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. 2015 Mar 13:14:22.
doi: 10.1186/s12938-015-0016-6.

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

Julián Espinosa  1   2 , Ana Belén Roig  3 , Jorge Pérez  4   5 , David Mas  6   7
Affiliations

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

Julián Espinosa et al. Biomed Eng Online. .

Abstract
in English, Spanish

Background: The pupillary light reflex characterizes the direct and consensual response of the eye to the perceived brightness of a stimulus. It has been used as indicator of both neurological and optic nerve pathologies. As with other eye reflexes, this reflex constitutes an almost instantaneous movement and is linked to activation of the same midbrain area. The latency of the pupillary light reflex is around 200 ms, although the literature also indicates that the fastest eye reflexes last 20 ms. Therefore, a system with sufficiently high spatial and temporal resolutions is required for accurate assessment. In this study, we analyzed the pupillary light reflex to determine whether any small discrepancy exists between the direct and consensual responses, and to ascertain whether any other eye reflex occurs before the pupillary light reflex.

Methods: We constructed a binocular video-oculography system two high-speed cameras that simultaneously focused on both eyes. This was then employed to assess the direct and consensual responses of each eye using our own algorithm based on Circular Hough Transform to detect and track the pupil. Time parameters describing the pupillary light reflex were obtained from the radius time-variation. Eight healthy subjects (4 women, 4 men, aged 24-45) participated in this experiment.

Results: Our system, which has a resolution of 15 microns and 4 ms, obtained time parameters describing the pupillary light reflex that were similar to those reported in previous studies, with no significant differences between direct and consensual reflexes. Moreover, it revealed an incomplete reflex blink and an upward eye movement at around 100 ms that may correspond to Bell's phenomenon.

Conclusions: Direct and consensual pupillary responses do not any significant temporal differences. The system and method described here could prove useful for further assessment of pupillary and blink reflexes. The resolution obtained revealed the existence reported here of an early incomplete blink and an upward eye movement.

Antecedentes: El análisis del reflejo pupilar a la luz caracteriza la respuesta directa y consensual del ojo al brillo percibido de un estímulo y puede utilizarse como indicador de patologías tanto neurológicas como en el nervio óptico. Al igual que otros reflejos, se trata de un movimiento rápido casi instantáneo y está ligado a la activación de la misma área del mesencéfalo. La latencia del reflejo pupilar es de alrededor de 200 ms, pero los reflejos oculares más rápidos son de sólo 20 ms. Por tanto, es necesario un sistema con suficiente resolución espacial y temporal para evaluarlos con precisión. En este trabajo, analizaremos si existe alguna discrepancia entre la respuesta directa y consensual en el reflejo pupilar a la luz así como si hay algún otro reflejo ocular anterior a éste.

Métodos: Hemos construido un video oculógrafo binocular con dos cámaras de alta velocidad simultáneamente enfocando a ambos ojos y, con éste, evaluamos la respuesta directa y consensual de cada ojo. Para ello, hemos desarrollado un algoritmo que mediante la transformada circular de Hough detecta y rastrea la pupila y permite obtener los parámetros temporales que describen el reflejo pupilar a la luz a partir de la variación del radio en el tiempo. Ocho sujetos sanos (4 mujeres y 4 hombres de edades entre 24 y 45) participaron en este experimento.

Resultados: Nuestra propuesta, que alcanza una resolución de 15 micras y 4 ms, ha proporcionado valores para los parámetros temporales que caracterizan el reflejo pupilar a la luz similares a los encontrados en trabajos previos y no se han hallado diferencias significativas entre los reflejos directo y consensual. Además, en torno a los 100 ms, encontramos un reflejo incompleto de parpadeo y un movimiento del ojo hacia arriba que puede corresponderse con el fenómeno de Bell.

Conclusiones: Las respuestas pupilares directa y consensual no presentan ninguna diferencia temporal apreciable. El sistema y el método descritos podrían ser útiles para un análisis más a fondo de los reflejos pupilares y de parpadeo. Así, su capacidad resolutiva ha revelado un parpadeo temprano incompleto y un movimiento del ojo hacia arriba.

Palabras clave: Medida binocular, reflejo pupilar a la luz, parpadeo temprano incompleto, fenómeno de Bell

Electronic supplementary material: The online version of this article (doi:10.1186/s12938-015-0016-6) contains supplementary material, which is available to authorized users.

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Figures

Figure 1
Figure 1
Picture of the general experimental setup. The image shows the arrangement of the elements used in the experiment.
Figure 2
Figure 2
Image processing phases. a) Original frame, b) Wiener-filtered region of interest, c) circle drawn after determining its center using the Circular Hough Transform.
Figure 3
Figure 3
Test of the method robustness using an artificial eye. Time variations for pupil center coordinates and radii obtained for an artificial eye. Pupil center coordinates x and y are blue and red crosses, respectively (left axes). Black dots represent pupil radius (right axes). Flash is shot at t = 0 s.
Figure 4
Figure 4
Time variations in pupil radii. a) Pupil radii relative to the radii at t = 0 s. b) Second time-derivative of the pupil radii evolution. Flash was shot at t = 0 s.
Figure 5
Figure 5
Pupil center tracking. Detrended mean evolutions in time of the pupil center: a) y coordinate and b) x coordinate, for the right (green) and left (black) eyes.
Figure 6
Figure 6
Example of the upward pupil movement. a) The first frame and b) the frame at 0.1 seconds after the flash shot, for one example pupil. The red line represents the initial position and the green dashed line represents the position at t = 0.1 s, clearly depicting the upward movement of the eye (Bell’s phenomenon) and the shadow of the upper eyelid (incomplete blink).
See this image and copyright information in PMC

References

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