Contents include:
1. Structure of the human eye
2. Diseases of the eye
3. Preventions and treatments for these diseases
4. Fun and interesting animations and pictures, including optical illusions!
5. Discussions and controversial issues regarding diseases of the human eye
6. And many more links and resources for you to research on your own (:
Created on 27 February 2008 by 4 Biology students (:
& best viewed using Internet Explorer Version 7 and above or Mozilla Firefox.
We'll be blogging in the perspectives of different people:
Yee Herng as an Ophthalmologist (eye surgeon),
Xiu Li as an Eye Refraction Defect Specialist
Xiu Han as a Corneal Specialist,
and Wen Yi as a Student majoring in Biology.
Blindness - Loss of vision
Definition
Blindness is the condition of a lack of vision or the inability to see. It may also refer to a loss of vision that cannot be corrected with glasses or contact lenses.
Partial blindness means you have very limited vision. Complete blindness means you cannot see anything and do not see light. People with vision worse than 20/200 are considered legally blind in the United States.
Causes
Blindness has many causes. The leading causes of chronic blindness include cataract, glaucoma, age-related macular degeneration, corneal opacities, diabetic retinopathy, trachoma, and eye conditions in children (e.g. caused by vitamin A deficiency).
Age-related blindness is increasing throughout the world, as is blindness due to uncontrolled diabetes. On the other hand, blindness caused by infection is decreasing, as a result of public health action. Three-quarters of all blindness can be prevented or treated.
Most visual impairment is caused by disease and malnutrition. According to WHO estimates in 2002, the most common causes of blindness around the world are: cataracts (47.8%), glaucoma (12.3%), uveitis - inflammation involving the interior of the eye (10.2%), age-related macular degeneration (AMD) (8.7%), corneal opacity (5.1%), diabetic retinopathy - damage to the retina (4.8%), and trachoma - infectious eye disease (3.6%).
Other causes include:
- Blocked blood vessels
- Complications of premature birth (retrolental fibroplasia - abnormal blood vessel development in the retina in a premature infant)
- Complications of eye surgery
- Lazy eye
- Optic neuritis (inflammation of the optic nerve)
- Stroke
- Tay-Sachs disease (deadly disease passed down through families that causes damage to the nervous system)
- Retinitis pigmentosa (an eye disease which causes damage to the retina. Causes problems with night vision and peripheral vision.)
- Retinoblastoma (cancer of the retina, affects children under age of 6)
- Lead poisoning
- Optic glioma (tumors that grow in various parts of the brain)
I will focus on two different causes of blindness - Cataracts and Trachoma in the later posts.
The world looks different to an insect because of the compound nature of its eyes and also because they are more sensitive to different wavelengths of light than our eyes are. For example some insects can see UV rays. Features of plants that are invisible to our eyes are apparent to insects because the patterns of the features are visible in the UV rays.Done by: Yee Herng
Labels: Blindness
5 Comments:
What is glaucoma?
It is related to cataracts right?
By 
-xiuli-, at
March 9, 2008 at 4:48 PM
Glaucoma is optic nerve damage, often associated with increased eye pressure, that leads to progressive, irreversible loss of vision.
In glaucoma, the canals through which the fluid drains become clogged, blocked, or covered. Fluid cannot leave the eye even though new fluid is being produced in the posterior chamber. Because there is nowhere in the eye for the fluid to go, pressure in the eye increases. When the pressure becomes higher than the optic nerve can tolerate, glaucoma results.
It usually has nothing to do with cataracts, and is just another cause of blindness.
For more information, you can check out 'glaucoma' under 'resources' in the 'credits' section.
By yh., at
March 9, 2008 at 5:06 PM
Okay. :) Now, I understand.
But, secondary cataract can be caused by glaucoma right?
By -xiuli-, at
March 9, 2008 at 5:22 PM
In the 'Cataracts' post, I mentioned that cataracts can form after surgery for other eye problems, such as glaucoma. But cataracts are usually not caused by glaucoma itself, rather, after the surgery for eye problems (infection). So the answer is no, as cataracts are not caused by glaucoma itself.
By yh., at
March 9, 2008 at 5:43 PM
O, I see. You cleared my queries!
By -xiuli-, at
March 9, 2008 at 5:48 PM
This is the vertical cut of the eye, where you can see EVERYTHING inside the eye! =P
The outer layer: the Sclera and Cornea
The sclera is the tough, fibrous outer layer of the eyeball that forms the whites of your eyes. The front of the sclera is covered by the conjunctiva — a thin, transparent membrane that’s involved in protecting your eyes. The conjunctiva also lines the insides of the eyelids. The cornea is a transparent dome-shaped structure at the front of the eye allowing light to enter the eye, and helps focus and direct light onto the retina together with the lens.
