Floaters and flashes: when they are urgent

A cobweb drifts across the page and you cannot blink it away

You are reading in good light and a small grey thread slides across the words. You look at it and it darts away. Against a clear sky or a white wall it is back, drifting. For most people this is a floater, and for most people it means nothing more than that the gel inside the eye is ageing. The question that matters is whether anything else has changed: new flashes, a sudden crowd of new floaters, or a shadow at the edge of your vision.

The Royal Australian and New Zealand College of Ophthalmologists puts it this way: by middle age most people see floaters, they are usually just annoying rather than harmful, but the sudden onset of many new floaters or flashes could be a warning of a retinal tear or a detached retina. This guide is about telling those two situations apart and knowing where to go for each.

What floaters and flashes actually are

The inside of your eye is filled with a clear gel called the vitreous. The American Academy of Ophthalmology explains that with age it thickens or shrinks and clumps or strands form inside it. Floaters are the shadows those clumps cast on the retina, the light-sensing layer at the back of the eye. That is why they move when your eye moves and settle when it stops.

Flashes are different. The RANZCO patient advisory says they are usually caused by the vitreous tugging on the retina as it shrinks. When the vitreous finally separates from the retina, that is a posterior vitreous detachment, or PVD. Healthify NZ describes PVD as an age-related change that causes no problems for most people. The catch is in the next sentence: if the vitreous pulls firmly enough as it separates, it can tear the retina, and PVD is the most common cause of retinal tears.

A tear matters because fluid can pass through it and lift the retina off the back of the eye. That is a retinal detachment. Healthify NZ calls it a medical emergency that can permanently affect sight if not treated quickly, and the National Eye Institute says the same: delay lets more of the retina detach and raises the risk of permanent vision loss. Early tears or small detachments sometimes cause no symptoms at all and are found at a routine eye check.

The same-day rule

Healthify NZ lists the warning signs of a retinal detachment: flashes of light, most obvious in dim light and in your side vision; new floaters or a sudden increase in floaters; a dark shadow in your side vision or the sensation of a curtain coming over your eye; and blurred, cloudy or distorted vision. Its advice is to contact your healthcare provider, optometrist or ophthalmologist immediately. The NHS says to ask for an urgent same-day eye appointment if floaters or flashes appear for the first time, appear suddenly, suddenly increase, come with blurred vision or eye pain, or start after eye surgery or an injury.

In practice, the rule is simple. New floaters or flashes today means an eye examination today, not next week. A shadow, curtain or loss of vision means the hospital, now. Some people are more likely to have a tear behind their symptoms; Healthify NZ lists being very short-sighted, being over 50, a previous retinal detachment, a family history, cataract or other eye surgery, a serious eye injury, and diabetic eye disease. If you are in one of those groups, lean towards being seen sooner.

Two patterns are usually something else. The AAO describes jagged, shimmering lines or heat-wave flashes lasting up to about an hour, often in both eyes, as a migraine, which can happen with or without a headache. And floaters you have had for years that have not changed are, as the NHS puts it, not usually serious. Mention them at your next routine exam.

• Same day, at an optometrist: new floaters or flashes with no shadow and no loss of vision. Call us on 09-475 5548 and say the words "new flashes" or "new floaters"; no referral is needed.
• Now, at a hospital emergency department or by calling 111: a shadow or curtain across any part of your vision, a sudden drop in vision, a sudden shower of floaters with flashes, or floaters after a blow to the eye.
• Outside our hours (we close at 5 pm on weekdays and 3 pm on Saturdays, and all day Sunday): go to the emergency department rather than waiting for us to open, or call Healthline free on 0800 611 116 for advice at any hour.
• Do not drive yourself: dilating drops blur your vision for hours.

What an optometrist can see, and what happens next

A dilated eye examination is the test for all of this. Healthify NZ and the NEI both describe it: drops widen the pupil so the back of the eye can be examined, the drops blur your vision for a few hours, and you may need someone to drive you home. The examination does not usually hurt, although pressing gently on the eyelids to check the far edge of the retina for tears can be uncomfortable. If the view is poor, an ultrasound or an OCT scan may be used.

Our optometrists do this at an eye examination at the Rosedale practice, and the widefield retinal photography and OCT on our technology page help record what is found. If the retina is intact and the picture is a posterior vitreous detachment, you will usually be asked to watch for new symptoms and return for a check, because a tear can still occur in the weeks after a PVD; ask when. Our guide to what a comprehensive eye exam checks covers the rest of the examination.

If a tear or detachment is found or suspected, the optometrist's job is to refer you to a hospital eye clinic or an ophthalmologist straight away, usually by phone, not to treat it. RANZCO describes a tear being sealed with laser or freezing treatment so that a detachment does not follow, and Healthify NZ says most people with a detachment need surgery by an ophthalmologist, usually under local anaesthetic, with recovery taking several weeks and restrictions on flying, heavy lifting and driving until the surgeon clears you. Nothing in that list happens in an optometry practice.

When an optometry appointment is the wrong place

Call 111 or go to the nearest hospital emergency department, without booking anything, for a shadow or curtain across part of your vision, a sudden loss of vision, flashes with a sudden shower of new floaters, floaters or vision change after a blow to the eye, or any injury that may have pierced the eye (Healthify NZ says to cover it with glasses and not to rub it). The same goes for a chemical splash, after flushing with clean running water for at least 15 minutes, and for a red and painful eye with light sensitivity.

A suspected retinal detachment is a hospital matter. We can examine, photograph and refer, and we will do that the same day, but we cannot repair a retina. If you are not sure which situation you are in, Healthline is free on 0800 611 116 at any hour, and our guide to optometrist versus GP versus hospital eye clinic sets out who does what in New Zealand. For new flashes and floaters, an optometrist or the hospital is the right first call.

If it turns out to be nothing serious

Most new floaters are not a tear, and most PVDs settle without harm. The AAO notes that floaters tend to fade or become less noticeable over time and that occasional flashes are common with ageing, and both the AAO and RANZCO say surgery to remove floaters carries risks and is seldom necessary. If you are short-sighted, note what your floaters look like today and treat any change as new; our guide to what myopia is explains why.