The Anatomy And Physiology Of The Eye

The Anatomy And Physiology Of The Eye

The eye is a spherical organ that is connected to the brain by the optic nerve. It is responsible for the perception of light stimuli. 

1. Upper eyelid
2. Rectus muscle
3. Sclerotic la ‘er
4. Suspensory
5. Ligament
6. Choroid layer
7. Aqueous humor
8. Retina
9. Fovea (: rails
10. Eye-lash
11. Lens
12. Cornea
13. Iris
14. Conjunctiva
15. Vitreous
16. Humour
17. Optic nerve
18. Blindspot
19. Ciliary body
20. Lower eyes
21. vertical section of the human eye

The different parts of the eye are:

optic nerve. It is responsible for the perception of light stimuli.  The continues across the surface of the eyeball. It protects the inner part

1. CONJUCTIVA:- This is a thin epithelium that lines the eyelid and it of the eye. It gets inflamed during infection instead of the entire eye.
2.  CORNEA:- This is a thick transparent tissue. It is a continuation of
3. AQUEOUS  HUMOUR:- This is a fluid occupying the front of the eye. the sclera in front of the eye. The fluid contains salt, sugar, and protein and supplies food and oxygen to the lens and cornea. The fluid is more watery than the vitreous humor. It also helps to maintain the shape of the eye.
4. CILIARY MUSCLE:- This muscle pulls on the lens. Varying its tension makes the lens either thinner or thicker from back to front This alters the focal length of the lens and results in proper accommodation
5. IRIS:- This is a continuation of the choroid in front. It forms a partition between the anterior and posterior chambers of the eye. The iris regulates the amount of light that enters the eye. It is pigmented and therefore responsible for the color of the eye. The space between the two iris is called the pupil, and through here light rays enter the eye.The 
6. THE LENS:-The lens is a transparent biconvex and elastic structure. It Is held in position by the suspensory ligament. Its main function is that of focusing of image on the retina.
7. VITREOUS  HUMOUR:- Unlike the aqueous humor which is more watery, the vitreous honor is a thick, jelly-like fluid that fills the back of the eye. It also contains salt, sugar, and protein. Together with the aqueous honor, help to refract light rays and produce an image on the retina. Both also help in keeping the eyeball firm and round and thus preventing its collapse.
8. RETINA:- The retina is the innermost layer of the eye. It contains two light-sensitive cells called the rods and the cones. The rods are sensitive to dim light while the cones are sensitive to bright light. It is on the retina that images are formed.
9.  CHOROID:- This is a black layer at the back of the eye. It is pigmented and rich in blood vessels. It also provides food and oxygen to the adjacent parts of the eye. The choroid also helps prevent the reflection of light within the eye. It continues in front of the eye as the iris.
10. SCLERA:- This is the outermost part of the eye. It is a thick fibrous Connective tissue forming the white of the eye. The sclera also contains dark pigments and also helps prevent the reflection of light within the eye.

• Fovea Centralis(yellow spot): – This is the most sensitive part of the retina and it is densely packed with cones. It gives the most accurate interpretation of an image.
• Optic Nerve:- This nerve carries impulses to and from the brain. The point at which the nerve fibers leave the retina is called the blind spot. This spot has neither rods nor cones and is insensitive to light.

The principle that if the light ray passes from a less dense medium to a denser medium it converges is upheld in image formation in the eye. Light rays from an object pass through the cornea and lens and are refracted. The image formed on the retina is inverted but the optic center in the brain corrects it as upright.

The ability of the eye to focus on objects at varying distances is called accommodation. There are certain changes that occur in the shape of the eye for it to see clearly objects at long distances and those at a near distance.

The Anatomy And Physiology Of The Eye

ADAPTATION FOR NEAR VISION

1. The ciliary muscles contract.
2. The suspensory ligaments relax.
3. The lens becomes thickened or more convex
4. The focal length shortens.

ADAPTATION FOR DISTANT VISION

1. The ciliary muscles relax.
2. The suspensory ligation contract.
3. The lens stretches into an elongated shape.
4. The focal length is increased.

EYE DEFECTS

• Short-sightedness (Myopia):

This is a defect in which patients see near objects clearly. They are unable to see distant objects clearly. The defect is due to the eyeball being slightly elongated from front to back. Light rays from distant objects are brought to a focus before reaching the retina. The actual image on the retina is blurred or distorted. It is corrected by wearing a spectacle with a concave lens. 

