GB2152692A - Optometer having ring test image superimposable on an external view - Google Patents

Abstract

An optometer giving an external view to allow the eye (2) under test to focus at a known distance, wherein a test image is a ring (10) superimposable on an external view (3) adjustable to a spot superimposable upon the external view by adjustment of a telescopic view by adjustment of a telescopic barrel (5,7) of the optometer to a configuration at which the focussing error of the eye from that known distance may be determined by reading measurement scales on the barrel (5,7) and a rotatable ring (16) mounted thereon. <IMAGE>

Description

SPECIFICATION Improvements in or relating to optometers The present invention relates to optometers, particularly to optometers which are portable in use.

Known optometers may be repackaged to provide for portability but in all types of optometer the head of the person whose eyes are to be tested has to be accurately located in relation to the optometer. The locating apparatus usually comprises a jaw rest and skull cramp to position the head of the subject in a frame and an adjustable clamp to hold the eye to be tested in the correct position relative to the optometer. As a result, known optometers may be made portable for the purpose of transportation but cannot be made portable in use.

The present invention, however, provides a simple optometer system which may be sufficiently accurately aligned with the eye under test without a head rest and skull cramp and which may be made portable in use.

According to the present invention there is provided an optometer giving an external view to allow the eye under test to focus at a known distance, having a test image being a ring superimposable upon the external view adjustable to a spot superimposable upon the external view by adjustment of the optometer to a configuration at which the focussing error of the eye from that known distance may be determined.

An advantage of the inventive optometer system lies in the continuous view the eye under test has of the target placed at a known distance from the eye allowing rapid adjustment of the optometer to the configuration at whih the focussing error may be determined.

Focussing of the test image over the range of target distances is accomplished by the test image being of small aperture relative to the eye lens aperture, giving the eye lens a wide depth of field of focus for the test image, but not for the external view.

A diffusely transmitting screen or an opaque cap may be placed to interrupt the external view to allow the testing of empty field focus.

The optometer system may be incorporated into a portable unit suitable for personal operation.

The presence of astigmatism in the eye under test may be determined by changes in shape of the test image from a ring to an ellipse adjustable to a line superimposed upon the external view.

An embodiment of the invention will now be described with reference to the accompanying drawing in which Figure 1 shows schematically an optometer incorporating the invention; Figures 2A, B show the view presented to a non-astigmatic eye; Figures 3A, B show the view presented to an astigmatic eye.

In Fig. 1 an optometric system indicated by the broad arrow 1 is shown in cross-section.

The eye 2 to be tested observes a target 3 through the combining cube 4. The combining cube serves,to superimpose the optometric test image on the view of the target seen by the eye. The combining cube is rigidly mounted on the inner barrel 5 of the optometer and contained within the inner barrel is a Badal lens 6. The outer barrel 7 of the optometer is rotatably mounted on the inner barrel by means of a screw thread 8. The outer barrel contains a high intensity green light emitting diode 9 and power supply battery (not shown) which illuminates a translucent ring 10 in a first opaque screen 11. The pin hole target 13 in a second opaque screen 14 is illuminated by light from the translucent ring 10 which has passed through the collimating lens 12. An extension 15 of the outer barrel 7 beyond the screw thread 8 provides an axial location for a rotatably mounted ring 16.Measurement scales (not shown) are marked on the adjacent portions of the inner and outer barrel and on the rotatable ring 16.

In operation the optometer is held horizontally by the user with the optometer located relative to the eye by an eye surround (not shown) which rests on the users face. The rotatably mounted ring is then rotated relative to the outer barrel to correspond to the distance from the eye 2 to the target 3 which in turn allows a direct reading of the eye focussing error to be made between the adjacent scales on the rotatable ring 16 and inner barrel 5 in a similar manner to the reading of a micrometer gauge.

The view presented to a non-astigmatic eye is shown in Figs. 2A and 2B. Fig. 2A shows the ring 21 superimposed upon target 3 which is seen when the optometer is not adjusted to the position at which the measure- ment of the focussing error may be made.

Adjustment of the optometer to the measurement position is made by rotating the outer barrel 7 until the view becomes as shown in Fig. 2B with a spot 22 superimposed upon the target 3.

The view presented to an astigmatic eye is shown in Figs. 3A and 3B. An astigmatic user will see an ellipse 31 superimposed upon the target 3 which becomes a line 32 superimposed upon the target 3, the line being parallel to the long axis of the ellipse 31.

A optometer incorporating the invention is thus able both to provide a measure of the focussing error of the eye under test and to indicate the presence of astigmatism in that eye.

Claims (2)

1. An optometer giving an external view to allow the eye under test to focus at a known distance, having a test image being a ring superimposable upon the external view adjustable to a spot superimposable upon the external view by adjustment of the optometer to a configuration at which the focussing error of the eye from that known distance may be determined.

2. An optometer substantially as described herein with reference to the drawings.