GB2026197A - Ophthalmic instrument - Google Patents

Abstract

An ophthalmic instrument in which a series of patterns of light spots is displayed briefly to a patient to test his field of vision has a shutter arrangement for displaying the patterns and a screen 3 visible only to the operator whereby a corresponding light spot pattern is displayed to enable the operator to check the patients performance. The light patterns on the screen 3 are preferably conveyed by light- transmitting fibres. <IMAGE>

Description

SPECIFICATION Opthalmic instrument This invention relates to an opthalmic instrument for use in testing the field of vision of a human eye.

A known instrument for this purpose is described in British Patent Specification No. 925006. In this instrument a pattern of spots of light, spatially distributed in a particular field, is briefly displayed to the patient and he is asked to indicate the number and position of the spots he saw. Asecond pattern is then displayed, the same information is requested, and the process is repeated as often as is necessary.

Since the object of the test would be defeated if the patient has time to move his eye so as to scan the pattern of light spots this pattern is displayed for only a short interval of time, say 1/500th second, and it is not practicable to include more than about four spots in each pattern. However, this means that if a full investigation has to be made of the field of vision a substantial number of patterns have to be displayed to the patient and this creates difficulties for the operator of the instrument especially if he is not very experienced.

It is customary for the operator to record information obtained from the patient on a chart which shows the spatial position of the light spots of all the patterns that the instrument can display, the operator recording on the chart adjacent the representation of a light spot whether or not the patient saw it.

Although the several spots of any one pattern are identified on the chart by the use of a common numeral or letter it is difficult for anyone who is not very experienced to locate them quickly and there is a real danger that information is recorded against the wrong spot. This difficulty is greatly increased if the instrument is equipped to display a substantial number of patterns since there may well be an unduly large number of representations of light spots on a chart which may be only 20 cms. square.

It is an object of the present invention to provide an improved instrument which avoids these and other difficulties and which can be used by a relatively unskilled operator.

According to the present invention there is provided an ophthalmic instrument for displaying briefly to a patient different patterns of light spots, the instrument comprising an apertured shutter arrangement for determining the light spot patterns and a light source for illuminating the shutter apertures, there being further provided a screen visible to the operator but not to the patient and means for presenting on the screen a pattern of light spots which correspond in position and number to the position and number of the light spots which the instrument is set up to display to the patient.

It will be appreciated that the illumination of the screen is prolonged in relation to the brief flash of illumination which the patient receives.

Conveniently the instrument includes means for presenting on the screen a reference identifying the particular pattern it is set up to display.

In a preferred arrangement the instrument includes means for locating on the screen the chart on which the operator records the results of the tests and may include means for providing a general and adjustable background illumination of the screen so that when the chart is superimposed thereon the markings and rulings of the chart can be seen by the operator.

The invention may be applied to a known type of such instrument in which the pattern to be displayed to the patient is produced by arranging a rotatable shutter over a fixed shutter, both shutters being provided with apertures so located that at given angular settings of the rotatable shutter some apertures in both shutters coincide to provide a desired pattern.

In such case the movement of the rotatable shutter between angular positions each corresponding to a pattern to be displayed may be arranged to move a source of illumination so that it illuminates the end of a respective bundle of light transmitting fibres which are separated into an appropriate number of parcels and arranged so as to produce light spots on the screen in such positions and in such number as correspond to the pattern determined by the angular position of the rotatable shutter.

In the improved instrument of this invention means may be provided for controlling the intensity of light of the display as seen by the patient.

Conveniently this may be achieved by arranging between the light source and the shutters a rotatable disc having a series of distributed openings each provided with a suitably graded neutral density filter.

In order to provide a sufficient range of control two such discs may be arranged with their openings in series between the light source and shutters, and after one disc has been turned through a complete circle the second disc may be rotated through one step as by means of a geneva mechanism.

Conveniently there may be provided at a convenient place on the screen a digital read out which indicates the light intensity obtained at any setting of the two discs.

One form of instrument in accordance with this invention will now be described with reference to the accompanying drawing which is a diagrammatic perspective view showing in dotted lines the outline of the instrument housing and in full lines certain components contained within the housing.

The housing 1 which is seen from the rear and one side has on its front face means for producing a pattern of light spots which is displayed to a patient whose head is located in a frame 2. The display is provided in known manner by providing on the front of the instrument housing a fixed shutter having a plurality of apertures and superimposing on this shutter a rotatable shutter which consists of a disc rotatably mounted at its centre and also having a plurality of apertures. The two sets of apertures are so arranged that at prescribed angular positions of the rotatable shutter certain apertures will coincide to form a desired pattern of openings. Aflash tube 16 is arranged within the housing so as to illuminate the openings for a short interval of time.The flash tube is controlled by the operator of the instrument and arranged when energised to produce a short flash of reproducible light characteristic.

Arranged on one side of the instrument housing, where it is not visible to the patient, is a screen 3 on which is produced a pattern of light spots which corresponds to the pattern which the instrument is set up to display to the patient.

A lamp 4 is mounted on the rotatable shutter and is supplied with current via arcuate conductor rails 5 carried on this shutter and which are engaged by sliding contacts carried on a socket 6 mounted on the housing 1, the socket receiving a plug connected with a suitable source.

Movement of the rotatable shutter, as by means of a handle 8, causes the lamp 4to move over a fixed arcuate manifold 9 in which is mounted the ends of a plurality of bundles 10 of light transmitting fibres, such that at any one of the predetermined angular positions of the rotatable shutter the lamp illumin atesthe end of a particular bundle of fibres. All these bundles are carried round within the housing to the screen 3 but for the sake of clarity only one such bundle is shown. As may be seen this bundle is split into four parcels 11 and the end of each parcel is secured on the inner face of the screen so as to produce a light spot thereon when the other end of the bundle is illuminated by the lamp 4.

