Abstract

For the purpose of understanding the influence of the use of magnifying loupes on the reading process, the reading field is a relevant concept. Three possible reading fields are distinguished: the monocular reading field, the binocular reading field, and the composite reading field. Theoretical expressions for the widths of reading fields are derived as a function of the physical parameters of the loupe and the geometry of the reading situation. Variation of reading-field width as a function of magnification is illustrated. For verification, experimentally determined reading-field widths were compared with the theoretical ones. There were small systematic deviations, probably caused by achromatic aberrations. In order to learn about the strategies that subjects use when reading with the aid of a loupe, loupe displacement was measured while subjects read text under conditions that provided a variety of reading-field widths. It was found that individual subjects use different strategies (i.e., they use different reading-field widths).

© 1987 Optical Society of America

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References

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  1. A. Linksz, “Optical principles of loupe magnification,” Am. J. Ophthalmol. 40, 831–840 (1955).
    [PubMed]
  2. J. E. Lebensohn, “Newer optical aids for children with low vision,” Am. J. Ophthalmol. 6, 813–819 (1958).
  3. S. Duke-Elder, D. Abrams, System of Ophthalmology (Kimpton, London, 1970), Vol. 5, pp. 793–807.
  4. L. L. Sloan, Reading Aids for the Partially Sighted: A Systematic Classification and Procedure for Prescribing (Williams and Wilkins, Baltimore, Md., 1977).
  5. G. E. Fonda, Management of Low Vision (Thieme-Stratton, New York, 1981).
  6. E. E. Faye, Clinical Low Vision (Little, Brown, Boston, Mass., 1976).
  7. H. Bouma, H. E. M. Mélotte, F. J. J. Blommaert, “On the field width of reading magnifiers,”IPO Ann. Prog. Rep. 19, 133–136 (1984).
  8. F. J. J. Blommaert, J. J. Neve, H. E. M. Mélotte, “Reading magnifiers: variation in magnification, image distance and field width,”IPO Ann. Prog. Rep. 20, 123–130 (1985).
  9. G. Westheimer, “The field of view of visual aids,” Am. J. Optom. 34, 430–438 (1957).
    [CrossRef]
  10. L. L. Sloan, M. D. Jablonski, “Reading aids for the partially blind,” Arch. Ophthalmol. 62, 465–484 (1959).
    [CrossRef]
  11. Y. Le Grand, Optique Physiologique (Editions de la Revue d’Optique, Paris, 1952), Vol. 1.
  12. A. L. Duwaer, G. van den Brink, “What is the diplopia threshold?” Percept. Psychophys. 29, 295–309 (1981).
    [CrossRef] [PubMed]
  13. H. Bouma, C. P. Legein, H. E. M. Mélotte, L. Zabel, “Is large print easy to read? Oral reading rate and word recognition of elderly subjects,”IPO Ann. Prog. Rep. 17, 84–90 (1982).
  14. D. H. A. Aberson, “Simulation of poor visual acuity: composition of silent-reading speeds,” submitted to Vision Res.
  15. G. E. Legge, G. S. Rubin, D. G. Pelli, M. M. Schleske, “Psychophysics of reading—II. Low vision,” Vision Res. 25, 253–266 (1985).
    [CrossRef]
  16. H. Bouma, “Visual reading processes and the quality of text displays,” in Ergonomic Aspects of Visual Display Terminals, E. Grandjean, E. Vigliani, eds. (Taylor and Francis, London, 1980), pp. 101–114.
  17. F. L. van Nes, J. C. Jacobs, “The effect of contrast on letter and word recognition,”IPO Ann. Prog. Rep. 16, 72–80 (1981).
  18. W. T. Welford, Geometrical Optics (North-Holland, Amsterdam, 1962), Vol. 1.

1985 (2)

F. J. J. Blommaert, J. J. Neve, H. E. M. Mélotte, “Reading magnifiers: variation in magnification, image distance and field width,”IPO Ann. Prog. Rep. 20, 123–130 (1985).

