Background

Accommodation is the process of adjusting the lens of the eye so that you can see both near and far objects clearly. We discussed this process in Chapter 3 in terms of focusing on near and far objects. To focus on a more distant object, we relax the ciliary muscles that contract the lens, and to focus on an object close to our eyes, we contract the ciliary muscles. These contractions and relaxations take place automatically as we change our focus. However, we can sense these muscle movements. And it is the sensing of these movements that gives us information about depth. However, the narrowness of the pupil during the day makes accommodation imprecise in day vision, and the poor acuity at night makes accommodation imprecise then as well.

Use this activity to explore how accommodation helps us keep objects at different distances in focus and as a result might provide information about the depth of an object.

Instructions

Full Screen Mode

To see the illustration in full screen, which is recommended, press the Full Screen button, which appears at the top of the page.

Illustration Tab

Settings

Below is a list of the ways that you can alter the illustration. The settings include the following:

Light Position: Moves the light closer or farther from the eye.
Turn Light On: Pressing this button will start the light. Pressing the button again removes the light.
Eye Accommodates: When checked the lens of the eye accommodates, or adjusts size to keep the light in focus. When not selected the eye does not accommodate and only one distance from the eye will be in focus.

Reset

Pressing this button restores the settings to their default values.