Hence, the pupil constricts. Alpha-adrenergic receptors are responsible for dilator muscle movements.
Inhibition and relaxation of the muscle is controlled by muscarinic and possibly, beta-adrenergic
receptors. (Monaco et al., 2012) The imbalance between the two causes pupillary response disorder.
In small pupils, the failure to dilate can be caused by either hyperactivity parasympathetic activity,
hypoactivity of the sympathetic system or both.(Maguire, Craig, Craighead, & Chan, 2007) In resting
phase, pupil size is under sympathetic control. Constriction results from reduced sympathetic outflow.
Thus, parasympathetic control is reflected the in pupil’s constriction phase. However, both are active
during the recovery phase where the stimuli from the pupillometry is absent.(Ferrari et al., 2010)
In the elderly population, there is a decrease of neurons in the norepinephrine locus coeruleus (LC).
This structure plays in vital role in pupillary control as it creates tonic inhibition through the
parasymphatetic Edinger-Westphal nucleus. (Hou et al., 2006) Damage in this area automatically
results in small pupil diameter in pupillometry.
As the elderly population are more prone to developing diabetes (Kirkman et al., 2012), the risk of
developing autonomy disorder also increases. Diabetes is characterized by the high glycemic index in
the blood. Prolonged exposure to high blood glucose can be damaging to the nerves, a condition
known as diabetic neuropathy.(NIH) This condition has various clinical manifestations such as
sensory, motoric and autonomic symptoms.
Dementia is a neurodegenerative disorder that could be found in the elderly. This covers a wide range
of cognitive impairment which progressive rostrocaudally. After affecting the cortex, it will reach the
brain stem. The cranial nerve nuclei are spared, while the autonomic parasympathetic outflow is
disturbed. This means that the Edinger-Westphal nucleus is affected.(Engelhardt & Laks, 2008) In the
pupillometry, patients who suffers from dementia are mostly likely to present small pupil diameter
due to the parasympathetic dysfunction.
With the efficacy of the pupillometer to be implemented in areas with geographic and equipment
limitation, and the reliability of the results compared to other methods (Ferrari et al., 2010),
pupillometer might be a way to detect disorders, especially autonomic disorder in elderly.
Furthermore, the method is simple and does not require a long time to train professional.(Herbst et al.,
2011)
Conclusion
The eye is not merely a visual organ. The ability to perceive light stimulation in the form of pupil
diameter movement can predict disorders that manifest in the abnormal dilation or constriction. Pupil
response test has been used in multidisciplinary medical research ranging from neurology, psychiatry
to endocrine metabolic disorder.
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