Abstract

We propose a simple method to measure the angle “α” that the visual axis (VA) makes with the optical axis of the human eye. In this method, we capture the images of the pupil from three different angles, one along the VA and the other two along angles that are symmetrical with respect to the VA. These views of the pupil are captured simultaneously by a camera in a single photograph using a pair of plane mirrors. Assuming a model eye and with the help of finite ray tracing, we compute the value of α from the measured diameters of the three images of the pupil. Having a simple means to measure the value of α can be useful for optical modeling and analysis of the human eye. Measurement of the VA may also be useful in monitoring progressive myopia.

© 2011 Optical Society of America

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References

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  1. M. Tscherning, in Physiological Optics, 4th ed., trans. C.Weiland, ed. (Keystone, 1924), pp. 150–154.
  2. R. B. Rabbetts, in Bennett and Rabbett’s Clinical Visual Optics, 4th ed. (Butterworth Heinemann, 2007), pp. 409–410.
  3. K. V. Avudainayagam and Chitra S. Avudainayagam, Clin. Exp. Optom. 92, 56 (2009).

2009

K. V. Avudainayagam and Chitra S. Avudainayagam, Clin. Exp. Optom. 92, 56 (2009).

Avudainayagam, Chitra S.

K. V. Avudainayagam and Chitra S. Avudainayagam, Clin. Exp. Optom. 92, 56 (2009).

Avudainayagam, K. V.

K. V. Avudainayagam and Chitra S. Avudainayagam, Clin. Exp. Optom. 92, 56 (2009).

Rabbetts, R. B.

R. B. Rabbetts, in Bennett and Rabbett’s Clinical Visual Optics, 4th ed. (Butterworth Heinemann, 2007), pp. 409–410.

Tscherning, M.

M. Tscherning, in Physiological Optics, 4th ed., trans. C.Weiland, ed. (Keystone, 1924), pp. 150–154.

Clin. Exp. Optom.

K. V. Avudainayagam and Chitra S. Avudainayagam, Clin. Exp. Optom. 92, 56 (2009).

Other

M. Tscherning, in Physiological Optics, 4th ed., trans. C.Weiland, ed. (Keystone, 1924), pp. 150–154.

R. B. Rabbetts, in Bennett and Rabbett’s Clinical Visual Optics, 4th ed. (Butterworth Heinemann, 2007), pp. 409–410.

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Figures (4)

Fig. 1
Fig. 1

Schematic of the experimental arrangement (left eye, top view). A, view along the VA; B, view at θ from the VA on the nasal side; C, view at θ from the VA on the temporal side.

Fig. 2
Fig. 2

VA, OA, and the three views obtained by the camera. A, view obtained by the camera along VA; B, view obtained at ( θ + α ) from OA on the nasal side; C, view obtained at ( θ α ) from OA on the temporal side. In practice, views B and C are obtained using the inclined mirrors.

Fig. 3
Fig. 3

(a) Three views of the subject’s pupil recorded by the camera. (b) Reference line and its images used to find the scaling factor involved in the imaging as well as adjust the inclination of the mirrors.

Fig. 4
Fig. 4

Illustration of ray tracing for the left eye (top view). PP, actual pupil diameter; QQ, entrance pupil diameter ( DT temporal ) for the temporal view. QQ/DT is the additional magnification factor m 1 in Eq. (2).

Tables (1)

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Table 1 Values of Alpha Obtained for Two Subjects

Equations (4)

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DC = DT cos α .
DP = m 1 DT cos ( θ α ) ,
DM = m 2 DT cos ( θ + α ) ,
tan ( α ) = [ 1 / tan ( θ ) ] [ ( m 2 DP m 1 DM ) / ( m 1 DM m 2 DP ) ] .

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