Most people get allergic conjunctivitis when their eyes come into contact with an allergen - a substance which makes the body's immune system overreact.
The eye becomes sore, inflamed and sometimes painful. Symptoms occur because the overreacting immune system makes the body release histamine and other active substances by mast cells - these cause dilation of blood vessels (blood vessels expand, widen), which irritates the nerve endings and causes increased secretion of tears.
Allergic conjunctivitis is not the same as infective conjunctivitis, the causes are different.
The following allergens are commonly found to cause allergic conjunctivitis:
- Pollen (hay fever)
- Animal fur
- Eye drops
- Dust mites.
Types of allergic conjunctivitis
Allergic conjunctivitis is usually broken down into different categories. Below are some of them:
1) Seasonal allergic conjunctivitis (allergic rhinoconjunctivitis)
Pollen is a common cause of allergic conjunctivitis
Pollen is the most common allergen to cause conjunctivitis in countries that have cold winters (not near the equator).
If you get conjunctivitis from pollen you will probably have symptoms of hay fever, which includes sneezing, blocked or runny nose, itchy nose, and itchy and watery eyes. When the conjunctivitis occurs along with sneezing and blocked nose, etc., the whole thing is called hay fever.
This type of conjunctivitis is called seasonal allergic conjunctivitis (allergic rhinoconjunctivitis) because it almost exclusively occurs during the spring and summer months when plants, especially grass, trees, and flowers are in pollen. Some people even have symptoms during early autumn (fall).
2) Contact conjunctivitis (Contact dermatoconjunctivtis)
These are usually caused by make-up (cosmetics), eye-drops or other chemical which irritate the conjunctiva of sensitive people, causing an allergic response. Some people are sensitive to specific substances.
Symptoms usually develop two to four days after the substance comes into contact with the eyes.
3) Giant papillary conjunctivitis
This is generally caused by contact lenses. When sensitive people put the contacted lenses on they cause discomfort - this can get progressively worse and more and more uncomfortable, causing the eyes to become red.
Giant papillary conjunctivitis (GPC) may also occur after eye surgery when the patient uses hard contact lenses.
Some people say that poor hygiene when handling contact lenses, solutions and cases may contribute to infections of the eye.
4) Perennial (all year round) conjunctivitis
As the name suggest, this type of conjunctivitis persists throughout the year. It is mainly due to an allergy to house dust mites - microscopic insect-like creatures that live mainly in bedding, upholstered furniture and carpets. Dust mites eat skin cells shed by people - they love warm, humid environments. Dust mite allergy is an immune system response to a specific dust mite protein, causing other problems as well as conjunctivitis, such as blocked/runny nose, sneezing, and contraction of the airways (asthma).
Other causes may be animal dander (small scales from animal skins or hair or bird feathers that can cause allergic reactions in some people).
Symptoms of allergic conjunctivitis
Most people with allergic conjunctivitis have problems with both eyes. Symptoms may appear quickly, soon after the eyes have come into contact with the allergen. In other cases, as with some eye drops, symptoms may take from two to four days to appear.
The following symptoms are most typical for allergic conjunctivitis:
Pink/red eye is a common symptom of conjunctivitis.
- Eyes become red/pink - by far the most common symptom. The eyes become irritated as the capillaries (small blood vessels) in the conjunctiva widen.
- Pain - some people have pain in one or both eyes. If the eyes are very red and painful it is important to see a doctor. Any patient with painful, red eyes, and has become sensitive to light (photophobia), and feels his/her vision is affected should see a doctor straight away.
- Itchiness - as the eyes are irritated they may itch. The itch may worsen if you keep rubbing them.
- Swollen eyelids - the eyelids may puff up when the conjunctiva becomes inflamed, or if the sufferer has been rubbing them a lot.
- Soreness - the inflammation may make the whole area feel sore and tender. Some people say the soreness feels like burning.
People with seasonal allergic conjunctivitis will experience symptoms at certain times during the year - usually from early spring, into summer, and even into autumn (fall). Those with perennial allergic conjunctivitis are susceptible at any time of year, and may find certain times of the day are worse than others.
If the eyelids are red, cracked and/or dry it is an indication that the patient most likely has contact conjunctivitis. Contact conjunctivitis and giant papillary conjunctivitis are not seasonal - symptoms may occur at any time of year.
On the next page we look at the diagnosis of allergic conjunctivitis and the available treatments for the condition.