• CSLO
  • What information
    does CSLO provide?
• SLP
  • What information
    does SLP provide?
• OCT
  • What Information
    does OCT provide?
    • Limitations
    • Imaging Artifact

What information does SLP provide?

The GDx VCC report contains a number of images: the reflectivity (fundus) image; the retardation (RNFL thickness) image; a statistical deviation image; and the Temporal-Superior-Nasal-Inferior-Temporal (TSNIT) graphs (RNFL profile plots).

Reflectivity Image

• The reflectivity (fundus) image displays the position of the peripapillary measurement annulus and allows an assessment of how well centred the annulus is on the optic disc.

Retardation Image

• The retardation (RNFL thickness) image displays a heat map of RNFL thickness, with hotter colors representing greater retardation values (and, therefore, thicker RNFL).

Statistical Deviation Image

• The statistical deviation image highlights pixels in which retardation values fall below those in the normative database. The color of the pixel indicates the level of probability of deviation from normal, with the probability values displayed in the central panel. The map allows the clinician to evaluate the anatomical distribution of abnormally low retardation.

TSNIT Parameters and Graphs

• The TSNIT values describe the retardation measurements in an annulus centered on the optic disc, initially scanning the temporal region then moving superiorly, nasally, inferiorly and lastly temporally.

Figure: TSNIT calculation annulus

• The TSNIT parameters are summary measures based on RNFL thickness values within the calculation circle. These parameters are automatically compared to the normative database and are quantified in terms of likelihood of normality.
• Three average values are calculated:
• TSNIT Average refers to the average RNFL thickness around the entire calculation circle.
• Superior Average refers to the average RNFL thickness in the superior 120° region of the calculation circle.
• Inferior Average refers to the average RNFL thickness in the inferior 120° region of the calculation circle.
• The TSNIT graphs (RNFL profile plots) display the RNFL thickness values around the measurement annulus in relation to the statistically normal range. The center panel allows an appreciation of the symmetry between the 2 eyes.
• The central panel displays values for the parameters that best discriminate between normal and glaucomatous eyes, with color-coded probability values to indicate the degree of deviation from the normative database. An inter-eye symmetry value is given; values near 1.0 represent good symmetry and values near 0 represent poor symmetry.
• The Nerve Fiber Indicator (NFI) is calculated using a support vector machine algorithm based on several RNFL measures. The cut-offs suggested by the manufacturer are 0 to 30 for within statistically normal limits, 31 to 50 for borderline and 51 to 100 for outside statistically normal limits.

GDx VCC Standard Report

A standard GDx VCC report is shown below:

Figure: Standard GDx VCC report              View Large

LIMITATIONS