Fourth nerve palsy / superior oblique underaction

This is a popular examination case. You will either be asked to perform the three step tests or the ocular
motility examination. Remember that the patient may have asymmetrical bilateral fourth nerve palsy.

On inspection, the patient may have an abnormal head posture in the primary position with the head tilt ot the 
unaffected side with chin depression. Alternatively, the patient may be wearing glasses with prism.

In ocular motility examination.

There is overaction of the inferior oblique on the affected side when the patient looks 
to the unaffected side. On looking in and down, the affected side has incomplete 
depression (see picture above).

In the cover/uncover test
(Combine with the three-step tests see picture below. The patient has a right fourth nerve palsy).

First step

Second step

Third step
    • In the primary position, there is hyperdeviation of the affected eye (first step). 

Left fourth nerve palsy
    • With the patient looking to either side, the test shows increased deviation when the eyes look to 

    • the unaffected side (second step). 

Left fourth nerve palsy
    • With the head tilt, the test shows increased deviation when the head is tilted to the affected side

    • (third step).

Left fourth nerve palsy
    Additional features:
    • beware that the patient may have bilateral fourth nerve palsy


1. What ocular sequelae can occur with long-standing fourth nerve palsy?

2. How can a unilateral palsy be differentiated from a bilateral palsy?

3. How can an unresolved fourth nerve palsy be treated surgically?


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