Innermost layer.

The choroid limit uncontrolled reflection with the help of a dark-colored pigment called melanin.

2.  Ciliary body

The ciliary body is another important structure present in the eye. It contains ciliary muscles and ciliary epithelium. The muscles control the shape of the lens while the epithelium produces the aqueous humor. It’s not pigmented portion produces the vitreous humor. It joins the orra serreta to the iris. When the ciliary muscles become relaxed it puts tension on the lens in order to focus light on the retina. The functions of the ciliary body are accommodation, humor production, resorption, and lens zonules maintenance.

The ciliary body does the function of accommodation when ciliary muscle contract or relaxed. The production of the aqueous humor is done by the ciliary epithelium.

3.  Cornea (eye anatomy)

It is the transparent front part. The cornea along with the lens and anterior chamber refract light. 43 dioptres are the optical power of the cornea.  unmyelinated nerve endings that are sensitive to touch and chemicals are present in the cornea. No blood vessels are present in the cornea and it is nourished through the process of diffusion. Albumin is the most abundant protein present in the cornea.

The cornea has five layers that are the corneal epithelium layers, Bowman’s layer, corneal stroma layer, Descemet’s membrane layer, and corneal endothelium layer.  The sensory supply of the cornea comes from the ophthalmic division of the trigeminal nerve.

4. Fovea

The fovea is a small central pit. It contains closely packed cones. It is located in the macula of the retina. The fovea function is to provide a sharp central vision. It is surrounded by a perifovea belt and perifovea region. The foveal avascular zone is the area in the fovea that is devoid of blood vessels. foveola is the center part of the fovea. The foveola is about 0.35 mm in diameter. The fovea is very small as compared to the retina but it takes up 50% or more visual cortex in the brain.

The fovea is not sensitive to dim light because it does not have the rods. Each millimeter of the fovea contains 383 cones.

 

5. Iris

It is a thin circular structure present in the eye. The iris controls the diameter and size of the pupil which means that iris indirectly controls the light reaching the retina. The iris is the structure that defined the color of the eye. It contains two-layers that are the stroma and pigmented epithelial cells layer. The iris is divided into the ciliary zone and the pupillary zone. Both the zones are separated by collarette which is the thickest region of the iris.

The microscopic study of the iris shows it contains six layers that are the anterior limiting layer, stroma, iris sphincter muscles, iris dilator muscles, anterior pigment epithelium layer, and posterior pigment epithelium layer.

6. Lens

It is a biconvex transparent structure that is present in the eye and along with the cornea it helps to refract the light. The lens can change its shape due to which the focal distance changes and the eye becomes capable to focus on objects at various distances. The kens contain three main parts that are the lens capsule, lens epithelium, and lens fibers. The capsule form the outer layer and the fibers formed the inner layer. The epithelium is located between the capsule and fibrous layer. The lens does not contain blood vessels, connective tissues, or nerves.

The lens is a flexible structure and it is controlled by the ciliary muscles of the ciliary body through zonules. Aquatic animals entirely rely on the lens for focus and refractive power.

 

7. Macula

The macula is the central and functional area of the retina. It is about 5mm in diameter. The center of the macula contains the fovea. The fovea is a very important structure in the human eye. The vision is directly related to the fovea. The vision is lost when the fovea becomes diseased. The functions of the macula are that it takes the pictures, and it provides the ability to see and read in detail.  The most common disease that affects the macula is Diabetic retinopathy.

 

8. Optic nerve

It is a nerve that carries the message from the retina to the brain. The optic nerve carries the image to the brain because the retina sees images upside down.

9. Pupil

It is a hole present in the center of the iris that allows the light to pass to the retina. In human pupil is round while on other species the pupil might be in different shapes. The pupil appears black because of the light entering the pupil is absorbed directly or absorbed after diffuse reflection. Mydriasis is the dilation of the pupil while miosis is the contraction of the pupil.

 

10. Retina (eye anatomy)

It is a thin layer of tissue located near the optic nerve. It receives the light that was focused by the lens. After receiving the light the retina converts it into electrical signals. Photoreceptors cells are the cells present in the eye that process the light.

11. Sclera

The sclera is the outer white coat that surrounds the iris of the eye.

 

12. Vitreous humor (eye anatomy)

Vitreous humor is a clear gelatinous substance that fills the central cavity of the eye.

 

How the eyes works

1. Light is focused by the cornea
2. The iris controls the light
3. Lens further focus the light
4.  Retina receives the focused light
5. The retina converts these light signals into electrical signals.
6. These neural or electrical signals then travel to the visual cortex of the brain through the optic nerve.

Eye diseases

1. Macular degeneration. It causes loss of the central vision.
2. Ambylopia. In this condition, one eye sees better than the other.
3. Astigmatism. In this condition, the eyes can not focus light on the retina.
4. Cataracts. Internal lens clouding.
5.  Chalazion. Oil making gland blocked and swell into a bump.
6.  Conjunctivitis.  Inflammation of the conjunctiva.
7.  Diabetic retinopathy. Blood vessels are damaged in the eye due to high blood sugar levels.
8.  Diplopia. Seeing double
9.  Dry eye. Poor tear quality or not enough tears are produced.
10.  Glaucoma. The progressive loss of vision.
11. Hyperopia. The person can not see near objects clearly.
12.  Hyphema. Bleeding into the front of the eye.
13.  Keratitis. Inflammation of the cornea.
14.  Myopia. The person cannot see the far object clearly.
15.  Pterygium. Thickened mass on the inner of the eyeball.
16.  Retinitis. Inflammation of the retina.
17.  Scotoma. The dark spot in the visual field.
18. Stye. Painful lump on edge of eyelids.
19. Iritis. Inflammation of the iris.

 

diagram of eye anatomy

 

eye anatomy

eye anatomy

 

tags

eye anatomy, human eye anatomy, anatomy of the human eye, diagrams of the human eye.