age            astigmatism, tp-rate, contact-lenses
---------------------------------------------------
young,          no,  normal,  soft
young,          yes, reduced, none
young,          yes, normal,  hard
pre-presbyopic, no,  reduced, none
pre-presbyopic, no,  normal,  soft
pre-presbyopic, yes, normal,  hard
pre-presbyopic, yes, normal,  none
pre-presbyopic, yes, normal,  none
presbyopic,     no,  reduced, none
presbyopic,     no,  normal,  none
presbyopic,     yes, reduced, none
presbyopic,     yes, normal,  hard

[Astigmatism = yes] -> [TP-Rate = normal] -> [Age = PP (pre-presbyopic)]