Evaluation of histamine-induced conjunctival oedema in guinea pigs by means of image analysis

Background Conjunctival oedema is commonly observed in patients with allergic conjunctivitis and can be induced by histamine. In animal models of allergic conjunctivitis, conjunctival oedema is generally evaluated by measuring the extravasation of Evans blue dye into the conjunctiva. A limitation of this method is that it only allows evaluation at a single time point. The aim of the present study was to investigate kinetic changes in histamine-nduced bulbar oedema. Methods Evans blue dye was injected intravenously into male guinea pigs. Histamine eye-drops were administered 30 min later. One group of animals received levocabastine (an antihistamine) eye-drops 10 min before histamine challenge. A digital camera was used to obtain images of the bulbar conjunctiva at 1 min intervals until 30 min after histamine challenge. The conjunctivas were then harvested, and the concentration of Evans blue was measured. The ImageJ software was used to analyse the images by counting the number of absolute pixel values. Results The degree of conjunctival oedema increased progressively until 20 min after histamine challenge and then stabilised. Correspondingly, the number of absolute pixel values increased significantly until 5 min after histamine challenge, then increased gradually until the 20 min time point and finally plateaued. Pixel values were significantly lower in animals treated with levocabastine than in control animals. A significant correlation was observed between the pixel values of the conjunctival images and the concentration of Evans blue in the conjunctiva. Conclusions This is the first study to have quantitatively evaluated kinetic changes in histamine-induced bulbar oedema by means of image analysis.