Since the early second century, the pupillary light response (PLR) has been utilized in neurological examinations to gain insight into patient conditions and neuroprognostication. Traditionally, manual pupillometry has been employed to evaluate PLRs. However, this method is subjective and exhibits low interexaminer consistency and reliability. The advent of quantitative pupillometry (QP) has provided clinicians with an objective and reliable method to evaluate and standardize pupillary metrics, most notably, the Neurological Pupil index (NPi). QP protocols have been instituted in many neuro intensive care units (ICUs) as a tool for quickly assessing patients and informing clinical decision-making. A literature review was conducted to understand the use of QP in neuro ICUs and document the relationships between pupillary measurements and clinical consequences. The databases PubMed, Embase, and Scopus were systematically searched for original research articles from 1995 to 2025 in which QP was used for adult patients in the neuro ICU. Using 21 search terms, a total of 52 articles were identified and analyzed. The findings demonstrated the widespread use of QP in patients with acute brain injuries, such as traumatic brain injury, aneurysmal subarachnoid hemorrhage, intracerebral hemorrhage, and stroke. Many studies have established NPi as a non-invasive surrogate measure of intracranial pressure (ICP), which is particularly useful in screening for elevated ICP owing to its high negative predictive value. Correlations were noted between abnormal NPi, poor neurological outcomes, and a greater risk of mortality in many types of brain injury. The identification of the relationship between NPi and clinical events in specific patient populations may aid clinicians in tailoring QP usage to patients.