Conjunctivitis, often colloquially referred to as "pink eye", is a relatively common eye disorder that affects the conjunctiva, which is the mucous membrane that lines the anterior sclera. The whitish fibrous tissue that covers the inner eyelid is known as the palpebral conjunctiva while that which covers the entire eyeball, with the exception of the cornea, is referred to as the bulbar conjunctiva. The transparent bulbar is the thinner of the two and contains cells that release mucin that protects the cornea from adverse environmental factors. Conjunctivitis occurs when the conjunctiva becomes inflamed, usually because of an allergic reaction. At its most severe, conjunctivitis can affect the whole ocular surface, including the cornea and the margins of the eyelids as well.

Viral, bacterial, and allergic are the three main types of conjunctivitis, each exhibiting slightly different characteristics.

Viral conjunctivitis is caused by a virus and is typically associated with a cold, sore throat or upper respiratory tract infection. Like the common cold, there is no cure for viral conjunctivitis but, like a cold, it is usually only temporary and may clear up on its own. It generally only affects one eye, although it is very contagious and can easily be spread to the other eye. Viral conjunctivitis causes the eyes to become red and watery and may cause swelling in the eyelids. The discharge for the eyes tends to lack the greenish or yellowish discolouration caused by bacteria conjunctivitis.

Bacterial conjunctivitis is an eye infection commonly caused by the bacteria staphylococcus, "staph", or streptococcus, "strep", and the severity of the infection will usually depend on the type of bacteria responsible for it. Although it may initially only affect one eye, it is very easily spread to the other so both eyes are usually involved. Typical symptoms include a reddening of the eyes, eye discomfort, a gritty sensation between the eye and the eyelid, and a noticeable amount of purulent discharge. The presence of pus colouring the discharge green or yellow is another indicator that the infection is bacterial in nature. This condition has no affect on vision, although sometimes the eyelids may be difficult to open in the morning because they are swollen and have become stuck together with congealed discharge. Depending on the severity of the infection, some people with bacterial conjunctivitis can get a secondary infection known as blepharitis, which affects the eyelash follicles, or chemosis, which is a swelling of the conjunctiva.

Allergic conjunctivitis occurs when the conjunctiva becomes inflamed because of the body's allergic reaction to an allergen, like pollen or mould. It has been estimated that about 20% of the general population will experience this condition, making it one of the most commonly experienced ocular allergies. While this rarely affects the vision, it typically affects both eyes at the same time. The eyes become red, itchy, and watery, perhaps also incorporating a small amount of mucous discharge. The eyelids may become swollen because of this reaction. Severe itching (pruritus) is a symptom common to all types of allergic conjunctivitis, helping to distinguish it from the other forms of conjunctivitis. Another condition, known as giant papillary conjunctivitis (GPC) is a special type of allergic conjunctivitis that affects those who wear contact lenses.

Allergic conjunctivitis can be seasonal or perennial. Seasonal allergic conjunctivitis occurs in response to the presence of seasonal allergens like grass, tree, or weed pollen while perennial allergic conjunctivitis can be triggered by allergens that are encountered all year round, such as dust mites or animal dander in the home. Seasonal allergic conjunctivitis is most frequently experienced by those who suffer from allergic rhinitis, or hayfever as it is usually known, and it is the ocular manifestation of this condition. When allergic conjunctivitis occurs at the same time as rhinitis it is referred to as rhinoconjunctivitis. While perennial conjunctivitis will be more persistent, its symptoms tend to be milder than that of seasonal allergic conjunctivitis and will only affect around 3% of the general population.

Giant papillary conjunctivitis (GPC) is a related condition largely associated with the use of contact lenses, especially those of the "soft" variety. The most likely cause of giant papillary conjunctivitis is an allergic reaction to the debris that collects on contact lenses. It is felt that some of the components in the lenses material itself or the solutions used to maintain them may contribute to the problem. The protein secreted by the eyes of contact lens wearers is believed to facilitate the allergic reaction, which people who suffer from asthma, hayfever or other allergies are more susceptible to. Giant papillary conjunctivitis is characterised by itchiness and giant bumps, or papillae, at least one millimetre in diameter inside the upper eyelid. Vision may become blurred as the conjunctiva thickens and mucus adheres to the contact lens. Giant follicular conjunctivitis (GFC) is another related condition.

Allergic conjunctivitis can also be caused by intolerance of a particular substance. Symptoms may result from a contact allergy to certain substances including cosmetics, especially nail polish, or medicines like antibiotics. The use of topical face or eye preparations that trigger an allergic reaction can cause a condition known as allergic dermatoconjunctivitis, or allergic contact dermatitis. Some cosmetics, soaps, medications and contact lens solutions can cause redness and swelling if they come in contact with the eye or the periocular area surrounding it. A patch test, where antigens are kept in contact with the skin of the upper back for about 48 hours, may be helpful in identifying the cause of this reaction.

When attempting to diagnose allergic conjunctivitis, your doctor or optician will take your medical history into consideration. If someone already has other allergic conditions such as asthma or eczema then they are going to be more prone to developing allergic conjunctivitis. There will be other physical indicators as to the nature of the condition. For example, if the discharge from the eye is clear then the conjunctivitis is likely to have either a viral or an allergic cause. An ophthalmologic examination will provide other information that will assist in the correct diagnosis.

