Allergies affect over 20% of the general
population and are on the rise in many developed countries. The
specific reason for the increasing prevalence of allergies has
not been determined; some believe it is due to the effects of
pollution in urban areas while others consider that modern
lifestyles don't allow for enough childhood exposure to
allergens to become acclimated to them.
Ocular allergies are often
accompanied by allergic rhinitis (nasal
symptoms). This is partly due to the fact
that the eyes and nose are so closely
connected by the tear ducts; substances that
enter the eye can then flow downward into
the nose. Symptoms include:
When exposed to these allergens, the
response in the eye is nearly immediate:
First, itching sets in and can become persistent
and extremely bothersome if exposure to the allergen is
Shortly after itching, redness of the eyes
follows and can last somewhat longer, as the blood
vessels of the eye are slower to recover.
The swelling of the eyes and eyelids comes to its peak
later than the itching, as swelling is also caused by
the blood vessels letting fluids out into the tissue
around them. Swelling is the sign of ocular allergies
slowest to disappear, due to the time it takes for
the displaced fluid to be removed.
The itching can be considered the most uncomfortable
symptom, whereas the swelling and redness are most
bothersome in terms of appearance.