ICD-10 Code H49.10 – Fourth [trochlear] nerve palsy, unspecified eye (2026): Diagnosis, Symptoms & Billing Guide
2026 ICD-10-CM Diagnosis Code H49.10 – Fourth [trochlear] nerve palsy, unspecified eye
What it is
H49.10 identifies paralysis or weakness of the fourth cranial, or trochlear, nerve affecting an unspecified eye. This nerve helps control the superior oblique muscle, which assists with downward and inward eye movement.
Clinical signs
Typical findings include vertical or diagonal double vision, especially when looking down, and difficulty reading or walking downstairs. Clinical features vary; refer to documentation.
When to use this code
Use H49.10 when the provider documents trochlear nerve palsy but does not specify the right or left eye. It also fits when the chart confirms fourth nerve dysfunction without laterality. If another cause, such as trauma or a neurologic disorder, is documented separately, code it as well.
Do not use for
Do not use this code when the affected eye is specified, because laterality should be coded instead. Avoid it for nonspecific diplopia or other cranial nerve palsies unless documentation clearly states fourth nerve involvement.
Coding tip
Check the note for laterality and for any documented underlying cause before assigning H49.10.