The posterior segment or back chamber of the eye is far bigger and constitutes the bulk of the eye. The total distance between the tip of the cornea and the tip of the back of the eye is typically 21-24mm.
This chamber contains a gel-like substance akin to egg white, called vitreous humour. It is made up of about 1% protein fibres and hyaluronic acid and around 99% water. When we are young it is the consistency of the white of a fresh egg, where all the water components is bound to the long strings of protein molecules.
As we age, it becomes like a 10-day old egg where the proteins start to degenerate causing the water component to become separated, leaving the long protein fibres to clump. These clumps can be sufficiently large or dense to cast a shadow on the retina, which we then perceive as ‘floaters’.
This degeneration is called vitreous syneresis. They are grey splodges or strings a bit like frog spawn, a cobweb, spots, a hair or even a fly moving across your vision. As you eye moves, they follow (with a small time delay). When your eye stops moving, the floaters also come to a slowing halt (again with a small delay). They can be very off putting, especially if they are near the centre of the vision. Most people grow accustomed to them. However, if they are nearer the back of the eye than the front, they may cast a denser shadow on the retina and be more persistently visible.
Floaters can also be a symptom of inflammation in the eye called uveitis. If you are also suffering even a small decrease in your vision, visual blurring, discomfort or redness of the eye alongside the floaters, these could be signs of inflammation in the eye. This is always SERIOUS and you need to be examined by a professional including an optometrist. If they find that you have uveitis you should be referred to an ophthalmologist as it can be serious and caused by serious diseases and infections. In most cases the reason for the inflammation isn’t found and is called ‘idiopathic’. This is generally an immune response to something unknown or a reaction of your own immune system attacking self cells. See uveitis page for more information.
Posterior Vitreous detachment
As the gel continues to change, shrink and collapse away from the retina, the whole body of the gel detaches from the retinal surface. It is more strongly bound to the retinal overlying blood vessels, at the very front edge of the retina, near the ciliary body, behind the iris.
This area is called the pars plana (the ‘plane bit’ in Latin) and also around the rim of the optic nerve. Sometimes there is a little connective that is pulled away where the gel has become detached from the rim of the optic nerve. This form is known as Weis’ Ring. This can be visible in the vision as a ring. As the floaters are positioned nearer the front of the eye, they can become less noticeable. If they are persistent and problematic, you can have an operation to just remove those clumps. This is called a partial vitrectomy. You will need to see a specialist vitreoretinal surgeon to explain and perform this for you.
By Jonathan Trobe, M.D. - University of Michigan Kellogg Eye Center - The Eyes Have It, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=16116032
