**Question:** Choose the local anaesthetic that is specifically used to produce corneal anaesthesia for tonometry

**Core Concept:** Tonometry is the measurement of intraocular pressure (IOP) in the eye. Corneal anaesthesia is necessary to prevent pain during the procedure. Local anaesthetics can be used for this purpose.

**Why the Correct Answer is Right:**

The correct answer, **Bupivacaine**, is a long-acting, amide-type local anaesthetic. It has a high selectivity for blocking voltage-gated sodium channels, which results in efficient anaesthesia while minimizing systemic absorption and toxicity. This makes it suitable for corneal anaesthesia during tonometry, ensuring minimal patient discomfort.

**Why Each Wrong Option is Incorrect:**

A. **Lidocaine (Xylocaine)** is a commonly used local anaesthetic but has a shorter duration of action than bupivacaine. It may not provide sufficient anaesthesia during tonometry, leading to patient discomfort.

C. **Levobupivacaine**: Although a long-acting local anaesthetic, it is not specifically designed for corneal anaesthesia. Bupivacaine is a more suitable choice due to its longer duration of action.

D. **Ropivacaine**: Similar to levobupivacaine, ropivacaine is a long-acting local anaesthetic but isn't specifically tailored for corneal anaesthesia. Bupivacaine is a more appropriate choice for tonometry due to its longer duration of action.

**Clinical Pearl:** Tonometry is a vital procedure for monitoring intraocular pressure in patients, particularly those with glaucoma. By using the appropriate local anaesthetic like bupivacaine, we can ensure patient comfort during the procedure, which is crucial for accurate and reliable test results.