title: A PC-based shutter glasses controller for visual stimulation using multithreading in LabWindows/CVI.
abstract: OBJECTIVE
  Amblyopia, commonly known as "lazy eye," is poor vision in an eye from prolonged neurologic suppression. It is a major public health problem, afflicting up to 3.6% of children, and will lead to lifelong visual impairment if not identified and treated in early childhood. Traditional treatment methods, such as occluding or penalizing the good eye with eye patches or blurring eye drops, do not always yield satisfactory results. Newer methods have emerged, based on liquid crystal shutter glasses that intermittently occlude the better eye, or alternately occlude the two eyes, thus stimulating vision in the "lazy" eye. As yet there is no technology that allows easy and efficient optimization of the shuttering characteristics for a given individual. The purpose of this study was to develop an inexpensive, computer-based system to perform liquid crystal shuttering in laboratory and clinical settings to help "wake up" the suppressed eye in amblyopic patients, and to help optimize the individual shuttering parameters such as wave shape, level of transparency/opacity, frequency, and duty cycle of the shuttering.
  
  
  METHODS
  We developed a liquid crystal glasses controller connected by USB cable to a PC computer. It generates the voltage waveforms going to the glasses, and has potentiometer knobs for interactive adjustments by the patient. In order to achieve good timing performance in this bidirectional system, we used multithreading programming techniques with data protection, implemented in LabWindows/CVI.
  
  
  RESULTS
  The hardware and software developed were assessed experimentally. We achieved an accuracy of ±1Hz for the frequency, and ±2% for the duty cycle of the occlusion pulses. We consider these values to be satisfactory for the purpose of optimizing the visual stimulation by means of shutter glasses. The system can be used for individual optimization of shuttering attributes by clinicians, for training sessions in clinical settings, or even at home, aimed at stimulating vision in the "lazy" eye.
  
  
  CONCLUSIONS
  Multithreading offers significant benefits for data acquisition and instrument control, making it possible to implement time-efficient algorithms in inexpensive yet versatile medical instrumentation with only minimum requirements on the hardware.
authors.affiliation: Towson University, Baltimore, MD, USA.
authors.forename: Ivan
authors.initials: I
authors.lastname: Gramatikov
authors.affiliation: Wilmer Eye Institute, Johns Hopkins University School of Medicine, Wilmer 233, 600 N. Wolfe St., Baltimore, MD 21209, USA.
authors.forename: Kurt
authors.initials: K
authors.lastname: Simons
authors.affiliation: Wilmer Eye Institute, Johns Hopkins University School of Medicine, Wilmer 233, 600 N. Wolfe St., Baltimore, MD 21209, USA.
authors.forename: David
authors.initials: D
authors.lastname: Guyton
authors.affiliation: Wilmer Eye Institute, Johns Hopkins University School of Medicine, Wilmer 233, 600 N. Wolfe St., Baltimore, MD 21209, USA. Electronic address: bgramat@jhmi.edu.
authors.forename: Boris
authors.initials: B
authors.lastname: Gramatikov
mesh_terms: D000550:Amblyopia / Q000628:therapy*; D003198:Computer Simulation; D003201:Computers; D004867:Equipment Design; D005123:Eye; D005139:Eyeglasses; D006801:Humans; D009883:Ophthalmic Solutions; D011381:Programming Languages; D012984:Software; D014584:User-Computer Interface; D014785:Vision, Ocular
chemical_list: D009883:Ophthalmic Solutions
keywords: Amblyopia; Liquid crystal shutter; Multithreading; Shutter glasses; Thread-safe queues