Abstract

Keratometry is currently achieved by projecting a circular mire onto the patient's cornea and analyzing the size and shape of its reflected image. The projection mires are decisive for the precision of the measurement. We have previously developed a keratometric module for slit lamps, and the development of four projection mires are presented. Mire 1 is composed of optical fibers and electrical cables; Mire 2, 48 LEDs; Mire 3, optical fibers and no electrical cables; and Mire 4, mechanical parts—cable free. Mires 2–4 provide accurate keratometry measurements at slit lamps. Mire 4 is the most adequate for the clinical environment.

© 2007 Optical Society of America

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References

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  1. R. Mohrman, "The keratometer," in Clinical Ophthalmology, E. D. T. D. Duane, ed. (Lippicott-Raven, 1995).
  2. M. D. Greivenkamp, Mellinger, R. W. Snyder, J. T. Schwiegerling, A. E. Lowman, and J. M. Miller, "Comparison of three videokeratoscopes in measurement of toric test surfaces," J. Ref. Surg. 12229-239 (1996).
  3. F. H. M. Jongsma, J. de Brabander, and F. Hendrikse, "Review and classification of corneal topographers," Lasers Med. Sci. 14, 2-19 (1999).
    [CrossRef]
  4. T. Swartz, L. Martin, and M. Wang, "Measuring the cornea: the latest developments in corneal topography," Curr. Opin. Ophthalmol. 18, 325-332 (2007).
    [CrossRef] [PubMed]
  5. L. Ventura, C. Riul, S. J. F. Sousa, J. G. S. De Groote, A. B. Rosa, and G. C. D. Oliveira, "Corneal astigmatism measuring module for slit lamps," Phys. Med. Biol. 51, 1-14 (2006).
    [CrossRef]
  6. L. Ventura, A. M. V. Messias, S. J. F. Sousa, and R. Coelho, "Automated keratometry at low cost," IEEE Eng. Med. Biol. 19, 97-103 (2000).
    [CrossRef]
  7. W. Tasman and E. Leger, "The Slit Lamp," in Clinical Ophthalmology, E. D. T. D. Duane, ed. (Lippicott-Raven, 1995).
  8. R. Bonnet, "La Topographie Cornéenne" (Desroches Éditeur, Paris, 1964).
  9. P. M. Kiely, G. Smith, and L. G. Carney, "The mean shape of the human cornea," Opt. Acta. 29, 1027-1040 (1982).
    [CrossRef]
  10. L. Ventura and C. Riul, "Light projection target mire for curvature measurements," W.O. Patent/2005/102149, 11 March 2005.

2007 (1)

T. Swartz, L. Martin, and M. Wang, "Measuring the cornea: the latest developments in corneal topography," Curr. Opin. Ophthalmol. 18, 325-332 (2007).
[CrossRef] [PubMed]

2006 (1)

L. Ventura, C. Riul, S. J. F. Sousa, J. G. S. De Groote, A. B. Rosa, and G. C. D. Oliveira, "Corneal astigmatism measuring module for slit lamps," Phys. Med. Biol. 51, 1-14 (2006).
[CrossRef]

2000 (1)

L. Ventura, A. M. V. Messias, S. J. F. Sousa, and R. Coelho, "Automated keratometry at low cost," IEEE Eng. Med. Biol. 19, 97-103 (2000).
[CrossRef]

1999 (1)

F. H. M. Jongsma, J. de Brabander, and F. Hendrikse, "Review and classification of corneal topographers," Lasers Med. Sci. 14, 2-19 (1999).
[CrossRef]

1996 (1)

M. D. Greivenkamp, Mellinger, R. W. Snyder, J. T. Schwiegerling, A. E. Lowman, and J. M. Miller, "Comparison of three videokeratoscopes in measurement of toric test surfaces," J. Ref. Surg. 12229-239 (1996).

1982 (1)

P. M. Kiely, G. Smith, and L. G. Carney, "The mean shape of the human cornea," Opt. Acta. 29, 1027-1040 (1982).
[CrossRef]

Curr. Opin. Ophthalmol. (1)

T. Swartz, L. Martin, and M. Wang, "Measuring the cornea: the latest developments in corneal topography," Curr. Opin. Ophthalmol. 18, 325-332 (2007).
[CrossRef] [PubMed]

IEEE Eng. Med. Biol. (1)

L. Ventura, A. M. V. Messias, S. J. F. Sousa, and R. Coelho, "Automated keratometry at low cost," IEEE Eng. Med. Biol. 19, 97-103 (2000).
[CrossRef]

J. Ref. Surg. (1)

M. D. Greivenkamp, Mellinger, R. W. Snyder, J. T. Schwiegerling, A. E. Lowman, and J. M. Miller, "Comparison of three videokeratoscopes in measurement of toric test surfaces," J. Ref. Surg. 12229-239 (1996).

