Pupil perimetry using M-sequence stimulation technique

PURPOSE. M-sequence stimulation technique allows mapping of the retinal fun ction by multifocal electroretinographic (ERG) recordings. However, the inf ormation provided about visual field is limited to retinal function. Optic nerve diseases and diseases of the higher visual pathways usually show norm al multifocal ERGs. Using pupillary responses instead of the electrical ret inal responses might enhance the diagnostic possibilities of this system. T he problems of local ERG recordings are very similar to those encountered i n pupil perimetry: Local stimuli have to be dim to avoid or at least reduce stray-light responses. Dim stimuli, close to the absolute threshold, elici t only subtle pupillomotor responses. Therefore, techniques that are able t o detect small focal responses are promising. METHODS. Pupillography was done by means of an infrared video camera and re al time image processing (50 Hz) using a custom-designed videoboard in a pe rsonal computer (486). Recording conditions: The stimulus was presented on a monitor (75 Hz) in 26 cm distance from the patient's eyes. It contained 3 7 hexagons in a 25 degrees visual field. Each element changed between black (1.6 cd/m(2)) and white (160 cd/m(2)) after a binary M-sequence independen tly from other elements. Four thousand ninety six different stimulus pictur es of 120-msec duration were shown during a single pupillogram recording. T hirty-seven local pupillograms were calculated in a cross-correlation of st imulus sequence and the pupil diameter. RESULTS. The pupillomotor fields in normals showed a shape and sensitivity distribution as known from conventional pupil perimetry techniques. Artific ial paracentral scotomas (5 degrees) created by masking different locations could be demonstrated convincingly. Even in patients with optic nerve lesi ons it was possible to demonstrate visual field defects. CONCLUSIONS. Pupil perimetry using the M-sequence technique is a promising method of objective perimetry that may find its entrance into clinical appl ication.