What is structure of human eyes and its common diseases 2020

Structure of human eyes and its common diseases

When a patient is examined by an ophthalmologist, the physician subjectively evaluates visual acuity, color vision and visual field, and general eye condition. Visual acuity is a measure of the perception of the details and outlines of objects. Visual acuity tests, such as a standard eye chart (Snellen font chart), measure the ability of the visual system to resolve a target.

This requires the eye to detect an object and dissolve it into its components, and then the information is transmitted to the cerebral cortex for processing against various forms of memory. Visual acuity depends on the ambient light (illumination), the contrast of the target, and the extent to which the target focuses on the most sensitive part of the retina (fovea).

It is said that the perfect vision in a person is 20/20, but young people tend to see better than this (20/15). The visual system is less sensitive with age, but many older people retain 20/20 vision. These measurements show the sharpness of the distance. The proximity of vision is assessed by reading standard printed cards of various sizes. Accommodation and magnification are more important for sightseeing nearby.

Color vision is most often clinically assessed using Ishihara test plates or mechanical or computer tests that require the patient to place colored objects in chromatic order. Field of view analysis is performed to diagnose an early disease or localize damage to the visual system. Visual field testing is most often performed by the examiner, who stands in front of the patient and leads a finger or object from the outside of the field of vision into the field of one eye while the other sees the member.

Diagnostic equipment commonly used in the optical examination

What is Slotted lamp?

This essential tool for clinical evaluation of the eye is a binocular microscope and a movable light source. They are used to examine the front of the eye, but can also be adapted to view the back of the eye.

What is Ophthalmoscope?

These devices focus a light source on the retina, allowing the doctor to view the retina and the vitreous side.

What is a keratometer?

This device allows the physician to examine the curvature and aberration of the cornea. Measurement of corneal curvature is essential for contact lens fitting, eye refractive surgery such as radial keratotomy, or correction of excessive astigmatism. Other photokeratoscope projects an image of the concentric rings of the cornea, and the reflected images are viewed and analyzed by a computer.

What is a tonometer?

Non-contact tonometers are sometimes used to measure glaucoma and excessive intraocular pressure. It creates air that deforms the cornea. The time required to arrange a defined amount of cornea is determined and is proportional to the intraocular pressure. Modern tonometers measure intraocular pressure by direct contact of anesthetized corneas with a small probe.

Anatomy of eye

What is structure of human eyes and its common diseases 2020

The eye is a complex sensory organ that specializes in gathering visual information. Each eye contains a lens system to focus the image, a layer of light-sensitive cells, and a network of cells and nerves that collect, process, and transmit visual information to the brain, each surrounded by a fibrous protective sphere.

The eyes are placed in the protective bony structures of the skull, called pathways. Each eye consists of a hard outer layer, the sclera, and the cornea; a middle layer, the hips, the ciliary body, and the iris; and the inner layer of nerve tissue called the retina. The photosensitive retina is connected to the brain through the optic nerve.

Word anatomy

Orbit: 

The conical cavity in the skull is formed by the frontal, maxilla, zygomatic, sphenoid, ethmoid, lacrimal, and palatinous bones. These bones are thin and often prone to fractures. The eye occupies the first part of the cavity, the rest is full of fat, nerves, blood vessels, muscles and the mammary gland.

Anterior chamber:

The three first ventricles in the eyeball are located between the cornea and the iris.

Posterior chamber:

This chamber takes up space between the iris and the lens.

Watery humor:

This fluid fills the anterior and posterior chambers. It is made by the cells of the ciliary body and circulates from the posterior chamber, above the lens, to the anterior chamber and exits through the Schlemmi channel. It is like plasma yet contains next to no protein.

Vitreous space:

This chamber takes up space behind the lens towards the retina. It is filled with a gelatinous substance called vitreous.

Sclera:

The fibrous protective covering of the eyeball, which we see as eye protein. It consists mainly of structural protein collagen.

cornea:

The transparent, colorless anterior sixth part of the eyeball. The cornea consists of 5 layers, the outer layer consists of an epithelial layer consisting of 5-6 cell layers, which are approx. This layer and the inner endothelium are responsible for the transparent preservation of the cornea.

