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Structure and Functions of Eye & Ear and their Disorders

Light rays penetrating your eye are focused on the retina's receptors by an ocular refracting system.
Structure of an eye
Light rays penetrating your eye are focused on the retina's receptors by an ocular refracting system.

Eyelids and lacrimal glands
A skeletal muscle is located at the base of each eyelid, which controls how the eyelids close and cover the eyeball. It is made possible by the eyelashes that line the eyelids that keep dust from entering the eyes. In addition to covering the white of the eye, the conjunctiva is a thin membrane that traces the edges of the eyelids and covers the corneal epithelium. Allergies, bacteria, and viruses can lead to conjunctivitis, an inflammation of this membrane. This can make the eyes red, itchy, and in most cases watery.

Lacrimal glands, located in the orbit and on the upper, outer side of the eyeball, generate tears. Water makes up the majority of tears, which are also 1% sodium chloride. On the wet, warm surface of the eye, tears contain an enzyme called lysozyme, which inhibits most bacterial growth. There are two small holes at the medial corner of the eyelids that lead into the inferior and superior lacrimal canals. This is the route tears take to reach the lacrimal sac (in the lacrimal bone), where they are removed via the nasolacrimal duct to the nasal cavity. Because of this, crying can make the nose run.

Eyeball
An eyeball is surrounded and protected by a bone called the orbit, which is comprised of elements like the lacrimal, maxilla, zygomatic, frontal, sphenoid, and ethmoid. It connects to the surface of the eyeball and these six extrinsic eye muscles. Specifically, four rectus muscles (straight ones) move the eyes up and down or from side to side. Their names indicate which direction they move. By pulling on the medial rectus muscle, for example, you can look at your nose while pulling your eyeball to the side. The eyes are rotated by the oblique (slanted) muscles.

In the human head, the oculomotor, trochlear, and abducens (3, 4, and 6 cranial nerves, respectively) innervate these two groups of muscles. It is not necessary to consider the rapid and complex coordination between muscles in both eyes. It is essential to see the same object with both eyes (to prevent double vision) and to be able to perceive depth and the three-dimensionality of the world.

Layers of the eyeball
There are three layers to the eyeball - fibrous, vascular, and inner. Layers have specialized structures and functions.

1. Fibrous
The fibrous layer covers the outside of the eye. Its two parts, the sclera, and cornea are continually joined one to the other. Keeping our eyes in shape and supporting deeper structures are their primary functions. In the fibrous layer, the scleral layer constitutes most of it (about 85%). It attaches to the eye's extraocular muscles, which facilitate eye movement. As seen in the eye, it is the white part. Transparent and positioned centrally, the cornea is at the front of the eye. By refracting light, the cornea directs light into the eye.

2. Vascular
The vascular layer lies below the fibrous one. There are three major parts of it: choroids, ciliary bodies, and iris.
Choroid - It is made up of connective tissues and blood vessels. A layer of outer retinal cells is nourished by it.
Ciliary body - ciliary process and ciliary muscle make up the ciliary body. In terms of anatomy, the ciliary muscle is usually composed of smooth muscle fibers. The ciliary processes attach the iris to the lens. It is composed of a ciliary body, a structure whose shape is determined by the shape of the lens, and a part of the ciliary fluid
Iris - An aperture in the center of the iris (the pupil) lends the iris its circular shape. An autonomic nervous system innervation controls the smooth muscle fibers within the iris that determine the diameter and shape of the pupil. In between the lens and cornea, the iris is located.

3. Inner
A large part of the inner eye is formed by the retina, which detects light. The retina is divided into two layers:
Pigmented (outer) layer - One layer of pigmented (outer) cells forms the outer layer. The choroid is attached to this membrane and serves to absorb light (ensuring light does not spread into the eyeball). Throughout the whole surface of the eye, it is present.
Neural (inner) layer - Photoreceptor cells, the cells in the retina that detect light, make up the inner (neural) layer. A posterior and lateral part of the eye contains it.
This is part of the retina that is not visible - this is known as the non-visual retina. The pigmented layer continues into the anterior portion of the retina. There are both posterior and lateral retinal layers. A retinal optic nerve lies within this portion.

Ophthalmoscopy enables us to observe the optic portion of the retina. A macula marks the retina's center. Besides being yellow, it is also highly pigmented. A depression known as the fovea centralis is located in the macula, which contains concentrated light-detecting cells. The high-acuity vision is controlled by this part of the brain.

