## Facts

- Martin Wilsher, the claimant, was born prematurely and developed retrolental fibroplasia (RLF), resulting in blindness.
- During neonatal care, he was administered excessive oxygen due to a misplaced catheter.
- The claimant alleged that this medical negligence caused or contributed to his RLF.
- RLF in premature infants can also result from other factors, such as hypercapnia, intraventricular hemorrhage, and apnea.
- The defendant, Essex Area Health Authority, admitted negligence in oxygen administration but disputed that this caused the RLF.
- The trial judge found in favour of the claimant, but the Court of Appeal reversed this, stating the claimant had not shown causation on the balance of probabilities.
- The matter was appealed to the House of Lords.

## Issues

1. Whether the claimant had proven, on the balance of probabilities, that the defendant’s negligent oxygen administration caused the RLF.
2. Whether increased risk of harm, absent proof of causation, was sufficient to impose liability in negligence.
3. How courts should assess causation where multiple possible independent causes could have resulted in the harm.

## Decision

- The House of Lords held that the claimant must prove the defendant’s breach was a material cause of the harm on the balance of probabilities.
- The Court rejected the argument that an increased risk of harm was sufficient for liability when there are multiple independent possible causes.
- The House of Lords found the medical evidence did not establish causation to the requisite standard, as it could not be shown that excessive oxygen rather than another factor caused the RLF.
- The ruling required claimants to provide clear evidence of a direct causal link between the alleged negligence and the injury.
- The decision of the Court of Appeal, denying compensation, was upheld.

## Legal Principles

- The burden of proving causation is on the claimant in negligence cases.
- Claimants must prove, on the balance of probabilities, that the defendant’s breach of duty was a material contributor to the harm.
- Mere evidence of increased risk, without proof that the negligence was the probable cause, is insufficient where multiple independent causes exist.
- Scientific or medical evidence must establish the causal link and cannot be speculative.
- The decision in Wilsher distinguishes cases where it is not possible to identify a single agent of harm, reserving the more flexible causation approach for those circumstances.

## Conclusion

Wilsher v Essex Area Health Authority [1988] AC 1074 established that, in cases involving multiple potential causes for the damage suffered, claimants must show on the balance of probabilities that the defendant’s negligent act was the material cause of harm, rather than relying on an increased risk; this decision has shaped the handling of causation in medical negligence and influenced subsequent case law.
