The causes of red eyes can be many.
> I have red eyes, no pain, no visual loss.
Most often, the redness is due to dilation of the blood vessels of the conjunctiva, a thin membrane covering the anterior part of the eye. In this case, it is conjunctivitis. The red eye may or may not be accompanied by tingling. The symptoms will disappear in a few days thanks to a suitable treatment.
Precautions to take? Wash your hands well, avoid rubbing the sick eye, as conjunctivitis may be contagious when it is infectious. Most often viral, it can also be of bacterial origin. In this case, the risk is a contamination in both eyes that will turn red.
There are also conjunctivitis of allergic origin. In addition to the symptoms of conjunctivitis, other signs of allergy may be associated, such as allergic rhinitis (sneezing) or eczema. In this case, antiallergic eye drops will most often be effective.
Finally, pay attention to eyedrops for aesthetic purposes. Some may cause irritation, red eyes, and sometimes inflammation. Then quickly consult an ophthalmologist.
> I have a bright red spot, suddenly appeared in one eye.
The eye can become bright red, because of a haemorrhage located more or less deeply under the conjunctiva. In this case, the coloring is most often brutal. The redness will disappear in about ten days. If in doubt, do not hesitate to consult your doctor.
> I have red eyes associated with headaches.
Red eyes, eyestrain, sometimes associated with headaches, can be the consequence of a defect of vision or a simple dryness of the eyes. In all cases, a diagnosis from your doctor is required.
> I have red eyes, painful, important secretions, significant swelling of the eyelid and a drop in vision.
The degrees of pain and visual decline may be different, in all cases an ophthalmologic diagnosis is required.
When there is a decline in vision, with a red eye (more rarely both red eyes) a quick consultation of a doctor - and if possible an ophthalmologist - is necessary. It will first of all be necessary to investigate whether there has been a context of ocular trauma. A foreign body (dust, sand) may have deposited on the cornea. Another possibility: if the pain in the red eye is intense, it may be an internal inflammation of the eye.
Wearing contact lenses can also be the cause of these disorders. If the symptoms do not resolve after removing the lenses, consult an ophthalmologist promptly. It may be an infection of the cornea, called infectious keratitis (or corneal abscess). Most often, this is unilateral: the infected eye is red, painful and sensitive to light, and the sight can be cloudy.