Reddening of the eyes: what diseases are linked to eye redness?

By Cristiano Antonino On Feb 1, 2023

Reddening of the eyes can be a symptom related to various conditions that are, in most cases, benign in nature and generally tend to resolve themselves, without causing any particular consequences

In some cases, however, especially when associated with other symptoms, reddened eyes can be a cause for concern, a precursor to more serious conditions or even represent a real medical emergency.

Find out below what you need to know about reddened eyes and in which cases it is necessary to consult a specialist.

Definition of eye redness

Reddening of the eyes is a reddening of the sclera and/or conjunctiva, i.e. the white outer layers covering the eye.

When seen, the eye becomes red or bloodshot due to dilation of the blood vessels on its surface, which, as they widen, pump more blood into the eye, causing what is medically known as hyperemia, i.e. increased blood flow.

The problem underlying the redness can affect different parts of the eye including, most commonly, the conjunctiva (i.e. the thin membrane that lines the inside of the eyelid and covers the front of the eye), the episclera (connective tissue membrane present between the sclera and the conjunctiva), but also the iris (i.e. the coloured part of the eye).

Two types of eye redness can be distinguished

The first is a transitory type, which lasts for a couple of days at most, tends to resolve itself and generally has no significant consequences.

The second, on the other hand, is a persistent or sometimes recurrent type of reddening, which could be a cause for concern and for which it is advisable to consult an ophthalmologist without delay.

Possible causes of eye redness

The causes of dilated blood vessels and the resulting symptom of reddened eyes can be of a different nature, including:

Infections
Allergies
Inflammation caused by an external agent
Trauma
High pressure in the eye

In rare cases, redness of the eyes is the only symptom present at eye level

Much more often, however, the affected person also complains of itching, tearing, hypersensitivity to light, a sensation of a foreign body inside the eye and, in some, sometimes severe cases, pain and altered vision.

There may also be symptoms involving other parts of the body such as coughing, rhinorrhoea or nausea and vomiting.

We can divide the causes of eye redness into two groups:

External causes
Internal causes

The former include:

Excessively dry air.
Exposure to dust.
Exposure to irritants such as chlorine, ammonia or fumes.
Excessive sun exposure.
Exposure to excessive fatigue or exertion.
Presence of corneal abrasions or scratches caused by foreign bodies trapped inside the eye.
Prolonged use of contact lenses.

The most common internal causes of reddened eyes include:

Inflammation of the conjunctiva caused by an infection such as viral conjunctivitis or acute bacterial conjunctivitis.
Inflammation of the conjunctiva caused by an allergic reaction such as allergic conjunctivitis.
Chalazion.
Styes.
Dry eye syndrome.
Asthenopia.

Serious cases causing reddening of the eyes are quite rare, however, they should not be excluded

Eye redness accompanied by persistent pain can be a symptom of uveitis, scleritis (a deep and painful inflammation of the sclera) or acute angle-closure glaucoma.

Other serious conditions that can lead to eye redness include corneal ulcers, ophthalmic herpes zoster (which develops in and around the eye) or herpes simplex keratitis (a herpetic infection of the cornea).

Deepening: conjunctivitis

Conjunctivitis is considered the most common cause of eye redness.

This inflammatory process affecting the conjunctiva can be bacterial, viral, allergic or irritative in origin.

The conjunctiva forms the front and outer part of the eye and lines the entire eyelid on the inside.

In the presence of conjunctivitis it appears reddened and swollen and secretes a watery substance that can be purulent in some cases.

Itching and redness may affect one or both eyes and may sometimes be accompanied by an uncomfortable sensation of the presence of a foreign body.

Leakage of watery substance and purulent material can lead to the formation of a typical crust that forms during the hours of rest and makes it difficult to open the eyes upon awakening, which appear as if glued shut.

Although the symptoms of conjunctivitis are rather irritating and annoying for the affected person, it is rare when there is interference with vision.

It usually occurs in cases of bacterial conjunctivitis, which can lead to blurred vision and the production of very sticky yellowish discharge.

When to seek medical advice?

It must be emphasised that cases in which eye redness is a symptom of a condition that is of concern for the patient’s health are rare.

Much more often the disorder does not require medical evaluation and tends to disappear on its own.

Moreover, in most cases, individuals experiencing reddening of the eyes can first be evaluated by their family doctor and then, if the problem persists or an underlying disease is suspected, by an ophthalmologist.

So what are the cases in which it is necessary to be concerned and seek immediate medical attention?

As mentioned above, reddening of the eyes can be a cause for concern when accompanied by other symptoms that act as warning signs such as:

Sudden and severe pain, sometimes accompanied by vomiting;
Eruptions on the face, particularly in the area around the eyes or at the tip of the nose;
Reduced sharpness of vision;
A blurring of the cornea, which loses its characteristic transparency.

If, on the other hand, the reddening of the eye is due to the presence of a foreign body inside the eye, it is best to seek emergency medical attention as soon as possible to avoid serious and permanent damage.

Medical test

If the reddening of the eye makes it necessary to consult a doctor, he or she will proceed by conducting an objective test, asking the patient questions about the symptoms and the patient’s medical history.

The results of the medical history, together with the objective examination, are crucial to discover the cause of the reddening of the eyes and to understand which tests are useful for further investigation.

The most common questions asked of the patient are generally:

How long has the redness been present?
Has the redness appeared before?
Is the redness associated with pain or itching?
Are there any eye secretions or tears present?
Is there any change in vision?
Is it possible that there has been an ocular trauma?
Are there other symptoms such as headache, rhinorrhoea, cough, sore throat or other?
Are any allergies present?

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In addition, the subject may be asked if he or she has recently been exposed to substances that could cause irritation to the eye or if he or she has been wearing contact lenses for a long time.

During the objective test, the doctor will examine the patient’s head and neck to see if the redness is due to any disease related to an upper airway infection, an allergy or a rash, which could indicate the presence of shingles.

The most important part of the objective examination is definitely the eye examination, during which the doctor will test the patient’s eyes and the surrounding area for any lesions or oedema.

Factors such as vision, pupil size and response to light exposure and eye movement are checked.

During the examination, the doctor may also measure the intraocular pressure after appropriately anaesthetising the eye with a drop of anaesthetic.

This test is known as tonometry.

The analysis of the different factors and the patient’s response to stimuli will allow the doctor to understand the cause of the reddened eye and be able to prescribe a suitable treatment to cure it accordingly.

Remedies for reddened eyes

In cases where reddened eyes are the consequence of over-exertion; prolonged use of contact lenses; exposure to the weather; contact with sea or swimming pool water (containing chlorine) or simply too much time spent in front of a computer, the most appropriate treatment is to try to rest.

It is also recommended to use tear substitutes in the form of eye drops that have a cooling and lubricating action, available in pharmacies without the need for a prescription.

The application of medicated gauze compresses or cold cotton wool pads, which help relieve discomfort, are also effective.

However, if the eye redness, accompanied by other discomforts, tends to persist for several days, it is advisable to seek a consultation with your doctor, who may prescribe precise pharmacological treatment.

Depending on the disorder underlying this symptom, the drugs prescribed by the doctor may be eye drops containing antibiotics or ointments with antiviral and anti-inflammatory action.

In cases of allergic conjunctivitis, the specialist may prescribe antihistamine eye drops that are intended to stop the immune reaction.

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