A 25-year-old student with 20/20 vision looks up from his book to view his girlfriend sitting on the other side of the room. Which of the following is most likely to occur when the student changes his view from his book to his girlfriend?
**Core Concept**
The human eye, specifically the lens, undergoes a change in shape when focusing on near or far objects. This process is known as accommodation, which involves the contraction and relaxation of the ciliary muscles to adjust the lens's curvature.
**Why the Correct Answer is Right**
When the student looks up from his book to view his girlfriend, his eye needs to focus on a distant object. To achieve this, the ciliary muscles relax, allowing the tension on the zonular fibers to increase. As a result, the lens becomes thinner due to the decrease in pressure on the lens capsule, enabling the student to focus on the more distant object. This process allows the student to see his girlfriend clearly without any difficulty.
**Why Each Wrong Option is Incorrect**
**Option A:** Thicker lens, contraction of ciliary muscle - This option is incorrect because a thicker lens is associated with near vision, and contraction of the ciliary muscles is involved in increasing the lens's curvature for near vision.
**Option B:** Thicker lens, relaxation of ciliary muscle - This option is incorrect because a thicker lens is associated with near vision, and relaxation of the ciliary muscles is involved in decreasing the lens's curvature for far vision.
**Option C:** Thinner lens, contraction of ciliary muscle - This option is incorrect because contraction of the ciliary muscles is involved in increasing the lens's curvature for near vision, which results in a thicker lens.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that the lens's shape changes in response to the tension on the zonular fibers, which are controlled by the ciliary muscles. This dynamic relationship between the lens and the ciliary muscles enables the eye to focus on both near and far objects.
**✓ Correct Answer: D. Thinner lens, relaxation of ciliary muscle. Relaxation of the ciliary muscles results in a thinner lens, allowing the student to focus on distant objects.**