Conjunctivitis is a fairly common condition that affects the conjunctiva, the mucuous membrane that covers the white area of your eyes and the inside of your eyelids. Conjunctivitis makes these areas appear to be pink in colour - hence its other more well-known name, pink eye. People who have conjunctivitis will notice a reddening in the white of the eye or the inner eyelid, and the condition is also usually accompanied by an increased amount of tears, thick yellow discharge that forms a crust over the eyelashes and further green or white discharge. Conjunctivitis can also result in itchy, burning or otherwise irritated eyes, blurred vision and an increased sensitivity to the presence of light in the person's surroundings. It can be treated fairly easily depending on the cause. An optometrist may prescribe antibiotic eye drops or ointments, lubricating tear drops, or a treatment for a related allergy. In some cases, conjunctivitis can be transferred to others.  In this instance your optometrist will advise you on ways to reduce the likelihood of transferring the condition.  For example washing your hands and not sharing towels.

What causes conjunctivitis?

Understanding what causes conjunctivitis can help you learn how to prevent the condition from happening to you. There are four main reasons why people get conjunctivitis, ranging from allergies, irritants, bacteria and viruses. Bacterial conjunctivitis is caused by organisms such as staphylococci, streptococci or haemophilus. These bacteria may already be residing on the body's skin or in the upper respiratory tract. Sometimes, the bacteria can be caught from contact with another person who has conjunctivitis. This type of conjunctivitis can be infectious, so you are at risk of getting it if you handle objects that have been contaminated such as cosmetics, false eyelashes, hands, washcloths, and goggles, if the person wearing or using them previously had an infectious type of conjunctivitis. People often rub or touch their eyes throughout the day, so if you have come into contact with a contaminated object and then transferred your hands to your eyes, this could increase your risk of getting the condition.

Viral conjunctivitis is highly infectious and can be spread even more easily than the bacterial form. It can be transferred from person to person through the touching of contaminated items as well as coughing or sneezing. It's also typically associated with viruses causing colds or sore throats. Allergic conjunctivitis is caused by an allergy to an antigen in the person's environment. Often these will be fairly common substances such as pollen, dust mites and some types of cosmetics. If you have other allergies such as asthma, hay fever or eczema then you are also more likely to experience this form of the condition. This will usually go away once the underlying allergy has been treated. Similarly, reactive conjunctivitis is caused by the eye's response to a chemical or other irritant. This could be anything from the chemicals in swimming pool water to smoke, fumes or other substances in the atmosphere. The conjunctiva may respond to these irritants by becoming red, watery and inflamed. If an irritant is the cause of conjunctivitis, an effective form of treatment is the avoidance of what has caused the reaction.

Sometimes the condition can also be caused by an organism called  Chlamydia trachomatis, which is the same pathogen responsible for the sexually transmitted infection chlamydia. If this is the cause, one or both eyes will produce a sticky discharge and the eyelids can swell visibly. Some people also get a sub-conjunctival haemorrhage, which is when one of the blood vessels located between the conjunctiva and the sclera (the white part of your eye) bursts. In most cases it will have no cause whatsoever, and it will fade away on its own. However, it can also be caused by an injury to the eye or head, excessive coughing or vomiting and in very rare cases, high blood pressure. A point to note is that niacin or vitamin B3 has been known to dilate blood vessels and in doing so, inflame the eyelids. Because of this, it may contribute to a sub-conjunctival haemorrhage but this is extremely rare and has not been linked sufficiently.