VISUAL PERCEPTION LABORATORY
   
Chicago Dark Adaptometer.    This is a self manufactured and computer controlled Dark Adaptometer. Major features:
  • Automated
  • LED based
  • Dynamic range: 9 log units
  • Mac Xcode Cocoa powered
  • Freely control waveforms and durations
  • Short test time
  • USB Gamepad for responses
  • Soundcard for digital control of LED output
   
Hardware.    The dark adaptometer is adapted from the four-primary photostimulator inveneted by Dr. Joel Pokorny (Pokorny, Smith & Quinlan. Visual Neuroscience 21: 263-267, 2004, Reprint), with light output from each LED digitally controlled an M-Audio PCI soundcard (Puts, Pokorny, & Quinlan,and Glennie. Journal of Neuroscience Methods 142: 77-81, 2005, Reprint). Four LEDs with the same spectral distribution and dynamic range are used with each LED sandwiched with different ND filters. The computer software will switch one LED to another automatically depending on the required light level during the staircase procedure. Other than ND filter controls, the computer also provides digital control of the LED output. The dark adaptometer can provide 9 log units of dynamic range.
Fixation. Two fixation points one on the left and one on the right. Each of the fixations is illuminated by a red LED powered by the same power supply as the LEDs for test stimuli. There is switch box that can switch on one of the red LEDs for fixation. The switch box can also adjust the intensity of the fixational LEDs. The test stimulus is about 10 deg away from fixation.
Stimulus Size. The test size is comparable to Goldmann-Weekers dark adaptometer.
   
Software.     The software for threshold measurement is developed in Mac OS-X Cocoa environment. The software can freely control the waveform (square wave or sine wave), its temporal frequency and duration. The threshold is determined by a 1-yes 1-no staircase. The software will switch one LED to another automatically depending on the required light level during the staircase procedure. The staircase will terminate automatically with a sound warning from the computer. It takes less than 2 minutes to complete a threshold measurement during the course of dark adaptation. The experimenter has to do nothing during the dark-adaptormetry test. This device is a completely automated instrument.
    We have two versions of software, one for full-dark adaptation curve (mainly for research purpose, light adapted first then measure threshold every 5 minutes till 45 min in the dark) and the other for one threshold measurement only (for clinical purpose, no light adaptation, only dark adaptation is required).
   
Validation.    We measured detection threshold in 7 observers with normal vision (age 20-67 yrs) after 20 minutes in the dark. The results (blue circles for data from individual observer and the red line for 95% confidence interval) are well within the range reported by Hecht (1939). See Figure on the right. We have tested patients with retinal diseases. The evelation in dark-adapted detection threshold among those patients are consistent with ERG measurements.
Interested?    Contact Dr. Cao (dcao98@uic.edu) .