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Mariela C Aguilar, Alex Gonzalez, Cornelis Rowaan, William Lee, Carolina de Freitas, Karam Alawa, Andres Bernal, David H Sliney, Byron L Lam, Jean-Marie A Parel; BPEI Photosensitivity Tester: Instrument Design and Test Results in Healthy Subjects. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4108.
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To develop an instrument capable of measuring a quantitative threshold for photosensitivity discomfort using light emitting diodes (LED) binocular light stimuli.
The autonomous instrument produces a light stimulus with a concave array panel configured with 210 LEDs focused at 50cm (Figure 1a). The computer controlled, calibrated (X1, Gigahertz-Optik, Inc., Newburyport, MA, USA) LED array ranges 14-9200 lux divided into 25 levels. The instrument was programmed for a 2 sec exposure at 4 sec inter-stimulus interval. In autonomous mode, the subject is instructed to press a button to indicate when the light intensity is uncomfortable, which is registered by the computer. The Garcia-Perez staircase technique is used to adjust each stimulus. This technique utilizes unequal ascending and descending steps. The test for each subject is completed after 10 response reversals. A photosensitivity threshold is calculated from the mean of these 10 response reversals. A computer graphical user interface (National Instruments, Austin, TX, USA) was designed to record high-resolution infrared video and subject responses and calculate the light intensity data within the interval between stimuli and for subsequent stimuli (Figure 1b). This instrument was thus far tested on 6 healthy subjects (2 males, 4 females, ages = 19-32) under an IRB approved protocol. All sessions were performed at the same time of day. Prior to testing, the subjects were allowed a 4 min adaptation period in the examination room with background lighting of 250 lux.
Five subjects were found to have a mean predicted photosensitivity threshold of 2767±1793 lux. One subject tolerated the maximal light intensity without experiencing any discomfort.
The BPEI photosensitivity testing device can detect and record individual differences in sensory capabilities. This instrument will be used to test the difference in sensory capabilities for those cases of blepharospasms, retinal degeneration, trauma, and dry eye. A 2nd generation instrument capable of producing up to 30,000 lux was built to include pupilometry, blink rate, and inter eyelid distance (Figure 2).
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