Fourth [trochlear] nerve palsy, bilateral

This code represents a condition where both fourth cranial nerves (trochlear nerves) are impaired, leading to weakness or paralysis of the superior oblique muscles in both eyes. This bilateral impairment typically results in vertical diplopia (double vision) that is worse on downward gaze and often accompanied by a compensatory head tilt.

Use this code when documentation clearly indicates a bilateral trochlear nerve palsy, affecting both eyes. This diagnosis is typically made based on clinical examination findings such as vertical strabismus, excyclotorsion, and a positive Bielschowsky head tilt test, confirmed by an ophthalmologist or neurologist.

• Ensure documentation specifies "bilateral" involvement; otherwise, consider H49.11 (right) or H49.12 (left).
• Do not confuse with other cranial nerve palsies; verify the specific nerve affected is the fourth (trochlear).
• Code any underlying cause of the palsy (e.g., trauma, tumor, vascular event) as a primary diagnosis if applicable, following sequencing guidelines.