Light rays entering the eye is controlled by:

Appeared in: OSSSC Nursing Officer-2023

Explanation

The iris is the pigmented, muscular part of the eye that controls the size of the pupil.
Its main function is to regulate the amount of light reaching the retina.
In bright light, the iris constricts the pupil (miosis) to limit light entry.
In dim light, the iris dilates the pupil (mydriasis) to allow more light to enter.

Option A: The pupil is a passive opening, not a control structure. Its size is determined by the action of the iris muscles.
Option C: The cornea's primary function is refraction, bending light to focus it. It provides about two-thirds of the eye's total refractive power but does not regulate the quantity of light.
Option D: The lens provides adjustable focus for objects at different distances (accommodation) by changing its shape. It does not control the amount of light entering the eye.

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, specifically the mechanism of light regulation as background academic context rather than a clinical decision trigger.
A key nursing assessment is checking pupillary response to light (part of PERRLA: Pupils Equal, Round, Reactive to Light and Accommodation). This tests the function of the iris and the associated cranial nerves (II and III).
Abnormal pupillary responses can indicate neurological damage, drug influence (e.g., opioids cause pinpoint pupils), or increased intracranial pressure.
What if? If a patient has a fixed, dilated pupil after a head injury, it is a critical sign. This indicates pressure on the oculomotor nerve (CN III), which controls the iris sphincter muscle. This is a neurosurgical emergency requiring immediate intervention.

How to Approach the Question

First, identify the core question: which part of the eye controls the amount of incoming light.
Recall the basic function of the main anterior structures of the eye.
Analyze the options: Pupil is the hole, Cornea and Lens are for focusing, and Iris is the colored muscle.
Differentiate between structures that focus light (Cornea, Lens) and the structure that regulates the amount of light.
Conclude that the iris, by changing the size of the pupil, is the structure that actively controls light entry.

Concept Tested & Keywords

Concept Tested: Anatomy and physiology of the eye, specifically the mechanism of light regulation.
Stem keywords: Light rays, eye, controlled by
Lead-in keywords: controlled by

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

E6 Pharmacology Nursing Lilley 11e Part 3 p. 256-258

Practise the full OSSSC Nursing Officer-2023

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