Ophthalmic instruments

A Friedmann analyser wtih an arrangement of fixed and rotatable shutters for displaying different patterns of light spots to a subject has a screen for displaying to the operator each light spot pattern selected by illumination of a series of light-emitting elements at fixed positions over the screen area. The light-emitting elements are actuated by a fixed array of infra-red emitting and receiving elements that direct radiation onto a binary-coded reflective pattern displaceable with the rotatable shutter and sense the radiation reflected by said pattern so that with the displacement of the shutter different reflected code signals are sensed associated with respective shutter light patterns displayed to the subject.

BACKGROUND OF THE INVENTION 
This invention relates to an ophthalmic instrument for use in testing the 
vision of a subject. 
A known type of instrument for this purpose briefly displays to the subject 
predetermined patterns of spots of light, the subject indicates what he 
has seen of these patterns, and from his observations of a number of 
successive patterns it is possible to characterise particular deficiencies 
in his field of vision. Examples of such an instrument, known commercially 
as a Friedmann Analyser, are described in British patent specifications 
Nos. 925 066 and 2 026 197A. 
Because each display pattern is shown only briefly to the subject, e.g. for 
1/500th of a second, in order to ensure the subject does not scan the 
field of vision each time but focusses on a fixed point, only a very 
limited number of points of light can be included in each pattern, e.g. 
not more than 4 points each time. This means that a large number of test 
patterns must be displayed to cover the field of view being examined. In 
order to assist the task of the operator in recording the results of these 
many tests, the specification of British patent application No. 2 026 197A 
describes how the patterns to be displayed can be shown on a screen that 
is visible only to the operator and not the subject, and the results of 
the successive tests can be recorded on a chart mounted over that screen. 
While the provision of monitoring display for the operator considerably 
simplifies his task and helps to avoid recording errors, it is found in 
practice that the means for producing the screen display is not always 
reliable and that the quality of the screen display is not easily 
controlled. The present invention is particularly concerned with improving 
the instrument in these respects. 
SUMMARY OF THE INVENTION 
According to the invention, in an ophthalmic instrument for displaying to a 
subject different patterns of light spots in a series of visual tests, the 
instrument comprising an apertured shutter arrangement for determining the 
pattern of light spots to be displayed, a member of said shutter 
arrangement being displaceable to select different light patterns and a 
screen or like display area being provided on the instrument for 
displaying to the operator but not the subject each light pattern 
selected, the means for producing the pattern on said screen comprises a 
series of light-emitting elements in fixed positions over the area of the 
screen, said elements being actuated by the use of radiation transmitting 
means which are arranged to transmit radiation onto reflecting means from 
which reflected radiation is received by sensing means in dependence upon 
the movement of the displaceable shutter member, said reflecting means 
transmitting to said sensing means a different radiation reflection 
characteristic for each light-spot pattern displayed at the first location 
and said sensing means responding to the reflected radiation 
characteristic to actuate the light-emitting elements corresponding to the 
selected pattern. 
In one form of the invention, the reflecting means is movable with the 
displaceable shutter member for transmission to the sensing means the 
different reflected radiation characteristics associated with the 
different light-spot patterns. Additionally or alternatively, there may be 
masking means for radiation transmission between the transmitting and 
sensing means movable with the displaceable member for selective exposure 
of the reflecting means to the radiation. 
By producing the operator's screen patterns in these ways, a major source 
of difficulty is avoided in that the active elements of the means for 
producing the pattern can all be mounted in fixed positions and the only 
movable elements are the passive elements that determine the reflection 
characteristic of the radiation. It is therefore possible to avoid the use 
of relatively movable electrical contacts which are prone to malfunction 
over an extended period of use. 
