GB2205661A - Laser speckle eyesight testing and exercising - Google Patents

Abstract

A multiple mode laser 9 speckle eye-sight testing and sight improvement machine uses sets of paired, demountable and interchangeable screens 1 to extend the usefulness of single screen machines and enables the speckle pattern to be controllably adjusted digitally by means of a liquid crystal display, the patterning of which is electrically alterable under microprocessor control 23. By selecting an appropriate screen combination testing for various eye-sight conditions can be made including twilight myopia. The use of a flat or curved liquid crystal display interlaced to external controls also enables a fixation target to be provided on screen with a different speckle speed to the rest of the screen thereby providing the means for digital calibration of corrective lenses. A further, optional liquid crystal display 27 is available for providing a moving spot of light to help induce involuntary exercise of the eyes. <IMAGE>

Description

Multiple Mode Sight Testing Apparatus This invention relates to an adaptable, multiple mode eye-testing and eye-training apparatus of the kind which employ one or more beams of laser light directed at a slowly moving screen to produce for the viewer the appearance of a laser speckle pattern that enables eye defects to be diagnosed. For the eye without defect the speckle pattern appears to have the well known circulatory or "boiling effect", (which is also visible in the light output from street lighting employing sodium lamps), no overall translational movement of the speckle pattern being detected, whereas a defective eye will see a definite overall movement of the pattern, the speed and direction of which depends on the extent and the type of the defect present.

It is believed that the type of screen and the condition or texture of the screen surface is a critical consideration for achieving a suitably good speckle pattern to be formed and many materials and methods are available for making such screens. GB Patent Specification 2 144 235 A ( Cook) describes one method of creating such a screen by air-blasting the surface of a permanently mounted screen with hard granular material much of which is retained as embedded particles. It is believed that the retained imbedded particles act as an integral multiple diffraction grating which, being fixed, is not adjustable. GB Specification 2 135 076A (Maroof) proposes the use of paraffin wax as a diffuser medium and is also not adjustable.Although these types of screen are useable with the present invention provided they are adapted to be in accordance with this invention, there are many other types equally well suited to use in accordance with this invention.

It is known that different eye defects, such as twilight myopia, can be detected by using screens which have been adapted to compensate for particular light conditions and light characteristics, e.g. colour. A disadvantage of the particular above mentioned apparatuses is that a single, permanently mounted screen that can only test for a limited number of eye defects is employed, a restriction which makes them much less versatile than they could be. It is also known that some screens are more useful than others as a means to inducing the eye to exercise for the purpose of sight improvement.

One object of the present invention is to provide an improved apparatus of the kind described that overcomes the disadvantage of single screen laser speckle machines by providing an apparatus useable with a wider range of improved and more versatile screens that can be provided as a set of demountable, interchangeable screens each suited to a particular need and which can be easily mounted within the apparatus as required by an unskilled operator, or alternatively to provide a single screen which is adaptable to meet testing needs on a more or less universal basis. This obviates the need of an optician, say, of having to buy more than one expensive machine in order to test for a greater range of eye-defects than can be undertaken with the limited single screen machines available hitherto.

A second object of this invention is to provide a screen which is not only relatively simple to make but which is also able to be controllably adjustable so as to alter the magnification characteristics r of the multiple diffraction grating and thereby the speckle pattern and its intensity and also the orientation of the screen, and thereby provide a multiplicity of screens to meet most needs within one single adjustable screen means.

For such a screen to be adjustable it is preferably comprised of two members in close, contactless contiguous relation or proximity with each other, one member, in order to produce the speckle effect,either being physically moveable relative to the second member which is normally stationary except for making adjustments, or one stationary member having a diffraction grating pattern which is itself moveable relative to the other moveable member,or one or both members being physically stationary.For example when two pieces of photographic negative or positive film each imaged with a suitable, regular pattern of lines or dots to produce a diffraction grating, are overlaid, an interference effect is caused and this can be altered by rotating the normal axis of one film relative to the other to produce a magnifying or reduction effect, a portion of the overall diffraction grating being present on both pieces of film. If one member is moved in a constant direction relative to the other no speckle pattern will be caused; instead a definite directional flow of the pattern will be observed.If, however, a single piece of such film is overlaid upon an illuminated glass plane, a surface of which has been shot-blasted so as to leave no residual imbedded particles, and one is slowly moved with respect to the other, a "boiling" speckle pattern is observed, the effect being analagous to a distribution of miniature lights switching on an off at random. In this example, the glass surface is abraded to cause similarly sized randomly arranged indentations or reflective appertures, and the film serves as a fixed pattern multiple diffraction grating which can only be adjusted by replacing it with another piece of film differently patterned.A second piece of film rotated upon the first will not produce an adjustable grating due to cancellation effects unless, perhaps, the pattern is totally random, in which case adjustment may be made by rotating the plane of one piece of film relative to the other. However, a controllably adjustable multiple diffraction grating is best achieved by means of a liquid crystal display used in combination with a reflective or light transmissive screen member.

