Red eyes: causes, symptoms, diagnosis and treatment

By Cristiano Antonino Last updated Jun 3, 2023

While it is true that in some cases red eyes are due to external factors such as air pollution or dryness, other times the redness is a symptom of something better investigated through an eye examination

What red eyes look like

Reddening of the eyes, also called ocular hyperemia, occurs as a result of dilation of the blood vessels that are present in the sclera, the white part of the eye.

This reddening is visible to the naked eye although it can take on different characteristics, being spread over the entire sclera or affecting only parts of it, involving only one eye or both.

The redness may also be accompanied by other symptoms such as tearing and itching, depending on the reason that triggered it.

Everything depends on the genesis of the redness and its cause.

Causes of red eyes

The causes of ocular hyperemia can be many and all very different.

One should not immediately worry about reddening of the eyes, but it is good to trace the cause especially if the redness tends to increase or does not disappear.

As a rule, when it is a temporary redness, it disappears by itself within a couple of days.

But if this is not the case, it is best to consult an ophthalmologist, who will try to find out the origin of the problem through an examination.

Red eyes can be caused by inflammation, infection, trauma, disease and external factors and are the most common ophthalmological symptom.

Therefore, their origin is not always in the eyes, but the first step is an eye examination.

Inflammation and ocular hyperemia

Inflammation of any part of the eye, including eyelids, lacrimal glands and changes in the tear film, can cause redness.

The most frequent ocular inflammations are:

conjunctivitis: involves the transparent membrane that lines the eyeball and the inside of the eyelid and can be caused by allergies, infections (bacterial, viral, fungal or due to parasites) and irritation
blepharitis: this is an inflammation of the eyelids and can be acute, such as a stye, or chronic, which if not properly treated can lead to chalazion
dacryocystitis: these can be acute or chronic and affect the lacrimal outflow pathways and more specifically the lacrimal sac
keratitis: these affect the cornea and can be of allergic, infectious, autoimmune, irritation or traumatic origin
scleritis and episcleritis: affect the sclera and often have an immune origin
iridocyclitis: affecting the iris and ciliary body and can be triggered by infections, allergies, autoimmune diseases or ocular trauma
uveitis: these are inflammations of the uvea that can lead to increased pressure in the eye and must be treated urgently

Many times, in the presence of inflammation, red eyes are accompanied by burning, tearing and pain.

Red eyes and conjunctivitis

Conjunctivitis remains one of the main causes of red eyes.

It is not always associated with burning or itching and there is no test for its origin, whether bacterial or viral, as there is for the respiratory system.

Most often, however, it is viral conjunctivitis: when the aetiology is bacterial, usually the redness is accompanied by a purulent discharge.

In the latter case, antibiotics will be necessary, but only the ophthalmologist can determine this and prescribe the appropriate medicine.

Red eyes and dry eye syndrome

Red eyes can also be caused by dry eye syndrome, which is caused by chronic dehydration of the cornea and conjunctiva.

In a nutshell, the eye produces few tears as a consequence of certain diseases or inflammations directly affecting the visual apparatus, or as a result of other illnesses, or with advancing age, the use of certain medications, hormonal imbalances and prolonged contact lens wear.

Red eyes and allergies

Another of the most common causes of red eyes is allergies.

Whether to animals, grasses or dust, allergic conjunctivitis affects many people and can be very annoying, if left untreated, because in addition to redness it causes itching, intense or zero tearing, tarsal pupils and oedema.

Allergic conjunctivitis can disappear as soon as you move away from the source (e.g. when you are in the presence of a cat), or it can be chronic.

Eye drops with an antihistamine function, or anti-inflammatory, steroid-based, mast cell-stabilising or decongestant eye drops can be used, particularly in the most acute phase, whether the allergy was caused by contact or not.

Main diseases associated with red eyes

In addition to inflammations affecting the eyes, there are diseases that may or may not directly affect the eyesight, but still trigger a reaction that causes the eyes to redden.

In order to distinguish the origin of the problem, whether ophthalmic or not, it is essential to consult a specialist.

Among the ophthalmological diseases that can redden the eyes are

glaucoma: a disease that damages the optic nerve and develops due to a significant increase in eye pressure
ophthalmic herpes zoster: the varicella-zoster virus reactivates in the eye, the initial manifestation of which may appear on the forehead and eyelids
retinoblastoma: a malignant ocular tumour affecting retinal cells, most common in children under 5 years of age and caused by a genetic mutation
trachoma: this is an infectious disease triggered by the bacterium Chlamydia trachomatis, is very contagious and in addition to red eyes triggers itching, oedema, tearing and photophobia
corneal ulcer: a serious injury to the cornea, it is like an open wound and can depend on various factors, some external such as trauma and lens wear or related to the eye, such as blepharitis or trachoma

Diseases that can trigger eye redness but do not directly affect the ocular system include

dengue
ebola
yellow fever
leptospirosis
molluscum contagiosum
zika virus
porphyria cutanea tarda
polycythaemia vera

Other causes of red eyes

Before thinking the worst, however, it is good to remember that many times red eyes can be due to bad habits, either related to vision or, more generally, applied to everyday life.

Or from other factors that affect the eyes directly, but which are easily resolved.

Habits that can cause red eyes include:

prolonged use of contact lenses
prolonged exposure to screens, such as TV and computers
exposure to the sun
scooter or bicycle use, especially air pollution

In general, dry and polluted air can cause reddening of the eyes because it interferes with the tear film.

If you notice that your eyes are red after a day’s work at the computer or in the evening, consult an ophthalmologist to find out if the origin of the redness is indeed related to one of these factors.

Red eyes and computers

Those who work long hours at the computer often complain of redness of the eyes in the evening.

In this case, it may be useful to visit an ophthalmologist to evaluate the possible use of protective lenses against blue light, or to have a check-up to investigate the eye discomfort related to prolonged screen viewing.

Sometimes it may be necessary to use eye drops to hydrate the eyes, which are often kept open too long because one is too focused on work.

But it is important that the doctor prescribes it, so in any case it is always best to see a specialist.

As a good habit, it is advisable to remember to ‘blink’ often and to take breaks to take your eyes away from the screen.

Similarly, it is best if natural light, where present, directly illuminates the screen.

How to treat red eyes

The first rule to follow in case of red eyes is to avoid DIY. Waiting a couple of days in the absence of other important symptoms (pain, severe itching, purulent discharge) can help to find out what the source of the problem is, as can trying to change your habits (e.g. if you spend a lot of time outdoors in a polluted city or in front of the computer without glasses).

If the discomfort does not go away in a couple of days, you should book an eye examination and report the problem to your doctor, who will decide how to intervene on the basis of your medical history and the tests you undergo.
In the case of inflammation due to bacterial infections, an antibiotic will be necessary.

In the case of inflammation due to other factors or viral infections, an eye drops could be used to rebalance the tear film.

If, on the other hand, the red eyes are due to a disease, the ophthalmologist will prepare more investigations to ascertain the exact origin and, consequently, choose the best medical strategy.

Ocular hyperemia, i.e. red eyes, is the main ophthalmological symptom involving the sclera, which may become completely or only partially red.

It can have different origins: in most cases it is a temporary or easily treatable problem, but other times it can be a symptom of an infection of a different nature or of an eye or other pathology.

In any case, consulting a specialist is undoubtedly the first step to managing it in the most appropriate manner.

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