**Question:** Which of the following is the outermost layer of the eyeball?

A. Sclera
B. Cornea
C. Conjunctiva
D. Retina

**Core Concept:** The human eyeball is composed of several layers that protect and support the sensitive internal structures. The outermost layer is crucial for both protection and vision.

**Why the Correct Answer is Right:**
The correct answer is option B, "Cornea." The cornea is a transparent, dome-shaped structure that covers the anterior part of the eye, including the sclera, iris, and pupil. Its primary function is to protect the eye from environmental factors, such as pathogens and physical damage. Additionally, the cornea plays a role in focusing light onto the retina, improving the overall visual acuity.

**Why Each Wrong Option is Incorrect:**

A. Sclera (Option A) is the white, fibrous outer layer of the eye that provides structural support and protection. While it is essential for the eye's overall health, it is not the outermost layer.

B. Conjunctiva (Option C) is a thin, transparent membrane that covers the sclera and the inner surface of the eyelids. Although it plays a role in maintaining the eye's health, it is not the outermost layer.

D. Retina (Option D) is the innermost layer of the eye responsible for vision. While the retina is essential for vision, it is located deeper within the eye rather than being the outermost layer.

**Clinical Pearl:** Understanding the anatomy of the eyeball is essential for diagnosing and treating eye-related disorders. A thorough knowledge of the eye's layers aids in interpreting ocular symptoms and signs, as well as formulating an appropriate treatment plan.