If you look away from this book and focus your eyes on a distant object, the eye muscles _________ and the lenses _________ to focus images on the retinas.
a. Relax . . . Flatten
b. Relax . . . Become more rounded
c. Contract . . . Flatten
d. Contract . . . Become more rounded

Verified step by step guidance

1. Understand the anatomy of the eye: The lens of the eye changes shape to focus light on the retina, a process called accommodation. The ciliary muscles control the shape of the lens.
2. Recognize the relationship between the ciliary muscles and the lens: When focusing on distant objects, the ciliary muscles relax, causing the lens to flatten. This allows light rays from distant objects to be properly focused on the retina.
3. Contrast this with focusing on nearby objects: When focusing on close objects, the ciliary muscles contract, making the lens more rounded to bend light rays more sharply.
4. Analyze the options provided: The correct answer must describe the relaxation of the ciliary muscles and the flattening of the lens when focusing on distant objects.
5. Select the correct answer based on the explanation: The correct choice is 'a. relax . . . flatten,' as this matches the physiological process of focusing on distant objects.

Key Concepts

Accommodation

Accommodation is the process by which the eye adjusts its focus on objects at varying distances. When focusing on distant objects, the ciliary muscles relax, allowing the lens to flatten, which is essential for clear vision. This mechanism ensures that light rays from distant objects are properly focused onto the retina.

Ciliary Muscles

Ciliary muscles are small muscles located around the lens of the eye that control its shape. When these muscles contract, they cause the lens to become more rounded for near vision. Conversely, when they relax, the lens flattens, which is necessary for focusing on distant objects.

Lens Shape and Light Refraction

The shape of the lens affects how light is refracted, or bent, as it enters the eye. A rounded lens increases the refractive power, allowing for better focus on nearby objects, while a flattened lens decreases refractive power, which is optimal for distant vision. This adjustment is crucial for maintaining clear vision across different distances.