Some diseases of the eye include conjunctiva which is inflammation of the conjunctiva, which is the membrane that covers the eye, and is caused by a virus or bacteria or allergy or injury. IT is contagious when caused by a germ only.
Trachoma is inflammation of the inner parts of the eyelids and is one of the most common instigators of blindness in Africa and Asia. It is caused by a bacteria and is extremely contagious.
Night blindness is caused by a lack of Vitamin A and leads to loss of vision.
A stye is an infection of an eyelash follicle which is the tiny hole where the eyelash grows from the skin.
There are two types of color blindness:
1. Monochromatic vision which occurs in 1 of every 40,000 people. These people see the world in black and white only.
2. Dichromatic vision is the more common form of color blindness where the retina misses one type of cone. People with this type of color blindness can be missing the red or green cone which leads to red-green color blindness and is also called anomalopia.
Movies area actually made of many still pictures that are shown quickly one after another at a rate of around 16 to 25 pictures each second. The still pictures pass by so quickly that the eye is still seeing the last one when the next one is shown which allows the pictures to appear to blur into one another and our minds see them as one continuous moving scene. Animals with eyes that react faster than ours do would not experience this blurring. So a cat, for example would see a series of still pictures that flick past each other separately and unmoving when looking at the tv screen.
Many people are confused upon the definitions of nearsightedness and farsightedness. Nearsightendess means the ability to things near oneself well but not able to see at a distance. I remember this by thinking “if you have nearsightedness, you are able to see things that are near to you”. This is the most common eye problem in the US and over 25% of the population has it.
It usually starts when people are young or in their teens and keeps getting worse until at the latest stabilizing around 30 years of age but can stabilize sooner as well.
Nearsightedness comes in two forms, one is axial myopia where the eyeball is too long and not circular enough so light entering the eye do not hit the retina in the center where they should. Refractive myopia causes the same issue which is not being able to see far away, however the cause is instead that the cornea has too strong a refractive power.
When someone is so nearsighted this puts them at risk for developing more eye issues, and is called high myopia when someone as a refractive error of -6 or more. This puts them at more risk of retinal detachment, choroidal neovascularization, and glaucoma.
To treat nearsightedness you can wear glasses, contact lenses, and some people can even have refractive surgery.
The opposite of nearsightedness is farsightedness which is also known as hyperopia, and is when you can see far away but not up close. Again I remember this by thinking “ if you have farsightedness you can see far away but not up close.”
This is propagated when the cornea is too flat, an eye lens is too weak, or an eyeball is too short. Around 25% of the US population has farsightedness.
Interestingly a lot of infants are born with this condition but lose it by the time they are teenagers and their eye has changed shape to be able to focus on nearby objects again.
To treat this it may require glasses or contacts like nearsightedness however young patients may be able to compensate without treatment. Refractive surgery is another option for adults.
There are many various designs for glasses both aesthetically and to correct diffent types of vision problems. There are single vision lenses which are albe to correct distance vision.
There are multifocal lenses which can fix distance and close vision at the same time. Theses lenses have the top part focused on corrected distance while the bottom focuses on close up vision tasks like reading.
Multifocal lenses come in many types including bifocals, trifocals and progressive.
Expert David Chang answers questions about multifocal lenses here.
Bifocals are two parts, with a top and bottom part. Trifocals are three parts that correct near, far, and intermediate. However bifocals and trifocals can interrupt the normal vision process because of the abrupt changes each present in the lens. It is often difficult to acclimate oneself to looking only in the top of your lens to see far away, only in the middle to see intermediately, and then only on the bottom to see up close.
Progressive lenses are able to help with this by making the transition between the different areas more smooth by taking away the lines. They are also more aesthetically pleasing as you can’t see the divisions when looking at the lines, however they have their own drawback as each area is smaller than they would be on a traditional bifocal or trifocal lens.
There are also many types of lens materials to choose from.
High index lenses are a thin and light plastic lens and are recommended for people with large visual issues because they take away the need for the ultra thick glasses that are often dreaded cosmetically.
Polycarbonate lenses can be worn during watersports or other dangerous activities because it is impact resistant and therefore less likely to shatter if hit.
Another option for lenses is to coat the lens with a anti-reflective coating to reduce glare and strain on the eyeball when driving or during other activities. Glasses can also protect against UV light, and you can purchase glasses that are both vision correcting and protect your eyes against UV light form the sun at the same time.
If glasses are not your thing, or you do not want to cover up your beautiful face, contact lenses are another option. They can correct close up vision problems, far away vision problems, astigmatism, and presbyopia.
Lenses can actually provide better peripheral and overall vision in comparison with glasses as they are able to cover the entire eyeball at one time and do not require looking through an outside piece of plastic or glass which may shift or fall off unexpectedly.
However they can be slightly uncomfortable and hard for those with very dry eyes, eye allergies, eye infections, or other conditions to wear, so they are not an option for all people.
They also can cause infection or injury, especially when not cared for or worn for too long of periods of time. Misused lenses can cause corneal abrasions, infectious keratitis, conjunctivitis which is also known as pink eye, infections and even more eye problems.
Lenses are also made of multiple types of materials including flexible plastic, and hard lenses that are made of hard plastic.
Soft lenses are much more comfortable and are designed to be disposed of more frequently.
Hard lenses are also called gas permeable lenses and can help correct astigmatism, and offer more oxygen a path to the eye, as well as more moisture in the cornea, and they are more durable as well as last for a longer amount of time. However they are usually not as comfortable for people to wear.
Soft lenses that treat astigmatism are actually available and have been recently developed as well, but when someone has keratoconus which is known as a severe form of astigmatism, sometimes hard lenses are the better option.
Soft and hard lenses actually need to be cared for, cleaned, and stored differently from eachother.
Different types of lenses can be worn for different amounts of time until they need to be replaced:
Conventional lenses can be replaced every year, disposable lenses can be replaced monthly, biweekly, weekly or daily depending on the lens. However the more often you replace disposable lenses, the healthier for the lens and your eye.
Some lenses are approved by the FDA to wear during sleep, and these lenses are known as “extended wear” lenses, while “daily wear” lenses are supposed to only be worn while one is awake. Sleeping with any type of lens on increases the risk of eye infections.
To care for contact lenses you should wash your ands before touching, and you should only use solutions that are specifically recommended by an eye care professional. Lenses should never be touched by saliva or tap water and only exposed to isotonic solutions.
You should never put mascara or any other eye makeup on your face until after you have put a lens in, as if you put the makeup on first there is a chance it could catch on the lens and cause an infection in your eye.
Any discomfort or red, swollen eye that develops while wearing a lens should cause you to take the lens out right away and tell your eye doctor you are having an issue. (Fekrat, Weizer, 2006).
Fekrat, Sharon, and Jennifer S. Weizer. All about Your Eyes. Durham: Duke UP, 2006. Print.