Visual purple is found in?

HPSSC Staff Nurse - 2021

Applied Physiology

Easy

Appeared in: HPSSC Staff Nurse - 2021

Explanation

Visual purple, also known as rhodopsin, is the specific photopigment found in the rod cells of the retina.
Rods are photoreceptor cells responsible for vision in low-light conditions (scotopic vision) and do not perceive color.
Rhodopsin is extremely sensitive to light, allowing it to detect even single photons, which is essential for night vision.
The structure of a rod cell includes an outer segment containing thousands of discs where rhodopsin molecules are embedded.

Option A: The cornea is the transparent, avascular outer layer of the eye that refracts light. It contains no photoreceptors or photopigments like rhodopsin.
Option B: Cones are photoreceptor cells responsible for color vision (photopic vision) in bright light. They contain different photopigments called photopsins (or iodopsins), not rhodopsin.
Option D: While rods are located within the retina, this option is too general. The retina is the entire light-sensitive layer containing both rods and cones. The question asks for the specific location of visual purple, which is exclusively in the rods.

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 location of photopigments as background academic context rather than a clinical decision trigger.
Understanding the role of rhodopsin is crucial for diagnosing conditions like night blindness (nyctalopia), which is often an early sign of Vitamin A deficiency, as rhodopsin cannot be regenerated without an adequate supply of Vitamin A (retinal).
Nurses should assess for dietary deficiencies in patients reporting difficulty with night vision or driving at night, and can provide education on Vitamin A-rich foods (e.g., carrots, sweet potatoes, leafy greens).
What if? If a patient has a genetic defect in the gene for rhodopsin, they may suffer from retinitis pigmentosa, a progressive degenerative disease of the retina leading to severe vision loss, which typically begins with night blindness.

How to Approach the Question

First, identify the key term in the question: 'Visual purple'. Recall or deduce that this is another name for the photopigment rhodopsin.
Next, consider the function associated with rhodopsin, which is vision in dim light (night vision).
Evaluate the options based on the anatomy of the eye. The retina is the light-sensing layer, while the cornea is the transparent outer covering.
Differentiate between the two types of photoreceptors in the retina: rods and cones. Rods are for dim light, and cones are for color/bright light.
Since rhodopsin is essential for dim light vision, it must be located in the rods. This makes 'Rods' a more specific and therefore more correct answer than the general term 'Retina'.

Concept Tested & Keywords

Concept Tested: Anatomy and physiology of the eye, specifically the location of photopigments.
Stem keywords: Visual purple
Lead-in keywords: is found in
Negative lead-in flag: false

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