Fourth [trochlear] nerve palsy, right eye

This code signifies a paresis or paralysis of the fourth cranial nerve affecting the right eye. This condition typically results in vertical diplopia, especially when looking down and inward, due to impaired superior oblique muscle function. Patients may present with a compensatory head tilt to the left to alleviate double vision.

Apply this code when documentation clearly indicates a diagnosis of fourth nerve palsy specifically affecting the right eye. This diagnosis is often supported by findings from an ophthalmological examination, including ocular motility testing, Hess screen, or Maddox rod testing, confirming superior oblique muscle weakness.

• Ensure laterality is explicitly documented as "right eye" to support this specific code.
• Distinguish from other cranial nerve palsies affecting ocular motility, such as oculomotor (third nerve) or abducens (sixth nerve) palsies.
• Consider co-occurring conditions or underlying etiologies, such as trauma, vascular events, or congenital causes, and code them additionally if documented.