According to a preferred feature of the invention, a considerable 
simplification of the radiation and sensing means is possible by arranging 
the reflecting means in the form of a coded pattern whereby a series of 
different reflection characteristics can be generated using a lesser 
number of radiation sensing means than the number of patterns to be 
displayed in a test series. As has already been mentioned, a large number 
of individual patterns must be shown to the subject because of the need to 
limit the number of light spots in each pattern. A standard series of 
tests for vision involves a total of 31 light spot patterns and, employing 
the fibre optics arrangement of patent application No. 2 026 197A for 
producing the pattern on the operator's screen, a corresponding number of 
fibre bundles must be provided. 
If, however, said reflecting means is arranged to produce a binary-coded 
reflection characteristic, all the alternatives can be identified using a 
five-character binary code, so that only five radiation sensing elements 
are necessary. This can lead to a considerable simplification and, in 
particular, because the total angular movement of the displaceable shutter 
member is limited, it makes it easier to dispose the radiation sensing 
means in a way that reduces any risk of spurious signals through 
misalignment. 
As a convenient and reliable arrangement, infra-red radiation transmitting 
and sensing elements can be used in the form of units in each of which a 
sensing element is adapted to receive reflected radiation from an integral 
emitting element. Radiation frequencies other than in the infra-red range 
can of course also be employed. 
The reflecting means may be economically produced as a patterned coating on 
one member of the apertured shutter arrangement. Such a coating may be 
formed by a conventional printed circuit technique and given a final 
highly reflective surface finish; other possibilities include hot 
stamping, or direct deposition of a highly reflective material directly 
onto the shutter surface. 
The invention will be described by way of example with reference to the 
accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The instrument comprises a chamber-like housing 2 on the front face of 
which is an apertured shutter arrangement 4 comprising a pair of discs 6,8 
one of which is fixed and the other of which is rotatably mounted at its 
centre. Both discs have a series of small apertures 4a and as the 
rotatable shutter disc is turned by its hand grip 10 to prescribed angular 
positions, different groups of apertures of the two discs will coincide to 
form particular patterns of openings. Within the housing is a flash tube 
11 of known form that is arranged to produce a very brief flash of light 
with reproducible characteristics, the characteristics being modified if 
required by the use of adjustable filter means (as described in GB No. 2 
026 197A) between the flash tube and the shutter arrangement. When the 
flash tube is energised, therefore, a pattern of light spots of controlled 
illumination intensity appears momentarily on the front of the apertured 
screen arrangement. 
The patterns so produced are observed by a subject seated in front of the 
housing, looking through a back-lighting ring 12 that throws its 
illumination onto the screen arrangement, with his gaze focussed on a 
fixed marker (not shown) at the centre of the screen arrangement. 
At one side of the housing, in a position in which it cannot be seen by the 
subject, there is a translucent screen 20 visible to the operator, and 
mounting means adjacent the screen allow the operator to attach a chart 
(not shown) over it. 
On the screen is indicated the pattern of light spots that are to be 
displayed to the subject when the flash tube is operated. The screen 
indication is itself in the form of a series of spots of light, but these 
are produced by a series of light-emitting diodes 22 (only a few of which 
are illustrated, for clarity) mounted at the required positions 
immediately under the screen surface and actuated independently of the 
illumination of the flash tube. 
For selecting the diodes 22 to be illuminated, the rotatable shutter disc 8 
carries a reflective pattern 24 on its rear face extending over an annular 
arc 25 of about 90.degree.. The pattern is in the form of five radially 
spaced binary-coded tracks and operates in conjunction with a group of 
five infra-red units 26 fixed in the interior of the housing, each unit 
having an emitting diode 28 directing a constant infra-red beam onto a 
respective one of the tracks, and a sensor 30 aligned to receive the 
reflected radiation from the track. The group of infra-red units therefore 
produces a five-bit binary signal that is transmitted by a ribbon cable 32 
to a decoding and driving circuit 34 mounted immediately behind the screen 
20. 
The coded signal signifies the angular position of the rotatable shutter, 
and therefore is indicative of the selected pattern of spots at that 
position. FIG. 2 also illustrates a sixth infra red unit associated with a 
sixth reflective track 24a. This serves simply to switch on the decoding 
and driving circuit when each test position is reached. 
