Question

multiple choice 2 points
adjustment to close-range vision involves all of the following except ______.
ciliary muscle activity
activity of the extrinsic eye muscles
light adaptation
constriction of the pupil
change in the curvature of the lens

Explanation:

Analyze the components of the near response

Adjustment to close-range vision (the near response) requires focusing light from a nearby object onto the retina. This process involves three coordinated physiological adjustments:

1. Accommodation of the lens: The ciliary muscle contracts, which relaxes the suspensory ligaments (zonules) and allows the elastic lens to become more spherical (increasing its curvature and refractive power).
2. Constriction of the pupil: The pupillary sphincter muscle contracts to reduce the pupil size, blocking peripheral light rays and increasing the depth of focus.
3. Convergence of the eyes: The extrinsic eye muscles (specifically the medial recti) contract to direct the visual axes of both eyes toward the nearby object.

Evaluate the options against the near response

Using our understanding of Eye Anatomy, let's examine each choice:

• ciliary muscle activity: Actively involved in accommodation to increase lens curvature.
• activity of the extrinsic eye muscles: Actively involved in convergence to align both eyes on the close object.
• light adaptation: This is a chemical and neural adjustment of the retina to changes in ambient light intensity, not a mechanical adjustment for focusing on close-range objects.
• constriction of the pupil: Actively involved in screening out peripheral light rays to sharpen the image.
• change in the curvature of the lens: The direct physical result of ciliary muscle contraction during accommodation.

Therefore, light adaptation is the only process listed that is not part of the adjustment to close-range vision.

Answer:

• (A) ciliary muscle activity
• (B) activity of the extrinsic eye muscles
• (C) light adaptation (Correct answer)
• (D) constriction of the pupil
• (E) change in the curvature of the lens