What defines a retinal flash burn?

A retinal flash burn specifically refers to an injury characterized by damage to the retina due to intense light exposure. The most defining scenario for this type of injury is indeed an event like a nuclear explosion's fireball. The intense and brief burst of light produced during such an explosion can cause damage to the retinal cells, leading to flash burn conditions.

In contrast, while prolonged exposure to sunlight can cause eye burns (like solar retinopathy), this type of exposure is less intense and typically occurs over time rather than in an instantaneous flash. Looking at a welding arc can also result in eye damage, specifically termed "arc eye," but it is not as severe as the damage from a nuclear blast. Chemical exposure to the eyes can lead to burns, but these are classified as chemical burns rather than retinal flash burns, as they involve different mechanisms and effects on ocular health.

Thus, the correct definition of a retinal flash burn is specifically associated with the extreme and rapid onset of light exposure from a potent source, such as that from the fireball of a nuclear explosion.