If the Shut Down for Transport procedure was performed the last time the system was powered down, or if it is unknown, the procedure for unlocking the scan head optics should be performed as a precaution before powering up the system. Insert the Phillips screwdriver, included in the GDxVCC accessory kit, into the optics lock down screw hole (larger of the air vent holes) on the right side of the unit, engage the spring loaded screw and turn the screw counterclockwise to insure that it is loosened and moves freely. This will ensure that the optic assembly is unlocked and it is safe to power up the system
1. With the GDxVCC and peripherals properly connected and the optics unlocked, switch the system on. If there is a printer connected, turn its power switch to the “on” position. Insert the AccessCard into the slot to the left of the LCD display.
2. When the warm-up test is complete, the LOGO screen will be displayed. Select New Patient or Existing Patient. Follow the prompts and enter patient information (or recall patient information if this is a returning patient).
- Enter the patient’s refractive error. Position the patient in front of the GDxVCC with her/his face placed comfortably against the mask.
- Select Full Exam, enter patient refraction manually and press OK (). When the ACQUISITION or ACQUISITION – CORNEA MEASUREMENT screen appears and the Please Wait caption has disappeared, you are ready to scan.
- ☞ IMPORTANT: For a patient’s first scan only, steps 5 through 10 will be performed for the cornea measurement, and then repeated for the RNFL measurement.5. Ask the patient to gaze at the blinking fixation target in the red field; the right eye will be first and the target will be on the patient’s left.6.Move and rotate the joystick to center the yellow crosshairs on the pupil, then move the joystick forward or back to center the white focus dot on the horizontal red line.
- With the patient’s eye and focus dot properly aligned, press the Image Acquisition button on top of the joystick to scan the eye. The system will automatically switch to the other eye. Repeat steps 4 through 6.
- If the ellipse is not well centered on the optic nerve head (ONH) or on the macula (for cornea measurement), reset the position of the ellipse. Press OK () to return to IMAGE CHECK.
- Review the scans on the IMAGE CHECK screen. If the images are not acceptable, select Retake Image and repeat steps 5 through 8. (On the IMAGE RETAKE SELECTION screen, choose Retake Both Eyes, Retake Right (OD) Eye, or Retake Left (OS) Eye as appropriate.)
10.When ellipse placement and image quality are satisfactory, select Accept. If this is a cornea scan, the ACQUISITION screen will reappear for the compensated RNFL scan (go to step 5). Otherwise, REVIEW CALCULATIONS will appear.
11.At the REVIEW CALCULATIONS screen, select Print, Export, Print & Export Options, Serial Analysis, or Save Only, as appropriate. If desired, enter operator initials and comments.
The Temporal-Superior-Nasal-Inferior-Temporal (TSNIT) graph displays the normal range (shaded area) and the patient’s values (dark line) of Polarimetric Thickness developed from the data obtained along the Calculation Circle.
The left side of the TSNIT graph starts the plot from the Calculation Circle, beginning at the temporal side of the retina. As the map progresses to the right it plots the Polarimetric Thickness values obtained by tracing around the Calculation Circle, passing through the Temporal, Superior, Nasal, Inferior, and then back to the Temporal positions.
☞ Note: Although the TSNIT graph provides a quick, easy look at how a patient compares to normal, it must be recognized that this analysis is based only on the data points within the Calculation Circle.
TSNIT Symmetry Graph
This graph matches and overlays the individual TSNIT graphs of the right and left eye to allow for better visualization of asymmetry.
On this graph, look for differences between the right and left eye with regard to Polarimetric Thickness and TSNIT shape and placement.
TSNIT Comparison Graph
This graph matches and overlays the individual TSNIT graphs of two right or two left eye scans to allow for analysis of change between visits.
On this graph, look for the degree of overlap between the two scans on the same eye.
TSNIT Serial Analysis Graph
This graph matches and overlays the individual TSNIT graphs of the same eye (either right or left) of the patient scanned at two, three, or four different visits to allow for visualization of change over time.
On this graph, look for the presence (or lack) of change in Polarimetric Thickness, as well as the amount of thinning, if present, over time.
Trend Analysis with Probability Graph
The Trend Analysis with Probability graph presents an analysis of the changes over time of the TSNIT measurements and the NFI, over two, three or four different visits. It is designed to facilitate interpretation of the rate of change between visits.
Deviation from Normal Map
This map shows how the patient’s RNFL measurements compare with values derived from the normative database. Small color-coded squares indicate the amount of deviation from normal at each given location and are presented over a black-and-white fundus image to provide a visual frame of reference. A color legend defines the statistical significance of deviation from normal using p-values.
When image acquisition (cornea or RNFL) is completed, the system displays the IMAGE CHECK screen. A good image is one that has a scan quality score of 7 or above, OK’s fo Alignment, Fixation, Refraction, and Other, and is well focused. In some cases and for some eyes, it will not be possible to achieve the recommended score value and avoid all warning messages. In those cases, accept the best scan that can be obtained. Strive to obtain the best image possible, and note any problems on the printout.
Modifying the Macular Ellipse
Following a cornea measurement, the MODIFY ELLIPSE – MEASURING CORNEA screen appears, showing how the system automatically placed the cornea measurement ellipse for each imaged eye. A dotted square shows the optimal optic nerve head centering, which allows you to verify correct patient fixation. To ensure accurate cornea measurement, the macular ellipse should be centered directly over the macula “bow tie” pattern.
Note: For accurate patient fixation, ensure that the ONH is within the dotted square.To change the macular ellipse position, use the arrow buttons. A dot in the center of the ellipse makes it easier to center the ellipse. Do not change the size of the macular ellipse.
If the macula “bow tie” is not well-defined, press the Irregular Pattern button. When Irregular Pattern is selected, the software uses an alternative cornea calculation based on the macula area within the dotted square which does not require macular ellipse placement, and the position buttons are not available. Press the Macula Ellipse button to re-enable the macular ellipse placement options.