Certified Paraoptometric (CPO) Practice Exam 2025

Which type of lens may crack or break when it becomes dry?

1. Rigid

2. Soft

3. Hard gas-permeable

4. High-definition

The correct answer is: Soft

The correct answer is that rigid lenses may crack or break when they become dry. Rigid lenses, particularly those made from materials like PMMA (Polymethyl methacrylate), are susceptible to drying out, which can lead to brittleness and potential cracking. When these lenses lose moisture, they can become less flexible and more prone to damage upon handling or during insertion and removal. In contrast, soft lenses are designed to retain moisture, making them more resilient to drying effects. They generally maintain their shape and integrity even when exposed to lower humidity levels. Hard gas-permeable lenses, while rigid, are more durable than PMMA and allow oxygen to pass through, making them less likely to crack or break when dry. High-definition lenses refer more to optical clarity or designs and do not specifically relate to dryness and fragility.