G. E. Legge, G. S. Rubin, D. G. Pelli, M. M. Schleske, “Psychophysics of reading—II. Low vision,” Vision Res. 25, 253–266 (1985).
[CrossRef]

1984 (1)

H. Bouma, H. E. M. Mélotte, F. J. J. Blommaert, “On the field width of reading magnifiers,”IPO Ann. Prog. Rep. 19, 133–136 (1984).

1982 (1)

H. Bouma, C. P. Legein, H. E. M. Mélotte, L. Zabel, “Is large print easy to read? Oral reading rate and word recognition of elderly subjects,”IPO Ann. Prog. Rep. 17, 84–90 (1982).

1981 (2)

A. L. Duwaer, G. van den Brink, “What is the diplopia threshold?” Percept. Psychophys. 29, 295–309 (1981).
[CrossRef] [PubMed]

F. L. van Nes, J. C. Jacobs, “The effect of contrast on letter and word recognition,”IPO Ann. Prog. Rep. 16, 72–80 (1981).

1959 (1)

L. L. Sloan, M. D. Jablonski, “Reading aids for the partially blind,” Arch. Ophthalmol. 62, 465–484 (1959).
[CrossRef]

1958 (1)

J. E. Lebensohn, “Newer optical aids for children with low vision,” Am. J. Ophthalmol. 6, 813–819 (1958).

1957 (1)

G. Westheimer, “The field of view of visual aids,” Am. J. Optom. 34, 430–438 (1957).
[CrossRef]

1955 (1)

A. Linksz, “Optical principles of loupe magnification,” Am. J. Ophthalmol. 40, 831–840 (1955).
[PubMed]

Aberson, D. H. A.

D. H. A. Aberson, “Simulation of poor visual acuity: composition of silent-reading speeds,” submitted to Vision Res.

Abrams, D.

S. Duke-Elder, D. Abrams, System of Ophthalmology (Kimpton, London, 1970), Vol. 5, pp. 793–807.

Blommaert, F. J. J.

F. J. J. Blommaert, J. J. Neve, H. E. M. Mélotte, “Reading magnifiers: variation in magnification, image distance and field width,”IPO Ann. Prog. Rep. 20, 123–130 (1985).

H. Bouma, H. E. M. Mélotte, F. J. J. Blommaert, “On the field width of reading magnifiers,”IPO Ann. Prog. Rep. 19, 133–136 (1984).

Bouma, H.

H. Bouma, H. E. M. Mélotte, F. J. J. Blommaert, “On the field width of reading magnifiers,”IPO Ann. Prog. Rep. 19, 133–136 (1984).

H. Bouma, C. P. Legein, H. E. M. Mélotte, L. Zabel, “Is large print easy to read? Oral reading rate and word recognition of elderly subjects,”IPO Ann. Prog. Rep. 17, 84–90 (1982).

H. Bouma, “Visual reading processes and the quality of text displays,” in Ergonomic Aspects of Visual Display Terminals, E. Grandjean, E. Vigliani, eds. (Taylor and Francis, London, 1980), pp. 101–114.

Duke-Elder, S.

S. Duke-Elder, D. Abrams, System of Ophthalmology (Kimpton, London, 1970), Vol. 5, pp. 793–807.

Duwaer, A. L.

A. L. Duwaer, G. van den Brink, “What is the diplopia threshold?” Percept. Psychophys. 29, 295–309 (1981).
[CrossRef] [PubMed]

Faye, E. E.

E. E. Faye, Clinical Low Vision (Little, Brown, Boston, Mass., 1976).

Fonda, G. E.

G. E. Fonda, Management of Low Vision (Thieme-Stratton, New York, 1981).

Jablonski, M. D.

L. L. Sloan, M. D. Jablonski, “Reading aids for the partially blind,” Arch. Ophthalmol. 62, 465–484 (1959).
[CrossRef]

Jacobs, J. C.

F. L. van Nes, J. C. Jacobs, “The effect of contrast on letter and word recognition,”IPO Ann. Prog. Rep. 16, 72–80 (1981).

Le Grand, Y.

Y. Le Grand, Optique Physiologique (Editions de la Revue d’Optique, Paris, 1952), Vol. 1.

Lebensohn, J. E.

