## Core Concept
Soft contact lenses are made from **hydrogel materials**, which are known for their high water content and flexibility. These materials allow for the creation of lenses that are comfortable to wear and can correct various vision problems. The primary component of soft contact lenses is a type of polymer that can retain a significant amount of water.

## Why the Correct Answer is Right
The correct answer, **Hydrogel**, is right because hydrogel materials are specifically designed to hold water, making them soft and pliable. This characteristic allows soft contact lenses to be comfortable on the eye while still providing the necessary vision correction. Hydrogels can be made from various polymers, but their ability to retain water is key to their use in soft contact lenses.

## Why Each Wrong Option is Incorrect
- **Option A: Cellulose** - While cellulose is a natural polymer, it is not primarily used to make soft contact lenses. Its properties do not lend themselves as well to water retention in the context of contact lens materials.
- **Option B: Polyethylene** - Polyethylene is a type of plastic used in various medical applications, but it is not known for its use in soft contact lenses due to its rigidity and lower water content compared to hydrogel materials.
- **Option D: Polymethyl methacrylate (PMMA)** - PMMA is actually a material used in rigid gas permeable contact lenses, not soft contact lenses. It provides good optical clarity but is not flexible or soft like hydrogel materials.

## Clinical Pearl / High-Yield Fact
A key point to remember is that soft contact lenses are preferred by many patients due to their comfort. The **high water content** of hydrogel lenses contributes to this comfort, but it also requires careful handling and maintenance to prevent contamination and eye infections.

## Correct Answer: C. Hydrogel