Floaters, Posterior Vitreous Detachment and Retinal Tears
What are Floaters?
Floaters, as the name suggests, are small shadowy shapes or lines that appear to float in your field of vision. They are located within the vitreous in the back of the eye. They can have multiple appearances, but often look similar to cobwebs, specks, spots, strands or squiggly lines. Floaters will often travel across your field of vision with movement of your eyes, and will dart away when you try to look directly at them. As floaters are suspended in the gel-like liquid in the back of they eye, they will often drift into different locations even if your eye is stationary.
In most cases, floaters are normal physiological phenomena that commonly develop as we age, but may also be present throughout life. The back of the eye, known as the posterior segment or cavity, contains a gel like substance referred to as the vitreous, which has a consistency similar to uncooked egg white. The vitreous serves a purpose to ensure the eye remains a spherical structure. As the aging process occurs, the vitreous will often change its consistency and will shrink (a process known as vitreous syneresis), whilst becoming stringy and strand-like with harmless 'imperfections'. These 'imperfections' interrupt the transmission of light onto the retina, the 'photographic film' layer which lines the back of the eye, casting shadows which are perceived as floaters.
Floaters can go unnoticed, but they can also be quite annoying and distracting. The will eventually settle to the bottom of the eye. Once they are no longer within the line of sight, floaters generally become less bothersome, however they will not disappear completely. Many people become accustomed to their floaters, only noticing them if they become more numerous, more prominent or when looking at something bright, such as white paper or looking up at a blue sky.
Who is likely to develop floaters?
Floaters are generally associated with aging, however they are seen more commonly and develop sooner in people who are a short-sighted (myopic), diabetic or have had previous eye surgery. Other more serious causes of floaters include infection, inflammation (uveitis), bleeding in the vitreous (vitreous haemorrhage), retinal tears or eye trauma.
What is a Posterior Vitreous Detachment (PVD)?
As discussed above, the back of the eye is filled with the gel like vitreous which is in close contact with the underlying retina (synonomous with photograph film in a camera). As the vitreous gel changes its consistency with age and begins to shrink, the vitreous will completely separate from the underlying adherent retina. This is known as a posterior vitreous detachment (PVD), and it will often cause a sudden onset of new floaters. A posterior vitreous detachment will usually occur between 50 and 70 years of age. Posterior vitreous detachments may be accompanied by flashes of light, due either to the vitreous gel and its imperferctions moving around within the back of the eye and interrupting the transmission of light, or due to tractional forces (pulling) on the retina which stimulates the underlying light-sensitive cells (photoreceptors), which is perceived as flashes of light similar to lightening strikes. If the tractional force is strong enough, a retinal tear may develop.
What Is a Retinal Tear?
The majority of PVD's are harmless and will occur without consequence, with the vitreous gel separating cleanly from the underlying retina without any damage to the retina. However in some people the retina and vitreous are abnormally adherent (tightly stuck to one another) and as the vitreous contracts, it pulls on the retina and creates a retinal tear or a retinal hole. A PVD can be thought of as a stress test on the retina.
The retina is a thin layer of nerve tissue that lines the back of the eye and is essential for normal vision. The retina contains millions of photoreceptors which are responsible for absorbing light and transferring visual information to the brain via the optic nerve. Vitreous traction, or pulling, on the photoreceptors causes them to become simulated, resulting in flashes of light. A retinal tear or hole can potentially develop into a retinal detachment, a potentially blinding condition if left untreated. If a retinal tear through all of the layers of the retina forms, fluid within the vitreous can migrate through the tear or hole and accumulate under the retina. This causes the retina to lift away, or detach, from its normal position.
A retinal detachment is a serious ocular emergency which requires urgent treatment to prevent vision loss or blindness. Retinal tears and detachments may also occur secondary to trauma. The diagnosis of a posterior vitreous detachment is made through a careful examination by a Retinal Specialist after your eyes are dilated through the use of eye drops, which enlarges your pupil(s) to allow a clear view into the back of the eye. Combined with special lenses and microscopes, a Retinal Specialsit will be able to identify the presence of any retinal tears or retinal detachment.
Even if no retinal tears are found at the time, a sudden increase in floaters or flashes and/or a loss of side vision later on could indicate a new retinal tear or early retinal detachment. If this occurs, you should seek urgent attention form your retinal specialist.
What treatment options are available for floaters and PVD's?
The majority of floaters and PVD's are somewhat of an inconvenience but are not sight-threatening, and therefore do not require treatment. Rarely, floaters may be so dense and numerous, casting significant shadows on the retina and interfering with normal vision and daily activities, that vitrectomy surgery may be recommended to remove the vitreous and debris from the eye.
Vitrectomy surgery is a process performed in the operating theatre under local anaesthesia with moderate sedation. Three very small instrument ports are inserted into the white of the eye (the sclera) at the front of the eye. These ports allow very fine surgical instruments to be inserted so that the vitreous can be removed under microscopic guidance and replaced with a salt solution. The process takes approximately 25-30 minutes and a thorough retinal examination is also completed to assess the peripheral retina to locate and treat any potential weak areas within the retina or to treat any tears or holes.
What treatments are available for retinal tears?
During your examination in the clinic, if a retinal tear is found, your retinal specialist will evaluate the risk of progression to retinal detachment and the need for treatment based on your history and clinical examination. For example, a tear that develops during a symptomatic PVD is more dangerous and more likely to progress to a retinal detachment than one that occurs during an asymptomatic PVD. If there is no risk of retinal detachment, treatment may not be required. The most common methods of repairing a retinal tear are retinopexy (laser) and cryoretinopexy (freezing laser).
Retinopexy and Cryoretinopexy are usually performed under local anaesthetic with some sedation in the operating theatre with specialised equipment. A special lens is utilised to allow a wide view of the back of the eye, and laser is applied around the retinal tear to effectively "spot weld" the retina and allow the tear to seal.
Treatment of a retinal tear will not prevent new tears from developing. For this reason, your retinal specialist will need to continue to monitor your retina after any treatment has been performed. If you notice sudden changes (increased flashes, floaters or loss of side vision) between visits, contact your retinal specialist for an urgent review.