FDT isolates a subset of retinal ganglion cell mechanisms in the magnocellular (M-cell) pathway. These M-cells have large diameter fibers and comprise only 3% to 5% of all retinal ganglion cells. The damage of these cells in the disease process makes FDT efficient and effective for the detection of visual field loss.
Here’s what we suggest saying:
“A demonstration of the test is running now. Can you see the black dot in the center and the entire lit video screen? You need to stare at the black dot in the center of the screen during the entire test.”
“From time to time, you will see patterns of flickering black and white vertical bars that will briefly appear in different areas of the screen. The patterns will sometimes be very faint and at other times be very distinct. You are not expected to see the bar patterns at all times. Each time you see the flickering black and white vertical bars of one of the patterns, press the response button once. Can you see these patterns in the demonstration running now? You may practice now by pressing the Button to respond to the patterns.”
“It is OK to blink and a good time to blink is when you press the response Button. If you need to rest or ask questions during the test, you can pause the test at any time by pressing and holding down the response Button. Do you have any questions? Do you understand how to take the test?”
“I will now start the test. There will be a few brief flashes and then the test will begin. Press the response Button once each time you see the flickering black and white vertical bars of one of the patterns, even if the bars are very faint. Please remember to stare at the black dot in the center of the screen during the entire test.”
Select either SCREENING TEST MENU or THRESHOLD TEST MENU from the RIGHT EYE TEST MENU. If running a screening test, choose either RUN SCREENING C-20-1 (or -5) or RUN SCREENING N-30-1 (or -5). If running a threshold test, choose either RUN THRESHOLD C-20 or RUN THRESHOLD N-30. The right eye test will begin immediately after a momentary check of the proper calibration.
The PERCENT COMPLETE scale, field location being tested, PATIENT RESPONSE, FIXATION ERRORS, FALSE POS ERRORS and FALSE NEG ERRORS are displayed on the Operator LCD Display during the test. Remind the patient to keep looking at the dot in the middle of the screen and inform them of the approximate percent complete 3 or 4 times during the test to encourage good patient compliance. Monitor the catch trials (FIXATION ERRS, FALSE POS ERRS, and FALSE NEG ERRS) during the test. The catch trial display fields will be highlighted on the Operator LCD Display if 2 or more catch trials have been responded to by the patient. A high ratio on any of the catch trials indicates unreliable results and that the test should be restarted or repeated.
For the right eye, near the end of a SCREENING N-30 TEST or a THRESHOLD N-30 TEST, the FDT will pause for approximately 15 seconds. The internal fixation target will move to the right on the screen. This allows two extra nasal points to be tested. At the same time the following instructions will appear on the screen: “Inform Patient Fixation Moved Right.” Advise the patient to re-fixate on the black spot in its new position and continue to press the Button until the test completes. The instruction will note fixation moved to the left when testing the left eye.
Patient reliability (Fixation, False Positive, and False Negative) errors that exceed 1 are highlighted on the operator LCD and marked with an asterisk (*) on the results printout.
False Negative and False Positive catch trial presentations are indicated by the symbols (+) & (-) on the operator LCD so they can be distinguished from regular teststimulus presentations.
You can both view the results on the Operator LCD Display and print them out from the test results menu. At the end of a test, the results will be automatically printed (default set-up is automatic printing) and then the test results menu will automatically appear on the Operator LCD Display.
Select either VIEW RIGHT EYE RESULTS (3rd Operator Button from the top) or VIEW LEFT EYE RESULTS (Bottom Operator Button) to view the individual eye results for the patient just tested on the Operator LCD Display. Use the GREEN Button to back-up to the previous screen to allow you to toggle between the eye results or to return to the FDT MAIN MENU (press it twice if necessary). Select PRINT REPORT (TOP Operator Button) to obtain additional copies of the results for the patient just tested (you can print as many copies as you’d like).
This instrument does not require scheduled calibration. The instrument calibration is checked each time the instrument is powered ON and at the start of each test to be sure the unit is properly calibrated. If the instrument detects the need for calibration, the Operator LCD Display will display a Needs Calibration warning. If not calibrated when the Needs Calibration warning is displayed, the unit will continue to operate normally until the unit reaches the calibration limits. Once the calibration limits are reached, the unit will not operate normally until a calibration is completed successfully. Calibration may be performed at any time, not only when requested by the instrument.
To calibrate the instrument, select UTILITIES MENU (BOTTOM Operator Button) from the FDT MAIN MENU and then RUN SELF-CALIBRATION (2nd Operator Button from the top) in the UTILITIES MENU. Follow the Operator LCD Display instructions to start the calibration. The calibration will take several minutes and requires no operator interaction during calibration. If the calibration cannot be completed successfully, repeat the RUN SELF-CALIBRATION sequence again (up to 3 times). If SELF-CALIBRATION cannot be completed after 3 attempts, record the information on Operator LCD Display and contact an authorized customer service representative for assistance.