A further object of the invention is to provide a simple means for aiding the eye to exercise for sight improvement as it is known that sight deterioration can be retarded by eye exercise and that prescription lenses, over a period of time, actually weaken the sight.

According to one aspect of this invention there is provided an eye-testing and eye-training apparatus comprising, for use within a suitable housing, one or more lasers; one or more sets of demountable, dual member screens, each set having different diffraction and light manipulation characteristics by reflection or transmission of light as a result of one textured surface screen member being either moveable in close contiguous relation to the other normally stationary screen member, or the other screen member having an adjustable pattern which is itself moveable in relation to the other screen member to produce changes in the optical interference produced by the combined screen members; means for directing one or more laser beams of coherent light onto or through the screen members to thereby generate the desired laser speckle effect for observation; means for easily mounting the appropriate screen members within the apparatus; and means for driving the movement of the mounted moveable screen or its pattern, the first screen member comprising a highly reflective or light transmissive member ,the surface of which has been converted into randomly angled micro-miniature deformations or shallow "pits" of similar size by air-blasting with a suitable abrasive so as to leave no retained imbedded particles, or any other suitable method such as will be subsequently described herein; and the second adjustment screen member comprising either an electronically alterable diffraction grating composed of one or more liquid crystal displays, or combination of such displays and photographic film, or of a separate photographic film which has been exposed to pulsed lasers of controllably variable angles of incidence or other suitable patterning means ; and one optional screen comprising a further liquid crystal display so arranged as to present to the viewer a controllably moveable spot or pattern of light for inducing the eye to exercise by involuntary following of the moving light.

By being demountable, the different types of screen may be interchanged and combined within the one apparatus according to the required use, the mounting means being dependent on the type of screen. The moveable screens may be demounted by removing the integral axle on which they may be disposed from the drive means or, alternatively, the screens may be formed in two halves, when they are cylindrical in shape, with suitable securing means for saddle mounting on a common permanent drive axle. For screens comprising a liquid crystal display the mounting means is any suitable socket such as an edge connector interfaced to electronic driving means. The screens could also be carousel mounted on a turntable mounted on a housing sidewall which turntable may be rotated to align the required screen with the drive means and have suitable means for securing one to the other.

Preferably, the dual member screen is mounted on a base turntable so that it may be axially adjusted relative to the observer.

For each screen set the similarly sized micro-miniature irregularities produced by preparation of the textured surface screens in the various ways described herein each form a virtual random array of reflective indentations or window apperture#s that act as reflective or light transmissive multiple diffraction gratings which are necessary to produce, in conjunction with the adjustment screen diffraction gratings, the laser speckle effect. The arrays must be purely random to produce the desired results, although highly regular arrays are useable for calibration and other purposes.

Through judicious choice of the type of screen required and the method of preparing the surface pattern thereon it is possible to ensure that the textured screen surface is composed largely of indentations or window appertures of the most advantageous and useful size, namely of the order of 100-200 micron diameter, said size obviating the problems of obscurfacation of the speckle pattern on a surface that is too smooth due to directly reflected lights, and greater side scattering of the laser lights when the surface is too rough, and being adjustable by means of the adjustment screen member. Surface reflection from liquid crystal display or photographic film adjustment screen members may be eliminated by attaching a thin, translucent film with a matt surface.

A selection of alternative textured screen types and some methods of manufacture for these will now be described.

To be usefully useable with the apparatus of the present invention it is implicit that a single member screen be demountable and that adjustable two member screens which are a specific feature and object of this invention, be demountable with one member being positioned in the manner of a close but contactless sleeve fitting or cover relative to the other; useable screen member shapes including cylinders, semi-cylinders, spheres, hemi-spheres,cones, and flat and curved plates and discs. For two member screens either screen may be caused to move relative to the other. For example a two member cylindrical screen comprising an inner and outer cylinder may have either the inner cylinder rotating within the outer or the outer cylinder rotating about the inner screen. Alternatively, the outer cylinder screen may be caused to rotate about an inner stationary semi-cylinder.Similarly, a sphere may be caused to rotate within, and therefore behind, a stationary hemi-sphere.

