Kinetics of ocular symptoms after exposure in the EEC
Time of onset and intensity of each symptom in the seven patients
following step 2 are reported in Figure 2. During all six exposures,
redness was the first symptom to appear, with a mean time of
16 ± 6.8 min, reaching maximum
intensity in 55 ± 20.2 minutes. Tearing and itching appeared second,
with a mean of 25 ± 3.4 min and 35 ± 16.9 min, respectively. Thus,
reproducibility of redness, tearing, and itching occurred in 100% of
individuals completing all six exposures. Chemosis was observed in Expo
4, 5, and 6 in six patients with a mean time of 28 ± 16.3 min after the
patient entered the EEC. The maximum TOSS was 9 and occurred in three
patients. No severe conjunctivitis was induced during exposure. All
observed ocular reactions were considered mild and were controlled with
a topical rescue treatment.
Nine patients (60% of the patients included) had a positive nasal
response on the first two exposures (Expo 1 and Expo 2), confirmed by a
positive TNSS ≥ 6 with a mean TNSS of 8.17 ± 1.47. This mean score was
reached in 61 min. Five out of 16 patients developed an early asthma
response during allergen exposure, with a mean decrease in
FEV1 of 21.9% in 65 min on average (min 30 minutes; max
100 min). All early asthma reactions were treated by inhaled
short-acting beta-2 agonist. Among patients presenting an early
asthmatic response in the EEC, only one had a late asthmatic response,
which was treated by oral corticosteroids and inhaled beta 2 agonist. No
prolonged observation period was needed. No severe asthma reactions were
observed during the study. No patients used the emergency kit provided
during the test.
Discussion
Different clinical studies have assessed the effect of allergen exposure
in EECs on rhinoconjunctivitis, but very few have focused on allergic
conjunctivitis. The time course of allergic signs and symptoms differed
between the CAC and EEC sessions. In a previous study evaluating 13
patients with a history of ragweed allergy who underwent CAC and EEC
exposure, the response time was different but the intensity of the
maximal response was similar.19 In the present study,
when comparing ocular symptoms of patients exposed to birch pollen in
the EEC compared to the reference CAC, we achieved the primary endpoint
of 50% positivity in 16 patients during the first exposure. The
following day, 75% of patients had a positive response. Furthermore,
the airborne concentration of birch pollen inducing the response was
very low, reaching a mean 60 ng/m3 of airborne Bet v 1
in the ALYATEC EEC.
The main inclusion criteria were a positive CAC, which is considered the
gold standard for objectively evaluating conjunctival reactivity to a
specific allergen at the mucosal surface. We chose a TOSS ≥ 5 during the
CAC as the threshold for a positive conjunctival response according to
European guidelines.11 This threshold has been
demonstrated to allow a specificity and sensitivity of 100% and 90%,
respectively, in mite allergic conjunctivitis.20 We
used the same clinical positivity criteria for EEC exposure. After EEC
exposure, the mean TOSS was not significantly different after CAC and
EEC exposure. The maximal TOSS was 9 in both the CAC and EEC. In
contrast, the time necessary to obtain a positive response was
significantly longer in the EEC than the CAC. To the best of our
knowledge, studies have not reported time between natural exposure and
the occurrence of ocular symptoms. Patients do not describe significant
conjunctivitis symptoms in day-to-day life within 30 minutes after being
exposed to birch pollen. Consequently, the duration to obtain a
significant clinical response to birch pollen in the EEC appeared to be
closer to natural exposure than after a CAC. Moreover, the quantity of
birch allergen inducing a positive conjunctival response was
dramatically different between these two exposures. During CAC, positive
responses were obtained with a mean cumulative dose of 980 ng of Bet v
1, whereas it was calculated to be 0.07 ng with the EEC. According to
the HIALINE study,21 the amount of Bet v 1 per pollen
grain can vary from 3.2 to 32 pg. Therefore, 980 ng of Bet v 1
corresponds to approximately 30,000 to 300,000 pollen grains. In the
EEC, the amount of Bet v 1 inducing a positive response corresponds to 2
to 21 pollen grains. The literature assumed that patients allergic to
pollen had symptoms as soon as the pollen grain threshold reached 22 to
30 grains/m3 for grass pollens22 and
70 grains/m3 for birch pollen.9 Even
though the manner of exposure is different, the results of natural and
EEC exposure are similar, whereas challenge of the ocular surface
through CAC exposes the individual to a much greater amount of allergen.
Moreover, exposure in the CAC is performed through diluted allergen in
physiological serum instilled onto the ocular surface, whereas in EECs
the allergens are nebulized in the air, which is a modality closer to
naturel exposure. This triangular comparison enhances the clinical
significance of the EEC challenge.
The positive conjunctival response in three-fourths of patients during
the second exposure in the EEC suggests that a priming effect occurs.
However, we did not observe a difference in the severity of the TOSS
between Expo 1 and Expo 2. Jacobs et al.22 suggested
that no priming effect exists when exposures are performed on 2
consecutive days and that the conjunctivitis reaction that occurred on
the second day may be a simple manifestation of a late phase reaction
captured within a 24-hour period after exposure.23Prior studies suggested that two, or even three, priming visits may be
required to obtain high levels of
symptoms.24-25However, the priming effect leads to
rapid onset of symptoms and signs rather than a greater allergic
response.26
We observed reproducibility of ocular response frequency during all
exposures. Reproducibility was assumed when challenging the ocular
surface in the EEC for the time and the quantity of allergen inducing a
clinical reaction.
Symptoms and signs induced in the EEC were comparable to those induced
by CAC. Ocular redness was the first sign to appear in the EEC and
lasted until the end of exposure. Its reproducibility was consistent
across six allergen exposures. Our findings were in line with Jacobs et
al.,22 who investigated phenotypes of allergic
conjunctivitis. Other clinical symptoms of conjunctivitis, such as
tearing and itching, occur rapidly. The kinetics of the appearance of
the three main signs and symptoms is the same as in real life. Chemosis
has also been associated with allergic conjunctivitis. When mild or
moderate, chemosis requires slit-lamp examination, which was used in
both CAC and EEC exposure. Chemosis was not observed in our patients who
submitted to CAC but was mild during EEC sessions. We observed good
reproducibility of the kinetics of conjunctival symptoms: ocular
redness, tearing, and ocular itching followed by chemosis. The latter
can be considered a sign of severity, occurring when conjunctivitis was
clearly present. The mild intensity of the chemosis when it was observed
enhances the safety aspect of EEC exposure. The absence of loco-regional
symptoms, such as rhinitis, is another argument that reinforces the
safety of the technique. Nevertheless, in five patients, we observed
mild asthma symptoms during EEC exposure. This makes it possible to
enroll mild asthma patients with allergic conjunctivitis when
investigating ocular allergy. A control of spirometry parameters before,
during, and after EEC challenge remains necessary.
The limitation of this study is the small number of patients. However,
we could demonstrate the clinical validity and good reproducibility of
the method. The estimation of the amount of allergen deposition on the
ocular surface could be discussed, but the calculation took into account
the different physiological factors involved in the pathophysiology of
conjunctivitis.