Which type of lens is used to correct myopia (nearsightedness)?

KGMU 2023

Applied Physiology

Easy

Appeared in: KGMU 2023

Explanation

Myopia, or nearsightedness, is a refractive error where the eye focuses images in front of the retina instead of directly on it.
This condition causes distant objects to appear blurry because the eyeball may be too long or the eye's lens system too powerful.
A concave lens is a diverging lens, which means it spreads out light rays before they reach the eye's lens.
This divergence effectively moves the focal point backward, allowing it to land correctly on the retina and thereby clarifying distant vision.

Option B: Convex lenses are converging lenses that increase the eye's refractive power. This would worsen myopia by causing light to focus even further in front of the retina.
Option C: Cylindrical lenses correct refractive power in only one specific plane (meridian) and do not address the overall spherical focusing error seen in simple myopia.
Option D: While a person with myopia can also have bifocals, the bifocal aspect itself addresses a different issue. The fundamental correction for their distance vision (myopia) within that lens is still a concave power.

Visual 1: Diagram - A comparison showing light rays focusing in a normal (emmetropic) eye, in front of the retina in a myopic eye, and behind the retina in a hyperopic eye.
Visual 2: Diagram - An illustration of how a concave (diverging) lens spreads light rays to move the focal point backward onto the retina, correcting myopia.
Visual 3: Diagram - An illustration of how a convex (converging) lens bends light rays to move the focal point forward onto the retina, correcting hyperopia.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Corrective lenses for refractive errors of the eye as background academic context rather than a clinical decision trigger.
Nurses play a key role in health screening and patient education. Understanding the basics of refractive errors helps in identifying potential vision problems in patients and explaining the purpose of their corrective lenses.
During patient assessment, observing a patient squinting or holding reading material very close can be an indicator of uncorrected myopia, prompting a referral for a vision test.
What if? - If a patient with myopia is accidentally given convex lenses, their distant vision will become significantly worse. The converging power of the convex lens would cause the light to focus even earlier (further in front of the retina), increasing the blur.

How to Approach the Question

First, identify the key term in the question: 'myopia' (nearsightedness).
Recall the basic pathophysiology of myopia: light from distant objects focuses in front of the retina.
Determine the goal of the corrective lens: to move the focal point backward so it lands on the retina.
Consider the properties of different lenses. A concave lens diverges (spreads) light, which will move the focal point backward. A convex lens converges (focuses) light, which would move it forward.
Based on this, select the concave lens as the correct option for myopia.
Rule out the other options by recalling their specific uses: convex for hyperopia, cylindrical for astigmatism, and bifocal for presbyopia.

Concept Tested & Keywords

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