( of )
Correct: 0
Incorrect: 0
A 24 year old woman reports that her vision has recently become blurred and that she is having trouble with her balance. When she covers either eye, vision improves. Your examination reveals that visual function is apparently normal, and eye movements are full. When you cover her right eye, her left eye moves down slightly. When you cover her left eye, there is no movement of the right eye. The amplitude of the downward movement in the left is present and of equal degree in all positions of eccentric gaze. You also notice a right-beating nystagmus in right gaze, left-beating nystagmus in left gaze, and upbeating nystagmus in upgaze.
Where is the lesion?
Incorrect
Incorrect
Incorrect
Correct!
You should find this combination of neuro-ophthalmic abnormalities challenging. Why?
First, the complaint of blurred vision suggests something wrong with the visual pathway. But patients will often interpret mild misalignment of the eyes as blurred vision. The clue that it is actually diplopia comes from the fact that covering either eye improves vision!
Second, because the eye movements are full, many examiners will assume that there is no disorder of ocular alignment. Not true. This patient has a vertical misalignment (“hypertropia”) discovered with the cover test. She is fixating the visual stimulus with her right eye; her left eye is deviated upward. When you cover the right eye, the left eye moves down to pick up fixation. But when you cover the left eye, there is no fixational movement of the right eye because it is already fixating!
A challenge here is that the misalignment is small, so that the fixating movement of the left eye is difficult to see. You could use the Maddox rod, in which the patient should report a consistent vertical separation of the two images, with the image seen by the left eye as lower than that seen by the right eye.
The vertical misalignment is called “skew deviation.” It results from an abnormal “ocular tilt reaction.” Here is how that happens. The pathway carrying the vertical vestibulo-ocular reflex travels from the medulla rostrally to the diencephalon. A lesion that affects this pathway on one side creates an imbalance that drives both eyes torsionally toward the spared side. For example, a lesion in the left medulla would cause clockwise displacement of the eyes, with the right eye ending up higher than the left eye The patient would not typically notice torsional displacement of the environment, but would experience the vertical misalignment of the eyes as diplopia or blurred vision
The pattern of oscillations of the eyes described in this case –called gaze-evoked nystagmus--is consistent with brainstem (rather than semicircular canal or otolith) dysfunction.
Tip: a handy rule is that lesions caudal to the midpons will result in skew deviation in which the lower eye is on the side of the lesion, whereas lesions rostral to the midpons will result in skew deviation in the lower eye is on the side opposite to the lesion.
The cause of skew deviation here proved to be multiple sclerosis. The brainstem did not show any MRI signal abnormalities, but there were characteristic T2/FLAIR signal abnormalities in the cerebral white matter.
First, the complaint of blurred vision suggests something wrong with the visual pathway. But patients will often interpret mild misalignment of the eyes as blurred vision. The clue that it is actually diplopia comes from the fact that covering either eye improves vision!
Second, because the eye movements are full, many examiners will assume that there is no disorder of ocular alignment. Not true. This patient has a vertical misalignment (“hypertropia”) discovered with the cover test. She is fixating the visual stimulus with her right eye; her left eye is deviated upward. When you cover the right eye, the left eye moves down to pick up fixation. But when you cover the left eye, there is no fixational movement of the right eye because it is already fixating!
A challenge here is that the misalignment is small, so that the fixating movement of the left eye is difficult to see. You could use the Maddox rod, in which the patient should report a consistent vertical separation of the two images, with the image seen by the left eye as lower than that seen by the right eye.
The vertical misalignment is called “skew deviation.” It results from an abnormal “ocular tilt reaction.” Here is how that happens. The pathway carrying the vertical vestibulo-ocular reflex travels from the medulla rostrally to the diencephalon. A lesion that affects this pathway on one side creates an imbalance that drives both eyes torsionally toward the spared side. For example, a lesion in the left medulla would cause clockwise displacement of the eyes, with the right eye ending up higher than the left eye The patient would not typically notice torsional displacement of the environment, but would experience the vertical misalignment of the eyes as diplopia or blurred vision
The pattern of oscillations of the eyes described in this case –called gaze-evoked nystagmus--is consistent with brainstem (rather than semicircular canal or otolith) dysfunction.
Tip: a handy rule is that lesions caudal to the midpons will result in skew deviation in which the lower eye is on the side of the lesion, whereas lesions rostral to the midpons will result in skew deviation in the lower eye is on the side opposite to the lesion.
The cause of skew deviation here proved to be multiple sclerosis. The brainstem did not show any MRI signal abnormalities, but there were characteristic T2/FLAIR signal abnormalities in the cerebral white matter.