The decoding and driving circuit can employ generally conventional 
components and is indicated in schematic outline in FIG. 2a. It comprises 
two 16-way CD4067 selectors 38 having inputs from four of the coded tracks 
and also controlled by a select switch 40 actuated by a fifth of the 
tracks. Respective groups 42 of transistor switches operate a pattern and 
indicator generating circuit 44 provided with constant current sources 46, 
48 for powering the patterns and the indicators. The circuit 44 thus has 
respective output lines 36 (only one of which is shown in FIG. 1) 
connected to the different groups of diodes 22 corresponding to the 
shutter light spot patterns, so that in accordance with the coded signal 
from the infra red units the illuminated diodes in each case display on 
the screen 20 the same pattern as that selected for the light spots to be 
displayed to the subject. The diodes remain illuminated while the 
apertured screen remains in its set position. 
The total number of light patterns used in a standard field-of-vision test 
is thirty-one. The binary coded signal is thus able to signify all these 
with only five transmission lines between the infra-red units and the 
decoding and driving circuit 34, although there will of course be 
thirty-one output lines from that circuit to the screen diodes. The 
thirty-second binary-coded signal may be used to hold all the diodes 22 
off, this being required when the instrument is being used without its 
apertured shutter arrangement for light-dark adaptation tests. 
When used for field-of-vision tests, the chart secured over the screen can 
indicate the light spot positions of the patterns to be displayed to the 
subject, and the illuminated diodes 22 appear at the positions of each 
selected pattern of spots in turn, so that the operator is left without 
doubt as to which point on the chart the subject's responses are to be 
entered. 
There may be a further 31 indicator diodes 22a behind the screen that are 
not part of a pattern of spots but that are illuminated simultaneously 
with the patterns by the operation of the generating circuit 44 to 
indicate which pattern is selected. If, for example, along a margin of the 
chart there is a row of spaces to record the patterns that have been used, 
these additional diodes can be similarly arranged in a row in register 
with the individual spaces, and the operator has only to mark the chart 
each time in the space indicated by the particular diode 22a that has been 
illuminated. 
The reflective pattern 24 on the rotatable shutter is conveniently formed 
by known printed circuit techniques, e.g. using copper foil. To provide 
the required degree of reflectivity it can be given a final bright-finish 
coating, e.g. of nickel. Although illustrated in FIG. 1 as a series of 
discrete areas, these code elements are preferably linked together as a 
continuously conductive series so that the nickel coating can be 
electrodeposited with a single terminal connection to the pattern. Linking 
of the code elements may not be needed if, for example, they are formed by 
being deposited directly onto the shutter. 
It may be noted here that it is possible alternatively to dispose the 
reflective pattern on the fixed shutter, an opening in the rotatable 
shutter behind it acting as a mask and exposing the appropriate part of 
the pattern to the radiation transmitting and sensing means as the 
rotatable shutter moves. This is also the case if the rotatable shutter is 
in front of the fixed shutter if the latter has a suitable opening in it. 
FIG. 3 illustrates in outline such an arrangement in which fixed shutter 
6a carries the binary-coded reflective pattern 24 and the rotatable 
shutter 8a has an aperture 50 that selectively masks the coded pattern as 
the shutter 8a is displaced so that the changed reflection characteristic 
thereby actuates the appropriate sensing elements of the infra-red units 
26. 
Although it is preferred to employ a coded signal to produce the light spot 
illumination of the operator's screen, because of the simplification this 
can achieve, it is not necessary within the scope of the invention. It is 
still possible to obtain the increased reliability of the described 
arrangement, with all the active elements of the signal generating means 
static and only a passive reflecting member displaceable, if there is a 
one-to-one correspondence between the number of signal sensors and the 
number of the spot patterns to be produced. It is also possible to employ 
other signal producing and transmitting means, e.g. with fibre optics, but 
the infra-red means described is preferred for economic grounds.