虹膜能控制適量的光線進入眼球。本資源的動畫顯示虹膜透過調節肌肉的收縮和放鬆而令瞳孔在不同的光強度下改變其大小，令適量的光線進入眼球。
學習重點：
學生能認識虹膜及瞳孔的功用。
教學建議：
教師可先讓學生觀看資源庫內有關瞳孔大小變化的錄像片段。透過有關錄像，學生能認識到瞳孔的大小會隨著光強度的變化而改變。 教師隨後可利用本動畫向學生解釋在不同光度下虹膜內的肌肉如何調節其收縮和放鬆而改變瞳孔的大小。 對於能力較高的學生，教師可請他們嘗試解釋控制瞳孔大小對保護眼睛的重要性。使用說明：
本資源需配合 Adobe Flash Player 10 使用。
下載Adobe Flash Player 10Description:
Iris can adjust the size of pupil for allowing appropriate amount of light to enter the eye. This animation illustrates the action of muscles in the iris in altering the size of pupil at different light condition and allowing appropriate amount of light to enter the eye.
Learning Objectives:
Students should be able to recognize the functions of pupil and iris.
Teaching Suggestions:
Teachers may allow students to watch the video "change in size of pupil" first (a resource in the science depository). Students should be able to recognize the change in size of pupil at different light intensities. After that, teachers may use the animation of this resource to explain the action of muscles of iris in changing the size of pupil to students. For students of higher ability, teachers may ask students to explain the significance of changing the size of pupil in eye protection.User Tips:
Adobe Flash Player 10 is required to play this resource.
Download Adobe Flash Player 10 
