Fig. 5.

Schematic illustration of the effects of the eyelid on astigmatic focal lines. As the eyelid fissure size becomes smaller than the diameter of the entrance pupil, a slit-like effect occurs and eventually shortens the vertical focal lines. In simple ATR astigmatism, the focus (circle of least confusion) moves to the nearer plane; in WTR astigmatism, the focus moves to the farther plane