This is done by keeping the middle layers relatively dry, which prevents the parallel collagen fibers therefrom becoming opaque. The cornea contains no blood vessels and receives its nutrients from the atrial fluid and surrounding blood vessels.

Schlemm channel:

This channel allows fluid from the anterior chamber. Blockage of this canal leads to increased intraocular pressure, which can damage the retitis. This condition is also called glaucoma.
corridor: This is the vascular layer of the eye.

Retinal pigment epithelium:

This layer, located between the retina and the choroid, contains melanocytes that provide their characteristic black color. This pigment allows the inside of the eye to absorb scattered rays of light, such as black ink inside the camera or in a dark room.

Ciliary body:

This is an extension of the choroid on the front of the eye at the level of the lens. The lens is attached to the ciliary body, which has smooth muscle in it. The contraction of the smooth muscle changes the shape of the lens and allows the eye to focus on objects. A part of the ciliary body specializes in making aqueous humor.

iris:

What is structure of human eyes and its common diseases 2020

Another augmentation of the choroid that halfway covers the focal point, which is shaped by color cells, fibroblasts, veins, contractile shade cells. The pigment in the iris prevents light from entering the eye except through the pupil.

Melanocytes (pigmented cells) are responsible for the color of the eye. When there is the little pigment in the cells, the light reflected from the choroid at the back of the eye turns the iris blue. As the number of pigment increases, the iris is greenish-blue, gray, or brown in color.

Pupil:

A round opening in the iris that allows light to pass through. The size of the students varies based on the amount of light present. Because of the more light, the pupil contracts, while the pupil widens in the dark to collect as much light as possible.

Lens:

This biconvex structure is very flexible, at least at a young age. Over time, the lens loses its flexibility, reducing the ability to focus near objects. The center of the lens is elongated cells (fibers) that have lost all their organelles and are full of special proteins called crystals.

These fibers are replaced throughout life, but regeneration slows with age. Mature cataracts occur when these fibers accumulate on the pigment granules, making them less transparent.

Retina:

The photosensitive part of the eye lies between the vitreous and the choroid layer at the back of the eyeball and is a complex network of photosensitive cells and different types of neurons. The light reaching the retina must pass through several layers of transparent neurons at the beginning of the retina before reaching the light-sensitive rods and cones.

The photosensitive portion of the rods and cones is located in an extension of the cell that looks exactly like its name. The rods are responsible for black and white vision, while the cones sense color. Retinal neurons integrate visual signals received by rods and cones and transmit information to the optic nerve.

Fovea:

This special area of ​​the retina is used for the most active vision. When someone is actively focusing or looking for an object at an object, their eyes are moved so that the image focuses on the fovea. It is thinner and contains only the cones needed to detect sharp images. The cones in this area are long and thin, with similar rods to be tightly packed. The blood vessels are also missing. Each cone connects directly to the optic nerve neuron.

Blindspot:

There are no photosensitive cells in this part of the retina. Here, the optic nerve and vascular system enter the eye through the optical disc.

Common Diseases of the Eye

Glaucoma

What is structure of human eyes and its common diseases 2020

Glaucoma is the name of a group of conditions that cause intraocular pressure (IOP) to rise above normal (21 mmHg) and cause changes in the characteristics of the field of view and the optical disc. In primary glaucoma, there is no known mechanism for the disease, in secondary glaucoma, eye symptoms are secondary to another eye disease.

Normal IOP is determined by the balance between the formation and removal of aqueous humor. IOP is usually roughly equivalent in both eyes and varies throughout the day. The most common form of glaucoma, primary open-angle glaucoma, affects about 0.5% of adults in Western countries. It often goes unnoticed until visual acuity is lost. Therefore, screening and early diagnosis of high-risk groups is important. High-risk groups include family members, high myopia, diabetes and the elderly.

In glaucoma, vision is lost due to damage to nerve cells as there is increased pressure on neurons that carry messages about motion perception and contrast sensitivity. The issue of neuronal damage remains questionable, but the two theories are as follows: 1) mechanical damage to neurons and 2) increased intraocular pressure occludes the vessels that supply neurons.

The goal of the treatments is to reduce the pressure in the eye to a normal or safer level. Options include laser surgery to open channels, medications to increase water removal or reduce water production, and/or surgery.

