The eyeball is approximately spherical in shape with a diameter of about

RRB Nsg. Superintendent-20 July 2019 (Shift-3rd)

Applied Anatomy

Easy

Appeared in: RRB Nsg. Superintendent-20 July 2019 (Shift-3rd)

Explanation

The average diameter of an adult human eyeball is approximately 2.3 cm (23 mm).
This specific dimension is crucial for the proper focusing of light onto the retina, which is the light-sensitive layer at the back of the eye.
The eyeball maintains its shape due to the tough outer sclera and the pressure of the internal fluids, the aqueous and vitreous humor.
While there are minor variations among individuals, 2.3 cm is the standard anatomical measurement used in medicine and ophthalmology.

Option A: A diameter of 3.0 cm is significantly larger than the average adult eyeball. An eye of this size would be highly myopic (nearsighted).
Option B: A diameter of 1.0 cm is extremely small, less than half the size of an adult eye. This would result in severe hyperopia (farsightedness).
Option D: A diameter of 1.8 cm (18 mm) is closer to the size of a newborn infant's eye, which is approximately 16-17 mm at birth and grows rapidly.

Visual 1: Diagram - A cross-section of the human eyeball with the anterior-posterior diameter clearly labeled as 2.3 cm. This helps visualize the measurement in context with other structures like the lens, retina, and cornea.
Visual 2: Infographic - A comparison of a normal-sized eyeball, a myopic (long) eyeball, and a hyperopic (short) eyeball, showing how the focal point of light changes in relation to the retina.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Anatomy of the human eye, specifically its dimensions as background academic context rather than a clinical decision trigger.
Understanding the standard size of the eyeball is fundamental for nurses to appreciate the pathophysiology of refractive errors like myopia and hyperopia.
During health screenings, nurses may assess visual acuity. A significant change or poor acuity could indicate an underlying structural issue, including abnormal growth or changes in the eye's dimensions, warranting referral to an ophthalmologist.
What if? - If a patient's medical record notes an axial length of 2.6 cm, the nurse should anticipate that the patient has moderate to high myopia and will require corrective lenses (glasses or contacts) for clear distance vision.

How to Approach the Question

This is a factual recall question that tests your knowledge of basic human anatomy.
First, identify the key term in the question: 'diameter' of the 'eyeball'.
Recall the standard anatomical value for the adult human eyeball's diameter.
Evaluate the given options. 2.3 cm is the accepted average.
Eliminate the other options by considering their plausibility. 1.0 cm is too small, and 3.0 cm is too large for a human eye. 1.8 cm is closer to the size of an infant's eye, not an adult's.

Concept Tested & Keywords

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