Abstract

A method of measuring the tear film thickness is described in which interference causes oscillations in the reflectance spectrum from the tears. Strong oscillations were usually observed when a contact lens was worn. Measurement of modulation and phase of these oscillations confirmed that they were associated with the tear layer in front of the contact lens. Calculated thickness of this layer averaged 2.7 µm. In one out of five subjects, weak oscillations were sometimes observed without a contact lens. These oscillations probably arose from the aqueous layer of the tears with a thickness of 3 µm. The relative merits of three interference methods of measuring the tear film are discussed.

© 1998 Optical Society of America

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References

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  1. E. Wolff, “The muco-cutaneous junction of the lid-margin and the distribution of the tear fluid,” Trans. Ophthalmol. Soc. U.K. 66, 291–308 (1946).
  2. J. I. Prydal, F. W. Campbell, “Study of precorneal tear film thickness and structure by interferometry and confocal microscopy,” Invest. Ophthalmol. Visual Sci. 33, 1996–2005 (1992).
  3. Y. Danjo, M. Nakamura, T. Hamano, “Measurement of the precorneal tear film thickness with a non-contact optical interferometry film thickness measurement system,” Jpn. J. Ophthalmol. 38, 260–266 (1994).
  4. J. I. Prydal, P. Artal, H. Woon, F. W. Campbell, “Study of human precorneal tear film thickness and structure using laser interferometry,” Invest. Ophthalmol. Visual Sci. 33, 2006–2011 (1992).
  5. J. P. Craig, P. A. Simmons, S. Patel, A. Tomlinson, “Refractive index and osmolality of human tears,” Optom. Vis. Sci. 72, 718–724 (1995).
    [Crossref] [PubMed]
  6. F. A. Jenkins, H. E. White, Fundamentals of Optics, 4th ed. (McGraw-Hill, New York, 1974).
  7. M. Born, E. Wolf, Principles of Optics, 5th ed. (Pergamon, Oxford, 1975), p. 359.
  8. T. Olsen, “Reflectometry of the precorneal film,” Acta Ophthalmol. 63, 432–438 (1985).
    [Crossref]
  9. G. Westheimer, “The Maxwellian view,” Vision Res. 6, 669–682 (1966).
    [Crossref] [PubMed]
  10. Y. le Grand, Light, Colour and Vision, 2nd ed. (Chapman & Hall, London, 1968).
  11. American National Standard for Safe Use of Lasers (American National Standards Institute, New York, 1993) (ANSI Z136.1-1993).
  12. J. J. Lagendijk, “A mathematical model to calculate temperature distributions in human and rabbit eyes during hyperthermic treatment,” Phys. Med. Biol. 27, 1301–1311 (1982).
    [Crossref] [PubMed]
  13. B. A. J. Clark, L. G. Carney, “Refractive index and reflectance of the anterior surface of the cornea,” Am. J. Optom. Physiol. Opt. 48, 333–343 (1971).
    [Crossref]
  14. J. P. Guillon, “Tear film structure and contact lenses,” in The Preocular Tear Film in Health, Disease and Contact Lens Wear, F. J. Holly, ed. (Dry Eye Institute, Lubbock, Tex., 1986), Chap. 85, pp. 914–939.
  15. S. Patel, J. Marshall, F. W. Fitzke, “Refractive index of the human corneal epithelium and stroma,” J. Refract. Surg. 11, 100–105, (1995).
  16. J.-P. Guillon, M. Guillon, “The role of tears in contact lens performance and its measurement” in Contact Lens Practice, M. Ruben, M. Guillon, eds. (Chapman & Hall Medical, London, 1994), Chap. 21, pp. 453–483.
  17. G. J. Strous, J. Dekker, “Mucin-type glycoproteins,” Crit. Rev. Biochem. Mol. Biol. 27, 57–92 (1992).
    [Crossref] [PubMed]
  18. National Research Council, International Critical Tables of Numerical Data, Physics, Chemistry and Technology (McGraw-Hill, New York, 1927), Vol. 2, p. 347.
  19. P. N. Dilly, “Structure and function of the tear film,” Adv. Exp. Med. Biol. 350, 239–247 (1994).
    [Crossref] [PubMed]
  20. J. M. Tiffany, “Composition and biophysical properties of the tear film: knowledge and uncertainty,” Adv. Exp. Med. Biol. 350, 231–238 (1994).
    [Crossref] [PubMed]
  21. S. Mishima, “Some physiological aspects of the precorneal tear film,” Arch. Opththalmol. 73, 233–241 (1965).
    [Crossref]
  22. N. Ehlers, “The thickness of the precorneal tear film,” Acta Ophthalmol. Suppl. 81, 92–100 (1965).
  23. M. G. Doane, “An instrument for in vitro tear film measurement,” Optom. Vis. Sci. 66, 383–388 (1989).
    [Crossref] [PubMed]
  24. D. G. Green, B. R. Frueh, J. M. Shapiro, “Corneal thickness measured by interferometry,” J. Opt. Soc. Am. 65, 119–123 (1975).
    [Crossref] [PubMed]
  25. P. E. King-Smith, B. A. Fink, N. Fogt, “Three interferometric methods for measuring the thickness of layers of the tear film: a review,” submitted to Optom. Vis. Sci.

1995 (2)

J. P. Craig, P. A. Simmons, S. Patel, A. Tomlinson, “Refractive index and osmolality of human tears,” Optom. Vis. Sci. 72, 718–724 (1995).
[Crossref] [PubMed]

S. Patel, J. Marshall, F. W. Fitzke, “Refractive index of the human corneal epithelium and stroma,” J. Refract. Surg. 11, 100–105, (1995).

1994 (3)

P. N. Dilly, “Structure and function of the tear film,” Adv. Exp. Med. Biol. 350, 239–247 (1994).
[Crossref] [PubMed]

J. M. Tiffany, “Composition and biophysical properties of the tear film: knowledge and uncertainty,” Adv. Exp. Med. Biol. 350, 231–238 (1994).
[Crossref] [PubMed]

Y. Danjo, M. Nakamura, T. Hamano, “Measurement of the precorneal tear film thickness with a non-contact optical interferometry film thickness measurement system,” Jpn. J. Ophthalmol. 38, 260–266 (1994).

1992 (3)

J. I. Prydal, P. Artal, H. Woon, F. W. Campbell, “Study of human precorneal tear film thickness and structure using laser interferometry,” Invest. Ophthalmol. Visual Sci. 33, 2006–2011 (1992).

J. I. Prydal, F. W. Campbell, “Study of precorneal tear film thickness and structure by interferometry and confocal microscopy,” Invest. Ophthalmol. Visual Sci. 33, 1996–2005 (1992).

G. J. Strous, J. Dekker, “Mucin-type glycoproteins,” Crit. Rev. Biochem. Mol. Biol. 27, 57–92 (1992).
[Crossref] [PubMed]

1989 (1)

M. G. Doane, “An instrument for in vitro tear film measurement,” Optom. Vis. Sci. 66, 383–388 (1989).
[Crossref] [PubMed]

1985 (1)

T. Olsen, “Reflectometry of the precorneal film,” Acta Ophthalmol. 63, 432–438 (1985).
[Crossref]

1982 (1)

J. J. Lagendijk, “A mathematical model to calculate temperature distributions in human and rabbit eyes during hyperthermic treatment,” Phys. Med. Biol. 27, 1301–1311 (1982).
[Crossref] [PubMed]

1975 (1)

1971 (1)

B. A. J. Clark, L. G. Carney, “Refractive index and reflectance of the anterior surface of the cornea,” Am. J. Optom. Physiol. Opt. 48, 333–343 (1971).
[Crossref]

1966 (1)

G. Westheimer, “The Maxwellian view,” Vision Res. 6, 669–682 (1966).
[Crossref] [PubMed]

1965 (2)

S. Mishima, “Some physiological aspects of the precorneal tear film,” Arch. Opththalmol. 73, 233–241 (1965).
[Crossref]

N. Ehlers, “The thickness of the precorneal tear film,” Acta Ophthalmol. Suppl. 81, 92–100 (1965).

1946 (1)

E. Wolff, “The muco-cutaneous junction of the lid-margin and the distribution of the tear fluid,” Trans. Ophthalmol. Soc. U.K. 66, 291–308 (1946).

Artal, P.

J. I. Prydal, P. Artal, H. Woon, F. W. Campbell, “Study of human precorneal tear film thickness and structure using laser interferometry,” Invest. Ophthalmol. Visual Sci. 33, 2006–2011 (1992).

Born, M.

M. Born, E. Wolf, Principles of Optics, 5th ed. (Pergamon, Oxford, 1975), p. 359.

Campbell, F. W.

J. I. Prydal, P. Artal, H. Woon, F. W. Campbell, “Study of human precorneal tear film thickness and structure using laser interferometry,” Invest. Ophthalmol. Visual Sci. 33, 2006–2011 (1992).

J. I. Prydal, F. W. Campbell, “Study of precorneal tear film thickness and structure by interferometry and confocal microscopy,” Invest. Ophthalmol. Visual Sci. 33, 1996–2005 (1992).

Carney, L. G.

B. A. J. Clark, L. G. Carney, “Refractive index and reflectance of the anterior surface of the cornea,” Am. J. Optom. Physiol. Opt. 48, 333–343 (1971).
[Crossref]

Clark, B. A. J.

B. A. J. Clark, L. G. Carney, “Refractive index and reflectance of the anterior surface of the cornea,” Am. J. Optom. Physiol. Opt. 48, 333–343 (1971).
[Crossref]

Craig, J. P.

J. P. Craig, P. A. Simmons, S. Patel, A. Tomlinson, “Refractive index and osmolality of human tears,” Optom. Vis. Sci. 72, 718–724 (1995).
[Crossref] [PubMed]

Danjo, Y.

Y. Danjo, M. Nakamura, T. Hamano, “Measurement of the precorneal tear film thickness with a non-contact optical interferometry film thickness measurement system,” Jpn. J. Ophthalmol. 38, 260–266 (1994).

Dekker, J.

G. J. Strous, J. Dekker, “Mucin-type glycoproteins,” Crit. Rev. Biochem. Mol. Biol. 27, 57–92 (1992).
[Crossref] [PubMed]

Dilly, P. N.

P. N. Dilly, “Structure and function of the tear film,” Adv. Exp. Med. Biol. 350, 239–247 (1994).
[Crossref] [PubMed]

Doane, M. G.

M. G. Doane, “An instrument for in vitro tear film measurement,” Optom. Vis. Sci. 66, 383–388 (1989).
[Crossref] [PubMed]

Ehlers, N.

N. Ehlers, “The thickness of the precorneal tear film,” Acta Ophthalmol. Suppl. 81, 92–100 (1965).

Fink, B. A.

P. E. King-Smith, B. A. Fink, N. Fogt, “Three interferometric methods for measuring the thickness of layers of the tear film: a review,” submitted to Optom. Vis. Sci.

Fitzke, F. W.

S. Patel, J. Marshall, F. W. Fitzke, “Refractive index of the human corneal epithelium and stroma,” J. Refract. Surg. 11, 100–105, (1995).

Fogt, N.

P. E. King-Smith, B. A. Fink, N. Fogt, “Three interferometric methods for measuring the thickness of layers of the tear film: a review,” submitted to Optom. Vis. Sci.

Frueh, B. R.

Green, D. G.

Guillon, J. P.

J. P. Guillon, “Tear film structure and contact lenses,” in The Preocular Tear Film in Health, Disease and Contact Lens Wear, F. J. Holly, ed. (Dry Eye Institute, Lubbock, Tex., 1986), Chap. 85, pp. 914–939.

Guillon, J.-P.

J.-P. Guillon, M. Guillon, “The role of tears in contact lens performance and its measurement” in Contact Lens Practice, M. Ruben, M. Guillon, eds. (Chapman & Hall Medical, London, 1994), Chap. 21, pp. 453–483.

Guillon, M.

J.-P. Guillon, M. Guillon, “The role of tears in contact lens performance and its measurement” in Contact Lens Practice, M. Ruben, M. Guillon, eds. (Chapman & Hall Medical, London, 1994), Chap. 21, pp. 453–483.

Hamano, T.

Y. Danjo, M. Nakamura, T. Hamano, “Measurement of the precorneal tear film thickness with a non-contact optical interferometry film thickness measurement system,” Jpn. J. Ophthalmol. 38, 260–266 (1994).

Jenkins, F. A.

F. A. Jenkins, H. E. White, Fundamentals of Optics, 4th ed. (McGraw-Hill, New York, 1974).

King-Smith, P. E.

P. E. King-Smith, B. A. Fink, N. Fogt, “Three interferometric methods for measuring the thickness of layers of the tear film: a review,” submitted to Optom. Vis. Sci.

Lagendijk, J. J.

J. J. Lagendijk, “A mathematical model to calculate temperature distributions in human and rabbit eyes during hyperthermic treatment,” Phys. Med. Biol. 27, 1301–1311 (1982).
[Crossref] [PubMed]

le Grand, Y.

Y. le Grand, Light, Colour and Vision, 2nd ed. (Chapman & Hall, London, 1968).

Marshall, J.

S. Patel, J. Marshall, F. W. Fitzke, “Refractive index of the human corneal epithelium and stroma,” J. Refract. Surg. 11, 100–105, (1995).

Mishima, S.

S. Mishima, “Some physiological aspects of the precorneal tear film,” Arch. Opththalmol. 73, 233–241 (1965).
[Crossref]

Nakamura, M.

Y. Danjo, M. Nakamura, T. Hamano, “Measurement of the precorneal tear film thickness with a non-contact optical interferometry film thickness measurement system,” Jpn. J. Ophthalmol. 38, 260–266 (1994).

Olsen, T.

T. Olsen, “Reflectometry of the precorneal film,” Acta Ophthalmol. 63, 432–438 (1985).
[Crossref]

Patel, S.

S. Patel, J. Marshall, F. W. Fitzke, “Refractive index of the human corneal epithelium and stroma,” J. Refract. Surg. 11, 100–105, (1995).

J. P. Craig, P. A. Simmons, S. Patel, A. Tomlinson, “Refractive index and osmolality of human tears,” Optom. Vis. Sci. 72, 718–724 (1995).
[Crossref] [PubMed]

Prydal, J. I.

J. I. Prydal, F. W. Campbell, “Study of precorneal tear film thickness and structure by interferometry and confocal microscopy,” Invest. Ophthalmol. Visual Sci. 33, 1996–2005 (1992).

J. I. Prydal, P. Artal, H. Woon, F. W. Campbell, “Study of human precorneal tear film thickness and structure using laser interferometry,” Invest. Ophthalmol. Visual Sci. 33, 2006–2011 (1992).

Shapiro, J. M.

Simmons, P. A.

J. P. Craig, P. A. Simmons, S. Patel, A. Tomlinson, “Refractive index and osmolality of human tears,” Optom. Vis. Sci. 72, 718–724 (1995).
[Crossref] [PubMed]

Strous, G. J.

G. J. Strous, J. Dekker, “Mucin-type glycoproteins,” Crit. Rev. Biochem. Mol. Biol. 27, 57–92 (1992).
[Crossref] [PubMed]

Tiffany, J. M.

J. M. Tiffany, “Composition and biophysical properties of the tear film: knowledge and uncertainty,” Adv. Exp. Med. Biol. 350, 231–238 (1994).
[Crossref] [PubMed]

Tomlinson, A.

J. P. Craig, P. A. Simmons, S. Patel, A. Tomlinson, “Refractive index and osmolality of human tears,” Optom. Vis. Sci. 72, 718–724 (1995).
[Crossref] [PubMed]

Westheimer, G.

G. Westheimer, “The Maxwellian view,” Vision Res. 6, 669–682 (1966).
[Crossref] [PubMed]

White, H. E.

F. A. Jenkins, H. E. White, Fundamentals of Optics, 4th ed. (McGraw-Hill, New York, 1974).

Wolf, E.

M. Born, E. Wolf, Principles of Optics, 5th ed. (Pergamon, Oxford, 1975), p. 359.

Wolff, E.

E. Wolff, “The muco-cutaneous junction of the lid-margin and the distribution of the tear fluid,” Trans. Ophthalmol. Soc. U.K. 66, 291–308 (1946).

Woon, H.

J. I. Prydal, P. Artal, H. Woon, F. W. Campbell, “Study of human precorneal tear film thickness and structure using laser interferometry,” Invest. Ophthalmol. Visual Sci. 33, 2006–2011 (1992).

