Abstract

We developed a model of corneal haze following photorefractive keratectomy (PRK) in Iber Braun hens and studied optical properties. The animals underwent PRK for -9.0 diopters of myopia and were divided into groups based on treatment with different wound-healing modulators. At different time points postoperatively, we evaluated haze by slit-lamp microscopy. An experimental device was developed to measure transmittance spatial maps and forward scattering of He–Ne laser light in the excised corneas. Subjective and objective haze measures were compared for each group at the different times. Keratocyte densities were determined by optical microscopy and keratocyte sizes by electron microscopy. The agreement between experimental results and a simple numerical model of scattering suggests that increases in stromal keratocyte density after PRK might explain the degree of corneal haze.

© 2001 Optical Society of America

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References

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    [CrossRef] [PubMed]
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    [CrossRef]
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    [CrossRef]

1999 (2)

S. V. Tsinopoulos, D. Polyzos, “Scattering of He–Ne laser light by an average-sized red blood cell,” Appl. Opt. 38, 5499–5510 (1999).
[CrossRef]

N. V. Shepelevich, V. V. Lopatin, V. P. Maltsev, V. N. Lopatin, “Extrema in the light-scattering indicatrix of a homogeneous sphere,” J. Opt. A: Pure Appl. Opt. 1, 448–453 (1999).

1998 (1)

1992 (2)

J. D. Klett, R. A. Sutherland, “Approximate methods for modeling the scattering properties of nonspherical particles: evaluation of the Wentzel–Kramers–Brillouin method,” Appl. Opt. 31, 373–386 (1992).
[CrossRef] [PubMed]

C. P. Lohmann, G. T. Timberlake, F. W. Fitzke, D. S. Gartry, M. K. Muir, J. Marshall, “Corneal light scattering after excimer laser photorefractive keratectomy: the objective measurements of haze,” J. Refract. Corneal Surg. 8, 114–121 (1992).

1990 (1)

F. E. Fantes, K. D. Hanna, G. O. Waring, Y. Pouliquen, K. P. Thompson, M. Savoldelli, “Wound healing after excimer laser keratomileusis (photorefractive keratectomy) in monkeys,” Arch. Ophthalmol. 108, 665–675 (1990).
[CrossRef] [PubMed]

1986 (1)

J. Marshall, S. L. Trokel, S. Rothery, R. R. Krueger, “Photoablative reprofiling of the cornea using an excimer laser: photorefractive keratectomy,” Laser Ophthalmol. 1, 21–48 (1986).

1975 (1)

P. Latimer, “Light scattering by ellipsoids,” J. Colloid Interface Sci. 53, 102–109 (1975).
[CrossRef]

1971 (1)

Benedek, G. B.

Bohren, C. F.

C. F. Bohren, D. R. Huffman, Absorption and Scattering of Light by Small Particles (Wiley, New York, 1983).

Eick, A. A.

Fantes, F. E.

F. E. Fantes, K. D. Hanna, G. O. Waring, Y. Pouliquen, K. P. Thompson, M. Savoldelli, “Wound healing after excimer laser keratomileusis (photorefractive keratectomy) in monkeys,” Arch. Ophthalmol. 108, 665–675 (1990).
[CrossRef] [PubMed]

Fitzke, F. W.

C. P. Lohmann, G. T. Timberlake, F. W. Fitzke, D. S. Gartry, M. K. Muir, J. Marshall, “Corneal light scattering after excimer laser photorefractive keratectomy: the objective measurements of haze,” J. Refract. Corneal Surg. 8, 114–121 (1992).

Freyer, J. P.

Gartry, D. S.

C. P. Lohmann, G. T. Timberlake, F. W. Fitzke, D. S. Gartry, M. K. Muir, J. Marshall, “Corneal light scattering after excimer laser photorefractive keratectomy: the objective measurements of haze,” J. Refract. Corneal Surg. 8, 114–121 (1992).

Hanna, K. D.