The middle layer: the uveal tract (iris, ciliary body and choroid) and lens
The iris is the coloured part of your eye that controls the size of the pupil — the black area in the centre of the iris. When you are in bright light, the iris reduces the pupil size to restrict the amount of light entering the eye; when in dim light or darkness, the iris opens up the pupil to allow more light in. the iris is between the posterior and anterior chamber, which contains aqueous humour which is a watery liquid formed by the ciliary body constantly. It keeps the lens and cornea nourished.
The lens is a clear, flexible structure that changes shape so that you can focus on objects at varying distances. It is connected to the ciliary body by suspensory ligaments, and changes it's length and thickness according to the relaxation and contraction of ciliary muscles to view objects at different distances.
The vitreous humour is a jelly-like substance that fills the back portion of the eye behind the lens. It helps the eye to keep its shape, and transmits light to the back of the eye.
The choroid is a membrane between the sclera and the retina that lines the back of the eye. It contains many blood vessels that supply oxygen and nutrients to the retina, and is highly pigmented to help absorb light and prevent scattering.
The inner layer: the retina
The retina lines the inside of the back part of the eye, and is light-sensitive part. It contains millions of cells known as photoreceptors, and each is linked to a nerve fibre. You have a blind spot, where all of these nerve fibres converge to form the optic nerve. Objects that fall on the blind spot of one eye are seen by the other eye.
Once an image is detected by the photoreceptors, this information is converted into nerve impulses that are sent to the brain via the optic nerve.
The macula is a small area of the retina that contains a high concentration of photoreceptors, and the middle part of the macula — the fovea — is the most sensitive area, providing the sharpest vision.
So after my long explanation, do you know more about our eyes? =)
-xh
These are some questions you may have on the eye. If you have any questions, feel free to drop a mail and i will try to answer! smilez!
Q: How does normal vision develop?
A:
Newborn infants are able to see, but as they use their eyes during the first months of life, vision improves.
During early childhood years, the visual system changes quickly and vision continues to develop. If a child cannot use his or her eyes normally, vision does not develop properly and may even decrease. After the first nine years of life, the visual system is usually fully developed and usually cannot be changed.
The development of equal vision in both eyes is necessary for normal vision. Many occupations are not open to people who have good vision in one eye only. If the vision in one eye should be lost later in life from an accident or illness, it is essential that the other eye have normal vision. Without normal vision in at least one eye, a person is visually impaired.
Q: Why does eyelids twitch sometimes?
A: Mild twitching of the eyelid is common. Though annoying, they are almost always temporary and completely harmless. When your eye is twitching, it is not visible to anyone else. Lack of sleep, too much caffeine or increased stress seem to be root causes of twitching. Often, gently massaging your eye will relieve the symptoms. Usually, the twitch will disappear after catching up on your sleep...so go and sleep if it's way past your bedtime! =)
Q: What is legal blindness?
A: You are legally blind when the best corrected central acuity is less than 20/200 (perfect visual acuity is 20/20) in your better eye, or your side vision is narrowed to 20 degrees or less in your better eye. Even if you are legally blind, you may still have some useful vision. If you are legally blind, you may qualify for certain government benefits.
Q: What is visual impairment?
A: If neither of your eyes can see better than 20/60 without improvement from glasses or contacts, you may be defined as visually impaired. In addition, poor night vision, limited side vision, double vision and loss of vision in one eye may also determine visual impairment.
Q: What is low vision?
A: Low vision is a term describing a level of vision below normal (20/70 or worse) that cannot be corrected with conventional glasses. Low vision is not the same as blindness. People with low vision can use their sight. However, low vision may interfere with the performance of daily activities, such as reading or driving.
Q: Will working at a computer screen hurt my eyes?
A: No, there is no evidence that working at a computer damages the eyes. However, long hours of work can be fatiguing to the eyes, neck and back. Monitor glare from various light sources can also be a problem. It is often helpful to take periodic breaks, looking off in the distance and adjusting your work station (angle of the monitor, height of the chair, changing the lighting).
Q: How does the eye work?
A: The front parts of the eye (the cornea, pupil and lens) are clear and allow light to pass through. The light also passes through the large space in the center of the eye called the vitreous cavity. The vitreous cavity is filled with a clear, jelly-like substance called vitreous humour. The light is focused by the cornea and the lens onto a thin layer of tissue called the retina, which covers the back inside wall of the eye. The retina is like the film in a camera. It is the seeing tissue of the eye. When the focused light hits the retina, a picture is taken. Messages about this picture are sent to the brain through the optic nerve. This is how we see.
-xh
Links to learn more, with more in-dept analysis.
Glaucoma
Cataracts
Sight
Credits to these websites we used for references
information:
Bee/Insect View
Optical Illusions
Cataracts
Myopia -1
Myopia -2
Hyperopia
Presbyopia
Colour blindness 1
Colour blindness 2
uploading:
background image
swf files
layout: detonatedlove edited by:xiuli
background image: collated by yeeherng
inspiration: wordpress