Hyperopia (Farsightedness)

Hyperopia, or farsightedness, is a common vision problem, affecting about a fourth of the population. People with hyperopia can see distant objects very well, but have difficulty seeing objects that are up close.
Hyperopia Symptoms and Signs
Farsighted people sometimes have headaches or eyestrain, and may squint or feel fatigued when performing work at close range. If you get these symptoms while wearing your glasses or contact lenses, you may need an eye exam and a new prescription.
What Causes Hyperopia?
This vision problem occurs when light rays entering the eye focus behind the retina, rather than directly on it. The eyeball of a farsighted person is shorter than normal.
Many children are born with hyperopia, and some of them "outgrow" it as the eyeball lengthens with normal growth.
Sometimes people confuse hyperopia with presbyopia, which also is a difficulty in seeing up close, but has a different cause.

The treatment for hyperopia depends on several factors such as the patient’s age, activities, and occupation. Young patients may or may not require glasses or contact lenses, depending on their ability to compensate for their farsightedness with accommodation. Glasses or contact lenses are required for older patients.
Refractive surgery is an option for adults who wish to see clearly without glasses. LASIK, Clear Lens Extraction And Replacement, LTK and intraocular contact lenses are all procedures that can be performed to correct hyperopia.

Myopia (Nearsightedness)

Nearsightedness, or myopia, is a vision problem experienced by up to about one-third of the population. Nearsighted people have difficulty reading highway signs and seeing other objects at a distance, but can see for up-close tasks such as reading or sewing.
Myopia Symptoms and Signs
Nearsighted people often have headaches or eyestrain, and might squint or feel fatigued when driving or playing sports. If you experience these symptoms while wearing your glasses or contact lenses, you may need a comprehensive eye examination as well as a new prescription.
What Causes Myopia?
Myopia occurs when the eyeball is slightly longer than usual from front to back. This causes light rays to focus at a point in front of the retina, rather than directly on its surface.

The nearsighted eye is longer than normal. Incoming light focuses in front of, instead of directly on, the retina. Far objects are blurry, while closer objects are more clear.
Nearsightedness runs in families and usually appears in childhood. This vision problem may stabilize at a certain point, although sometimes it worsens with age. This is known as myopic creep.

The treatment for nearsightedness depends on several factors such as the patient’s age, activities, and occupation. Vision can corrected with glasses, contacts, or surgery. Refractive procedures such as LASIK can be considered for adults when the prescription has remained stable for at least one year.

Macular Degeneration

Sometimes the delicate cells of the macula (part of the retina) become damaged and stop working, and there are many different conditions which can cause this. If it occurs later in life, it is called “age-related macular degeneration”, also often known as AMD.
Broadly speaking, there are two types of macular degeneration or AMD, usually referred to as “wet” and “dry”. This is not a description of what the eye feels like but what the optometrist or ophthalmologist can see when looking at the macula.
“Dry” AMD is the most common form of the condition. It develops very slowly causing gradual loss of central vision. Many people find that the vision cells simply stop working like the colours fading in an old photograph. There is no medical treatment for this type. However, aids such as magnifiers can be helpful with reading and other small detailed tasks.
“Wet” AMD results in new blood vessels growing behind the retina, this causes bleeding and scarring, which can lead to sight loss. “Wet” AMD can develop quickly and sometimes responds to treatment in the early stages. It accounts for about 10 per cent of all people with AMD.
AMD usually involves both eyes, although one may be affected long before the other. This sometimes makes the condition difficult to notice at first because the sight in the “good” eye is compensating for the loss of sight in the affected eye.
You cannot wear out your sight, so do not be afraid to continue to use the “good” eye as normal.
The good news is that AMD is not painful, and almost never leads to total blindness. It is the most common cause of poor sight in people over 60 but very rarely leads to complete sight loss because only the central vision is affected. This means that almost everyone with AMD will have enough side (or peripheral) vision to get around and keep his or her independence.

http://www.nei.nih.gov/health/maculardegen/armd_facts.asp#1a

Glaucoma

Glaucoma refers to a group of diseases in which your optic nerve becomes damaged and causes a gradual loss of peripheral vision. There are many types of glaucoma, but the most common is primary open angle glaucoma which is characterized by increased intraocular pressure (IOP). Glaucoma is the second leading cause of blindness, and has no symptoms, hence it's well-earned nickname "the sneak thief of sight". Glaucoma can be controlled with eyedrops or surgery to lower the IOP, but cannot be cured. Long term follow up care and treatment is neccessary to minimize vision loss. For more detail see:

http://en.wikipedia.org/wiki/Glaucoma

Flashes and Floaters

Flashes and Floaters(Posterior Vitreous Detachment)
Overview
The space between the crystalline lens and the retina is filled with a clear, gel-like substance called the vitreous humor. In a newborn, the vitreous has an egg-white consistency and is firmly attached to the retina. With age, the vitreous thins and may separate from the back of the eye. This is called posterior vitreous detachment (PVD), a very common, usually harmless condition.
As the vitreous pulls free from the retina, it is often accompanied by light flashes or floaters. Floaters are caused by tiny bits of vitreous gel or cells that cast shadows on the retina. Flashes occur when the vitreous tugs on the sensitive retina tissue.
There are other more serious causes of flashes and floaters, however. Retinal tears, retinal detachment, infection, inflammation, hemorrhage, or an injury such as a blow to the head may also cause floaters and flashes. (Have you ever seen stars after bumping your head?) Occasionally, flashes of light are caused by neurological problems such as a migraine headache. When related to a headache, the flashes of light are seen in both eyes and usually lasts 20-30 minutes before the headache starts.

Signs and Symptoms
1. Black spots or “spider webs” that seem to float in the vision in a cluster or alone
2. Spots that move or remain suspended in one place
3. Flickering or flashing lights that are most prominent when looking at a bright background like a clear, blue sky
4. Symptoms that may indicate a more serious problem
5. Sudden decrease of vision along with flashes and floaters
6. Veil or curtain that obstructs part or all of the vision
7. Sudden increase in the number of floaters

Detection and Diagnosis
Notify your optometrist or ophthalmologist immediately if you notice a sudden shower of floaters, new light flashes, a veil or curtain obstructing your vision, or any other change. The doctor will dilate your pupils with drops and examine the vitreous and retina inside the eye with an ophthalmoscope.