Schedule a consultation
It was my first time in a grand auditorium surrounded by doctors. My head swiveled around trying to take it all in, not realizing that I probably looked like a fish out of water. I was 22 years old at my first clinical neurology lecture with the fabled Dr. Frederick Carrick. He showed video after video of two solitary eyes on the screen and spoke deeply about the subtle errors in the way the eyes moved. I was thoroughly confused. Just as my brain was entering overload he pulled up another video.
This video was of a woman whose eyes seemed like they moved out of her control. She couldn’t walk without falling, her speech was choppy and difficult. She was trapped inside a body in a meltdown. I leaned forward in my chair. He gently rotated her head, shined a colored light in her eye, and made a gesture with her hand, and all of a sudden you could see her coming back. Like a movie where the ghost re-enters the body and she is able to look at him and smile.
Soon enough, her voice came back and we could hear what she naturally sounded like.
She could stand and walk smoothly. I thought, “He got all this from looking at her eyes?!”
I think this was where my obsession began.
Below are 6 of the different types of eye movements that we examine in depth when evaluating brain function. I hope it helps you on your path.
Eye movements are integral to various cognitive and motor functions, governed by complex neural networks. Disruptions in these eye movements can serve as potent indicators of underlying brain dysfunction. This blog explores the significance of six aberrant eye movements—nystagmus, gaze holding, pursuits, saccades, optokinetic nystagmus, and vergence—and how they function as 'neurological fingerprints' in identifying specific brain malfunctions.
Nystagmus involves involuntary, rhythmic oscillation of the eyes and is commonly indicative of vestibular system dysfunction.
Vertical nystagmus often indicates a central nervous system (CNS) disorder. This assertion is supported by studies such as one by Baloh et al. ("Clinical Neurophysiology of the Vestibular System"), which observed vertical nystagmus in patients with cerebellar lesions, affirming its role as an indicator for central vestibular pathways.
Gaze holding is the ability to fixate the eyes steadily on a single point. Abnormalities in gaze holding often manifest as drifts or saccadic intrusions.
Difficulty in gaze holding often indicates issues with the neural integrator. A seminal work by Leigh and Zee ("Neurology of Eye Movements") found that lesions in the medial vestibular nucleus caused difficulties in gaze holding, providing substantial evidence for localizing dysfunction to specific brainstem or cerebellar regions.
Smooth pursuit movements allow the eyes to follow a moving object smoothly. Aberrations can result in saccadic or jerky movements.
Impaired pursuits are often tied to parietal lobe dysfunction. A study by Suh et al. ("Altered Scanning of Faces Following Early Brain Injury") demonstrated that individuals with traumatic brain injuries exhibited disrupted smooth pursuit eye movements. Imaging in these subjects revealed parietal lobe involvement, thereby validating the clinical relevance.
Saccades are rapid eye movements that redirect the fovea to a new target. Delays or inaccuracies can be significant.
Dysfunction in saccadic movements usually points to issues within the frontal eye fields or the superior colliculus. Research by Pierrot-Deseilligny et al. ("Cortical Control of Saccades") found that lesions in the frontal eye fields led to impaired saccadic initiation and velocity, confirming its diagnostic implications.
Optokinetic nystagmus is a reflexive eye movement that occurs when the visual scene drifts across the retina.
A compromised OKN reflex often indicates a lesion in pathways involving the cortex, brainstem, or cerebellum. A study published in "Practical Neurology" by Bronstein ("Optokinetic Nystagmus") demonstrated abnormal OKN in individuals with multiple sclerosis. Imaging confirmed demyelination in these areas, validating OKN's clinical importance.
Vergence movements align both eyes to focus on an object at different distances.
Impaired vergence can indicate midbrain or cranial nerve dysfunction. In a study by Rambold ("Neural Basis of Vergence Movements"), patients with Parkinson’s disease showed abnormal vergence movements. Subsequent imaging studies revealed lesions in the midbrain areas responsible for controlling vergence, further affirming its clinical relevance.
Understanding the types of eye movements and their underlying neural bases can provide valuable insights into various brain dysfunctions. Aberrations like nystagmus, gaze holding deficits, impaired pursuits, saccadic errors, abnormal optokinetic nystagmus, and vergence issues serve as sensitive markers for neurological diagnosis and localization.
References
- Baloh, R. W., & Honrubia, V. (2001). Clinical Neurophysiology of the Vestibular System. Oxford University Press.
- Leigh, R. J., & Zee, D. S. (1999). Neurology of Eye Movements. Oxford University Press.
- Suh, M., Basu, S., Kolster, R. (2006). Altered Scanning of Faces Following Early Brain Injury. Visual Neuroscience, 23(5), 809–816.
- Pierrot-Deseilligny, C., Müri, R. M., Nyffeler, T., & Milea, D. (2004). Cortical Control of Saccades. Annals of Neurology, 57(5), 626–641.
- Bronstein, A. M. (2005). Optokinetic Nystagmus. Practical Neurology, 5(6), 332–339.
- Rambold, H. A. (2013). Neural Basis of Vergence Movements. Encyclopedia of Computational Neuroscience.
Schedule
