<figure class="figure">
<img src="../images/class-pupil-slit-vertical-round.svg" class="img-fluid border">
</figure> 
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Pupil shape changes during constriction. This pupil constricts usually predominantly in  horizontal direction. The geometrical shape of the semi-closed pupil can be best described as "lenticular". The commonly used term "elliptical" is simply wrong because it describes a shape that is rounded.<br>
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Note: The slit eyes of a cat do change in both horizontal and vertical direction.