The accommodation reflex of the eye is the involuntary response your eye has when it switches from an object far away to one that is closer to you. This lesson discusses what this reflex is and why it’s important.
What Is Accommodation Reflex?
Let’s say you are eating a salad for lunch. As you lift the fork up to your mouth to eat a bite, you happen to blink. You have just performed two different kinds of actions, voluntary and involuntary.
The body’s motor system has voluntary actions (those you choose to do, like raising a fork to your mouth to eat) and involuntary actions (those that happen automatically, like breathing or blinking). Within this set of involuntary actions are reflexes, or automatic responses to some type of stimulus.
Now let’s say that after you take your bite, you look out the window. Your eyes go from focusing on the fork to a distant building outside. Your eyes adjust involuntarily so that you can focus on both objects even though they are at different distances.
The accommodation reflex of the eye is a response that automatically occurs when you switch focus from an object that’s far away to one that’s closer. This response enables you to switch between objects and still maintain focus (meaning neither object appears blurry when you’re looking at it).
How It Works
The muscles that control the shape of the lens are called ciliary muscles. When you’re looking at an object far from you, like the building out your window, the ciliary muscles around your eye are relaxed, the lens is stretched out, and the fibers around the eye are tight. This maximizes your ability to see objects at a distance clearly – called negative accommodation.
In contrast, when you’re looking at an object close to you, like the fork full of salad during lunch, the ciliary muscles around your eye tighten, the lens becomes rounder in shape, and the fibers around the lens are relaxed. This maximizes your ability to see objects close to you in focus – called positive accommodation.
This ability of your eye to automatically switch from one condition to the other is referred to as the accommodation reflex. This reflex ultimately affects the way light enters the eye. Objects farther away require less refraction than objects that are closer to you, so the eye automatically adjusts its shape accordingly. When the lens is rounded in shape, it has more refractive power. A trick to remembering this: objects far away require less refraction, so you experience negative accommodation, whereas objects close to you require more refraction, so you experience positive accommodation.
Typically, both eyes work in tandem, so vision isn’t disrupted; however, it is possible for the eyes to adjust separately. This is called absolute accommodation. For example, if one eye is closed, the open one will still adjust as necessary. If damage to the eye prevents this reflex from taking place, the field of vision will be blurry when switching between different objects.
There is a quick test you and a friend can do to test your accommodation reflex. Have your friend stand directly in front of you. Move your finger from side to side and up and down, instructing them to follow the movement with their eyes but not moving their head. Then move your finger right to the tip of their nose and watch how their pupils (the black dots in the center of the eyes) change shape, constricting to adjust to the new distance of the object (they will also look cross-eyed as they try to follow the finger). This change is the accommodation reflex occurring. Then you can switch and have them try it on you.
I think we’ve learned a little bit more about how fascinating the human body is. Our bodies are constantly responding to stimuli around us, often without us even being aware of it. One involuntary reflex our eyes make is called the accommodation reflex. This reflex enables us to switch focus between objects far away and objects closer to us.
The ciliary muscles that control the lens tighten and relax, and our lens will actually change shape to help refract light, enabling us to see. A lens that is more round in shape has more refracting power, meaning it allows you to focus on objects close to you (called positive accommodation); whereas, a lens that is stretched out allows you to focus on objects farther away (called negative accommodation). Both eyes do this in tandem, but they can do it independently if one eye is closed, called absolute accommodation. If our eyes didn’t make this automatic adjustment, our vision would be blurry.