Image Analyses of the Kinetic Changes of Conjunctival Hyperemia in Histamine-Induced Conjunctivitis in Guinea Pigs

Abstract

Conjunctival hyperemia is the most common finding in patients with allergic conjunctivitis. Histamine is a typical chemical mediator involved in allergic conjunctivitis and induces hyperemia. Here, we investigated the kinetic changes in bulbar hyperemia induced by histamine in eyedrops. Male guinea pigs were challenged with histamine in eyedrops. Bulbar conjunctival images were taken every 10 seconds by a digital camera up to 8 minutes after histamine challenge, and the software program ImageJ was used to analyze the images. Images were binarized, and a region of interest unobscured by corneal and scleral vessels was selected as the evaluation area. Evaluations were carried out before and after histamine challenge by counting the numbers of absolute pixel values, percent changes in pixels, or the fractal dimension in acquired images. After histamine challenge, the conjunctival vessel area continued to increase up to 5 minutes before stabilizing. The various parameters used to evaluate the images (numbers of absolute pixel values, percent change in pixels, or the fractal dimensions) markedly increased 1 minute after histamine challenge, gradually increased up to 5 minutes, and then gradually decreased before reaching a level that remained significantly higher than that before histamine challenge. This is the first report to quantitatively evaluate bulbar hyperemia induced by histamine using image analysis. The development of software that can automatically yield meaningful values for hyperemia from hyperemia images will be a useful objective tool in clinical trials for evaluation of drug effects in animal models and in humans.