Transmissive screen members may be combined with reflective screen members. Screen sets comprising a liquid crystal display member and textured screen may be both stationary with the illusion of movement being caused by movement of the liquid crystal pattern. Alternatively, the liquid crystal pattern may be stationary whilst the textured member is moveable.

Many alternative methods and materials are available for making screen sets which provide a suitably good laser speckle and these include both reflective and transmissive techniques or a combination of the two. For reflective methods employing particulate textured surfaces on a substrate, suitable attachment substrates include wax, resin gums, lead, thermoplastics, glass, aluminium and telerium combined with a carrier where necessary, to mention a few.

Suitable particulate materials include powdered egg shell, salts, sugar, particularly castor and icing sugar, crushed silvered mirror glass and glass bead which may, for application, be sprinkled, air-blown, rolled, dipped, milled, or air-blasted on depending on the substrate being used. Transmissive techniques are generally best suited to the use of photographic films and liquid crystal display devices and can also be combined with reflective techniques.

Photographic film and liquid crystal display means are probably the most adaptable of the available methods for producing adjustable, that is to say, controllably variable screens with a very distinctive black and red laser speckle, and such film and liquid crystal display methods include colour film transparencies and coloured liquid crystal displays with suitable patterning which may help in the detection of colour blindness.

Non particulate textured surface screens may also be formed by heat treating a meltable material with randomly impinging, controllably variable angles of incidence laser beams; by mill rolling a coating of a metltable material onto a screen substrate member from a suitable source duct and roller fed from a bladed, heated duct; or by etching with acid.

Some alternative types of two member screens and their method of manufacture will now be described.

An alternative form of the screen described in GB Patent Specification No 2 33 235 A as mentioned above is formed by splitting the rotable drum into two semi-cylindrical members and inserting one of the halves into a cylindrical cage comprising a fine wire mesh which is revolvable about the static semi-cylinder to cause the required diffraction interference, means being provided to controllably compress the mesh so as to enlarge or reduce the grating and thereby form an adjustable screen. Preferably, however, the rotatable drum is enclosed in an adjustable cylindrical cage, moveable only for adjustments, comprising similarly formed vanes attached to moveable arms to permit the vanes to be opened up or closed up in a fan like manner by bringing additional vanes from behind the drum to the front.As with most screen types in accordance with this invention, the screen adjustment means may be liquid crystal or photographic film gratings in place of the wire or vane type cages.

An alternative reflective screen is made by mill transfer rolling a meltable binder material such as a wax, incorporating a reflective particulate material such as silica powder, from a heated duct onto a target cylinder by means of contact with a transfer roller. The material is held at a temperature sufficient to keep the consistency of the material mobile but tacky. Due to the milling action of the rotating rollers the surface tension of the material is constantly "picked" in the manner of printing inks on the rollers of a printing press and causes a dimpled texturing of the material surface which texture can be adjusted by varying the speed of the rollers and the flow of material from the duct. When texturing of the desired size is reached the target roller is allowed to cool to make the texturing permanent. Such a textured screen may also be used to create a mould from which to replicate the required screens such as by injection moulding of thermoplastics.

Suitable textured screens may also be formed by acid etching a suitable substrate such as glass or a metal with a randomly patterned array of points printed in an acid resist on the surface after exposure to a suitable light source.

In an alternative embodiment of the invention there is provided an optional second screen with means to provide a moving spot or pattern of light for inducing the eye to exercise. Such a screen, which may be used in conjunction with a controllably moveable spot of laser light, may be provided as a hinged translucent plate or translucent roller blind so that it can be swung out of the way when not in use, and is provided as an additional means for eye training to that provided by the laser speckle pattern. It is known that the laser speckle pattern has no definite plane of position, and by existing at every point in space between the screen and the observer, causes the eye muscle to quickly go into an involuntary state of relaxation, an ideal condition for eye test and self taught exercise of the eye.However, not all subjects have the capability to learn eye exercises from an invouluntary relaxed state without some further stimulous and this stimulous is preferably provided by the second screen.