J. E. Lebensohn, “Newer optical aids for children with low vision,” Am. J. Ophthalmol. 6, 813–819 (1958).

Legein, C. P.

H. Bouma, C. P. Legein, H. E. M. Mélotte, L. Zabel, “Is large print easy to read? Oral reading rate and word recognition of elderly subjects,”IPO Ann. Prog. Rep. 17, 84–90 (1982).

Legge, G. E.

G. E. Legge, G. S. Rubin, D. G. Pelli, M. M. Schleske, “Psychophysics of reading—II. Low vision,” Vision Res. 25, 253–266 (1985).
[CrossRef]

Linksz, A.

A. Linksz, “Optical principles of loupe magnification,” Am. J. Ophthalmol. 40, 831–840 (1955).
[PubMed]

Mélotte, H. E. M.

F. J. J. Blommaert, J. J. Neve, H. E. M. Mélotte, “Reading magnifiers: variation in magnification, image distance and field width,”IPO Ann. Prog. Rep. 20, 123–130 (1985).

H. Bouma, H. E. M. Mélotte, F. J. J. Blommaert, “On the field width of reading magnifiers,”IPO Ann. Prog. Rep. 19, 133–136 (1984).

H. Bouma, C. P. Legein, H. E. M. Mélotte, L. Zabel, “Is large print easy to read? Oral reading rate and word recognition of elderly subjects,”IPO Ann. Prog. Rep. 17, 84–90 (1982).

Neve, J. J.

F. J. J. Blommaert, J. J. Neve, H. E. M. Mélotte, “Reading magnifiers: variation in magnification, image distance and field width,”IPO Ann. Prog. Rep. 20, 123–130 (1985).

Pelli, D. G.

G. E. Legge, G. S. Rubin, D. G. Pelli, M. M. Schleske, “Psychophysics of reading—II. Low vision,” Vision Res. 25, 253–266 (1985).
[CrossRef]

Rubin, G. S.

G. E. Legge, G. S. Rubin, D. G. Pelli, M. M. Schleske, “Psychophysics of reading—II. Low vision,” Vision Res. 25, 253–266 (1985).
[CrossRef]

Schleske, M. M.

G. E. Legge, G. S. Rubin, D. G. Pelli, M. M. Schleske, “Psychophysics of reading—II. Low vision,” Vision Res. 25, 253–266 (1985).
[CrossRef]

Sloan, L. L.

L. L. Sloan, M. D. Jablonski, “Reading aids for the partially blind,” Arch. Ophthalmol. 62, 465–484 (1959).
[CrossRef]

L. L. Sloan, Reading Aids for the Partially Sighted: A Systematic Classification and Procedure for Prescribing (Williams and Wilkins, Baltimore, Md., 1977).

van den Brink, G.

A. L. Duwaer, G. van den Brink, “What is the diplopia threshold?” Percept. Psychophys. 29, 295–309 (1981).
[CrossRef] [PubMed]

van Nes, F. L.

F. L. van Nes, J. C. Jacobs, “The effect of contrast on letter and word recognition,”IPO Ann. Prog. Rep. 16, 72–80 (1981).

Welford, W. T.

W. T. Welford, Geometrical Optics (North-Holland, Amsterdam, 1962), Vol. 1.

Westheimer, G.

G. Westheimer, “The field of view of visual aids,” Am. J. Optom. 34, 430–438 (1957).
[CrossRef]

Zabel, L.

H. Bouma, C. P. Legein, H. E. M. Mélotte, L. Zabel, “Is large print easy to read? Oral reading rate and word recognition of elderly subjects,”IPO Ann. Prog. Rep. 17, 84–90 (1982).

