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.