The Development of Strabismus Test Instrument Using Liquid Crystal Shutter Glasses and IR Camera

Abstract

Cover test is the most widely used technique for detecting strabismus. We adopted liquid crystal (LC) shutter glasses in order to replace cover test. Shutter glasses do not block infrared ray, therefore image could be photographed through the shutter glasses using an infrared (IR) camera. Our proposed instrument is comprised of shutter glasses and control system. Control system is composed of transmitter and receiver in the purpose of easy control while the examiner is monitoring the IR camera. One of the most important parts is receiver. It is composed of pulse generating circuit, multiplexor and microcontroller. The specific frequency signals from pulse generating circuit were transferred to the multiplexor switching parts and inverter. Through the inverter, exactly opposite signals were transferred to the multiplexor switching parts. Actuating signals were sequentially selected according to control signals of the microcontroller and transferred to the right-side or left-side of the glasses respectively. To determine the optimal operation voltage for blocking visible light LC glasses, we measured the transmittance of light according to the voltage. As voltage was gradually increased, transmittance dramatically decreased at 2.5 V in an exponential manner. This shows saturation over 5.5V of the range. Therefore, in order to avoid changing the transmittance, we had to choose a source of 5.5 V or more. Flowchart for clinical decision support was made, and the experiment was performed to evaluate the feasibility of the proposed system. We tested the validity of the instrument based on the results examined by an ophthalmologist.