Red eye

A red eye is an eye that appears red due to illness or injury.

It is a condition where the white part of the eye, called the sclera, appears reddened or bloodshot.

It is usually injection and prominence of the superficial blood vessels of the conjunctiva.

It may be caused by disorders of these or adjacent structures. 

Conjunctivitis and subconjunctival hemorrhage are two of the less serious but more common causes.

Causes of red eye:

Allergies: Exposure to allergens such as pollen or pet dander can cause the eyes to become inflamed and red.

Eye infections: Viral or bacterial infections can cause the eyes to become red and irritated.

Dry eyes: A lack of moisture in the eyes can cause them to become red and uncomfortable.

Eye strain: Spending long periods of time staring at a computer or phone screen can cause eye strain and redness.

Environmental factors: Exposure to smoke, wind, or dry air can also cause red eyes.

Contact lenses: Wearing contact lenses for extended periods of time can cause the eyes to become red and irritated.

Subconjunctival hemorrhage causing red coloration as result of ruptured blood vessel in the eye.

In most cases, red eye is not a serious condition and can be treated with over-the-counter eye drops or home remedies such as warm compresses. 

Management includes assessing whether emergency action is needed, or whether treatment can be accomplished without additional resources.

Slit lamp examination is invaluable in diagnosis but initial assessment can be performed using a careful history, testing vision and carrying out a penlight examination.

Particular signs and symptoms may indicate that the cause is serious and requires immediate attention.

Seven such signs are:

Reduced visual acuity

Ciliary flush 

Corneal abnormalities including edema or opacities 

Corneal staining

Pupil abormalities including abormal pupil size

Abnormal intraocular pressure

Severe pain

The most useful  findings is a smaller pupil in the red eye than the non-red eye and sensitivity to bright light.

A reduction in visual acuity in a red eye is indicative of serious ocular disease: such as keratitis, iridocyclitis, and glaucoma, and never occurs in simple conjunctivitis without accompanying corneal involvement.

Ciliary flush is usually present in eyes with corneal inflammation, iridocyclitis or acute glaucoma, though not simple conjunctivitis. 

A ciliary flush is a ring of red or violet spreading out from around the cornea of the eye.

The cornea is required to be transparent to transmit light to the retina. 

Because of injury, infection or inflammation, an area of opacity may develop which can be seen with a penlight or slit lamp. 

In rare instances a corneal opacity is congenital.

In some, there is a family history of corneal growth disorders which may be progressive with age. 

The misuse of contact lenses may be a precipitating factor in corneal opacities.

Corneal opacities  are potentially serious and sometimes necessitates urgent treatment and corneal are the fourth leading cause of blindness. 

Opacities may be keratic, that is, due to the deposition of inflammatory cells, hazy, usually from corneal edema, or they may be localized in the case of corneal ulcer or keratitis.

Corneal epithelial disruptions may be detected with fluorescein staining of the eye, and careful observation with cobalt-blue light. 

Corneal epithelial disruptions would stain green, reflecting some injury of the corneal epithelium. 

These types of disruptions may be due to corneal inflammations or physical trauma to the cornea, such as a foreign body.

In an eye with iridocyclitis, which is inflammation of both the iris and ciliary body, the involved pupil will be smaller than the uninvolved, due to reflex muscle spasm of the iris sphincter muscle. 

Cnjunctivitis does not affect the pupils. 

With acute angle-closure glaucoma, the pupil is generally fixed in mid-position, oval, and responds sluggishly to light, if at all.

Shallow anterior chamber depth may indicate a predisposition to narrow angle glaucoma, but requires slit-lamp examination or other special techniques to determine it. 

The presence of a red eye and a shallow anterior chamber may indicate acute glaucoma, which requires immediate attention.

Patients with conjunctivitis may report mild irritation or scratchiness, but never extreme pain, an indicator of more serious disease.

Usually nonurgent sources of red eye:

airborne eye irritants



dry eye syndrome 

acute glaucoma, angle closure type

subconjunctival hemorrhage

inflamed pterygium 


inflamed pinguecula



Usually urgent red eyes: 

Acute closed-angle glaucoma

Eye injury


Tick-borne illnesses

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