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Bas Bikker, Gregoor van Diepen, Marijn Swart, Flip Somerwil, Just L Herder, Huibert Jan Simonsz; Scanning Brückner test with tilting mirror for objective calibration of the projection of the fovea in small children. Invest. Ophthalmol. Vis. Sci. 2016;57(12):2445.
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© ARVO (1962-2015); The Authors (2016-present)
De Groot (Strabismus 2015;23:85-100) has shown that a luminance map of retinal reflection can be made by a scanning procedure with the Brückner reflex using a stationary camera and a moving fixation object. To use this on a young child for objective calibration of the projection of the fovea in measurement of angles of strabismus, scanning must be completed within a second. However, we developed a scanning procedure with a tilting mirror.
Subjects aged 23-26 placed their head in a headrest opposite to a GC2450 camera (Allied Vision Technologies with a Sony ICX625 CCD-sensor) used for eye tracking with a coaxial fixation object, a green LED, at 1.5m. A second GC2450 camera, also at 1.5m, registered the Brückner red pupillary reflex via a partial (30%) reflecting mirror (170x280mm) between the subject and the first camera. A coaxial infrared (870nm) LED in front of the second camera elicited the Brückner reflex. A high-pass IR filter blocked wavelengths below 720nm. The images were recorded as an 8-bit grayscale found previously to be linearly proportional to luminance. Angular position of the mirror was recorded with a hall rotary sensor.
Control measurements showed no influence of the fixation LED on reflex intensity. The intensity variation due to mirror rotation was negligible. With foveal fixation the luminance with fixed mirror was 22.1 SD 0.49 grayscale units on repeated measurements. Luminance profiles (Figs. 1-2 for horizontal rotation of mirror), were obtained by rapid step rotation of the mirror while the subject fixated on the green LED.
Reflex-intensity variation caused by mirror rotation was less than the reflex-intensity noise while keeping the mirror fixed. The luminance profile showed decreased pupillary reflectance at foveal fixation, as found previously. The results show that a tilting mirror can be used for objective calibration of the projection of the fovea with a scanning Brückner test in optical measurement of the angles of strabismus in young children.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
Image 1: Luminance profile of Brückner pupillary reflectance (all data points)
Image 1: Luminance profile of Brückner pupillary reflectance (mean and standard deviation)
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