Am. J. Ophthalmol. (2)

A. Linksz, “Optical principles of loupe magnification,” Am. J. Ophthalmol. 40, 831–840 (1955).
[PubMed]

J. E. Lebensohn, “Newer optical aids for children with low vision,” Am. J. Ophthalmol. 6, 813–819 (1958).

Am. J. Optom. (1)

G. Westheimer, “The field of view of visual aids,” Am. J. Optom. 34, 430–438 (1957).
[CrossRef]

Arch. Ophthalmol. (1)

L. L. Sloan, M. D. Jablonski, “Reading aids for the partially blind,” Arch. Ophthalmol. 62, 465–484 (1959).
[CrossRef]

IPO Ann. Prog. Rep. (4)

H. Bouma, H. E. M. Mélotte, F. J. J. Blommaert, “On the field width of reading magnifiers,”IPO Ann. Prog. Rep. 19, 133–136 (1984).

F. J. J. Blommaert, J. J. Neve, H. E. M. Mélotte, “Reading magnifiers: variation in magnification, image distance and field width,”IPO Ann. Prog. Rep. 20, 123–130 (1985).

H. Bouma, C. P. Legein, H. E. M. Mélotte, L. Zabel, “Is large print easy to read? Oral reading rate and word recognition of elderly subjects,”IPO Ann. Prog. Rep. 17, 84–90 (1982).

F. L. van Nes, J. C. Jacobs, “The effect of contrast on letter and word recognition,”IPO Ann. Prog. Rep. 16, 72–80 (1981).

Percept. Psychophys. (1)

A. L. Duwaer, G. van den Brink, “What is the diplopia threshold?” Percept. Psychophys. 29, 295–309 (1981).
[CrossRef] [PubMed]

Vision Res. (1)

G. E. Legge, G. S. Rubin, D. G. Pelli, M. M. Schleske, “Psychophysics of reading—II. Low vision,” Vision Res. 25, 253–266 (1985).
[CrossRef]

Other (8)

H. Bouma, “Visual reading processes and the quality of text displays,” in Ergonomic Aspects of Visual Display Terminals, E. Grandjean, E. Vigliani, eds. (Taylor and Francis, London, 1980), pp. 101–114.

D. H. A. Aberson, “Simulation of poor visual acuity: composition of silent-reading speeds,” submitted to Vision Res.

W. T. Welford, Geometrical Optics (North-Holland, Amsterdam, 1962), Vol. 1.

Y. Le Grand, Optique Physiologique (Editions de la Revue d’Optique, Paris, 1952), Vol. 1.

S. Duke-Elder, D. Abrams, System of Ophthalmology (Kimpton, London, 1970), Vol. 5, pp. 793–807.

L. L. Sloan, Reading Aids for the Partially Sighted: A Systematic Classification and Procedure for Prescribing (Williams and Wilkins, Baltimore, Md., 1977).

G. E. Fonda, Management of Low Vision (Thieme-Stratton, New York, 1981).

E. E. Faye, Clinical Low Vision (Little, Brown, Boston, Mass., 1976).

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Figures (14)

Fig. 1
Fig. 1

Definitions of the monocular (Wm), binocular (Wb), and composite (Wc) reading fields. WmR and WmL indicate the monocular fields for the right and the left eyes, respectively. The parameters v, a, L, and DP, denote the object-to-loupe distance, the eye-to-loupe distance, the loupe width, and the distance between the two eye pupils, respectively.

Fig. 2
Fig. 2

The theoretical binocular reading field Wb as a function of the object-to-loupe distance v for a loupe with f = 10 cm. The straight lines have been calculated for some values of the eye-to-loupe distance a (in centimeters). The dashed curve corresponds to an eye-to-image distance −b + a of 25 cm. The hatched areas are not allowed (see the text).

Fig. 3
Fig. 3

The width L of 29 commercially available loupes, plotted as a function of the focal length f. The straight line obeys the expression L = f/4 + 4 (in centimeters).

Fig. 4
Fig. 4

Theoretical field width W of the unmagnified text portion that can be viewed binocularly, monocularly, and with both eyes alternately, as a function of the magnification M25 The curves have been calculated for a fixed ratio v/f of 0.75 and for an eye-to-loupe distance a of 15 cm. As is indicated in the figure, the focal distance f varies monotonically from large values on the left-hand side to small values on the right-hand side. The pupil distance DP was taken to be 6 cm.

