The majority of secondary eye symptoms can be traced back to the aggression of the nasal mucosa:

• Mast cells (containing histamine) are predominantly present in areas with good blood flow (i.e. nasal mucosa), once in contact with pollen the histamine is released and causes the allergic reaction. The histamine is distributed by the blood flow to neighbouring areas (i.e. eyes), and cause symptoms there as well. In the eye itself only the conjunctiva contains mast cells, but much fewer than in the nasal mucosa, and the surface area is also considerably smaller.

• The conjunctiva will not be exposed to allergens directly, so the symptoms that origin from the conjunctiva’s mast cells will be less severe than the ones caused in the nasal mucosa. The mast cells are also present in the conjunctiva underneath the eyelids. Although the conjunctiva is not exposed directly to allergens in the air, allergens touching the exposed cornea may be trapped by tears and could be distributed to the conjunctiva.

• As there are fewer mast cells in the conjunctiva than in the nasal mucosa, there will be less symptoms, even if challenged with same quantum of pollen. Furthermore, the eyes are constantly moistened/ washed by the tears. As such, most of the allergens are being washed down before they can reach the conjunctiva.