**Question:** Oldest lens fibres are found in -

**Core Concept:** Lens fibre cells are responsible for maintaining the transparency and refractive power of the lens in the eye. The lens is composed of two types of fibre cells: the nucleus (central zone) and the cortex (peripheral zone). The nucleus contains the oldest fibre cells, which are responsible for maintaining the lens's rigidity and transparency.

**Why the Correct Answer is Right:** The correct answer, option **C**, indicates that the oldest lens fibre cells are located in the nucleus, or central zone of the lens. This is because the nucleus is responsible for maintaining the lens's rigidity and transparency, which are essential for proper vision. The nucleus is made up of denser fibre cells, which take longer to regenerate compared to the more numerous and younger fibre cells found in the cortex.

**Why Each Wrong Option is Incorrect:**

A. The lens's periphery (cortex) contains the youngest fibre cells, not the oldest. These cells are more numerous and regenerate more quickly, contributing to the lens's flexibility and transparency.

B. The lens's equator (the boundary between the nucleus and cortex) houses no fibre cells. Instead, it is a region where the nuclear and cortical layers meet.

D. The cornea, located at the front of the eye, is not related to lens fibre cells. The cornea is responsible for refracting light entering the eye, not lens fibre cells.

**Clinical Pearl:** Understanding the composition and structure of the lens fibre cells is crucial for understanding the eye's refractive power and transparency. This knowledge is essential for diagnosing and treating vision-related disorders, such as cataracts and presbyopia, which are associated with changes in lens fibre cells' integrity and regenerative capacity.