Visualization is possible because of the brain's ability to understand information our eyes receive when light is reflected off objects.
The front surface of the eye is also known as cornea, which is a dome-shaped clear structure that allows light to enter the eye. It covers the iris - the coloured part of the eye, which has the pupil in its centre. The pupil is actually an opening through which light enters and is passed to the back of the eye.
In bright conditions, the muscles of the iris contract to reduce the size of the pupil, which decreases the amount of light entering the eye. In poor lighting, the iris muscles expand, making the pupil bigger, to allow more light to enter the eye.
Behind the iris is the lens of the eye, which allows us to focus on objects at different distances. The lens focuses light rays that reflect from objects and places them as images on the retina, which can be compared to a camera film for the eye.
Images received by the retina are transformed into electrical signals. The retina then sends these signals along the optic nerve to the brain. Once received by the brain, the signals recreate pictures.
Following are few common eye diseases in human being:
Amblyopia, commonly known as lazy eye, is the eye condition noted by reduced vision not correctable by glasses or contact lenses and is not due to any eye disease. The brain, for some reason, does not fully acknowledge the images seen by the amblyopic eye. This always affects only one eye however may manifest with reduction of vision in both eyes. It is estimated that three percent of children under six have some form of amblyopia.
Causes of Amblyopia
Both eyes must receive clear images during the critical period. Anything that interferes with clear vision in either eye during the critical period (birth to 6 years of age) can result in amblyopia (a reduction in vision not corrected by glasses or elimination of an eye turn). The most common causes of amblyopia are constant strabismus (constant turn of one eye), anisometropia (different vision/prescriptions in each eye), and obstacle of an eye due to trauma, lid droop, etc. If one eye sees visibly and the other sees a blur, the good eye and brain will ignore the eye with the blur. Thus, amblyopia is a active process. The inhibition process can result in an everlasting decrease in the vision in that eye that cannot be corrected with eyeglasses, lenses , or laser surgery.
Diagnosis of Amblyopia
Amblyopia usually occurs in one eye only; many parents and children may be unaware of the condition. There are many parents who fail to take their infants and kids for an early complete vision examination and many children go undiagnosed until they have their eyes examined at the eye doctor's office at a later age.
The most important diagnostic tools are the special visual acuity tests other than the standard 20/20 letter charts currently used by schools, paediatricians and eye doctors. Examination with cycloplegic drops can be necessary to detect this condition in the young.
The treatment of amblyopia may be followed by:
Covering one eye might be required for a period of time ranging from a few weeks to as long as a year. The better-seeing eye is covered, forcing the "lazy" one to work, thereby strengthening its vision.
Medication in the form of eye drops or ointment might be used to smear the vision of the good eye in order to force the weaker one to work. This is generally a less successful approach.
Improvements are possible at any age, but early detection and treatment offer the best outcome. Amblyopia can cause a permanent loss of vision with related loss of stereopsis (two eyed depth perception) if not detected and treated early in life. The 20/20 eye chart screening is not sufficient, as better vision screenings are needed for young children.
Amblyopia causes more visual loss in the under 40 group than all the injuries, and diseases combined in this age group.
Blepharitis refers to constant swelling of the eyelids. It is one of the most common disorders of the eye and is often the basic reason for eye discomfort, redness and tearing. Other eye symptoms of blepharitis include: Burning, itching, light sensitivity, an irritating, dirty, gritty sensation that is worse upon awakening. There are 3 forms of blepharitis staphylococcal, seborrheic and MGD. All three forms of blepharitis are chronic in nature. Patients with staphylococcal blepharitis are relatively young between ages of 42 years with a small record of ocular symptoms (mean 1.8 years). Seborrheic blepharitis and MGD blepharitis patients are generally older and have a longer history of ocular symptoms.
In staphylococcal blepharitis there is scaling and crusting along the eyelashes whereas in seborrheic blepharitis there is greasy scaling along the eyelashes. Seborrheic dermatitis is very frequent in patients as well. In Meibomian gland dysfunction (MGD) there are prominent blood vessels crossing the eyelid margin. In addition there is disappointment of meibomian gland openings as patients are noted to have coexisting rosacea and seborrheic dermatitis with MGD frequently. Use of isotretinoin (Accutane), an oral medication for severe cystic acne, has also been implicated as a cause of blepharitis.
It is a chronic disease, which is tough to manage because it tends to reoccur, and require long-term treatment to keep it under control. Treatment consists of 2 phases known as acute phase and Maintenance phase.
