Because the medication used to treat ADHD is a stimulant, researchers expected (as observed) that it would increase arousal, thus reducing the rates of microsaccades and blinks. Such a test may have diagnostic value because it cannot be manipulated by subjects. Since the test is completely objective, “our findings may contribute to a more accurate differential diagnosis of ADHD,” added Fried.

When recorded under resting conditions, rather than during a test of attention as in the ADHD study, blink rate may  be used to detect another problem — mild cognitive impairment (MCI). MCI is thought to be a precursor to Alzheimer’s disease.

According to findings reported in July 2014 in the International Journal of Psychophysiology, participants with MCI exhibited a significantly higher blink rate than healthy controls, and blink rate was also negatively correlated with scores on a cognitive test.4 

In addition to the assessment of gaze duration, researchers have also investigated the quality of eye movements as a characteristic of pathology. Another study from Vision Research, published last September, was the first to explore vergence eye movements in patients with schizophrenia.5

“Vergence eye movements are used to shift gaze from near objects to distant objects or vice versa,” said Paul Gamlin, PhD, study co-author and professor in the department of ophthalmology at the University of Alabama at Birmingham. “They are also used to track objects moving in depth. During vergence, the eyes move in opposite directions.”

Compared with healthy control subjects, those with schizophrenia displayed substantial vergence deficits at various speeds.5

“One theory is that these deficits are due to disruptions in the visual areas of the brain that are involved in the motion perception required,” he added. “Another theory is that these eye movement deficits are due to problems with sensory motor integration in the parietal and frontal cortices of patients with schizophrenia.”

Eye movements will be impaired if there is a disruption in the integration of visual information with feedback of the motor commands that control the eye muscles.

Though such deficits are neither specific to schizophrenia nor present in all patients with the disorder, they do point to the involvement of specific brain regions in the neuropathology of schizophrenia. They may also prove to be useful in genetic studies by allowing classification of subgroups of heterogeneous patient populations, noted Gamlin.

“In addition, problems with vergence eye movements in patients with schizophrenia may result in binocular vision problems that can lead to other issues in daily life,” he added.

Taken together, these findings may ultimately help to paint a more comprehensive diagnostic picture by offering objective markers that could help guide diagnosis and treatment, while deepening our understanding of the various disorders.

Tori Rodriguez, MA, LPC, is a psychotherapist and freelancer writer based in Atlanta.

References

  1. Isaac L, Vrijsen JN, Rinck M, et al. Shorter gaze duration for happy faces in current but not remitted depression: Evidence from eye movements. Psychiatry Research; 2014; 218(1-2):79-86.
  2. García-Blanco A, Salmerón L, Perea M, Livianos, L. Attentional biases toward emotional images in the different episodes of bipolar disorder: An eye-tracking study. Psychiatry Research; 2014; 215(3):628-33.
  3. Fried M, Tsitsiashvili E, Bonneh YS, et al. ADHD subjects fail to suppress eye blinks and microsaccades while anticipating visual stimuli but recover with medication. Vision Research;  2014;101:62-72.
  4. Ladas, A, Frantzidis, C, Bamidis, P, Vivas, A. Eye Blink Rate as a biological marker of Mild Cognitive Impairment. International Journal of Psychophysiology; 2014;93(1):12-6. 
  5. Bolding MS, Lahti AC, White D, et al. Vergence eye movements in patients with schizophrenia. Vision Research; 2014;102:64-70.