D: Facial measures and Frames - Week 5

Question 1

What types of lenses and conditions is vertical centration important for and why? (4-6)

Answer 1

• Aspheric lenses: are designed for on-axis viewing. The benefits of asphericity may not occur if off-axis
• High index materials and Polycarbonate: potential for chromatic fringing if not centred
• High Rx, incl. astig.: off-axis astig effects
• PALs and BFs: because certain parts of the lens have different powers