The slant (obliquity, incline) of the palpebral fissure is the angle taken by a line through the canthi relative to a facial axis.
Evaluation: The patient has both eyes open and relaxed. The patient must sit perfectly still.
Lines drawn:
(1) Frankfurt horizontal line (a line drawn from the upper edge of the external auditory meatus on each side that passes through the inferior margin of the orbit as identified by palpation)
(2) line through the inner and outer canthi for each eye
The angle for the palpebral fissure is the angle between these 2 lines.
Problems affecting the measurements:
(1) facial asymmetry
(2) history of midfacial trauma
(3) presence of epicanthal folds
If the outer canthus is higher than normal (greater angle) then the eyes are said to have a mongoloid slant.
If the outer canthus is lower than normal (negative angle) then the eyes are said to have an antimongoloid slant.
Angle in degrees
Interpretation
> 7.5
beyond 2 SD
5.5 to 7.5
1 to 2 SD
4 to 5.5
within 1 SD
3 to 4 degrees (mean 3.5)
normal
1.5 to 3
within 1 SD
-0.5 to 1.5
1 to SD
< - 0.5
beyond 2 SD
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