Preferably, the second screen means is provided in the form of a liquid crystal display so organised as to present to the viewer a moving spot of light or pattern of moving lights for the eye to follow, said movement being driven by a microprocessor controlled by a digital memory containing the necessary program for the moving spot routines. By suitable organisation and layering of the liquid crystal screen nematic cells, light may be passed through the screen from a suitable light source as a controllably moveable spot of light, which may be a portion of the laser speckle or a separate light source, thus providing the eye with a moving target to follow and thereby automatically inducing the eye to exercise.Such a screen may also be arranged so as to provide an electronically manipulatable multiple diffraction grating useable in conjunction with an unbroken light source, the speckle effect being caused by movement of the electronic diffraction grating picture elements.

For maximum adaptability of the present invention there is preferably provided a computer interface so that the apparatus can be interconnected with devices such as internal calibration means linked to a joy stick or "mouse" for controlling the speed and indicating the apparent directional movement of a portion of the speckle pattern, and other external electronic measuring instruments and monitoring devices including line printers to provide hard copy results. Thus a subject using the apparatus for eye training or eye testing purposes can do so interactively.

The essential features and further optional features of a specific embodiment of the invention will now be described with reference to the accompanying drawings of Figures 1 to 6 which illustrate aspects of a multiple mode eye testing apparatus in accordance with the invention in schematic form.

Figure 1 is a schematic perspective illustration of a dual member laser speckle screen set representative of the genre of screen sets useable in accordance with the invention and which comprise a combined demountable speckle adjustment screen member and a demountable textured surface screen.

Figure 2 is schematic side elevation of the apparatus with, for purposes of clarity, a side panel of the housing removed.

Figures 3,4 and 5 illustrate alternative arrangements of the dual screen members useable in accordance wih the principles of the invention.

Figure 6 illustrates an alternative dual member screen in which the screen members comprise a flat liquid crystal screen in front of a flat textured screen member.

Referring to Figure 1 the apparatus comprises a speckle adjustment screen 1 composed of a liquid crystal display mounted on an edge connector 11 for ' interfacing with a microprocessor by interface means 12 said screen being capable of being raised out of the way when not in use by means of hinge 10 hich may be electrically bridged by ribbon cable. The adjustment screen 1 is in close contiguous non-contact relation with surface textured screen member 2 which is shown as a cylinder mounted on an axle 3 one end of which is secured to shaft 6 by means of a locking collar 5 fastened by a screw 7, and the other end shaft bearing being supported by a yoke 4 which may also have a locking means (not shown), the shaft being driven to slowly revolve by electric motor 8.A laser 9, the elevation of which is adjustable, directs a beam of coherent monochromatic light to screen member 1 via reflection mirror 13 to create a laser speckle by reflection mode for observation by an eye at 14, or alternatively by adjusting the elevation of the laser directs the beam via a diverging lens (not shown) to the rear of the screen in transmission mode.An area 15 of liquid crystal screen 1 is preferably reserved for providing a calibration speckle portion as well as a definite fixation target for the eye, the pattern in this area being controlled by a microprocessor as to the speed of movement of the pattern and interactively linked to an input device such as a joy stick, "mouse" or push button (not shown) so that an observer may adjust the speed of the speckle portion to the speed of the overall speckle and also indicate the direction of overall movement, thus facilitating the prescribing of suitable correction lenses.The adjustment screen 1 is physically demountable so that it can be replaced by alternative screens, for example a colour liquid crystal display which preferably has a liquid crystal having two stable states, or by screens composed of photographic film with differing multiple diffraction grating patterns so that the apparatus can be readily adjusted for different sight defect and lighting conditions. Adjustment screens composed of photographic film are preferably mounted on a transparent carrier which may in turn be mounted in an adjustable ring, adjustment preferably being made by means for rotating the ring about its normal vertical axis. The surface textured screen 2 is also demountable so that it can be replaced by alternative textured screens.

