Walsh & Hoyt: Classification

Optic nerve injuries are classically divided into direct and indirect injuries. Direct injuries are open injuries where an external object penetrates the tissues to impact the optic nerve. Indirect optic nerve injuries occur when the force of collision is imparted into the skull and this energy is absorbed by the optic nerve. The prognostic value in knowing that an injury was direct or indirect is unclear. Historically, direct optic nerve injury is associated with a poor visual outcome. It may be safe to classify an optic nerve injury as direct if orbital imaging reveals a bullet at the orbital apex, but this provides no insight into the cellular injury mechanism. The classification does not illuminate whether the nerve is severed with no hope of recovery or only mildly injured with significant recovery potential. This becomes important as strategies for treating nerve injuries evolve.