Macular degeneration

Macular degeneration is the most widely recognized reason for visual deficiency in developed nations. This is most common in the elderly Caucasian population. Most common in the 60-70 age group. Dietary and environmental factors, as well as age, inheritance, and species, may be important in the incidence of macular degeneration.

Loss of vision is caused by the accumulation of lipid and protein in the membrane at the back of the eye, as well as the formation of a new vascular system that interferes with normal vision.

Sometimes laser treatment is used to destroy the new vasculature, but the underlying disease process remains and continues that the long-term stability of visual acuity is in doubt. Oral zinc and antioxidants may have a beneficial effect on senile macular degeneration.

Retinitis pigmentosa

This progressive disease is characterized by degeneration of the retinal epithelium, especially rods, atrophy of the optic nerve, and changes in retinal pigmentation. The house is unknown and usually begins in early childhood. Night vision is lost, followed by a gradual loss of peripheral vision to tunnel vision. There is no specific treatment, but low vision treatment can be helpful.

Retinal detachment

The most common cause of detachment of the photosensitive retina and the underlying pigmented epithelium is a fracture or rupture that allows the vitreous humor to pass behind the retinal epithelium. Rupture of the retina is often accompanied by bleeding that is experienced as floats in the field of view. If the retina continues to detach, it will atrophy within a few months. Occasionally, though rarely, the retina returns spontaneously.

Treatments consist of laser or cryosurgery, vitrectomy (drainage of the subretinal fluid and replacement of the retina by microsurgery), or placement of external means to retract the sclera (to make the retina more in contact with the pigmented epithelial region).

The gas tampon can also be used to close breaks. In this procedure, an air bubble is injected intraocularly to apply pressure to bring the separated lid closer to the pigmented epithelium. Gas tamponade is often used in conjunction with other methods to achieve better results.

The cataract

Cataracts are lens opacities that can be caused by aging, diabetes, trauma, radiation, medications, or intraocular diseases. They are also visible from birth as a result of birth trauma, maternal infection (rubella), genetic, metabolic, or chromosomal abnormalities. If the cause is not severe or prolonged, the cataract will return as normal lens growth continues. The degree of blurred vision depends on the location of the cataract inside the lens and the proximity of the axis of vision. Mature or congenital cataracts can be removed, but the ability of the eye to break is compromised. this can be solved with contact lenses, glasses, or intraocular lenses.

Astigmatism

The blurring of the image on one axis, as on another, is caused by the cornea having an uneven curvature. Lenses that balance refraction in all meridians can correct astigmatism.

Myopia

Visibility is the result of the eyeball being too long or the cornea so steep that the focused image falls in front of the retina. Biconcave lenses can correct this error if parallel rays of light differ from each other before coming into contact with the eyes.

Presbyopia

This is vision loss caused by aging and loss of lens flexibility. The point closest to the eye that an object can bring into clear focus moves further with age. Generally, the loss of accommodation between the ages of 40 and 45 is such that additional (convex) lenses are useful for reading and close work.

Nyctalopia

The first sign of night blindness shows a deficiency of vitamin A. Long-term deficiency results in irreversible degeneration of rods and cones. Vitamin A treatment can restore vision if given before photoreception cells are destroyed.

Color-blindness

There are different types of color blindness, mainly based on which of the three conical systems in which the individual operates. For example, a person has a cone that senses all three colors, but one is weak (trichromats); or only two cone systems work as with dichromates. Monochromes have only one conical color sensing system.

Abnormal color vision is more common in men because the two genes (green and red) of the cone pigments are located on the X chromosome. Caucasian men are approx. Vision is abnormal in 8% and 0.4% of women. Because all cells in the male body, with the exception of sperm, have X and Y chromosomes in addition to the 44 other chromosomes, color blindness occurs in men in whom the abnormal gene is located on the X chromosome. In order for women to be blind, they must receive two recessive genes, one from each parent. Colorblind female children have a recessive gene and pass the bug on to their sons.

The color blindness tied to the X appears in every second generation of men. The most common tests for color blinds are yarn-matching tests and Ishihara diagrams. During the yarn test, the individual is asked to match one of the yarn colors to the color close to it. Ishihara graphs are multicolored tables that consist of colored numbers or letters from a background of colored spots. Numbers or letters are printed in colors that look the same as background spots when there are blinds of different colors.

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