Hi everyone, this is Dr. Diab, board-certified ophthalmologist.

One of the most common reasons patients call me urgently is this: “I suddenly started seeing spots, or flashes of light, in one eye.”

In many cases, what is happening is called a posterior vitreous detachment.

Inside your eye is a clear gel, called the vitreous. When we are young, that gel is firm and fills the back of the eye, sitting right against the retina — the light-sensitive tissue at the back of the eye, a bit like film in a camera.

As we get older, that gel naturally starts to liquefy and shrink. At some point it pulls away from the retina. That separation is a posterior vitreous detachment.

It happens to almost everyone at some point, usually after age 50 or 60, and it is usually a normal part of aging. It does not mean your eye is falling apart, and it does not usually mean you will lose vision.

So why do you notice it? As the gel pulls away, you may see new floaters — dots, cobwebs, or shadowy shapes that drift when you move your eye. You may also see flashes of light, often in the far corner of your vision, often at night. That happens because the pulling gel tugs lightly on the retina.

Most of the time, once the gel has fully separated, the floaters settle and become less noticeable, and the flashes fade. I usually tell my patients that the brain also learns to ignore floaters over time, a bit like learning to ignore a small smudge on your glasses.

But here is the important part: we still need to check.

In a small number of people, as the gel pulls away, it can tear the retina. A tear does not always cause pain or vision loss right away, so you cannot tell from symptoms alone whether a tear is there. That is why a sudden onset of new floaters or flashes should prompt a full dilated eye exam, usually within a couple of days.

A tear, if we find one, can often be treated right away in the office with laser, to help prevent a retinal detachment. A retinal detachment is more serious and usually needs a retinal specialist and surgery.

So, in short:

• New floaters or flashes in one eye: get a dilated exam promptly, within a couple of days.
• Floaters and flashes together: be more urgent.
• A new dark curtain, shadow, or black area in your vision, or a sudden drop in vision: that is an emergency, even on a weekend night. Please do not wait until Monday for that.

If you are ever unsure, it is always better to call and ask. I would much rather see you and find that everything is fine than have you wait at home worrying.

In a future post, I will talk more about what we look for during that dilated retinal exam.

If you want the short visual version, watch one of my videos on eye floaters — it covers the same warning signs in a few minutes, while this article goes a bit deeper on what is happening inside the eye.

As always, this is general information, not medical advice for your specific situation. Please do see an ophthalmologist if you have new floaters or flashes.