WHAT ARE FLASHES AND FLOATERS?

Flashes and floaters are common ocular symptoms that can range from a large floater across the vision (sometimes mistaken for a “piece of dirt” on one’s glasses) to episodes of photopsias (small flashing white lights in the peripheral field of vision). Moreover, a patient can experience “thousands” of small floaters coming down through the field of vision. The question that arises is, do these symptoms indicate that an urgent ophthalmology assessment is required? Should this patient wait for a regular follow-up appointment or be advised to seek ophthalmic care immediately? The answer is almost always that this patient should be seen in a timely manner and you can see why below.

WHO GETS FLASHES AND FLOATERS?

Most cases of acute onset monocular floaters and/or flashes, unassociated with other symptoms, are ocular in nature and are due to posterior vitreous detachment (PVD). Uncomplicated floaters and flashes typically represent PVD, which is an age-related event.  The reported prevalence of PVD increases from 24% in adults aged 50 to 59 years, 37% amongst those 60-69 years, 59% amongst those 70 to 79 years, to 87% amongst 80 to 89 years.  The prevalence of PVD also increases with the presence of myopia, trauma, and intraocular inflammation. While most people will develop PVD at some point in their lives, it is often asymptomatic and in the majority of cases a benign occurrence without any long-term complications.  However, 10-30% of individuals who present to an eye care professional with acute symptoms have a full-thickness tear or hole in the retina; this complication of PVD can lead to retinal detachment and permanent visual loss in 33-46% of cases if left untreated. While floaters and/or flashes are common, retinal detachment is uncommon with an estimated incidence of 0.8-1.8/10,000 persons per year and prevalence of 0.3%. Prompt diagnosis and surgical treatment can restore vision and prevent impending vision loss in those patients.

 POSTERIOR VITREOUS DETACHMENT (PVD)

Posterior vitreous detachment (PVD) involves separation of the posterior vitreous from the retina as a result of vitreous degeneration and shrinkage that produces floaters and/or flashes.

Figure : Diagram of the human eye.  Posterior vitreous detachment is shown.  There is an associated retinal detachment with subretinal fluid between the neurosensory retina and the retinal pigment epithelium.

Floaters are a sensation of gray or dark spots moving in one’s visual field  and they are caused either by light bending at the interface of fluid pockets in the vitreous jelly or cells located within the vitreous.  This symptom involves one or more monocular “cobwebs” within or near the central vision that blurs but does not eliminate sight.  Flashes of light are caused by traction forces on areas of the peripheral retina applied by the tightly adherent vitreous jelly.  Patients typically describe monocular, repeated, brief flashes of white light that occur in their peripheral visual field.

Figure: Artist representation of floaters as viewed from the patient.

Retinal detachment occurs when the neurosensory layer of the retina separates from the underlying retinal pigment epithelium disrupting the photoreceptors and eventually precipitating tissue necrosis if untreated.  In the majority of cases fluid gains entry to the subretinal space through a full-thickness retinal tear or hole as a result of traction on the retina from PVD.  The decrease in visual acuity associated with a retinal detachment is typically due to secondary vitreous hemorrhage, significant vitreous debris, or detachment of the central retina.  Such symptoms may create a progressive monocular visual field defect (‘curtain of darkness’).