Why eye pain often affects one eye
It is worth noticing that the pain is in one eye rather than both, because that in itself is a clue. Discomfort that affects both eyes together, a tired, dry, strained ache after a long day or a lot of screen time, is usually a surface or environmental problem, and is rarely serious. Pain that settles firmly in one eye is more likely to reflect something happening in that particular eye.
Many of the conditions that cause a genuinely painful eye are one-sided by their nature. A scratch, a foreign body, or an infection affects the eye it lands in. Inflammation inside the eye, a sudden rise in pressure, and shingles around the eye all tend to strike one side. So while one-sided pain is often still something minor, the fact that it is confined to one eye is a reason to pay a little more attention to it, and to look carefully at what else is happening in that eye.
Is it on the surface, or deep?
The front of the eye is exquisitely sensitive, so problems on the surface produce a sharp, scratchy, foreign-body sensation that is often worse with blinking. Pain that feels deeper, a dull ache in or behind the eye, points to something further in, and is more likely to matter, particularly if the eye is also red, light-sensitive, or seeing less well.
Deciding which of the two you have is the most helpful thing you can do, and it shapes everything that follows.
Common surface causes
Dry eye, a stray eyelash, a speck of grit, or a small scratch to the surface, a corneal abrasion, all cause a gritty, watering, uncomfortable eye. Most settle quickly, although a scratch that follows an injury, or pain that does not ease, should be examined.
A tender lump at the lid margin, a stye, or sore, crusted lids, blepharitis, cause a localised soreness that is usually easily managed with warmth and lid care. Overwearing contact lenses, or sleeping in them, irritates the surface and, more seriously, raises the risk of corneal infection.
Deeper causes that need assessment
Several causes of a painful eye need prompt assessment. Inflammation inside the eye, uveitis, causes a deep ache, light sensitivity, redness, and blur. Scleritis produces a severe, boring pain that can wake you from sleep and is sometimes linked to inflammatory conditions elsewhere.
An infected or ulcerated cornea, keratitis, causes a painful, red, light-sensitive eye and can threaten sight, especially in contact lens wearers. Optic neuritis causes an ache on moving the eye together with blurred vision, more often in younger adults. Shingles affecting the eye area, herpes zoster, causes pain and a rash on one side of the forehead or nose and can involve the eye itself.
Pain that must be seen at once
Two situations deserve particular mention. Acute angle-closure glaucoma causes a sudden, severe, painful red eye with blurred vision, haloes around lights, headache, and often nausea and vomiting. It is an emergency, and the pressure in the eye must be brought down quickly.
Orbital cellulitis, an infection of the tissues around the eye, causes pain, redness and swelling around the eye, restricted or painful eye movements, and a feeling of being unwell. It also needs emergency care, particularly in children.
- Reduced or blurred vision, or sensitivity to light
- A red, painful eye with haloes around lights, headache, or nausea
- Pain on moving the eye
- A rash on the forehead, nose, or around the eye
- Swelling, redness, or bulging around the eye, or difficulty moving it
- Contact lens wear, or a recent injury or chemical splash
Surface soreness settles, deep pain should be checked
Surface soreness that is easing, with normal vision and no light sensitivity, can usually be watched. Deep pain, pain with reduced vision or light sensitivity, a red painful eye with haloes, pain on eye movement, a rash, or swelling around the eye should all be assessed promptly, and several of these are emergencies. A painful eye in a contact lens wearer should always be seen the same day.
Common questions
My eye feels gritty and scratchy. What could it be?
A gritty, scratchy, foreign-body feeling usually comes from the surface: dry eye, a stray lash, a speck of grit, or a small scratch. Most settle quickly. If it follows an injury, or does not ease, have it examined.
I have eye pain and wear contact lenses. What should I do?
Take the lenses out and seek same-day assessment, keeping the lenses and case in case they are needed for testing. A painful eye in a lens wearer can signal a serious corneal infection and should not be left, and the lenses should not go back in until the eye has been checked.
I have a deep aching pain in one eye. Is it serious?
A deep ache, especially with light sensitivity, redness, or blur, can indicate inflammation inside the eye such as uveitis, and a severe boring pain that wakes you at night can indicate scleritis. Both need prompt assessment, so a deep, persistent eye pain should be checked.
My eye hurts and I have a headache. What does that mean?
It may be benign, such as eye strain or a migraine, but a severe, painful, red eye with haloes around lights, headache, and nausea can be acute angle-closure glaucoma, which is an emergency. Pain on moving the eye with blurred vision also needs checking.
