Certified Paraoptometric (CPO) Practice Exam 2026

The human cornea consists of five distinct layers. From the outside to the inside, these layers are:

1. The Epithelium - This is the outermost layer that acts as a barrier to protect against foreign substances and helps maintain hydration.

2. The Bowman's Layer - A thin layer that adds to the structure and strength of the cornea while also helping to protect the underlying stroma.

3. The Stroma - This thick, middle layer is composed of collagen fibers and makes up about 90% of the cornea's thickness, playing a crucial role in maintaining transparency.

4. The Descemet's Membrane - A thin but strong sheet of tissue that serves as a protective barrier and is produced by the corneal endothelium.

5. The Endothelium - This is the innermost layer that regulates fluid and solute transport between the aqueous humor and the stroma, ensuring optimal hydration.

Each layer contributes to the overall function of the cornea, which is vital for clear vision. Understanding the function and structure of these layers is important in paraoptometric practice as it aids in the diagnosis and management of various ocular conditions.