F. E. Fantes, K. D. Hanna, G. O. Waring, Y. Pouliquen, K. P. Thompson, M. Savoldelli, “Wound healing after excimer laser keratomileusis (photorefractive keratectomy) in monkeys,” Arch. Ophthalmol. 108, 665–675 (1990).
[CrossRef] [PubMed]

Hielscher, A. H.

Huffman, D. R.

C. F. Bohren, D. R. Huffman, Absorption and Scattering of Light by Small Particles (Wiley, New York, 1983).

Johnson, T. M.

Klett, J. D.

Krueger, R. R.

J. Marshall, S. L. Trokel, S. Rothery, R. R. Krueger, “Photoablative reprofiling of the cornea using an excimer laser: photorefractive keratectomy,” Laser Ophthalmol. 1, 21–48 (1986).

Latimer, P.

P. Latimer, “Light scattering by ellipsoids,” J. Colloid Interface Sci. 53, 102–109 (1975).
[CrossRef]

Lohmann, C. P.

C. P. Lohmann, G. T. Timberlake, F. W. Fitzke, D. S. Gartry, M. K. Muir, J. Marshall, “Corneal light scattering after excimer laser photorefractive keratectomy: the objective measurements of haze,” J. Refract. Corneal Surg. 8, 114–121 (1992).

Lopatin, V. N.

N. V. Shepelevich, V. V. Lopatin, V. P. Maltsev, V. N. Lopatin, “Extrema in the light-scattering indicatrix of a homogeneous sphere,” J. Opt. A: Pure Appl. Opt. 1, 448–453 (1999).

Lopatin, V. V.

N. V. Shepelevich, V. V. Lopatin, V. P. Maltsev, V. N. Lopatin, “Extrema in the light-scattering indicatrix of a homogeneous sphere,” J. Opt. A: Pure Appl. Opt. 1, 448–453 (1999).

Maltsev, V. P.

N. V. Shepelevich, V. V. Lopatin, V. P. Maltsev, V. N. Lopatin, “Extrema in the light-scattering indicatrix of a homogeneous sphere,” J. Opt. A: Pure Appl. Opt. 1, 448–453 (1999).

Marshall, J.

C. P. Lohmann, G. T. Timberlake, F. W. Fitzke, D. S. Gartry, M. K. Muir, J. Marshall, “Corneal light scattering after excimer laser photorefractive keratectomy: the objective measurements of haze,” J. Refract. Corneal Surg. 8, 114–121 (1992).

J. Marshall, S. L. Trokel, S. Rothery, R. R. Krueger, “Photoablative reprofiling of the cornea using an excimer laser: photorefractive keratectomy,” Laser Ophthalmol. 1, 21–48 (1986).

Martín, R.

J. M. Merayo-Lloves, B. Yánez, A. Mayo, R. Martín, J. C. Pastor, “Experimental model of corneal haze,” J. Refract. Surg. (to be published).

Mayo, A.

J. M. Merayo-Lloves, B. Yánez, A. Mayo, R. Martín, J. C. Pastor, “Experimental model of corneal haze,” J. Refract. Surg. (to be published).

Merayo-Lloves, J. M.

J. M. Merayo-Lloves, B. Yánez, A. Mayo, R. Martín, J. C. Pastor, “Experimental model of corneal haze,” J. Refract. Surg. (to be published).

Mourant, J. R.

Muir, M. K.

C. P. Lohmann, G. T. Timberlake, F. W. Fitzke, D. S. Gartry, M. K. Muir, J. Marshall, “Corneal light scattering after excimer laser photorefractive keratectomy: the objective measurements of haze,” J. Refract. Corneal Surg. 8, 114–121 (1992).

Pastor, J. C.

J. M. Merayo-Lloves, B. Yánez, A. Mayo, R. Martín, J. C. Pastor, “Experimental model of corneal haze,” J. Refract. Surg. (to be published).

Polyzos, D.

Pouliquen, Y.

F. E. Fantes, K. D. Hanna, G. O. Waring, Y. Pouliquen, K. P. Thompson, M. Savoldelli, “Wound healing after excimer laser keratomileusis (photorefractive keratectomy) in monkeys,” Arch. Ophthalmol. 108, 665–675 (1990).
[CrossRef] [PubMed]

Rothery, S.

J. Marshall, S. L. Trokel, S. Rothery, R. R. Krueger, “Photoablative reprofiling of the cornea using an excimer laser: photorefractive keratectomy,” Laser Ophthalmol. 1, 21–48 (1986).

Savoldelli, M.

F. E. Fantes, K. D. Hanna, G. O. Waring, Y. Pouliquen, K. P. Thompson, M. Savoldelli, “Wound healing after excimer laser keratomileusis (photorefractive keratectomy) in monkeys,” Arch. Ophthalmol. 108, 665–675 (1990).
[CrossRef] [PubMed]

Shen, D.

Shepelevich, N. V.

N. V. Shepelevich, V. V. Lopatin, V. P. Maltsev, V. N. Lopatin, “Extrema in the light-scattering indicatrix of a homogeneous sphere,” J. Opt. A: Pure Appl. Opt. 1, 448–453 (1999).

Sutherland, R. A.

Thompson, K. P.

F. E. Fantes, K. D. Hanna, G. O. Waring, Y. Pouliquen, K. P. Thompson, M. Savoldelli, “Wound healing after excimer laser keratomileusis (photorefractive keratectomy) in monkeys,” Arch. Ophthalmol. 108, 665–675 (1990).
[CrossRef] [PubMed]

Timberlake, G. T.

C. P. Lohmann, G. T. Timberlake, F. W. Fitzke, D. S. Gartry, M. K. Muir, J. Marshall, “Corneal light scattering after excimer laser photorefractive keratectomy: the objective measurements of haze,” J. Refract. Corneal Surg. 8, 114–121 (1992).

Trokel, S. L.

J. Marshall, S. L. Trokel, S. Rothery, R. R. Krueger, “Photoablative reprofiling of the cornea using an excimer laser: photorefractive keratectomy,” Laser Ophthalmol. 1, 21–48 (1986).

Tsinopoulos, S. V.

Van de Hulst, H. C.

H. C. Van de Hulst, Light Scattering by Small Particles (Dover, New York, 1981).

Waring, G. O.

F. E. Fantes, K. D. Hanna, G. O. Waring, Y. Pouliquen, K. P. Thompson, M. Savoldelli, “Wound healing after excimer laser keratomileusis (photorefractive keratectomy) in monkeys,” Arch. Ophthalmol. 108, 665–675 (1990).
[CrossRef] [PubMed]

Weibel, E. R.

E. R. Weibel, Stereological Methods. Practical Methods for Biological Morphometry (Academic, London, 1979), Vol. 1.

Yánez, B.

J. M. Merayo-Lloves, B. Yánez, A. Mayo, R. Martín, J. C. Pastor, “Experimental model of corneal haze,” J. Refract. Surg. (to be published).

Appl. Opt. (4)

Arch. Ophthalmol. (1)

F. E. Fantes, K. D. Hanna, G. O. Waring, Y. Pouliquen, K. P. Thompson, M. Savoldelli, “Wound healing after excimer laser keratomileusis (photorefractive keratectomy) in monkeys,” Arch. Ophthalmol. 108, 665–675 (1990).
[CrossRef] [PubMed]

J. Colloid Interface Sci. (1)

P. Latimer, “Light scattering by ellipsoids,” J. Colloid Interface Sci. 53, 102–109 (1975).
[CrossRef]

J. Opt. A: Pure Appl. Opt. (1)

N. V. Shepelevich, V. V. Lopatin, V. P. Maltsev, V. N. Lopatin, “Extrema in the light-scattering indicatrix of a homogeneous sphere,” J. Opt. A: Pure Appl. Opt. 1, 448–453 (1999).

J. Refract. Corneal Surg. (1)

C. P. Lohmann, G. T. Timberlake, F. W. Fitzke, D. S. Gartry, M. K. Muir, J. Marshall, “Corneal light scattering after excimer laser photorefractive keratectomy: the objective measurements of haze,” J. Refract. Corneal Surg. 8, 114–121 (1992).

Laser Ophthalmol. (1)

J. Marshall, S. L. Trokel, S. Rothery, R. R. Krueger, “Photoablative reprofiling of the cornea using an excimer laser: photorefractive keratectomy,” Laser Ophthalmol. 1, 21–48 (1986).

Other (4)

H. C. Van de Hulst, Light Scattering by Small Particles (Dover, New York, 1981).

C. F. Bohren, D. R. Huffman, Absorption and Scattering of Light by Small Particles (Wiley, New York, 1983).

E. R. Weibel, Stereological Methods. Practical Methods for Biological Morphometry (Academic, London, 1979), Vol. 1.

J. M. Merayo-Lloves, B. Yánez, A. Mayo, R. Martín, J. C. Pastor, “Experimental model of corneal haze,” J. Refract. Surg. (to be published).

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Figures (13)

Fig. 1
Fig. 1

Front and sectional views of corneal support camera.

Fig. 2
Fig. 2

Experimental device.

Fig. 3
Fig. 3

Geometric schemes showing the sequence of transmittance measurements for each cornea (upper) and the forward scattering measurement (lower).

Fig. 4
Fig. 4

Transmittance spatial distribution of a control cornea (without PRK ablation). Each plotted contour band corresponds to 10% in transmittance.

Fig. 5
Fig. 5

Transmittance spatial distribution of a PRK-ablated cornea.

Fig. 6
Fig. 6

Mean-square deviation, D, of the experimental transmittance data to the half-ellipsoid function versus mean value of transmittance, T, taken in a central region 2 mm in diameter, for each cornea.

Fig. 7
Fig. 7

Scatter plot of subjective value versus opacity (1 - T in percentage) for all eye samples corresponding to time point 30 days after PRK. The treatments of each cornea are labeled as follows: diamond, normal or control corneas without PRK; square, PRK corneas treated with fluorometolone FML-F ® 0.25%; triangle, PRK corneas treated with CM Chitosan 0.5%; circle, PRK corneas treated with hyaluronic acid 1%, cross, PRK corneas treated with PBS pH 7.2 (i.e., a placebo treatment with an isotonic saline solution); plus, untreated corneas after PRK.

Fig. 8
Fig. 8

Comparison between different wound-healing treatments by means of haze quantification parameters obtained for the corneas measured 15, 30, 90, and 180 days after PRK. The x axis of the graph gives the four different time points. Mean values with error bars (standard deviation) are given for each group, which usually correspond to five corneal samples. Pseudoabsorption or opacity measurements (i.e., 1 - T), given in percentage, appear at the upper part of the graph. The subjective mean values graded clinically by slit-lamp microscopy appear at the lower part of the graph (scale on the right y axis). The treatments of each group plotted with different symbols are labeled as in Fig. 7.

Fig. 9
Fig. 9

Light micrograph (×400) showing a PRK-treated cornea with epithelial hyperplasia, undulating basal membrane, and focal keratocyte activation at the anterior stroma in days after PRK. The darker upper band corresponds to epithelium, whereas the small dark points distributed around the stroma correspond to keratocyte nuclei.

Fig. 10
Fig. 10

Transmission electron micrograph (×6000) of corneal stroma showing activate keratocyte. Surrounded by a dark line, the large keratocyte nuclei can be easily distinguished. Also, the photograph shows the scale of 1 µm.

Fig. 11
Fig. 11

Contour level map shows the relative difference σ, given in percentage and logarithmic scale, between experimental and theoretical Rayleigh ratio values, versus sphere radius, a, and relative refractive index, m, assuming a simple model of spheres for the stromal keratocytes.

Fig. 12
Fig. 12

Scattered measured light relative to incidence (in percentage, left-hand side, and in Rayleigh ratio units, right-hand side) versus transmittance for each cornea.

Fig. 13
Fig. 13

Transmittance value T versus stromal keratocyte density.

Equations (5)

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

Nv=Na/t+D,
ESR, θ=fθexpikRR,
fθ=αa01 J0α sin θ1-t21/2sinρttdt+i 01 J0α sin θ1-t21/21-cosρttdt,
Rθ=IθE×V,
σ2=138Rexp2k=1k=38Rkexp-Rtha, m, Nv2

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