Procedure:
(1) Have the patient gaze into the distance.
(2) With a rigid ruler held against the face, measure:
(a) the inner canthal distance in cm (distance between the 2 inner canthi)
(b) interpupillary distance in cm (distance between the centers of both pupils)
(c) outer canthal distance in cm (distance between the 2 outer canthi)
X =
= ((2 * (inner canthal distance)) – (0.2119 * (outer canthal distance)) – 3.909) / (outer canthal distance)
Y =
= ((2 * (inner canthal distance)) – (0.2479 * (interpupillary distance)) – 3.909) / (interpupillary distance)
Z =
= (inner canthal distance) / (interpupillary distance)
W index =
= (X) + (Y) + (Z)
average W index across affected family members =
= SUM(W index for all affected members) / (number of affected members)
Interpretation:
• A family with the average W index >= 1.95 maps to 2q (PAX3 mutation) and is classified as Waardenburg Syndrome Type 1.
• A family with the average W index < 1.95 does not map to 2q and is classified as Waardenburg Syndrome Type 2.
NOTE: The original cutoff was 2.07 but was later lowered to 1.95.
