ICD-10 Code H49.1 – Fourth [trochlear] nerve palsy (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code H49.1 – Fourth [trochlear] nerve palsy
What it is
H49.1 identifies palsy of the fourth cranial nerve, also called the trochlear nerve. It usually means weakness or loss of function in the superior oblique muscle, which affects eye movement.
Clinical signs
Typical findings include vertical or diagonal double vision, especially when looking down, and difficulty reading or descending stairs. Clinical features vary; refer to documentation.
When to use this code
Use H49.1 when the provider documents fourth nerve palsy, trochlear nerve palsy, or a confirmed superior oblique palsy. This code fits congenital or acquired palsy if the record clearly identifies the fourth nerve as involved. Check documentation when the cause is unclear.
Do not use for
Do not use this code for unspecified cranial nerve palsy or for other ocular motor nerve palsies, such as third or sixth nerve involvement. If the note does not specify the fourth nerve, check documentation.
Coding tip
Code the documented nerve involved, and verify laterality or cause only if the record supports it.