It will be appreciated that the number of parcels 11 and the position at which their ends are secured on the screen will correspond to the number and positions of the coincident apertures in the rotatable and fixed shutters at that particular setting of the rotatable shutter, and that accordingly the operator can see the pattern which will be or has been displayed to the patient.

The instrument is provided with means for securing over the screen 3 a chart which is printed to indicate the position of all the light spots to be displayed to the patient. However, since those positions corresponding to a particular pattern to be displayed to the patient are illuminated by light transmitted through the fibre bundles there can be no uncertainty on the part of the operator as to which point on the chart information received from the patient is to be entered.

The screen 3 may also include indicating spots of illumination which light up to identify the particular pattern the instrument is set up to display and if the superimposed chart is appropriately printed the operator only has to mark the chart over each indicating spot in order to obtain a record of those patterns he has used in carrying out his tests. Such indicating spots are conveniently arranged in a row along a margin of the screen and are illuminated from an additional light-transmitting parcel from each bundle, the position of the spot in the row designating the appropriate pattern.

The illustrated instrument also includes means for controlling the intensity of light in the display as seen by the patient. These means include two rotatable discs 12 and 13 each formed with five openings in which are mounted neutral density filters.

The disc 12 which is rotatable by means of the knob 14 extending outside the housing 1 has filters giving attenuations from 0 - 0.8 logarithmic units (in steps of 0.2 units) while the disc 13, which is driven through a conventional geneva mechanism 15, has filters giving attenuations from 0 - 4 logarithmic units (in steps of 1.0 units). It will be appreciated that the filters of the two discs are arranged in series between the flash tube 16 and the shutters. Conveniently a read out mechanism is incorporated which produces a digital display on the screen 3 showing the actual light intensity of the display for any setting of the disc 12 and 13. This can be a mechanical or electronic read-out driven from the knob 14.

There is the facility for varying the colour of illumination. This provided by a set of colour filters (not shown) which may be interposed, one at a time, between the filter disc arrangement 12, 13 and the shutter arrangement. Thus, there may be exhibited spots of light which are white (no colour filter), red, blue, green, yellow, etc. A corresponding colour indicator (not shown) is provided at the screen.

Another neutral density filter (not shown) is provided to give a dimming effect for normal purposes.

Thus, the illumination given to the light spots is determined normally with the additional filter in place to be of a convential brightness range. However, for certain eye conditions useful information can be obtained by brighter illumination and under these circumstances the additional filter is removed.

It is to be understood that the invention is not restricted to the details of the foregoing description of one embodiment. For example, the movable means for illuminating the ends of the bundles of light transmitting fibres may be a shutter aperture or the end of another bundle of light transmitting fibres instead of a lamp.

Claims (10)

1. An ophthalmic instrumentfordisplaying briefly to a patient different patterns of light spots, the instrument comprising an apertured shutter arrangement for determining the light spot patterns and a light source for illuminating the shutter apertures, there being further provided a screen visible to the operator but not to the patient and means for presenting on the screen a pattern of light spots which correspond in position and number to the position and number of the light spots which the instrument is set up to display to the patient

2.An ophthalmic instrument as claimed in Claim 1 wherein the means for presenting the patterns of light spots on the screen comprises bundles of light-transmitting fibres, each bundle being fixed at one end and being split into parcels of lighttransmitting fibres, the ends of the parcels being fixed at positions on the screen corresponding to a respective pattern for that bundle, and there being means associated with the shutter arrangement for selectively illuminating the fixed ends of the bundles in accordance with the pattern of light spots which the instrument is set up to display to the patient.

3. An opthalmic instrument as claimed in Claim 2 wherein the shutter arrangement comprises a fixed shutter with apertures and a movable shutter with apertures, and the means for selective illumination comprises a light source which moves with the movable shutter to illuminate the fixed end of the appropriate bundle of light-transmitting fibres.

4. An ophthalmic instrument as claimed in Claim 3 wherein the movable shutter has a lamp fixed to it for illuminating the ends of the bundles, and current is supplied to the movables lamp by means of contacts which slide over a conductor track.

5. An ophthalmic instrument as claimed in any of claims 2 to 4 wherein a further light-transmitting parcel is taken from each bundle and fixed to the screen at a particular place in a row to identify, by its position, the pattern which the instrument is set up to display.

6. An ophthalmic instrument as claimed in any of the preceding claims wherein means are provided for locating on the screen a chart on which the operator may record the results of the tests.

7. An ophthalmic instrument as claimed in any of the preceding claims wherein the light source comprises a lamp and a set of neutral density filters which may be interposed before the lamp to control the intensity of illumination.

8. An ophthalmic instrument as claimed in Claim 7 wherein the filters are arranged on two filter discs, the arrangement being such that the light from the lamp passes in series through a filter on each of the two discs, the filters being graded and the discs being rotatable to present different total densities, the discs being coupled by a geneva mechanism.

9. An ophthalmic instrument as claimed in Claim 8 8wherein there is a further neutral density filter between the light source and the shutter arrangement, the arrangement being such that a normal range of light intensity is achieved with the additional filter in place and temporary removal of the additional filter provides an abnormally high intensity.

10. An ophthalmic instrument substantially as hereinbefore described with reference to the accompanying drawings.