Acute phase treatment involves intensive therapy to bring the disease under control swiftly.
In the maintenance phase the objective is to forever continue the minimum amount of therapy that is necessary to keep the disease quiet. Herein we will not focus on the treatment of specific steroid responsive complications of blepharitis like marginal ulcers and phlyctenules, as they are less common and require specific diagnosis. Treatment depends on the type of blepharitis you have. It may consist of applying warm compresses to the eyelids, cleaning them, using an antibiotic or massaging the lids. The doctor may also prescribe artificial tears or lubricating ointment if your blepharitis makes your eyes feel dry.
The warm compact segment of treatment is designed to loosen crusts on your eyes before you rinse them; it can also warm up and loosen the plugs blocking the meibomian glands in meibomianitis. Wash your hands, then wet a clean washcloth with warm water and place it over your closed eyes. The doctor will probably suggest that you do the above procedure four times a day, for about five minutes each time when you first begin treatment. Later on, you might apply the compress once a day, for a few minutes. Your doctor will tell you the specific treatment needed for your eyes.
Cleaning the eyelids is important in blepharitis treatment. Your doctor will recommend what to clean them with: warm water only, salt water, baby shampoo diluted with warm water or a special product exclusively made for cleaning the lids. First wash your hands, and then dip a clean washcloth, cotton swab or gauze pad into your cleaning solution. Gently wipe it across your lashes and lid margin. Rinse with cool water. Use a different washcloth, swab or pad for your other eye, and repeat the process. When you first begin treatment, your doctor may ask you to clean your lids numerous times a day. Later on doctor can instruct you to clean them about once a day.
It is a condition in which the lens of the eye becomes thick or opaque and does not properly transmit light. A cataract is a clouding of the normally clear lens of the eye.
Fading or yellowing of colors.
The amount and pattern of cloudiness within the lens can vary. If the cloudiness is not near the center of the lens, you may not be aware that a cataract is present.
What causes cataract?
In most cases, a cataract is a natural part of aging. In fact, if they live long enough, every individual will develop a cataract. Some people develop dense cataracts at age sixty, while others remain cataract-free until the age of ninety.
While aging accounts for most cataracts, there are also other causes. Certain diseases, such as uveitis (inflammation inside the eye), can lead to cataracts. Exposure to radiation such as ultraviolet (like that from the sun) and infrared rays can also lead to cataracts. Poor nutrition may cause cataracts to develop earlier and progress faster, as often happens in underdeveloped countries. A cataract can also be caused from injury to the eye and by certain prescription drugs, such as steroids.
Children are born with cataracts on rare occasions. They require immediate treatment to prevent permanent loss of vision.
Children are born with cataracts on rare occasions. They require immediate treatment to prevent permanent loss of vision.
Congenital Cataracts may be present at birth or may develop in infancy or early childhood. Surgery must be done on time or the eye will not develop fundamental connections to areas of the brain that allow individuals to interpret the images they see. If not treated on time, the condition of amblyopia or lazy eye can lead to permanent visual loss.
Currently medications are not available to prevent or treat cataracts. However, exposure to ultraviolet radiation (from the sun) and a poor diet have been linked with cataracts, so it is wise to wear a hat and sunglasses to protect yourself and eat a balanced diet that includes the major antioxidants like vitamins C, E, and A or beta-carotene. Researchers also believe good nutrition can help reduce the risk of age-related cataract. They recommend eating green leafy vegetables, fruit, and other foods with antioxidants. Antioxidants are found in green leafy vegetables, carrots, citrus fruits, melons, eggs, garlic, avocado, asparagus, onion and red meat. If you do not have a balanced diet, taking multi-vitamins on a regular basis may be useful. If you are of age 60 or older then you should have a complete eye exam at least once every two years.
Vision may be reduced or people may notice blurring of their vision. Objects may also be out of shape and may appear washed out and colours less bright. This may be noticed more in poor lighting conditions and in bright light conditions glare may reduce vision. In the evening, cataracts may lead to the look of halos around car headlights and other lights. As cataracts become increasingly opaque, reading, watching television and driving at night become more complicated they are one of the major reasons because of which people stop driving.
Some people might also experience "second sight" in the early stages of a cataract and would find that they are able to see without their reading glasses. This will last a few months, but as the cataract becomes denser, vision will begin to blur.
