Abstract

A device is described that provides an electrical signal proportional to the instantaneous refractive power of the human eye. Infrared light illuminates a target whose optical distance from the subject’s eye can be changed rapidly. The position of this target is servo controlled in such a way that it remains conjugate with the retina regardless of changes of the subject’s state of accommodation. The position of the target provides a direct measure of refractive power. The device may be used on an undrugged eye and does not interfere with normal visual tasks.

© 1970 Optical Society of America

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References

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  1. See Y. Le Grand, Form and Space Vision, rev. ed. (Indiana University Press, Bloomington, Ind., 1967), for an interesting review of early techniques. Recently, optometers have been described by M. J. Allen and J. H. Carter, Am. J. Optom. 37, 403 (1960); F. W. Campbell and J. G. Robson, J. Opt. Soc. Am. 49, 268 (1959); J. G. Carter, Arch. Soc. Am. Ophthal. Opt. 4, 137 (1962); N. Roth, Rev. Sci. Instr. 36, 1936 (1965); J. Warshawsky, J. Opt. Soc. Am. 54, 375 (1964). All of these instruments operate on the same underlying principle. The one described here most closely resembles Campbell and Robson’s optometer.
    [Crossref] [PubMed]
  2. This is a consequence of the fact that the eye is in the focal plane of L2. The relationship is derived, e.g., in G. Westheimer, Vision Res. 6, 669 (1966).
    [Crossref] [PubMed]
  3. We will use the convention, here, of stating the refractive power of the eye relative to its power when accommodated for infinity. That is, 0.0 diopters of refractive power means that the retina is conjugate with_infinity; at 2.0 diopters, the retina is conjugate with a plane 1/2.0 m away, etc. The absolute refractive power of a normal eye accommodated for infinity is about 60 diopters (i.e., its equivalent focal length is about 17 mm).
  4. We are using a quadrant cell, Electro Nuclear Labs (Menlo Park, Calif.) model 640A, in which the two members of each vertical pair are connected in parallel.
  5. The dc component of the sum is directly proportional to the area of the subject’s natural pupil, and may be monitored if pupil size is of interest.
  6. If there were inhomogeneities of transmittance across the entrance pupil of the eye, the relative amounts of light transmitted to the retina from the two source positions might vary with eye movements. The resulting artifact could be avoided if the sum signal were used continuously and automatically to control the relative intensities of the sources.
  7. A. Ivanoff, Les abérrations de l’oeil (Editions de la Revue d’optique, Paris, 1953).
  8. R. A. Weale, J. Physiol. (London) 186, 175 (1966).
  9. The optical display system used in these experiments is described in Crane and Cornsweet, J. Opt. Soc. Am. 60, 577 (1970).
    [Crossref]

1970 (1)

1966 (2)

This is a consequence of the fact that the eye is in the focal plane of L2. The relationship is derived, e.g., in G. Westheimer, Vision Res. 6, 669 (1966).
[Crossref] [PubMed]

R. A. Weale, J. Physiol. (London) 186, 175 (1966).

Cornsweet,

Crane,

Ivanoff, A.

A. Ivanoff, Les abérrations de l’oeil (Editions de la Revue d’optique, Paris, 1953).

Le Grand, Y.

See Y. Le Grand, Form and Space Vision, rev. ed. (Indiana University Press, Bloomington, Ind., 1967), for an interesting review of early techniques. Recently, optometers have been described by M. J. Allen and J. H. Carter, Am. J. Optom. 37, 403 (1960); F. W. Campbell and J. G. Robson, J. Opt. Soc. Am. 49, 268 (1959); J. G. Carter, Arch. Soc. Am. Ophthal. Opt. 4, 137 (1962); N. Roth, Rev. Sci. Instr. 36, 1936 (1965); J. Warshawsky, J. Opt. Soc. Am. 54, 375 (1964). All of these instruments operate on the same underlying principle. The one described here most closely resembles Campbell and Robson’s optometer.
[Crossref] [PubMed]

Weale, R. A.

R. A. Weale, J. Physiol. (London) 186, 175 (1966).

Westheimer, G.

This is a consequence of the fact that the eye is in the focal plane of L2. The relationship is derived, e.g., in G. Westheimer, Vision Res. 6, 669 (1966).
[Crossref] [PubMed]

J. Opt. Soc. Am. (1)

J. Physiol. (London) (1)

R. A. Weale, J. Physiol. (London) 186, 175 (1966).

Vision Res. (1)

This is a consequence of the fact that the eye is in the focal plane of L2. The relationship is derived, e.g., in G. Westheimer, Vision Res. 6, 669 (1966).
[Crossref] [PubMed]

Other (6)

We will use the convention, here, of stating the refractive power of the eye relative to its power when accommodated for infinity. That is, 0.0 diopters of refractive power means that the retina is conjugate with_infinity; at 2.0 diopters, the retina is conjugate with a plane 1/2.0 m away, etc. The absolute refractive power of a normal eye accommodated for infinity is about 60 diopters (i.e., its equivalent focal length is about 17 mm).

