Night blindness is caused by

Appeared in: RUHS, Jaipur, M.Sc Nursing Entrance Exam-2024

Explanation

The retina has two main photoreceptors: rods and cones.
Rods are responsible for vision in low-light conditions (scotopic vision) and peripheral vision.
Night blindness (nyctalopia) is the inability to see clearly in dim light.
Therefore, diseases that cause the degeneration or dysfunction (dystrophy) of rod cells, such as Retinitis Pigmentosa, directly result in night blindness.

Option A: This is a vascular condition involving a blockage of the main retinal vein. It causes a sudden, painless, and often severe loss of vision, not isolated night blindness.
Option C: Cones are responsible for color vision and sharp central vision in bright light. Dystrophy of cones leads to symptoms like color blindness and decreased visual acuity, not night blindness.
Option D: This is a physical separation of the retina from its underlying supportive tissue. It presents acutely with flashes of light (photopsia), floaters, and a progressive shadow or 'curtain' in the visual field.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Pathophysiology of night blindness as background academic context rather than a clinical decision trigger.
A patient's complaint of difficulty seeing at night or navigating in dark rooms is a key symptom (nyctalopia) that should prompt a nursing assessment and referral for ophthalmologic evaluation.
Night blindness can be an early indicator of underlying conditions such as Vitamin A deficiency or genetic disorders like Retinitis Pigmentosa, making early detection crucial.
What if? If a patient reported a loss of color vision and difficulty reading fine print, the nurse's suspicion should shift towards a problem with the retinal cones or the macula, rather than a rod dystrophy.

How to Approach the Question

First, identify the key term in the question stem, which is 'Night blindness'.
Recall the basic physiology of the eye, specifically the two types of photoreceptor cells in the retina: rods and cones.
Differentiate the primary functions of these cells: Rods are for night/dim-light vision, while cones are for color/bright-light vision.
Logically connect the symptom 'night blindness' to the dysfunction of the cells responsible for night vision, which are the rods.
Review the other options to confirm they describe different ocular pathologies with distinct symptoms (e.g., vascular occlusion, retinal separation) to solidify the correct choice.

Concept Tested & Keywords

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E6 Medicine Harrison 22e Part 1 p. 272-274

E6 Pathology-Textbook of PATHOLOGYHarsh Mohan Part 2 (215-514) p. 82-84

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