Chiari II Affects Normal Eye Movements

May 31, 2007 -- Chiari has been linked to a number of eye problems, including nystagmus, severe near-sightedness and lazy eye. Now, a team of researchers from Canada, who have previously published on Chiari related eye problems, have found that a subset of Chiari II children have abnormal smooth pursuit.

When a person looks at an object that is moving slowly, their eyes automatically move to stabilize the image of the object and keep it in the center of their focal area. These eye movements are known as smooth pursuit and allow an object to be seen in detail even though it is moving. Smooth pursuit only refers to looking at slowly moving objects and is different than saccades, which is where the eyes move as quickly as possible (or jump) to an object. Saccades results in a momentary disruption of vision, but smooth pursuit does not.

In a study published in the April, 2007 issue of the journal, Developmental Medicine & Child Neurology, the Canadian group (Salman et al.) analyzed the smooth pursuit of 21 Chiari II children and compared them to a group of healthy controls. The children ranged in age from 8-19 years and all suffered from hydrocephalus as well as MRI verified Chiari II. None of the children had additional problems which would affect their eyes and potentially their ocular smooth pursuit, and all had corrected vision of at least 20/40. To help control the experiment, none of the children had severe cognitive deficits.

Both the brainstem and cerebellum play important roles in smooth pursuit functioning, so the researchers hypothesized that the Chiari II children would exhibit problems when tested as compared to their healthy counterparts. In addition, the team wanted to see if the level of spinal lesion (the spina bifida opening) or the number of shunt revisions the children had undergone influenced their smooth pursuit performance. To this end, they categorized the children as having upper spinal lesions (6) or lower spinal lesions (15). Similarly, they grouped the children by number of shunt of revisions (see Table 1) which would indicate periods of increased CSF pressure.

Table 1
Number of Shunt Revisions (21 Total Children)

# of Revisions # of Children
None 5
One 9
Two or More 7

An infrared eye tracking device was used to quantify the smooth pursuit of both the Chiari children and the healthy controls. The device measured eye position and velocity as the children tracked a slow moving sinusoid wave (see Figure 2).

Figure 2
Sinusoid Target


Somewhat surprisingly, the researchers found that only a subset of the Chiari children demonstrated problems with the smooth pursuit task. Specifically, those children with nystagmus - involuntary, rapid eye movements - showed abnormal smooth pursuit as compared to both the healthy controls and the Chiari children without nystagmus. Conversely, neither level of spinal lesion or number of shunt revisions had any influence on whether the children had normal smooth pursuit functioning.

Since the number of shunt revisions was not a factor, the researchers believe that the smooth pursuit problems are not due to hydrocephalus, but rather the malformation of the brainstem and cerebellum. Although they were not able to identify a structural difference between the children with smooth pursuit problems and those without, since every child with pursuit problems also had nystagmus, clearly there is something about their brain structure which is affecting their eye functions.

It is said that the eyes are a window to the soul, but it also may be that the eyes are a window into some of the more subtle.htmlects of Chiari. For now, most of the eye related Chiari research involves Chiari II, it would be interesting to expand the studies that have already been done to Chiari I and adults.

Related C&S News Articles:

Treating Chiari Related Eye Problems

Study Identifies Cognitive Impact Of Chiari II

Some Good News For Chiari II Families