Lasers Med. Sci. (1)

F. H. M. Jongsma, J. de Brabander, and F. Hendrikse, "Review and classification of corneal topographers," Lasers Med. Sci. 14, 2-19 (1999).
[CrossRef]

Opt. Acta. (1)

P. M. Kiely, G. Smith, and L. G. Carney, "The mean shape of the human cornea," Opt. Acta. 29, 1027-1040 (1982).
[CrossRef]

Phys. Med. Biol. (1)

L. Ventura, C. Riul, S. J. F. Sousa, J. G. S. De Groote, A. B. Rosa, and G. C. D. Oliveira, "Corneal astigmatism measuring module for slit lamps," Phys. Med. Biol. 51, 1-14 (2006).
[CrossRef]

Other (4)

L. Ventura and C. Riul, "Light projection target mire for curvature measurements," W.O. Patent/2005/102149, 11 March 2005.

W. Tasman and E. Leger, "The Slit Lamp," in Clinical Ophthalmology, E. D. T. D. Duane, ed. (Lippicott-Raven, 1995).

R. Bonnet, "La Topographie Cornéenne" (Desroches Éditeur, Paris, 1964).

R. Mohrman, "The keratometer," in Clinical Ophthalmology, E. D. T. D. Duane, ed. (Lippicott-Raven, 1995).

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Figures (10)

Fig. 1
Fig. 1

Schematic diagram for determining the size of the target mire to be projected onto the patient's lachrymal film.

Fig. 2
Fig. 2

First device with an adapted target Mire 1 commercially available by KOM®: (a) optical fiber continuous ring target mire attached to the objective lens of the slit lamp; (b) image of the reflected target projected onto the patient's eye; and (c) image obtained from an astigmatic patient with keratometric results and the graphical analysis of the patient's astigmatism (darker plotting) compared to an ideal nonastigmatic cornea (lighter plotting).

Fig. 3
Fig. 3

(a) 48 LEDs Mire attached to the objective lens of the slit lamp; (b) image of Mire 2 reflected by a precision sphere; and (c) interface software presenting the keratometry of an astigmatic eye.

Fig. 4
Fig. 4

72 optical fibers Mire 3 attached to the light tower of the slit lamp: (a) back view; (b) front view attached to the microscope; (c) image of the reflected light spots projected onto the cornea; (d) image of the reflected light spots projected onto a steel sphere; and (e) interface software presenting the result of a steel sphere.

Fig. 5
Fig. 5

Holes of the target mire being illuminated by the white light from the slit lamp after reaching the reflective surfaces.

Fig. 6
Fig. 6

(a) Illustration of the reflection of the ray at Surface 2, and the manufacturing angle φ; and (b) drawing of the reflective Surface 3, with a ray reflected at an angle β. Angle σ is the angle for manufacturing the target. (c) Details of the illustration of the path of the light ray at the reflective surfaces, reaching the holes.

Fig. 7
Fig. 7

(a) Four views of target Mire 4; and (b) three-dimensional view of the light path through target Mire 4.

Fig. 8
Fig. 8

(a) 72 passing-through holes Mire 4 attached to the light tower of the slit lamp; (b) image of the reflected light spots projected onto a steel sphere; (c) the interface software (for alignment, capturing the image, and calibrating and presenting the results) presenting an image from a patient's eye with tear breakup; and (d) the keratometric result.

Fig. 9
Fig. 9

Arc shaped target attached to the light tower of the slit lamp: (a) front view; (b) side view; (c) back view; and (d) reflected image of the projected target onto a steel sphere.

Fig. 10
Fig. 10

Histogram (3D) of the light intensity of the image reflected back from a steel sphere of the: (a) optical fiber mire; (b) 48 LEDs mire; (c) 72 optical fiber spots; and (d) 72 passing-through holes.

Tables (1)

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Table 1 Comparison Among the Four Target Mires

Equations (10)

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h = y ( d + d 2 + r 2 ) r .
d = a + b
φ + [ ( 2 β + ψ ) 180 ] = 90 ,
ψ = arctan d h ,
β = 270 φ arctan d / h 2 ,
α = 90 + δ arctan d / h 2 .
σ = 90 β ψ ,
σ = 90 β arctan d h ,
ϕ = α δ
ϕ = 1 2 [ 90 δ arctan d h ] .

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