Most common cause of floaters are opacities in the vitreous (clear gel filling the posterior segment of the eye). These opacities can be inflammatory infiltrates, haemorrhage, degenerative changes of the gel itself and glial tissue that normally attaches the posterior vitreous cortex to the retina and can be seen after posterior vitreous detachment. Cause of flashes not so well understood but probably due to stimulation of the retina by vitreoretinal traction.
Incidence These are a common cause of referral to an ophthalmic emergency department and in around ? of cases patient has a sight threatening condition.
Posterior vitreous detachment (PVD) Separation of the posterior vitreous cortex from the inner surface of the retina is the underlying cause in over 60-70% of cases, with vitreous haemorrhage accounting for around 5%, migraine just over 1%, posterior uveitis <1%. In nearly 25% of cases no abnormality is found.
Commonly, PVD is associated with a retinal tear caused by traction on the retina during detachment of the vitreous cortex. This, in turn, can lead to retinal detachment. In fact, PVD is a common factor predisposing to retinal detachment and also a frequent cause of vitreous haemorrhage when retinal blood vessels are damaged during detachment.
Risk factors for PVD are age (rarely occurs in age under 45 and then only in the very short sighted), ocular trauma or surgery. Onset can be: