The Abbe number indicates the degree of transverse chromatic aberration that a lens material will produce. It is a measure of a material's dispersion or ability to disperse light of different wavelengths. Materials with a lower Abbe number have higher dispersion and will produce greater chromatic aberration at the periphery of a lens. When prescribing higher-power lenses, those with a higher Abbe number should be chosen to reduce chromatic aberration. Common plastic materials have Abbe numbers ranging from 29-59, with higher values indicating lower dispersion and chromatic aberration.

1. Abbe
Value/Number
Trisruta Deb
1st year, M.Optom
BV(DU)MC School of Optometry

2. Lens Properties
The main material properties of spectacle lenses fall into
several categories, including:
• Refractive index
• Specific gravity or density
• Abbe number or V-value*
• UV absorption
• Impact resistance
• Durability
• Reflectance

3. Introduction
 The Abbe number is optical properties of the material
rather than of its mechanical characteristics.
 The Abbe number is the reciprocal of the dispersive
power of the material and indicates the degree of
transverse chromatic aberration (TCA) which the wearer
will experience.
 It also called as ‘nu’ value
 ABBE value defined after the German Physicist Ernst
Abbe (1840-1905), who defined this useful
measurement of optical quality.

4. Key Notes
 Lower Abbe value lenses will have the higher
Chromatic Aberration at periphery of the lens & vice-
versa.
 ABBE value of the human eye is about 45 to 50
To reduce Chromatic aberration in high power
lenses one should prescribe lenses with high ABBE
value.

5. Cont....
 Chromatic Aberration depends on the 2
properties:
1. Wavelengths of the light rays
2. Refractive Indices of the lens material

6. Chromatic Aberration of Lens
 Light entering an optical medium will be
dispersed into different refractive effects
according to the variation in refractive index
with wavelength(4)
. This is known as chromatic
aberration.

7. Transverse Chromatic Aberration
 It is the type of Chromatic aberration in which
there is the differences in image size of
chromatically formed images.

8. Refractive Index (R.I)
 Defined as the ratio of the velocity of light in
vacuum to the velocity of light in another
medium is called refractive index.

9. Abbe value formula
 Equation for calculating the ABBE Value(v):
 Where, nD, nF & nC are the refractive indices of
the material at the wavelengths of the
Fraunhofer D- , F-, & C- Spectral lines

11. Fraunhofer Lines

12. We can classifies materials in terms
of their Abbe number as follows:
Low dispersion V ≥ 45 (e.g- Crown=59)
Medium dispersion V ≥ 39 but < 45
High dispersion V < 39 (e.g- high density flint = 29)
Therefore, low dispersion materials almost never give rise
to complaints of coloured fringes or off-axis blur.

13. Often in optical practice we notice the
complain:
“These lenses are fine when I look through the
centres but vision is blurred when I look through the
edge”

14. Solution:
 Off- axis blur is due to the TCA (Transverse Chromatic
Aberration)
 TCA at any given point on a lens can be found by calculating
the prismatic effect, P, at that point and dividing by the Abbe
number of the material, that is,
TCA = P/V. (where, P= d.F)
Where, P= prismatic effect (Prentice’s rule) & V= ABBE value

15. Cont...
It is generally considered that the average
threshold value for TCA is 0.1∆.
 TCA less than 0.1∆ is unlikely to give rise to
complaints.

16. ABBE Values of Plastic Lens Materials:
R.I

17. ABBE Values of Glass Lens Materials:
R.I

18. Clinical Application:
 For an example,
If distance prescription of -4.00 DS, and the
patient is looking through 15mm temporal to the
optical centre.
 In this case, for CR-39(ABBE 58) lens the value
of TCA will be around 0.10 ∆.

19. Cont..
 For Polycarbonate (ABBE 30) lens the value
of TCA will be around 0.20 ∆,
 Therefore, we can say in polycarbonate lens
TCA will be more than CR-39 lens & thus off-
axis blur will be more.

20. Important dispensing factors
for lenses with low Abbe value
 Use monocular interpupillary distances.
 Use shorter vertex distances.
 Use sufficient pantoscopic tilt angle, but not
more than 10 degree in case of high power
lenses.
 Measure major reference point heights,
considering pantoscopic angle

21. References:
 System for Opthalmic Dispensing, 2nd
Edition, Irvin M
Borish, O.D, D.O.S, L.L.D, D.Sc.
 Clinical Optics, 2nd
Edition, Troy E. Fannin
 www. pmoptics.com(Pricision Micro Optics)
 Ot Article; CET Continuing Education & Traning, Course
code: C-34968 (Module 2), Course Code: C-12758 (Module 3)

22. THANK YOU!