Eye Movements in Gaucher Disease
The diagnosis of type III Gaucher Disease is a clinical one. Abnormal eye movements are often the first sign. Since it is vital that the diagnosis is made at diagnosis, careful examination of eye movements is critical.
Voluntary shifting of gaze occurs in one of two ways, smooth pursuit or saccades.
Smooth pursuit eye movements allow the eyes to closely follow a moving object.
Saccades refer to the eye’s ability to quickly and accurately shift from one target to another. This is a critical skill in reading, involving very specific eye movements. The eyes must along a straight line without deviating up or down to the lines above or below. In addition, when they reach the end of a line, they must sweep back to the beginning of the next line. If a child cannot control these eye movements, he’ll lose his place and comprehension becomes a problem. Understandably, this can impact significantly on reading.
Both smooth pursuit and saccades can be tested in horizontal or vertical planes. In type III Gaucher Disease, smooth pursuit may be affected early. This is illustrated in the video below
However, it is often normal, as in the video below, showing normal smooth pursuit in a patient with type III GD.
Horizontal saccades, on the other hand, are always affected. In the next video, horizontal saccades are being generated in the same patient as above. Note that when the examiner’s fingers are placed close together, the saccades are normal. As the distance increases, compensatory blinking appears.
The abnormality may be more subtle, as in the video below
Therefore, unless saccades are specifically looked for, the diagnosis of type III may be missed.
By contrast, horizontal saccades are entirely normal in type I Gaucher disease.
Vertical saccades may be affected as well. This usually indicates disease progression. As with horizontal movements, vertical smooth pursuit may be normal.
Here is a video of normal vertical smooth pursuit
In the same patient, abnormal vertical saccades can be seen
If the child is unable to obey the above commands, assessment in an eye movement laboratory may be required.
An eye movement laboratory. The child sits on a stool, or in the case of a small child, on the lap of a parent who in turn sits on the chair. The chair is surrounded by a curtain with bright patterns. Either the curtain can turn around the child inducing optokinetic nystagmus, or the chair can rotate, inducing vestibulo-ocular nystagmus. Both have the effect of generating horizontal saccades.
The pictures below, and the videos that follow, were all taken at the Eye Movement Laboratory at Great Ormond Street Hospital (videos kindly provided by Professor Chris Harris)
Many young children with Type III Gaucher Disease are very irritable and locking cannot be observed in the light. This is illustrated in the video below.
Often, in such children, it is possible to capture this in dark surrounding using infra-red, as can be seen in the next video. In the next video, the same child is being examined. This time, the stool on which the child is sitting is spun around, thereby eliciting vestibulo-ocular nystagmus. The child is far less irritable and therefore assessment is possible. Locking can be observed.