To measure the "absent light reflex" with an infrared pupillometer.
Intensive care unit of the Moffitt-Long Hospitals at the University of California—San Francisco.
Three patients lacking a pupillary light reflex early in the postresuscitation period and a consecutive sample of comatose patients in the intensive care unit in whom clinical (penlight) examination demonstrated an absent light reflex.
A portable infrared pupillometer was moved to the bedside of patients thought to have an absent light reflex, and a series of individual scans were averaged to detect the presence or absence of a light reflex.
The study of patients in the intensive care unit was prompted by the observation of three postresuscitation patients whose pupillary light reflex was thought to be clinically absent but found to be present, although small, with infrared pupillometry. All patients in the intensive care unit with known brain death had an absent light reflex, whereas four of nine of those without brain death but with dilated nonreactive pupils had a small light reflex detectable by the infrared pupillometer. This reflex was characterized by a low maximum constriction velocity and low amplitude of constriction.
Infrared pupillometry can sometimes reveal the presence of midbrain function that might otherwise be missed in paralyzed patients.
Merlin D. Larson, Isobel Muhiudeen. Pupillometric Analysis of the 'Absent Light Reflex'. Arch Neurol. 1995;52(4):369–372. doi:10.1001/archneur.1995.00540280051018