In Figure 2 the apparatus is shown contained within a housing 30 having access means comprising hinged doors 24 and 25 hinged at 26. Preferably, a safety cut out switch is provided to cut off electrical power to the apparatus whenever the access doors 24 or 25 are opened thus preventing accidental exposure to the laser light. Alternatively, the housing 30 may be slidably mounted on its base 17 so that access may be gained by sliding the two members apart. The liquid crystal display adjustment screen member 1 is connected via interface means 12 to a microprocessor 23 which controls the operation of the apparatus.The dual member speckle screen 1 and 2 are mounted on supporting posts one of which is shown as yoke 4 which is inserted into threaded fixing hole 16 in a turntable 29 which is rotatable on bearing 18 in the base 17, the perimeter of said turntable being extended through a slot in the housing side walls so that is can be turned. By this means, and after removal of yoke support 4, alternative geometry screens such as spheres, hemi-spheres, discs and cones may be mounted on drive shaft 6 of Figure 1 and adjustment screens may be mounted in front in a ring support inserted into mounting hole 29. The laser 9 is pivotally mounted on a fulcrum 21 so that its angle of elevation can be adjusted by means of pivot 22 so that the beam can be directed to the rear of the mounted screen for transmissive mode use screens.To the front of the housing an apperture frame 20 is provided for viewing through and shielding out unwanted light. A further and optional liquid crystal display 27 may be hinge mounted at 28 so that it can be swung into view and on which may be displayed a moving spot of light to induce the eyes to exercise.

Figures 3 to 5 show alternative arrangements of dual member screens which make it clear that the practice of this invention encompasses dual member screens in which the revolvable member of which may be arranged to revolve either around or within the static member screen, and that neither member need revolve in the case of screens incorporating a liquid crystal display. In each example, screen member 1 is either a liquid crystal adjustable diffraction grating screen or a photographic film grating screen and member 2 is a revolvable light reflection or transmission screen with a textured surface. Within the scope of this invention many variations are possible. For example, the rotation of a moveable screen may be changed to a back and forth rocking motion by repeated reversing of the rotational direction of the drive means.

Turning to Figure 7 there is shown an alternative dual member screen comprising a flat liquid crystal display 1 mounted contiguously to a reflection or light transmission screen 2. The screen member 1 is arranged to have a microprocessor driven pattern the display of which mimics the laser speckle pattern produced by conventional rotational systems, the individual specks 31 of which having sizes in appropriate proportion relative to their position and in relation to the radius of the hypothetical curved screen which they portray, thus conveying the illusion of depth and distance. As with previous liquid crystal displays an area 15 may be reserved to provide a combined fixation target and calibration pattern. Such a display may comprise either a black and white or colour liquid crystal and preferably has a liquid crystal having two stable states. Such mimicry could also be produced by a single screen member composed of multiplexed light emitting diodes Thus has been described a state of the art laser speckle eye-sight testing and exercise apparatus of considerable versatility and in what is believed to be sufficient detail, together with the accompanying drawings, for anyone skilled in the art to put into practice.

Claims (8)

1. A multiple mode, laser speckle pattern eye-sight testing and training machine comprising a plurality of demountable paired sets of moveable screens on which to exhibit an adjustable and controllably manipulatable laser speckle pattern;means for controllably adjusting and manipulating the speckle pattern comprising a liquid crystal; a laser and lens combination for expanding the laser beam;and means for directing the laser light onto the selected screen; means for moving the exhibited screen member;means for moving all or part of the adjustable pattern;and further screen leans comprising a further liquid crystal display for displaying a moving spot of light to induce the eyes to exercise, such means being housed in a housing having an observation window through which the speckle pattern and other effects can be viewed.

2. A machine as in Claim 1 wherein the means for controllably adjusting and manipulating the laser speckle pattern is a semi-cylindrical liquid crystal display used in conjuction with moveable and interchangeable reflective or light transmissive screens to provide a duality of multiple diffraction gratings where a portion of the grating is present on both members to thereby provide a combined grating.

3. A machine as in Claim 1 and Claim 2 wherein the liquid crystal display means worming an electrically alterable diffraction grating is a flat liquid crystal display incorporated into the lens combination and means for directing the laser light onto a selected screen.

4. A machine as in Claim 1,2 and 3 wherein the liquid crystal display means is a liquid crystal display having two stable states and the displayed pattern is driven and controlled by a suitably programmed micrporocessor.

5. A machine as in Claim 4 wherein the liquid crystal display is a full coloured display.

6. A machine as in any preceding claim wherein the surface textures of the demountable interchangeable screens includes conditioning by etching, milling, embossing, heating, vacuum deposition or spraying of diffuse white relectances; thermographic printing or attachment of photographic film on any suitable transparent or highly reflective substrate.

7. A machine as in any preceding claim wherein the duality of paired screen members comprises one member which is moveable, or the pattern of which is moveable, relative to the other stationary member.

8. A machine as in any preceding claim wherein the speckle pattern adjustment means includes means for providing a calibrating fixation target.

A machine essentially as described and with reference to the accompanying drawings.