**Core Concept:**
The multiple-choice question tests our understanding of the maximum safe dose of lignocaine with adrenaline for local blocks in ophthalmic surgeries. Lignocaine is a local anaesthetic agent, while adrenaline (epinephrine) is a vasoconstrictor that reduces bleeding and enhances the spread of the local anaesthetic. However, excessive doses of adrenaline can lead to serious adverse effects.

**Why the Correct Answer is Right:**
The correct answer is **C. 1.8% Lignocaine with 1:100,000 adrenaline**. This combination provides effective anaesthesia with minimal systemic absorption and decreased bleeding during ophthalmic surgeries. The concentration of lignocaine (1.8%) is a reasonable level for local anaesthesia, while the adrenaline concentration (1:100,000) ensures minimal systemic absorption and helps reduce bleeding.

**Why Each Wrong Option is Incorrect:**
A. **1.5% Lignocaine with 1:500,000 adrenaline (Option A)** is incorrect because the adrenaline concentration (1:500,000) is too high, leading to significant vasoconstriction and increased risk of systemic toxicity.

B. **1.5% Lignocaine with 1:100,000 adrenaline (Option B)** is marginally better than Option A but still has an adrenaline concentration that can lead to systemic toxicity if not used with extreme caution.

D. **1% Lignocaine with 1:1,000,000 adrenaline (Option D)** is even less effective for ophthalmic surgery due to a lower concentration of lignocaine and too high adrenaline concentration, increasing the risk of systemic toxicity.

**Clinical Pearl:**
In ophthalmic surgeries, it is essential to use local anaesthetic solutions with a low adrenaline concentration (1:100,000) for effective anaesthesia, minimal systemic absorption, and reduced bleeding without compromising patient safety.

**Correct Answer Explanation:**
**C. 1.8% Lignocaine with 1:100,000 adrenaline (Option C)** is the correct answer because it balances the desired effects of local anaesthesia, reduced bleeding, and minimal systemic absorption. The 1.8% concentration of lignocaine provides adequate anaesthesia, while the adrenaline concentration (1:100,000) ensures minimal systemic absorption and reduced bleeding without significantly increasing the risk of systemic toxicity.