Fig. 5
Fig. 5

Comparison of the reading-field widths for peripheral vision of a stationary eye (½y1) and for foveal vision of a rotating eye (½ y2). (Top) The nodal point N of the eye is the reference point for the eye-to-loupe distance a. (Bottom) The center of rotation C is the reference point for the eye-to-loupe distance ar in the second case. The reading-field width is always larger for peripheral vision than for foveal vision, since a is always smaller than ar.

Fig. 6
Fig. 6

The experimental reading-field widths measured for subject HN, versus the corresponding theoretical reading field widths. The experimental W values are obtained for loupes with a focal length of 30.8 cm and different loupe widths (L = 6, 8, 10, and 11.9 cm, respectively). For each loupe, the distance v was fixed at 23.1 cm while the eye-to-loupe distance a was taken to be 10, 20, 30, and 40 cm, successively. For each value of f, L, v, and a, the theoretical field width W was calculated; the effect of eye rotations was taken into account. Open circles represent the experimental values for the monocular field, and filled squares represent the experimental values for the composite field. The straight line represents equal values for the experimental and theoretical reading-field widths.

Fig. 7
Fig. 7

Experimental reading-field widths, measured for all subjects, versus theoretical field widths. The experimental values for the monocular field Wm are given by the open symbols (□, f = 19.1 cm; •, f = 30.8 cm) respectively, and the filled symbols (■, f = 19.1 cm; •, f =30.8 cm) represent the experimental values for the composite field Wc. The dashed curves are taken from Fig. 6. The straight line again represents equal values for the experimental and theoretical field widths.

Fig. 8
Fig. 8

Horizontal reading-field displacements, for subject HM, as a function of experimental reading-field widths. (a) δxW versus the measured Wm values when one eye is covered. These curves are reproduced in (b)–(d) (dashed curves). For the case in which both eyes are uncovered, the solid curves represent δxW versus (b) the experimental Wm values, (c) the experimental Wc values, and (d) the experimental Wb values. The open symbols represent data obtained by using a loupe with f = 19.1 cm and L = 8 cm, and the filled symbols represent data obtained by using a loupe with f = 30.8 cm and L = 11.9 cm.

Fig. 9
Fig. 9

The horizontal displacements ΔxW for all subjects as a function of the experimental reading-field widths. Dashed curves represent δxW versus the measured Wm values obtained when one eye is. covered. Solid curves represent the values obtained when both eyes are uncovered. (a) ΔxW versus the experimental Wb values. (b), (c) ΔxW versus the experimental Wb values, for subjects WK (b) and NH (c). (d), (e) δxW versus the experimental Wm, Wb, and Wc, values for subjects KW (d) and TD (e), since these subjects only use a small part of the loupe. The open symbols represent the results obtained by using a loupe with f = 19.1 cm and L = 8 cm, and the filled symbols represent the results obtained by using a loupe with f = 30.8 cm and L = 11.9 cm.

Fig. 10
Fig. 10

Definition of the monocular reading-field width.

Fig. 11
Fig. 11

Definition of the binocular reading-field width.

Fig. 12
Fig. 12

Definition of the retinal magnification M25.

Fig. 13
Fig. 13

Definition of the loupe displacement ΔxL and the reading-field displacement δxW for the monocular case.

Fig. 14
Fig. 14

Definition of the loupe displacement δxL and the reading-field displacement δxW for the case of reading through a loupe with both eyes.

Equations (19)

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W m = ( 1 + v a - v f ) L ,
W b = W m - v a D p ,
W c = 2 W m - W b .
L = f 4 + 4.
M 25 = 25 v + a - a v / f ,
Δ x W = a r + v a r Δ x L .
W m = y .
y y = b v ,             y L = - - b + a a ,
W m = - v b ( - b + a a ) L .
1 v + 1 b = 1 f ,
W m = ( 1 + v a - v f ) L .
W b = z .
z z = - b v ,             z - D p z - D p = - b + a a .
W b ( 1 + v a - v f ) L - v a D p = W m - v a D p .
M 25 = β α ,
α y / 2 25 ,             β y / 2 - b + a .
y y = - b v .
M 25 = 25 v + a - a v / f .
Δ x W = a r + v a r Δ x L .

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