What causes spontaneous eye movements in albinism?

(Image Credit: AdobeStock/AnnaStills)

Individuals with albinism often have poor vision and a new study¹ from the Netherlands Institute for Neuroscience (NIN) reveals the underlying cause.

According to a news release from the NIN, in Europe, albinism occurs in 1 in 20,000 individuals. In the united states, the rate is 1 in every 18,000 to 20,000 people, according to the Cleveland Clinic. However, it is much more common in some populations, affecting 1 iikjiun 1,000 people.

People with albinism lack pigment and frequently have poor eyesight. For example, they may see at a distance of 20 meters what someone with pigment sees at 80 meters. But what exactly causes this?

According to the news release, one of the causes of vision issues in people with albinism is the spontaneous back-and-forth movement of the eye, called “pendular nystagmus.” The researchers noted the phenomenon not only makes seeing difficult but also hinders social eye contact. Treatment sometimes involves medications or surgery on the eye muscles, but these methods have unpleasant side effects and are not fully effective.

Moreover, the researchers noted that understanding the underlying mechanisms behind this condition is essential for developing alternative treatment strategies.

Moving train

According to the institute’s news release, pendular nystagmus resembles the eye movements people make when looking outside while riding a moving train: the eyes automatically move along with the moving landscape and then spring back to the resting position. Nerve cells in a small brain area (known as the nucleus of the optic tract) selectively respond to this movement and become active. In healthy individuals, this activity leads to the tightening of the eye muscles to stabilize the image. However, in albinism, this process works a bit differently.

Jorrit Montijn, PhD, Valentina Rugiccini, and their colleagues, under the supervision of Alexander Heimel, PhD, have now demonstrated in albino mice that the cells in this brain area are no longer selective for the direction of image movement.¹

The researchers noted the image cannot stabilize, leading to pendular nystagmus. Currently, surgery on this brain area is not possible, but their work offers hope that in the future, pendular nystagmus can be reduced through manipulation of activity in this brain region, according to the release.

Ruling out cortex

According to Montijn, the researchers have demonstrated that the nucleus of the optic tract might be the source of the problem.

“Previous research already suggested that this area is involved in eye movements, but it could not be ruled out that (also) other areas, such as the cortex, cause pendular nystagmus,” he said in the news release. “By simultaneously measuring both the cortex and the nucleus of the optic tract in the same mice, we were able to eliminate this question.”

Montijn also pointed out the researchers do know there is something wrong with this area, but they still don’t know what can be done about it.

“The next steps would be to translate this into practice,” he concluded in the release. “One possible option could be Deep Brain Stimulation of the area, but this still needs to be tested, and it is not known if it has an effect. Another option is perhaps surgery or even gene therapy in the future. It is now up to more clinically oriented scientists to investigate this.”

According to the NIN, the study was made possible by a donation from Mrs. Van Hessen-Israels for research on the consequences of albinism.

Reference:

1. Jorrit S. Montijn, Valentina Riguccini, Christiaan N. Levelt, J. Alexander Heimel. Impaired Direction Selectivity in the Nucleus of the Optic Tract of Albino Mice. Investigative Ophthalmology & Visual Science, Published August 2023, Vol.64, 9. doi: https://doi.org/10.1167/iovs.64.11.9