This lens will lengthen the focal length as well as cause the light rays to diverge slightly before entering the eye. Thus the image is formed on the retina Rays from a distant object

• Short-sighted eye
• Focus
• (uncorrected)
•  Short sight
• Long-sightedness ( hypermetropia):-

The patients with this defect see distant objects very clearly but cannot see near objects: clearly. The eyeball may be shorter than normal or the lens and the ciliary muscle have lost their elasticity with age. Light rays from near objects are brought to a focus behind the retina. Focus (uncorrected) Near object long-sighted eye

• Long sight:

This defect is corrected by we ling a spectacle with a convex (2): lens. This will shorten the focal length as well as cause the light rays to converge slightly before entering the eye. The image will then be formed on the retina.

• Presbyopia:-

This is the loss of accommodation power due to age. The lens is less elastic and near objects become difficult to bring to a focus. It is corrected by wearing bifocal lenses.

• Astigmatism:

This is an eye defect due to irregularities in the curvature of the cornea and the lens. It is corrected by wearing cylindrical lenses.

SOME EYE PROBLEMS

• CONJUNCTIVITISThis is the inflammation of the conjunctiva and it is associated with redness of the eye. This infection is commonly called apollo.

CAUSES OF CONJUNCTIVITIS:-

1. Bacteria such as Staphylcus Streptococcus and Gonococcus. simplex virus.
2. Virus such as Adenovirus a
3. Allergy
4. Trauma

CLINICAL FEATURES OF CONJUNCTIVITIS

1. Redness of the eyes.
2. Prickly or sand-like sensation in the eye
3. Lacrimation
4. Purulent eye discharge if due to bacterial infection
5. Inability to look at a bright light with the affected eye.
6. The itching of the eye is due to allergy.

Investigations:

There is usually none except if due to bacteria infection and there is purulent eye discharge. The swab is taken for microscopy, culture, and sensitivity

TREATMENT

1. Broadspectrum antibiotics are usually taken orally
2. Analgesics
3. Vitamin supplements
4. Eye drops or ointments depending on the cause.

If bacterial, Chloramphenicol, or Geneticin eye drops or ointments are commonly used. For viral, Dendric or Herpic eye drops or ointment are in use. For allergic conjunctivitis (or vernal conjunctivitis) option, Spersallerg and Steroid eye drops are commonly used. It is important to note that in conjunctivitis, pain is not usual, and blurring of Vision is not a feature.

1. COMPLICATION The infection may become chronic and invade the cornea.
2. CATARACT

A cataract is the opacity of the lens. The cause may be congenital or acquired

CONGENITAL CAUSE

1. Genetic as in Down’s syndrome.

2. Familial tendency.

3. Infections in the uterus; such as Rubella, Cytomegalovirus, and Toxoplasmosis.

ACQUIRED CAUSES

1. Senility (old age).

2. Trauma.

3. Eye infections.

4. Excessive heat.

5. Hypertension.

6. Diabetes mellitus.

CLINICAL FEATURES OF CATARACT

1. Smoke-like and cobweb-like vision.

2. Gradual loss of vision without any pain.

3. Whitish patch in the eye.

It is significant to note that cataract does not prevent light perception However, there may be decreased visual acuity in severe cases.

Investigations:-

There are no specific investigations done for cataracts.

Routine tests include:

1. Haemoglobin level.

2. Urinalysis to rule out diabetes is Mellitus.

3. Blood pressure measurement: not to rule out hypertension.

TREATMENT

Surgery is the only remedy. Then the lens is removed and ret ‘aced with an artificial lens. The chemical

chymotrypsin is injected into the  3 posterior chambers is often the lens and this facilitates its removal.

For patients aged twenty-five years and below, the surgery done is Needing and Aspiration, while Extraction is done for those above

COMPLICATIONS OF CATARACT

1. Glaucoma.

2. Blindness

Definitive diagnosis of pregnancy is done by the pregnancy test. A urine test or ultrasound scan can be used to confirm pregnancy in the early stage. The blood test is more accurate.

PSEUDOCYESIS

This means false pregnancy. The woman has a false but firm belief psychological that she is pregnant whereas she is not. It is a problem. Amenorrhoea may occur and other symptoms of pregnancy may also occur. Palpation of the abdomen will definitely show no fetal part and the pregnancy test is negative. The difficult thing is to convince the patient that she is not pregnant. The majority of them have marital problems. It occurs in childless mothers as well as in women with children.

TRIMESTERS

The duration of pregnancy is divided into three. Each is called a trimester. As already stated, the gestational period in man is nine months and this translated to 39 weeks. The firth 13 weeks is called the first trimester. The second 13 weeks is the second trimester,  while the last 13 weeks is the third trimester,

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