![]() In addition, the percentage change (%CH) in pupil constriction was analyzed using the difference between the maximum and minimum pupil diameters. During these phases, DV was calculated using the changes in diameter over time. Following peak constriction, the pupil quickly starts dilating from its constricted state to its initial size. MCV is usually observed during the initial constriction phase before reaching the minimum pupil diameter. After the latency period, the pupil starts constricting, and the CV is analyzed and reported using changes in the pupil diameter (mm) per second (mm/sec) as well as the maximum CV (MCV). Latency (ms) is the delay time in pupil constriction following the light stimulus, which is affected by the intensity of the light and the iris smooth muscle. A quantitative pupillometer, especially Neuroptics neurological pupil index (NPi), which measures constriction response to light, provides measured objective parameters during four phases: pupil diameter, latency, constriction velocity (CV), and dilation velocity (DV) ( Fig. The dynamics of PLR measured by a quantitative pupillometer consisted of four phases, which were based on changes in pupil diameter over time by light stimuli ( Fig. Ī quantitative pupillometer is a noninvasive portable device with a light-emitting diode light source, liquid crystal display screen, and digital video camera based on infrared that measures and analyzes both PLRs. When the afferent and efferent pathways for pupil reactivity are intact in functional and structural processes, both pupils show equal sizes and brisk constriction responses when stimulated with bright light. Parasympathetic input for pupil constriction is balanced and controlled by sympathetic signals from the superior cervical ganglion for pupil dilatation. ![]() The parasympathetic pupillary efferent signal stimulates the short posterior ciliary nerves that innervate the iris for pupil constriction. After stimulation of the Edinger-Westphal nucleus, the parasympathetic signal is delivered by the oculomotor nerve to the superior orbital fissure of the eye and ciliary ganglion. Under normal conditions of pupillary reactive responses, the stimulant signal of retinal cells is carried through the synapse between the optic nerve and the optic tract in the pretectum of the midbrain, which projects to the Edinger-Westphal nucleus in the dorsal midbrain. In addition, changes in PLR could strongly predict neurological worsening after acute brain injury. Neuromonitoring of the PLR is important to detect changes in brain lesions, identify newly developed pathologies, and prevent impending secondary brain injury.
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