System and measurement method for binocular pupillometry to study pupil size variability

Abstract

BackgroundAn objective and noninvasive examination of pupil size variability can be used to assess the activity of the autonomous nervous system. We designed a system that enables binocular, fast, and accurate recordings of different types of pupil variabilities, which are synchronous with other biosignals. This type of measurement system is needed to extend the scope of pupillometry applications.MethodsIn the proposed system, the left and right eyes are independently and interchangeably illuminated to generate alternating images, which are successively acquired by a single camera. The system is composed of four functional modules: the image acquisition module, the image processing unit, the light stimulator, and the controller. The proposed image processing algorithm approximates the shape of the pupil using the best-fit ellipse. The user control panel (controller) precisely sets the stimuli parameters and controls the entire measurement procedure.ResultsThe computer-based binocular system records the pupil size during the pupil light reflexes (direct and indirect) and spontaneous pupil size fluctuations, at a sampling rate up to 75 Hz, with a resolution better than 0.02 mm. Our initial laboratory tests confirmed that the new system is fast and precise (system accuracy better than 0.5% and repeatability better than 4%).ConclusionsThe proposed system’s unique geometry and construction, and the method it uses to detect images from each eye, allows us to monitor the right and left eyes using a single camera with no overlap between the images. The system does not require a very experienced operator, because it is relatively simple and easy to use. Importantly, it is comfortable for the subjects. Additionally, the presented system can operate with other bio-measurement systems using a synchronous signal. These system capabilities can expand the scope of pupillometry research applications.

A high-resolution binocular video-oculography system: assessment of pupillary light reflex and detection of an early incomplete blink and an upward eye movement

“…Noncircularities of real pupils are in the order of 0.02 [ 45 ], so we assumed a circular pupil. There are basically two ways of approaching pupil image processing reported in the literature; the Hough Transform [ 46 , 47 ] and best ellipse fitting [ 18 , 35 - 37 , 48 ]. We used a Circular Hough Transform (CHT) [ 49 ] based algorithm to detect circles in the images (Figure 2 c), selecting this approach is used because of its robustness in the presence of noise, occlusion and varying illumination.…”

“…Binocular registration of the PLR is required in clinical and research applications to assess direct and consensual pupil reactions. A binocular system has recently been proposed [ 37 ] based on a single camera that alternately records images of the left and right eyes. With a sampling rate up to 75 Hz and a resolution of more than 20 μm, this is sufficient to assess the PLR but again falls below the requirements to accurately register the fastest eye reflexes.…”

Analysis for Extracted Features of Pupil Light Reflex to Chromatic Stimuli in Alzheimer’s Patients

“…The duration of observations was 10 seconds, with the first 2s being a prestimulus phase as a rest period, followed by a 1s light pulse and 7s as a restoration phase. Pupil diameters were measured in mm at 60Hz using a system developed by some of the authors, which is illustrated in Figure 1 [37]. Figure 1 shows a diagram of the measuring unit, which is installed on an ophthalmological slit lamp base as the image acquisition module, and it consists of the infrared (IR) illumination, the optical path, and a single camera with a frame grabber.…”

Prediction of Alzheimer's Disease in Patients using Features of Pupil Light Reflex to Chromatic Stimuli

“…The duration of observations was 10 seconds, with the first 2s being a pre-stimulus phase as a rest period, followed by a 1s light pulse and 7s as a restoration phase. Pupil diameters were measured in mm at 60Hz using a system developed by some of the authors [11]. PLRs for each stimuli were observed in single trials using a repeated-measure design.…”