Causes of Conjunctivitis
There are two predominant causes of conjunctivitis:
- Infective
- Allergic
This can be caused by a wide range of viruses, such as adenovirus which commonly causes respiratory illness. Viral conjunctivitis can often be concurrent with cold or influenza symptoms. Symptoms usually start in one eye then affect both eyes after a few days.
Further symptoms of infective viral conjunctivitis include a burning sensation in the eyes, the sensation of gritty or itchy eye/s, and sticky discharge on the eyelashes usually on waking or an enlarged lymph node in front of the ear. Some mild soreness may develop but it is unusual for the condition to cause pain. Vision is not normally affected although there may be some blurring of vision due to discharge, but this will usually clear after blinking.
Bacterial conjunctivitis
This is most often caused by bacteria such Streptococcus pneumoniae, Haemophilus influenza or Staphylococcus aureus and is more common in children than adults. Bacterial conjunctivitis can often be distinguished from viral conjunctivitis by the presence of a thick yellow-white mucus and pus discharge, with the eyes being difficult to open on waking in the morning.
Allergic Conjunctivitis
In allergic conjunctivitis both eyes are usually affected and the symptoms develop quickly. The eyes are usually itchy or gritty, a burning feeling can be experienced, the eyelids tend to swell, the eyes water more than usual and those with hay-fever commonly describe excessive tearing.
The cause of the allergic reaction could be from one of the following sources:
Seasonal conjunctivitis – this tends to occur during the hay-fever season and at the same time each year and is due to pollens. Grass pollens tend to cause symptoms in the UK in early summer from April to July, and tree pollens may trigger symptoms at different times dependent on the tree species. There may be other pollen's or moulds that also affect people later in the summer. The duration of symptoms will vary in line with pollen counts, with some customers being allergic to more than one pollen type. This form of conjunctivitis often occurs at the same time as other hay-fever symptoms.
Perennial conjunctivitis – perennial means that the symptoms persist throughout the year and can be due to allergens present all year round such as pet hair or house dust mites. Dust mites are tiny microscopic organisms that live off human skin scales; they are often found in carpets, beds, mattresses and soft furnishings making symptoms worse each morning when waking up. An individual will usually have perennial allergic rhinitis also which causes sneezing and a runny nose.
Giant papillary conjunctivitis – this is commonly associated with the use of contact lenses and can arise as a direct consequence of the lens itself causing irritation, although the exact cause of inflammation is often unclear. It can also occur following eye surgery. It is now not as common due to the widespread use of disposable contact lenses, however any customer who wears contact lenses and complains of irritation, discomfort or inflammation should be referred to their contact lens practitioner, optician or optometrist.
Contact dermatoconjunctivitis – this occurs when an irritant comes into direct contact with the eye such as chemicals used in swimming pools or people can develop an allergic reaction to items such as cosmetics, contact lens solution or eye drops. It is characterised by the symptoms of conjunctivitis alongside allergic dermatitis of the eyelids and will usually clear up as soon as the cause is removed.