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Wednesday, August 7, 2019

Eye Anatomy

                    Eye Anatomy 





Eye Anatomy




The word ophthalmology derives from the Greek word ophthalmos, which means "eyeball" or "eye". Ophthalmology is the branch of medicine that treat eye diseases. Note that the word is written 2 h’s and 2 l’s 

What is an ophthalmologist?


An ophthalmologist is a doctor (MD) or an osteopathic doctor (DO), specially trained in medical and surgical care and in the treatment of the eyes. Becoming an ophthalmologist can take 12 or more years of education and advanced training

An ophthalmologist can practice the profession of complete or general ophthalmologist, a doctor who treats a wide range of eye problems and conditions



The eye:


    (A machine to capture the light)


Although it weighs only 7 grams and its average diameter is only 24 millimeters, the human eye is a biological camera whose complexity and performance far exceeds modern optical devices. This advanced optical system includes two lenses and a charged pupil to deflect a precise amount of light rays onto the retina, where over 130 million photoreceptors convert light into nerve signals that the brain can interpret

 Anatomy of the eye:



The eye can be described as a hollow ball (the eyeball) filled with liquid. This ball, also known as a globe, rests in a bone cavity in the skull called an orbit. Six specialized extraocular muscles attach to each eyeball and orbital bones in various places. These muscles help rotate the eyes and move them up, down, left and right. The orbit is a pyramid of bone walls that converge in a posterior apex. The orbit is surrounded superiorly by the frontal sinus, medially by the ethmoid sinus, inferiorly by the maxillary sinus and laterally by the zygomatic bone. 

The ethmoid bone  or lamina papiracea is very thin and is the most likely sinus wall to break in a blunt eye injury or puncture due to sinusitis with consequent spread of infection in the orbit. The orbital content includes:

  • The eye muscles
  • Retroseptal fat  
  • The optic nerve


The anterior limit of the orbital cavity is a layer of fascia that extends from the periosteum along the orbital edge, what is know as the orbital septum, to the aponeurosis of the levator of the upper eyelid and to the edge of the tarsal plate of the lower eyelid. Through the apex of the orbit, the nerves and vessels of the eye enter, which is also the site of origin of the extraocular muscles. The optic nerve is subject to compression due to mass effect due to tumors, abscesses or bruises. The inflow of arterial blood to the eye and orbit is the ophthalmic artery, the first major branch of the intracranial portion of the internal carotid artery, which enters the orbit under the optic nerve

The central artery of the retina is the first intraorbital branch of the ophthalmic artery and extends through the optic nerve. Venous drainage from the eye and orbit occurs through the ophthalmic veins, which drain into the central vein of the retina. Ophthalmic veins communicate directly with the cavernous sinus. This venous system has no valves and this fact is the basis for the spread of facial and periorbital infections of the cavernous sinus

When most people think of the eye, they think of the color ring in the center (the iris), the black circle in the center of the iris (the pupil) and the white of the eye (the sclera). If you take a closer look, you can see a clear, round dome, like a watch glass, covering the iris and pupil. This is the cornea, which helps to focus the light rays that enter the eye. Another clear membrane, the conjunctiva, covers the sclera and internal eyelids. Normally you cannot see this transparent cover. However, it is full of small blood vessels which can swell and appear when the eye is irritated, giving the appearance of bloodshot eyes

The upper and lower eyelids cover  the outer eyeball, which are movable folds of skin. Eyelashes are the small hairs on the upper and lower edges of the eyelids. Although not part of the eyeball itself, the eyelids and eyelashes are important for eye health. Eyelashes help trap dust and dirt that might otherwise enter the eyes. "Empty" spaces in the eyes are also important. For example, a dome-shaped space called the anterior chamber is located between the cornea and the iris

A fluid produced by the eye, called aqueous humor, flows through this chamber to help maintain uniform pressure within the eye. Behind the iris is the lens, which, like the cornea (helps to focus the light rays on the back of the eye). Behind the lens there is another large camera, filled with a gelatinous substance called a glassy fluid, or simply vitreous. Vitreous fluid (helps the eyeball to maintain its round and firm shape)

