Certified Paraoptometric (CPO) Practice Exam 2025 – All-in-One Study Guide to Ensure Exam Success!

The sclera is best described as tough, fibrous tissue. It serves as the protective outer layer of the eye, providing structural support and maintaining the shape of the eyeball. This robust composition is essential as it withstands pressure and provides stability for the more delicate internal components of the eye. The sclera is made up of densely packed collagen fibers, which contribute to its strength and resilience, making it crucial in protecting the eye from injury and supporting the overall integrity of the eye structure.

The other options do not accurately represent the nature of the sclera. For instance, a soft, jelly-like substance does not align with the sclera's composition, as that would suggest a more flexible or malleable structure rather than the tough and robust nature of the sclera. A fluid-filled space might refer to structures like the vitreous body or aqueous humor, rather than the sclera itself. Lastly, muscle fibers are primarily associated with the extraocular muscles of the eye, which control movement, not with the scleral structure.