Main structure
I. Vitreous body
The vitreous body is a transparent gel found behind the lens of the eyeball (the posterior segment). A hyaloid canal is the only passageway that links the optic disc to the lens. It is a remnant of the fetal tissue.
Three functions are performed by the vitreous body:
  1. Provides the eye with magnifying power
  2. Keeps the retina in place
  3. Maintains the lens in place and supports them.
II. Lens
There is a lens situated between the vitreous humor and the pupil in the anterior portion of the eye. The shape, refractive power, and shape of the lens are affected by the ciliary body.

The eye has two chambers filled with fluid - an anterior chamber and a posterior chamber. Iris and ciliary processes make up the posterior chamber, located between the anterior chamber and iris. Among the chambers of the eye is aqueous humor, a clear fluid similar to plasma that provides nourishment and protection to the eye. In the cornea, near the anterior chamber, a trabecular meshwork drains aqueous humor continuously. It is continuously produced and drains from the trabecular meshwork, an area near the anterior chamber surrounded by a tissue bundle. A condition called glaucoma can occur if aqueous humor drainage is blocked.

Functions of an eye
In every eye, light is constantly adjusted, focusing on objects nearby and far away, and producing continued images that are transmitted instantly to the brain.

Disorders of an eye
1. Cataract

Cataracts are cloudy or opaque areas of the eye lens, which occurs when the lens becomes opaque. Among elderly people, cataract formation is caused primarily by aging. As the lens ages, its proteins degrade and become less transparent.

2. Glaucoma
Intraocular pressure is the pressure created by the aqueous humor within the eye's anterior chamber. Glaucoma, which affects the optic nerve and causes blindness, can occur when this pressure increases. In addition to diabetes, heart disease is also a risk factor. Glaucoma, the most common type, results from an inability to resorb aqueous humor into the canal of Schlemm.

3. Errors of refraction
Visual acuity is expressed as 20/20 or being able to see something 20 feet away. Having near-sightedness (myopia) means having difficulty seeing distant objects clearly when you look at them closely. Near-sighted eyes, which are typically near-sighted, are only able to see an object at 20 feet when it is brought to a distance of 80 feet. A large eyeball and a thick lens allow the retina to focus on distant objects, so images from distant objects can be seen directly in front of it.

The eye is farsighted (hyperopia) when distant objects are visible. The normal eye can see at 10 feet what the eye with acuity of 20/10 can see at 20 feet. Since the distance eyeball is too short or the lens too thin, light from near objects is focused "behind" the retina.

Structure of an ear
Organs such as the ear are delicate and complex. You can hear everything around you with it since it collects sound waves. An ear's other function is to keep you balanced. There are 3 main parts to your ear. Inner, middle, and outer ears are all included. It helps collect and amplify sound with the middle ear and outer ear. Within the inner ear, sound waves are transformed into neural messages that are transmitted to the brain. The inner ear is also responsible for sensing and detecting the movement of the head and the body. When you change positions, it keeps you balanced and helps you see clearly.

Functions of an ear
  1. Those sound waves travel from your ear canal to your eardrum.
  2. External ears collect sound waves.
  3. As a result of the sound waves, the eardrum vibrates, moving the middle ear bones.
  4. Sound waves travel to the inner ear with the help of vibrating middle ear bones (ossicles). A healthy middle ear has a balanced air pressure. Middle ear air pressure is controlled by the Eustachian tube.
  5. Maintaining balance is easier with semicircular canals.
  6. Balance signals are carried to the brain by the vestibular nerve.
  7. Sound waves are picked up by the cochlea and transmitted to the brain as nerve signals.
Disorders of an ear
Deafness

A person with deafness is unable to hear well; types are grouped according to the components of the hearing process that do not function normally:
Conductance deafness - A defect of the structures transmitting vibrations of the ear causes conductance deafness. The eardrum may be punctured, the auditory bones may have arthritis, or the middle ear cavity may be filled with fluid because of an infection.
Nerve deafness - Hearing loss caused by nerve deafness, caused by loss of an 8th cranial nerve or hearing receptors in the cochlea, several antibiotics used to treat bacterial infections can damage the 8th cranial nerve. Viruses such as mumps and congenital rubella (German measles) can cause nerve deafness as an outcome. The cochlea does not preserve its hair cells as we age, and our hearing becomes less acuate as we age.
Central deafness - Deafness resulting from damage to the temporal lobe auditory areas, Deafness caused by this type of tumor, meningitis, or brain trauma in the temporal lobe is rare, but it may be caused by these conditions.
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Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of Pharmaceutical Guidelines, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.
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