Determining saccade deficits can assist in Alzheimer’s diagnosis

Issue: August/September 2013

Abnormalities of latency and latency-accuracy-speed variability reflected deficits of cerebral areas involved in the triggering and execution of vertical saccades in patients with Alzheimer’s disease and amnestic mild cognitive impairment, according to a recent study.

Horizontal and vertical saccades were measured in 18 amnestic mild cognitive impairment (aMCI) patients, 25 Alzheimer’s disease (AD) patients and 30 healthy elderly patients as controls. Patients performed gap and overlap tasks, where the fixation target extinguishes prior to target onset and fixation stays on after target onset, respectively.

No significant differences were found among AD, aMCI and control groups for the robust gap effect. Abnormal long latency of saccades in gap and overlap tasks were found in AD patients, relative to aMCI and control patients, although aMCI also showed long latency in overlap tasks compared to controls. A higher coefficient of variation in latency was observed in AD patients, as well as an abnormally high variability of accuracy and speed, compared with both aMCI and control patients.

“Saccades are a big thing for AD patients,” Primary Care Optometry News Editorial Board member Leonid Skorin Jr., OD, DO, MS, FAAO, FAOCO, said in an interview. “Sometimes they have difficulty initiating or even maintaining saccadic eye movements. This can affect their ability to read, for instance, or to gaze from one direction to the other.”

Of course, saccadic deficits present with other diseases, not just AD, Skorin said, so they are not diagnostic on their own; but if a patient shows deficits in his or her saccades, and all other signs point to AD, then AD is likely the cause behind those deficits.

This will likely be indicative in AD patients who have the occipital parietal and occipital temporal regions of their brain degenerate first, Skorin continued. These are the higher cognitive areas that process vision.

“When this happens, they have a hard time recognizing what they are seeing,” he said. “It affects their reading, their driving, but not their ability to see; their visual acuity could be fine. Where you’ll find the problem is in the saccades. You need to have good, accurate saccades to be able to read, for instance, because you’re jumping from letter to letter, word to word, line to line, as you’re moving along. If it’s inaccurate, you’ll overshoot or undershoot. If it’s slowed, then you might have a comprehension problem, where by the time you move from one word to the other, you may have already forgotten what the previous word was.

“So, if you have a patient who is complaining of reading problems and their visual acuity is normal, then you might want to check their saccades. If their saccades are off, then you should think Alzheimer’s,” Skorin said. – by Daniel R. Morgan

Reference:

Yang Q, et al. Age. 2013;35(4):1287-1298.

For more information:

Leonid Skorin Jr., OD, DO, MS, FAAO, FAOCO, practices at the Mayo Clinic Health System in Albert Lea, Minn., and is a member of the Primary Care Optometry News Editorial Board. He can be reached at Mayo Clinic Health System, 404 West Fountain St., Albert Lea, MN 56007; (507) 373-8214; skorin.leonid@mayo.edu.