Opthalmic lens materials

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Last updated 1:52 PM on 7/13/26
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10 Terms

1
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What is the correlation between Vd (contingence), abbe number and chromatic aberration?

Higher Vd = higher abbe number = lower chromatic aberration

2
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What is the correlation between Refractive index and Vd?

Higher refractive index = lower Vd

3
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How do you work out dispersion power?

1/ Vd

4
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How do you work out LCA (Longitudinal chromatic aberration?

F/ V

(BVP/ Vd. It is noticeable >0.5mm)

5
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How do you work out TCA? (Transverse chromatic aberration)

(F/V)y

(BVP/ Vd) x distance from optical centre (cm)

It is noticeable >0.1-0.2mm

It is more bothersome

6
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What are the highest to lowest Vds in some lens materials?

58- crown glass, CR39, PMMA

46- trivex

31- glass 1.9

30- polycarbonate

7
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Properties of CR39

  • can coat, tint, made easily

  • Shrinks

8
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Properties of trivex

Strong, light, good for rimless

9
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Properties of glass

  • to increase refractive index, can add lead, titanium, lanthanum oxide

  • To decrease dispersion/ chromatic aberration- can add barium oxide + fluoride

10
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Properties of polycarbonate

  • Soft→ scratches

  • Higher dispersion

  • Bad CA

  • Worse as power increases