It is the transparent membrane that focuses the light that enters the eyes to the retina?

DSSSB Public Health Nurse - 2015

Applied Anatomy

Easy

Appeared in: DSSSB Public Health Nurse - 2015

Explanation

The cornea is the transparent, dome-shaped outer layer at the very front of the eye.
It functions as the eye's primary window, allowing light to enter and providing the initial and most significant refraction (bending) of light.
It is responsible for about two-thirds of the eye's total focusing power, directing light toward the lens, which then fine-tunes the focus onto the retina.

Option A: While the lens is transparent and focuses light, its primary role is accommodation—changing shape to provide fine-tuning for focusing on objects at different distances. The cornea provides the initial, fixed, and more powerful refraction.
Option B: The sclera is the tough, white, opaque outer layer of the eyeball. Because it is not transparent, it does not allow light to pass through to the retina.
Option D: The pupil is not a membrane but an opening (aperture) in the center of the iris. Its function is to control the amount of light that enters the eye by dilating or constricting, but it does not focus the light.

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 function of structures involved in light refraction as background academic context rather than a clinical decision trigger.
Refractive errors like myopia (nearsightedness) and hyperopia (farsightedness) are often due to the cornea's shape causing light to focus in front of or behind the retina, respectively.
Surgical procedures like LASIK work by permanently changing the shape of the cornea to correct these refractive errors.
What if? If a patient has a scarred or misshapen cornea (e.g., from keratoconus or an injury), their vision will be significantly blurred because the primary focusing surface is compromised. This often cannot be fully corrected with glasses and may require specialized contact lenses or a corneal transplant (keratoplasty).

How to Approach the Question

First, identify the key requirements from the question: the structure must be a 'transparent membrane' and its function must be to 'focus the light'.
Evaluate each option against these two criteria.
Eliminate 'Sclera' because it is the white, opaque part of the eye, not transparent.
Eliminate 'Pupils' because it is an opening that controls light quantity, not a membrane that focuses light.
This leaves 'Lens' and 'Cornea'. Both are transparent and both focus light.
Recall or deduce the primary function. The cornea is the outermost surface and provides the initial, most powerful, fixed refraction. The lens provides adjustable focus (accommodation).

Concept Tested & Keywords

Concept Tested: Anatomy and physiology of the eye, specifically the function of structures involved in light refraction.
Stem keywords: transparent membrane, focuses light, retina, eye
Lead-in keywords: is the

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