By Ronald Allen, DO, ophthalmologist at The Portland Clinic.

Gradual changes in eyesight are a fact of life. Even if you’ve been lucky enough to have 20/20 vision your whole life, you’ll start to find, sometime after your 40th birthday, that you’re squinting more and more to read, until eventually you’ll join the rest of us who need reading glasses. As life goes on and you enter your golden years, you may notice that the world is looking a little blurrier, and eventually, like about half of us, you may need cataract surgery to clear it up. These gradual changes, though annoying, are a normal part of getting older, and can be monitored by your eye doctor at your regular checkups.

Vision changes that come on suddenly, however, are a different story. Sudden vision loss or eye pain can indicate a serious and possibly permanent threat to your eyesight. Symptoms like these should be evaluated immediately:

Sudden loss of vision in one eye

Several serious conditions can cause partial or total vision loss to come on very suddenly in one eye. One is a severe form of macular degeneration known as the “wet” form, so called because of bleeding in the eye. Another is a type of stroke in the eye known as ischemic optic neuropathy. Both of these are urgent medical issues that can cause permanent vision loss without immediate attention.

Sudden flashes and floaters

The sudden appearance of bright flashes of light and new floaters in one eye could be signs of a detached retina, a very serious condition that can result in permanent vision loss if not treated right away.

Sudden rainbows or halos around lights, with eye pain and redness

These symptoms, sometimes accompanied by nausea, can be caused by a form of glaucoma known as angle-closure glaucoma. By the time they appear, extremely high eye pressure could lead to blindness rapidly — typically within 90 minutes. Immediate treatment is critical to preserve eyesight.

Eye pain and redness

Even without the rainbows and halos, sudden eye pain and redness should be checked by a doctor. The irritation could be caused by infection, inflammation, elevated eye pressure (which can lead to glaucoma), or a scratch or cut in the eye. In any of these cases, waiting too long to follow up could lead to permanent loss of vision, and sometimes to blindness.

Red, crusty eyelids

Inflammation in the eyelids, known as “blepharitis,” can cause these symptoms. It’s not usually serious, but in some cases in can lead to permanent scarring and vision loss, so it should be evaluated quickly.

Any injury, object or chemical in the eye

Any injury to an eye, whether it’s sharp or blunt, and any foreign substance that gets into your eye, whether it’s solid or chemical, should be evaluated quickly by your eye doctor.

In all of these cases, your ability to see for the rest of your life could be riding on your quick response. If you notice any of these symptoms, or any other sudden vision change, don’t delay. Try to contact your ophthalmologist first (our office sees urgent issues on a same-day basis), but if you can’t reach one or can’t get in right away that day, go to the nearest ER.

Not all problems are obvious

A gradual loss of vision over time may just mean that you need a new prescription for glasses or lenses, but if changes are concerning, call your ophthalmologist for the next available office appointment.

Not every problem comes with obvious signs. Glaucoma, macular degeneration, diabetic retinopathy, cancer and other threats may begin with very subtle changes or no symptoms at all, yet can have a devastating impact on your vision and health if they continue without treatment. Getting your eyes checked regularly, whether you’ve noticed changes or not, is the best way to catch problems early, when they’re most treatable.

The ability to see the world around you, to look into the eyes of someone you love, or even to read a newsletter from your doctor’s office is an irreplaceable gift. Do everything you can to protect it.