The eye is 2.5cm diameter. The cornea and lens make up the optical system of the eye and they focus light onto the retina at the back of the eye not unlike a camera where the retina is the photosensitive CCD chip. The retina converts light energy into electrical signals which are conducted along the optic nerve to the vision centres of our brain. The space between the lens and pupil at the front of the eye and the retina at the back is filled with a special gel called the vitreous humour. This gel is typically quite stiff as its name implies (Vitreous: like glass).
Floaters occur when the gel undergoes some changes and becomes less stiff with age. The gel may fold or come away from the retina causing opacities that cast shadows on the retina which are seen as particles, strands or bits floating in front of our vision. These are seen as floaters. While these are very common and harmless in themselves; they may be associated with tugging on the retina, as parts of the vitreous adhere to the retina. This traction on the retina causes the sensation of flashes of light.
If this traction is severe or violent enough it may cause a hole or tear in the delicate retina. Liquid may seep through the hole under the retina causing it to blister and peel off the back wall of the eyeball. This is a retinal detachment.
- If you have had occasional floaters for years and they haven’t changed much the chances of retinal detachment is very small.
- If you notice a sudden change in what your floaters look like, or see them for the first time you need to have your eyes examined thoroughly and promptly. This purpose of this examination is to look for any retinal holes or tears. Should you have a small tear at this early stage it is possible to prevent a retinal detachment by “spot welding” the retina in place with a laser or by freezing (cryotherapy).
- If you develop flashing lights, often more easily seen in the dark you should also have your eyes examined urgently. Seeing flashing lights may imply pulling on the retina and the risk of detachment is significant, but there are other possible causes of flashes, one of which is migraine. Nevertheless the sudden onset of flashes demands prompt examination of the retina. Floaters and flashes are warning sign which need prompt examination; even though most people who experience them never develop a retinal detachment.
Retinal detachments are relatively uncommon but are more common in myopic (short sighted) people. When the retina detaches it pulls away from its blood supply and can’t function normally. The part of the retina that is detached will not work properly.
Retinal detachments cause a loss of part or all of the vision in the eye which happens suddenly. This is often experienced as a curtain that is drawn across part of the visual field. It is painless and as discussed above may be preceded by new floaters and flashing lights.
As mentioned, retinal tears can be welded down with a laser or cryotherapy (freezing). Treatment of retinal tears causes little or no discomfort and is performed on the same day – no hospital stay is generally required. Almost all retinal detachments require surgery, which should be carried out within a few days. Retinal detachment repairs may require bedrest and some stay in hospital is possible.