We are using a quadrant cell, Electro Nuclear Labs (Menlo Park, Calif.) model 640A, in which the two members of each vertical pair are connected in parallel.

The dc component of the sum is directly proportional to the area of the subject’s natural pupil, and may be monitored if pupil size is of interest.

If there were inhomogeneities of transmittance across the entrance pupil of the eye, the relative amounts of light transmitted to the retina from the two source positions might vary with eye movements. The resulting artifact could be avoided if the sum signal were used continuously and automatically to control the relative intensities of the sources.

A. Ivanoff, Les abérrations de l’oeil (Editions de la Revue d’optique, Paris, 1953).

See Y. Le Grand, Form and Space Vision, rev. ed. (Indiana University Press, Bloomington, Ind., 1967), for an interesting review of early techniques. Recently, optometers have been described by M. J. Allen and J. H. Carter, Am. J. Optom. 37, 403 (1960); F. W. Campbell and J. G. Robson, J. Opt. Soc. Am. 49, 268 (1959); J. G. Carter, Arch. Soc. Am. Ophthal. Opt. 4, 137 (1962); N. Roth, Rev. Sci. Instr. 36, 1936 (1965); J. Warshawsky, J. Opt. Soc. Am. 54, 375 (1964). All of these instruments operate on the same underlying principle. The one described here most closely resembles Campbell and Robson’s optometer.
[Crossref] [PubMed]

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Figures (6)

Fig. 1
Fig. 1

Imaging a point target at infinity through a small aperture that alternates between two positions, A and B. The intercepted-ray position at the retina will be stationary, or move with the aperture, or opposite to the aperture, respectively, according to whether the eye is focused for infinity (a), beyond infinity (b), or closer than infinity in (c).

Fig. 2
Fig. 2

Schematic diagram of the optometer. Legend: S, gallium arsenide diodes; ST1, input stop; DM, dichroic mirror; BS, beam splitter; LT, light trap; RI, plane conjugate to retinal image; ST2, corneal stop; D, split-field photocell; P, preamplifier; DF, difference signal; SM, sum signal; PR, phase reference; ΦS, phase sensitive detector; SD, servo driver; M, linear motor; GN, sine-wave generator; LD, light-source driver; C, light-emitter chip; RA, radiating area. ST1, L4, and ST2 are mechanically coupled and are driven by M, a linear motor. The eye views any target through the dichroic mirror along the path indicated by the arrow. The inset referring to D illustrates the position of the nominal retinal image on the detector.

Fig. 3
Fig. 3

Detecting retinal image movement. The smooth curve represents the spatial distribution of irradiance on the photodetector, and the two dashed lines represent two positions of the dividing line between the halves of the photodetector. (For ease of illustration, assume that the photocell moves, rather than the image.) The magnitude of the signal from each half of the photocell is directly proportional to the shaded area, i.e., to the product of the peak irradiance of the image and the movement distance ab.

Fig. 4
Fig. 4

Typical optometer records. The lower trace in each record is the stimulus distance as a function of time. The calibration marks represent 1-diopter shifts. The time markers indicate 1-sec intervals. Note the automatic recovery from an eye blink (EB) and from closing the eye (EC).

Fig. 5
Fig. 5

Response to a 3.5-diopter peak-to-peak sinusoidal target displacement of increasing frequency. The lower trace is the stimulus distance as a function of time. The upper trace is the optometer record. The arrow pairs indicate 1-diopter calibration marks. The time markers indicate 1-sec intervals. The response is 180° out of phase and is down to 1 2 amplitude at approximately 1 Hz.

Fig. 6
Fig. 6

Spherical aberration of the human eye for two different fixation distances, corresponding to 0.3- and 4.0-diopter refractive powers. These curves represent the refractive power measured along a vertical line down the center of the pupil. At both fixation distances, the center of the entrance pupil manifests greater refractive power than the edges. That is, the eye exhibits overcorrected spherical aberration over the entire normal viewing range of this particular subject, at least in the vertical meridian. (This particular subject’s aberration is quite symmetric, but many eyes show strong asymmetries.)

Equations (1)

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D e = 1 f 2 ( 1 - d f 2 ) ,