Acta Ophthalmol. (1)

T. Olsen, “Reflectometry of the precorneal film,” Acta Ophthalmol. 63, 432–438 (1985).
[Crossref]

Acta Ophthalmol. Suppl. (1)

N. Ehlers, “The thickness of the precorneal tear film,” Acta Ophthalmol. Suppl. 81, 92–100 (1965).

Adv. Exp. Med. Biol. (2)

P. N. Dilly, “Structure and function of the tear film,” Adv. Exp. Med. Biol. 350, 239–247 (1994).
[Crossref] [PubMed]

J. M. Tiffany, “Composition and biophysical properties of the tear film: knowledge and uncertainty,” Adv. Exp. Med. Biol. 350, 231–238 (1994).
[Crossref] [PubMed]

Am. J. Optom. Physiol. Opt. (1)

B. A. J. Clark, L. G. Carney, “Refractive index and reflectance of the anterior surface of the cornea,” Am. J. Optom. Physiol. Opt. 48, 333–343 (1971).
[Crossref]

Arch. Opththalmol. (1)

S. Mishima, “Some physiological aspects of the precorneal tear film,” Arch. Opththalmol. 73, 233–241 (1965).
[Crossref]

Crit. Rev. Biochem. Mol. Biol. (1)

G. J. Strous, J. Dekker, “Mucin-type glycoproteins,” Crit. Rev. Biochem. Mol. Biol. 27, 57–92 (1992).
[Crossref] [PubMed]

Invest. Ophthalmol. Visual Sci. (2)

J. I. Prydal, F. W. Campbell, “Study of precorneal tear film thickness and structure by interferometry and confocal microscopy,” Invest. Ophthalmol. Visual Sci. 33, 1996–2005 (1992).

J. I. Prydal, P. Artal, H. Woon, F. W. Campbell, “Study of human precorneal tear film thickness and structure using laser interferometry,” Invest. Ophthalmol. Visual Sci. 33, 2006–2011 (1992).

J. Opt. Soc. Am. (1)

J. Refract. Surg. (1)

S. Patel, J. Marshall, F. W. Fitzke, “Refractive index of the human corneal epithelium and stroma,” J. Refract. Surg. 11, 100–105, (1995).

Jpn. J. Ophthalmol. (1)

Y. Danjo, M. Nakamura, T. Hamano, “Measurement of the precorneal tear film thickness with a non-contact optical interferometry film thickness measurement system,” Jpn. J. Ophthalmol. 38, 260–266 (1994).

Optom. Vis. Sci. (2)

J. P. Craig, P. A. Simmons, S. Patel, A. Tomlinson, “Refractive index and osmolality of human tears,” Optom. Vis. Sci. 72, 718–724 (1995).
[Crossref] [PubMed]

M. G. Doane, “An instrument for in vitro tear film measurement,” Optom. Vis. Sci. 66, 383–388 (1989).
[Crossref] [PubMed]

Phys. Med. Biol. (1)

J. J. Lagendijk, “A mathematical model to calculate temperature distributions in human and rabbit eyes during hyperthermic treatment,” Phys. Med. Biol. 27, 1301–1311 (1982).
[Crossref] [PubMed]

Trans. Ophthalmol. Soc. U.K. (1)

E. Wolff, “The muco-cutaneous junction of the lid-margin and the distribution of the tear fluid,” Trans. Ophthalmol. Soc. U.K. 66, 291–308 (1946).

Vision Res. (1)

G. Westheimer, “The Maxwellian view,” Vision Res. 6, 669–682 (1966).
[Crossref] [PubMed]

Other (8)

Y. le Grand, Light, Colour and Vision, 2nd ed. (Chapman & Hall, London, 1968).

American National Standard for Safe Use of Lasers (American National Standards Institute, New York, 1993) (ANSI Z136.1-1993).

F. A. Jenkins, H. E. White, Fundamentals of Optics, 4th ed. (McGraw-Hill, New York, 1974).

M. Born, E. Wolf, Principles of Optics, 5th ed. (Pergamon, Oxford, 1975), p. 359.

J.-P. Guillon, M. Guillon, “The role of tears in contact lens performance and its measurement” in Contact Lens Practice, M. Ruben, M. Guillon, eds. (Chapman & Hall Medical, London, 1994), Chap. 21, pp. 453–483.

