Which of the following was a drawback of CAB lenses?

The correct answer highlights a significant issue with CAB (Cellulose Acetate Butyrate) lenses, specifically their tendency to chip easily. This characteristic made them less durable compared to other lens materials available at the time. When lenses chip, it can lead to discomfort for the wearer and may cause sharp edges that could irritate the eye.

Durability is a crucial aspect of contact lens design since lenses are frequently handled during insertion and removal. The propensity to chip means these lenses could require more frequent replacement, increasing costs and inconveniences for users. In the broader context of lens materials, knowing the mechanical strength and resilience is essential for ensuring user satisfaction and safety.

Exploring the other options provides a better understanding of the distinct attributes of CAB lenses. They did not melt at room temperature, nor were they described as epileptic, terms not applicable to lens characteristics in this context. The statement regarding breaking into fragments if touched in the center suggests an extreme weakness that wasn't specifically noted as a typical issue with CAB lenses, rather than chipping. Hence, the correct identification of chipping as a drawback captures a relevant concern in contact lens use and care.