Spots or floaters are small, semi transparent or cloudy particles within the vitreous, (which is the clear, jelly-like fluid that fills the inside of your eyes). They are quite common and usually, but not always, harmless.

Appearing as specks, threadlike strands or cobwebs, floaters are most visible when you look at a light background, such as the sky.

Spots and floaters are caused by:

• Deterioration of the vitreous fluid, which is part of the natural ageing process.
• Certain eye diseases or injuries.
• Small flecks of protein or other matter trapped during the formation of the eye before birth.

Seeing flashes or streaks of light usually means that the vitreous is shrinking. It may become detached from the back of your eye. Vitreous detachment is common and rarely leads to serious eye problems. However, it is very important that these flashes are checked immediately as it may also be a symptom of retinal detachment, which although rare, requires urgent treatment.

Although spots and floaters are usually harmless, you should see your optometrist for a thorough eye examination when you first begin to see them or when you notice changes or increases in them. The optometrist can determine if what you are seeing is harmless or the symptom of an eye health problem in need of treatment.

http://www.eye-care.org.uk