Dangerous Alarming Diameter Assessment (DADA Index) in Which the Ratio of Iris Surface/Pupil Surface Size Is More Reliable than Pupil Diameter Measurement in Comatose Patients After Subarachnoid Haemorrhage: An Experimental Rabbit Model

Objective/Background: Pupil diameter varies across individuals, limiting its reliability in assessing cerebral pathologies, particularly in comatose patients following subarachnoid haemorrhage (SAH). The Dangerous Alarming Diameter Assessment (DADA) index, defined as the ratio of iris surface to pupil surface, may offer a more precise diagnostic tool. This study evaluates the efficacy of the DADA index compared to pupil diameter in predicting neurodegeneration in the Edinger–Westphal nucleus (EWN) and diagnosing brain death in an SAH model. Methods: Twenty-three rabbits were divided into Control (n = 5), Sham (n = 5), and Study (SAH, n = 12) groups. Pupil diameter and DADA index values were measured via spectral-domain optical coherence tomography (SD-OCT) in groups at post-intervention (0.75 cc serum physiologic injection for Sham, 0.75 cc autologous blood injection for Study). After one week, animals were sacrificed, and EWN degenerated neuron density was quantified using stereological methods. Data were analysed with Kruskal–Wallis and Mann–Whitney U tests, with correlations assessed for pupil diameter and DADA index against EWN neurodegeneration. Results: Pupil diameter assessment classified all 12 study group subjects as deceased, primarily due to fixed and dilated pupils. In contrast, the DADA index identified only 8 of these 12 subjects as deceased, with EWN degenerated neuron density exceeding 80%, while the remaining 4 subjects showed less than 80% neurodegeneration, indicating viability. Strong negative correlations were observed between pupil diameter (r = −0.972, p < 0.001) and DADA index (r = −0.977, p < 0.001) with EWN neurodegeneration. The DADA index demonstrated superior precision in distinguishing severe neurodegeneration, suggesting its potential as a criterion for brain death assessment. Conclusions: The DADA index provides a more accurate and nuanced evaluation of EWN neurodegeneration compared to pupil diameter, offering a promising diagnostic tool for brain death in SAH-induced comatose states, with potential implications for future brain transplantation diagnostics.