ICD-10 Code H49.12 – Fourth [trochlear] nerve palsy, left eye (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code H49.12 – Fourth [trochlear] nerve palsy, left eye
What it is
Use this code for paralysis or weakness of the left trochlear nerve, which affects the superior oblique muscle. This condition can cause vertical or torsional eye misalignment and binocular double vision.
Clinical signs
Typical findings include left hypertropia, excyclotorsion, and diplopia that often worsens when looking down or reading. Clinical features vary; refer to documentation.
When to use this code
Assign H49.12 when the provider documents left fourth nerve palsy, left trochlear nerve palsy, or left superior oblique palsy. Use it for confirmed neurologic or ocular motility diagnoses affecting the left eye. If the laterality is not stated, check documentation before coding.
Do not use for
Do not use this code for unspecified trochlear palsy, bilateral involvement, or palsy affecting the right eye. Do not use it when the chart only notes diplopia without a documented fourth nerve palsy.
Coding tip
Always verify laterality in the assessment or impression, because the code is specific to the left eye.