Ocular motility: the normal patient can move the eye through the six cardinal positions of the gaze, and the six extraocular muscles attached to each eye control the eye movements. The extraocular muscles are innervated by the cranial nerves III, IV and VI. The cranial nerve IV controls the superior oblique muscle, the cranial nerve VI controls the lateral rectus muscle and all other extraocular muscles are controlled by the III cranial nerve. Extraocular movement can be affected by restriction, interrupted or reduced innervation or trauma


The role of the retina:

Eye Anatomy



The light rays reaching the retina pass through several layers of cells before reaching the photoreceptor cells, the only cells that have pigments that can transform light into electrical impulses. Through the intermediate neurons, these impulses are transmitted to the optic nerve I, which carries the information to the brain

The retina composes two types of photoreceptor cells: rods and cones. These largely more numerous (125 million), they do not perceive colors but are very sensitive to light contrasts. Conversely, the cones (6 million)  disclose perfectly the colors



View:

   (Our most developed sense)

The human being has a remarkable visual sensitivity, much higher than that of the other senses. The perception of shapes, distances, colors and movements in our environment is a complex process that puts in a chain of optical and nervous elements, from the cornea to the cortex

The light rays of an object we are observing are first deflected from the cornea and then pass through the lens. Unlike the cornea, the curvature of the objective is variable, allowing the image of objects located at different distances to converge on the retina. However, the exactness of this optical system makes it particularly fragile: the slightest negative in the form of the eyeball or in the curvature of the cornea causes an imbalance that the lens is not always sufficient to compensate. By focusing the image not on the retina but in front of or behind it, the vision is blurred

How do you see the eye? Corney's vision of the bark

Eye Anatomy



In our field of vision, when an object enters, each eye perceives it from a slight angle different, which facilitates us to appreciate the distance and better vison its relief in three dimensions. As it passes through the cornea and the lens, the light rays are deflected, so that the image of the object is reversed when it reaches the retina. The optical image is converted by the photoreceptor cells into electrical impulses which borrow the optic nerve. The two optic nerves meet in the optic chiasm, then the lateral geniculate bodies, the growths of the thalamus increase. The information is then transmitted by the optical radiation to the visual cortex, where the image is reconstructed in its place

What is blindness?

Many people think that anyone with vision problems is "blind". But just as there is more than one type of vision, there is more than one type of "blindness". Each of these visual disturbances can be physical disabilities, but they are not necessarily completely disabling



Eye diseases and injuries:


By now you already have an idea of ​​the complexity and delicacy of the eye. As you can imagine, many diseases and other problems can affect such a complex organ. Germs can invade the exposed different parts of the eyes. Eye trauma can be the result of flying objects or other types of accidents. Pathological processes can cause malfunctions to a specific structure of the eye. Sometimes diseases in other parts of the body can cause eye problems


1. Conjunctiva and its diseases: 


It is an inflammation of the small blood vessels in the conjunctiva. Inflammation can be caused by an infection (invasion by microscopic organisms such as bacteria and viruses). Conjunctivitis can also be caused by an allergy. The ophthalmologist generally prescribes eye drops to treat conjunctivitis.

  • Conjunctival chemosis
  • Subconjunctival hemorrhage
  • Conjunctival xerosis

2. Inflammatory conditions: 


An inflammatory case is known as conjunctivitis, also  named "pinkeye". These can include:


3. Corneal Diseases: 


Although the cornea appears clear in such conditions, the patient's vision can be very blurry

  • Corneal abrasion
  • glaucoma

4. Cataract: 


Is another well-known eye problem. Cataract is a gradual clouding of the lens of the eye, which can occur as a natural part of aging. If the lens becomes too cloudy, it will not allow light rays to hit the retina correctly. For a person with a cataract, objects may appear stained and cloudy, but some cataracts hardly interfere with vision. The elderly develop cataracts more often than the young, but children can also have them


Why is total eye care important?


Like "body windows", the eyes can reveal diseases in the brain and other parts of the body. The eyes themselves can get sick. For these reasons, the best total eye care is provided by a periodic complete medical examination by an ophthalmologist, the doctor who is legally and professionally qualified to diagnose and treat all eye problems


Vision is one of our most important senses. Taking care of our eyes is the best way to ensure that we don't lose this precious ability to see

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