J. P. Guillon, “Tear film structure and contact lenses,” in The Preocular Tear Film in Health, Disease and Contact Lens Wear, F. J. Holly, ed. (Dry Eye Institute, Lubbock, Tex., 1986), Chap. 85, pp. 914–939.

P. E. King-Smith, B. A. Fink, N. Fogt, “Three interferometric methods for measuring the thickness of layers of the tear film: a review,” submitted to Optom. Vis. Sci.

National Research Council, International Critical Tables of Numerical Data, Physics, Chemistry and Technology (McGraw-Hill, New York, 1927), Vol. 2, p. 347.

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Figures (8)

Fig. 1
Fig. 1

Constructive and destructive interference from an intermediate-index film, i.e., one whose refractive index is intermediate between those of the surrounding materials; an example would be the tear film between air and a contact lens. (a) Constructive interference. The film thickness is one wavelength of light. The incident wave is shown above, whereas the reflections from the two surfaces of the tear film R1 and R2 are shown below (displaced vertically for clarity). These two reflections are in phase, and their sum R1+R2 is shown at the left. (b) Destructive interference. In this case, light of a shorter wavelength is used so that the thickness of the film is now 1.25 wavelengths of light. The two reflections R1 and R2 are now out of phase, so the total reflection R1+R2 is relatively small. In summary, reflectance should be high at some wavelengths and low at others, giving rise to oscillations in the reflectance spectrum.

Fig. 2
Fig. 2

Optical system for measuring spectral oscillations from interference in the tear film (not to scale). See text for details.

Fig. 3
Fig. 3

(a) Spectrophotometer outputs for reflectance from the front surface of a crown glass prism and from the tear film over a contact lens. Results are plotted as a function of wave number (reciprocal wavelength). (b) The solid curve is the reflectance spectra of the tear film derived from the measurements in (a) with use of Eqs. (7) to (9). Circles show a weighted least-squares fit to this curve with Eq. (10). The derived thickness of the tear film is 2.21 µm. See text for details.

Fig. 4
Fig. 4

Solid curves are examples of spectral oscillations from thin and thick tear films in front of a contact lens; circles correspond to least-squares fits, as in Fig. 3(b). Upper and lower curves correspond to tear film thicknesses of 0.63 and 4.44 µm. Vertical dashed lines show the spectral range used by Danjo et al.3

Fig. 5
Fig. 5

Histograms of tear film thickness in front of a contact lens for five subjects (nine measurements for each subject, except only seven for G). An overall histogram is given at the bottom.

Fig. 6
Fig. 6

To illustrate the derivation of phase of the spectral oscillations, ϕ in Eq. (10), the fitted curve from Fig. 3(b), shown by the circles, has been extrapolated back to zero wave number. A maximum at zero wave number would correspond ϕ=0; it is seen that a maximum does indeed occur close to the origin; the calculated phase was -2°.

Fig. 7
Fig. 7

Circles give the modulation [Eq. (13)] and phase derived from least-squares fits [Eq. (10)] to 43 reflectance spectra from the five subjects when wearing a contact lens. The triangle is the centroid of these 43 points.

Fig. 8
Fig. 8

Solid curve shows weak spectral oscillations in a reflectance spectrum from subject B, with no contact lens. Circles give a least-squares fit [Eq. (10)] indicating a film thickness of 2.42 µm. This may correspond to the thickness of the aqueous layer between air and mucus boundaries (see text for discussion).

Equations (14)

Equations on this page are rendered with MathJax. Learn more.

mλ=2nd cos ϕ,
χ=1/λ=m/2nd,
Δχ=1/2nd
d=1/(2nΔχ).
Vt=Vt-VdVg=Vg-Vd.
Lt=f(Vt*),
Lg=f(Vg*)
rt=Ltrg/Lg,
rg=(ng-1)2/(ng+1)2,
ng=P+Q/λ2,
rt=B+Cχ+Dχ2+A cos(2πFχ+ϕ)exp(-Eχ)
rt=B+A cos(2πFχ+ϕ)
F=2nd.
M=A exp(-Eχ)/(B+Cχ+Dχ2).

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