Personal studies in allergic eye diseases reviewed in this paper indic
ate that: 1. An increased number and an abnormal distribution of eosin
ophils is present in conjunctival biopsies of patients with vernal ker
atoconjunctivitis (VKC). 2. Eosinophil and eosinophil products, such a
s ECP, are also increased in tears of VKC patients and, in hay fever c
onjunctivitis, accumulate during the late-phase of allergic reaction f
ollowing specific allergen challenge. 3. Circulating eosinophils of VK
C patients show a typical activation phenotypic profile which is assoc
iated with increased serum level of eosinophil cationic protein and eo
sinophil-derived neurotoxin/protein X. A clinical study of the modulat
ory effect of cetirizine on the early and late phase of the allergic r
eaction as well as on the eosinophil activation and tissue recruitment
following conjunctival allergen challenge is reported as an example o
f the need to evaluate eosinophil functions when investigating anti-al
lergic drugs. Drugs modulating various aspects of eosinophil function
could play a primary role in the treatment of allergic eye disease.