The diagnosis of allergic conjunctivitis can be confirmed by a slit-lamp examination administered by a doctor or optician. The slit-lamp consists of a mobile light source and a binocular microscope used to examine the eye under extreme magnification. This will help to eliminate infection as a possible cause of the conjunctivitis. A skin prick test will help to confirm the allergen responsible for the reaction. A RAST (radioallergosorbent) test may be used to ascertain the allergen-specific IgE (Immunoglobulin E) involved. Tear film analysis may be used to measure the level of IgE present in tears. A high level of IgE in tears generally indicates that the condition is more likely to be allergic conjunctivitis than viral or bacterial conjunctivitis, which both tend to have lower levels of IgE.

Treatment of allergic conjunctivitis usually concentrates on controlling the symptoms of the condition. Medications containing a combination of an antihistamine and a vasoconstrictor are usually the most efficient means of achieving this. In each case, and especially with regards to seasonal or perennial allergic conjunctivitis, antihistamines should be combined with efforts to reduce your exposure to the allergens that you are sensitised to. If, for example, your allergy is triggered by pollen then staying indoors and keeping doors and windows closed on days when the pollen count is high can help. If you suffer from perennial allergic conjunctivitis then ensuring that your home environment is kept clean of allergens is most important.

Antihistamine eye drops or tablets will help to alleviate the symptoms of allergic conjunctivitis while antibiotic eye drops will effectively treat bacterial conjunctivitis. Bleph-10 is a particularly efficient medication for treating bacterial conjunctivitis and is available directly from pharmacies in some countries, including New Zealand. Cold compresses or a facecloth moistened in cold water can help the condition if you only have a mild case of allergic conjunctivitis. Eye drops that contain 'mast cell stabilisers' like Optrex Hayfever Allergy Eye Drops and Lomide Eye Drops will be effective in reducing the itching.

While antihistamines, mast cell stabilisers, and decongestants are also available as tablets, eye drops will bring faster relief to eye conditions because they are applied directly to the affected area. Be aware, however, that all eye drops contain preservative and should be discarded after they have been opened for the length of time stated in the instructions to avoid any bacterial contamination of the medication.

Allergic conjunctivitis is not contagious and will not affect anyone who is not susceptible to that particular allergen. Both viral and bacterial conjunctivitis are, however, highly contagious and can be easily spread to others or can cause re-infection if basic precautions are not taken. If you have either of these types of conjunctivitis you should avoid rubbing or touching your eyes and wash your hands if you do. Rubbing your eyes will only stimulate the release of more of the chemicals that made your eyes itchy in the first place. Avoid sharing towels or facecloths with other people and wash them after each use. Use tissues instead of handkerchiefs. Avoid swimming because some of the bacteria that cause conjunctivitis can be spread through water. Do not share eye drops or cosmetics used on or around the eye with other people. It is a good idea to replace any of these items that you were using around the time you developed the infection. If the condition is caused by the use of contact lenses, a doctor or optician may recommend that you refrain from using them until your eyes have recovered.

The term allergic conjunctivitis actually covers a wide range of conditions affecting the eye. It includes irritating complaints such as seasonal and perennial conjunctivitis and giant papillary conjunctivitis (GPC), which do not pose a danger to someone's vision, as well as much more severe conditions that can affect the cornea itself, such as vernal keratoconjunctivitis (VKC) and atopic keratoconjunctivitis (AKC). These serious conditions can cause pain, extreme sensitivity to light (photophobia), and vision loss.

Vernal keratoconjunctivitis (VKC) is a rare inflammatory disease that has seasonal incidence, affects both eyes, and afflicts mainly children. The term keratoconjunctivitis relates to the inflammation of both the cornea, a condition known as epithelial keratitis, and the conjunctiva. Frequently associated with atopic dermatitis, rhinitis, or asthma, VKC is more likely to affect people with multiple allergic sensitivities. More common in topical or temperate climates, the symptoms of VKC include hard, raised bumps (papillae) on the upper eyelid, itching, painful red eyes, mucous discharge, swelling and a thickening of the conjunctiva. Vernal keratoconjunctivits is characterised by large papillae with flat tops, which have been described as having a "cobblestone" appearance. In particularly severe cases a shield ulcer may develop on the cornea causing temporary or permanent vision impairment. Cataracts and the increased risk of eye infections are other possible complications of this condition.

Atopic keratoconjunctivitis (AKC) is another rare allergic condition that can cause vision impairment. Atopy is a hereditary condition that creates a predisposition towards developing allergic reactions and prompts the body to produce greater than normal numbers of antibodies when responding to an allergen. Atopic keratoconjunctivitis is often associated with atopic dermatitis, and causes the conjunctivitis lining of the eyelid, especially the lower eyelid, to become red and swollen. In some case the bacteria staphylococcus aureus may cause a secondary infection in the eyelash follicles. Over time, the patient can develop an aversion to bright light known as photophobia. If left untreated, the resulting cataracts, ulceration, and scarring of the conjunctiva can prove damaging to sight.