The treatment of cataract
With new eyeglasses, brighter lighting, anti-glare sunglasses or magnifying lenses the symptoms of cataract has been approved. However if these measures do not help then surgery is the only effective treatment. It will remove the cloudy lens and replace it with an artificial lens. It needs to be removed only when vision loss your everyday activities, such as driving, reading, or watching TV.
Delaying cataract surgery will not cause long-term damage to your eye or make the surgery more difficult in most cases. However sometimes a cataract should be removed even if it does not cause problems with your vision. If your eye care professional finds a cataract, you may not need cataract surgery for several years or might never need cataract surgery.
Many people who need cataract surgery also have other eye conditions, such as age-related macular degeneration or glaucoma. If you have other eye conditions in addition to cataract, consult your doctor.
It is a small bump that develops on the upper or lower eyelid. Inflamed meibomian glands that produce the oil in tears cause it. Chalazion is a lump in the eyelid that is caused by inflammation of a gland within the skin. The lump grows from days to weeks and is occasionally red, temperate, or painful.
In the formation of a chalazion the gland is a modified sweat gland that lies within the eyelid. This gland produces oil and when it becomes blocked, it can break and the inflammation process will begin. Inflammation is a process in which the body reacts to a condition and produces a biologic reaction. This reaction can cause swelling, redness, pain, or warmth.
It is caused by the oil in the gland becoming too broad to flow out of the gland and blocks the gland however the gland still produces more oil. Since there is no place to go the oil builds up inside the gland and forms a lump in the eyelid. Finally, the gland ruptures and releases the oil into the tissue of the eyelid, causing inflammation.
The symptoms of chalazion Swelling of the upper eyelid may occur gradually over weeks. The condition rarely involves the lower eyelid. It will appear as a restricted hard lump that may grow as large as an eighth of an inch. You may feel pain and your eyelid may be red occasionally.
Treatment of Chalazion
They require intensive steroid therapy as chalazion reside deep under the skin, no relevant medications will be able to penetrate adequately. Antibiotic eye drops or ointment are sometimes used for the initial acute infection, but are of little value in treating a chalazion. You shoul consult your doctor for the treatment.
It is also called pink eye. It is an inflammation of the blood vessels in the conjunctiva the membrane that covers the sclera and inside of the eyelids. Inflammation of this membrane is called conjunctivitis. Bacteria or viruses, making it very contagious, may cause conjunctivitis.
Viral conjunctivitis causes excessive eye watering and a light discharge usually affects only one eye.
Bacterial conjunctivitis causes a heavy discharge, sometimes greenish affects both eyes.
Allergic conjunctivitis causes itching and redness in the eyes and sometimes the nose, as well as extreme tearing affects both eyes.
Giant papillary conjunctivitis (GPC) causes contact lens intolerance, itching, a heavy discharge, tearing and red bumps on the underside of the eyelids usually affects both eyes.
To locate the cause and then choose an appropriate treatment, your doctor will ask some questions.
It is found in some people who have diabetes. It is a disorder of the retina resulting from changes in the eye blood vessels. It is the most common diabetic eye disease and an important cause of blindness in adults.
In some people suffering from diabetic retinopathy, blood vessels might swell and leak fluid. However in other people, abnormal new blood vessels grow on the surface of the retina. The retina is the light-sensitive tissue at the back of the eye. A healthy retina is necessary for good vision.
If you are suffering from it then at first you might not notice change to your vision. But as the time will go, it can get worse and cause vision loss. Diabetic retinopathy usually affects both eyes.
Diabetic retinopathy has four stages:
Mild Nonproliferative Retinopathy. This the first stage where micro aneurysms occur. They are minute areas of balloon-like swelling in the retina's tiny blood vessels.
Moderate Nonproliferative Retinopathy. In this stage the disease progresses and some blood vessels that nurture the retina are blocked
Severe Nonproliferative Retinopathy. In the third stage more blood vessels are blocked and depriving several areas of the retina with their blood supply. These areas of the retina send signals to the body to grow new blood vessels for nourishment.
Proliferative Retinopathy. In the advanced stage, the retina sends the signals for nourishment activate the growth of new blood vessels. This condition is called proliferative retinopathy. These new blood vessels are inconsistent and breakable. They grow along the retina and along the surface of the plain, vitreous gel that fills the inside of the eye. By it these blood vessels do not cause symptoms or vision loss. However, they have thin, delicate walls. If they leak blood, severe vision loss and even blindness can result
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