Certified Paraoptometric (CPO) Practice Exam 2025

Which type of contact lens was once commonly referred to as "hard" lenses?

1. Soft

2. Rigid

3. Disposable

4. Scleral

The correct answer is: Rigid

Rigid contact lenses are indeed the type that was commonly referred to as "hard" lenses. In the past, these lenses were typically made from rigid gas permeable (RGP) materials, which allowed for better oxygen transmission compared to earlier versions. These rigid lenses are known for their durability and ability to provide clear vision by maintaining their shape on the eye's surface, especially for individuals with astigmatism or other irregular corneal shapes. The term "hard" encompassed the earlier generation of contact lenses, which were made of PMMA (polymethyl methacrylate) and did not transmit oxygen as effectively as modern materials. Consequently, patients often transitioned to the more breathable RGP lenses, which maintained the rigid form while improving comfort and ocular health. Other types of contact lenses, such as soft lenses, disposable lenses, and scleral lenses, do not fall under the "hard" lens category. Soft lenses are made of flexible materials that conform to the shape of the eye, disposable lenses are intended for short-term use, and scleral lenses are larger and vault over the cornea, designed for specific therapeutic purposes. Therefore, the correct identification of rigid lenses as the "hard" type is accurate and reflects the historical terminology used in