Which of the following parts of an eye alters the size of the pupil to regulate the amount of light entering the eye?

Appeared in: AIIMS Patna NO - 2020

Explanation

The iris is the pigmented, muscular part of the eye that surrounds the pupil.
It contains two muscles: the sphincter pupillae (for constriction) and the dilator pupillae (for dilation).
These muscles contract and relax in response to the intensity of light, thereby controlling the size of the pupil.
This function regulates the amount of light that reaches the retina, similar to the aperture of a camera.

Option A: The lens is responsible for focusing light onto the retina by changing its shape (accommodation). It does not control the size of the pupil.
Option B: The cornea is the transparent front part of the eye that covers the iris and pupil. Its primary function is to refract, or bend, light. It has a fixed shape and cannot alter the pupil size.
Option C: The retina is the light-sensitive tissue at the back of the eye. It detects light and converts it into electrical signals sent to the brain. It initiates the pupillary light reflex but does not physically alter the pupil's size.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Anatomy and Physiology of the Eye as background academic context rather than a clinical decision trigger.
Assessing the pupillary light reflex is a critical nursing assessment. The acronym PERRLA (Pupils Equal, Round, Reactive to Light and Accommodation) is used to document normal findings.
Abnormal pupillary responses can indicate serious medical conditions, such as neurological damage (e.g., from a stroke or head injury), optic nerve damage, or the effects of certain drugs (e.g., opioids cause pinpoint pupils, while stimulants can cause dilation).
What if? - If a patient presents with one pupil significantly larger than the other (anisocoria) after a head trauma, it could signify increased intracranial pressure compressing the oculomotor nerve (cranial nerve III), which is a medical emergency requiring immediate intervention.

How to Approach the Question

First, identify the key function described in the question: 'alters the size of the pupil to regulate... light'.
Next, review the options provided, which are all parts of the eye.
Recall the primary function of each part. The lens focuses, the cornea refracts, the retina detects light, and the iris controls the pupil.
Match the function from the question to the correct anatomical part.
Eliminate the other options by confirming their primary roles are different from controlling pupil size.

Concept Tested & Keywords

Concept Tested: Anatomy and Physiology of the Eye
Stem keywords: parts of an eye, alters the size of the pupil, regulate the amount of light
Lead-in keywords: Which

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E6 Physiology Guyton 4SAE Part 3 pp. 141-143, 168-170

E6 Nursing Brunner Adult Health 3SA Vol 2 Part 1 p. 84-86

Practise the full AIIMS Patna NO - 2020

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