Which of the following correctly describes the changes that take place during dark adaptation? A) Retinol is converted to vitamin D B) Dilated pupils C) Eyes sensitive to light D) Functional rhodopsin is formed (Opsin binds with 11-cis-retinal)

Appeared in: INI-CET EXAM -2026

Explanation

Dark adaptation is the process by which the eye increases its sensitivity to low light, primarily involving the rod cells.
The fundamental mechanism is the regeneration of rhodopsin, the light-sensitive pigment essential for scotopic (dim light) vision.
In the dark, the protein opsin recombines with 11-cis-retinal (an active form of Vitamin A) to form functional rhodopsin.
This biochemical process is slower than pupil dilation but is responsible for the significant increase in light sensitivity over time.
Therefore, the formation of functional rhodopsin is the most accurate and central description of the change occurring during dark adaptation.

Option A: This option is incorrect because it includes statement A, which is factually false. Retinol is Vitamin A and is not converted into Vitamin D in the body.
Option B: This option is incomplete. While pupil dilation (Statement B) is a part of the response to darkness, it omits the primary and most significant biochemical change, which is the regeneration of rhodopsin (Statement D).
Option C: Although statements B, C, and D are all related to dark adaptation, this option is not the 'best' answer in a physiological context. Statement C (increased sensitivity) is the result, not the mechanism. Statement B (pupil dilation) is a secondary physical adjustment. Exam questions on this topic typically target the core biochemical mechanism, which is statement D.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Physiology of Vision: Dark Adaptation as background academic context rather than a clinical decision trigger.
A deficiency in Vitamin A impairs the body's ability to produce 11-cis-retinal, which is necessary for rhodopsin regeneration. This leads to a condition called nyctalopia, or night blindness.
Nurses play a key role in identifying patients at risk for Vitamin A deficiency (e.g., those with malnutrition, malabsorption syndromes, or liver disease) and providing dietary counseling on sources like carrots, sweet potatoes, and leafy green vegetables.
What if? If a patient has chronic liver cirrhosis, their ability to store and mobilize Vitamin A is severely impaired. In this case, they would be at high risk for night blindness, and a nurse would need to monitor for visual complaints and collaborate with the physician on potential supplementation, which may need to be administered parenterally if oral absorption is poor.

How to Approach the Question

First, understand the question is asking for the changes that occur during the process of dark adaptation.
Evaluate each individual statement (A, B, C, D) for its scientific accuracy and its role in the process.
Identify Statement A as factually incorrect (Retinol is Vitamin A, not converted to Vitamin D). This immediately eliminates any option containing A.
Analyze the remaining statements. Recognize that pupil dilation (B) is a rapid physical adjustment, increased sensitivity (C) is the functional outcome, and rhodopsin formation (D) is the core biochemical mechanism.
In physiology questions, distinguish between contributing factors, primary mechanisms, and results. The primary mechanism is often considered the 'best' answer.
Conclude that the regeneration of rhodopsin (D) is the fundamental process responsible for the significant increase in sensitivity during dark adaptation, making 'D only' the most precise answer.

Concept Tested & Keywords

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E6 Physiology Guyton 4SAE Part 3 pp. 154-156, 152-154

E6 Textbook of Biochemistry for medical StudentsDM Vasudevan Part 2 — Subpart A (pp 1-239 of 478) p. 119-121

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Attempt every question from this paper in a timed mock, then review the full solution for each one.