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In future, comatose patients—the bulk of those seen in emergency departments—could have the cause of their coma identified by simple eye tests. A prospective probabilistic study has for the first time confirmed loss of light reflex and unequal pupil size as important diagnostic criteria.
These two criteria independently predicted coma with a structural cause in multivariate analysis corrected for age, sex, and level of consciousness (odds ratio 11.02 (95% confidence interval 3.9 to 30.9) for loss of light reflex and 7.5 (1.4 to 39.4) for unequal pupil size). The likelihood ratio of a positive result in structurally caused coma was 9.0 for unequal pupil size and 3.59 for loss of light reflex. The results were based on tests in 115 patients, 113 of whom had a final diagnosis of structurally (40%) or metabolically (60%) caused coma. The precise cause was also ascertained. The results for the cohort matched probability estimates quoted in textbooks but not rigorously evaluated until now.
Comatose patients aged ⩾15 years seen in the emergency department of a community teaching hospital during a year were recruited consecutively. All had initial eye tests, full physical and neurological examinations, basic biochemical tests, and imaging tests, if clinically necessary. They were followed up as inpatients, and their medical records were reviewed after a year. One clinical researcher, two if there was disagreement, reviewed the likely cause of the coma.
Usefulness of these two criteria in differential diagnosis of coma has been poorly described before. Differential diagnosis is usually based on clinical experience.
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