GB2367123A

GB2367123A - Measurement of pupil response

Info

Publication number: GB2367123A
Application number: GB0023018A
Authority: GB
Inventors: Tharaka Gunarathne; Stari K Gunarathne; Godallawaththa Path Gunarathne
Original assignee: Individual
Current assignee: Individual
Priority date: 2000-09-20
Filing date: 2000-09-20
Publication date: 2002-03-27
Also published as: GB0023018D0

Abstract

A system for measuring the autonomous response of pupil comprises a light source 1 with associated means 2, 3 for controlling the intensity and duration of its output 6, means 5 for forming an area of uniform illumination on the eye and for directing the beam, e.g. a partial reflector 7, and means for recording or measuring the pupil response, such as a CCD or a video camera 8. The pupil size is measured before and after the light stimulus and is recorded and analysed by the system to obtain the steady state and transient behaviour of the pupil. The eye 13 may be illuminated by an infra-red source 14 to allow observations of the dark-adapted pupil size or measurements in low light conditions. The light from the source 1 may be controlled using variable slits, optically graded neutral filters, polarising filters or liquid crystal elements. The system may be mounted on a bench or in a headset and may further comprise filters 4 and optical fibres. A handset may be provided for remote control of the apparatus.

Description

A SYSTEM FOR MEASUREMENT OF THE AUTONOMOUS RESPONSE OF THE EYE'S PUPIL TO LIGHT This invention relates to the measurement of static and dynamic responses of the pupil of the eye to light.

Ophthalmologists and other medical professionals use various instruments to examine eyes for the diagnosis of visionary defects and/or underlying medical conditions affecting vision. Some examples of these are: hand-held opthalmoscope for examining the retina and the back of the eye, bench mounted vision testing systems for general examination of the eye or for specific tasks such as testing the pressure build up within the eye. Although it is known that the size of the pupil and the speed of its reaction to light is affected by various medical and physiological conditions, the response of the pupil of the eye to light has traditionally been used so far for qualitative examination, for example to check for brain damage or death.

This invention allows quantitative measurement of the static (steady state) and dynamic (transient) responses of the eye to input light, to enable new diagnostic information and/or patient records to be generated.

In the context of the present invention, static response of the pupil means the settled size of the pupil diameter as a function of light input of different intensity and colour.

Dynamic response refers to the pattern of variation and/or transient behavior of the pupil size with time, in response to different light stimuli such as step, pulse and sinusoidal light inputs of monochromatic or white light or any other known light composition.

When light falling onto the eye changes (i. e. intensity, colour, exposure) the pupil of the normal eye or eyes adjusts accordingly to accommodate the change. A particular pattern of pupil reaction may depend on a range of underlying conditions, just like other conditions that may influence physiological parameters such as body temperature and blood pressure. In the same way as body temperature aids diagnosis, the quantitative measurement of the autonomous response of the pupil may also be used as a diagnostic parameter in appropriate situations. This invention allows the steady-state and transient response of the pupil of the eye/s in response to controlled light stimuli to be measured, monitored and recorded (even under dark conditions) with the aim to generate diagnostic data and patient records or profiles.

According to the present invention there is provided a system for the measurement of the response of the pupil of a single or both eyes to controlled light input, comprising a monochromatic and/or white light source (with or without colour filters), means of controlling light intensity and exposure time, optical beam forming/focusing means to produce an adequately uniform patch of incident light partially reflected via a partial reflector or similar means to which the eye/s are exposed and means of observing, recording and/or measuring the response of the pupil to that incident light and also means for observing, recording and or measuring the size of the pupil in low light level or in complete darkness within the eye's visible wavelength range of light.

Embodiment of the invention will now be described by way of 3 representative examples with reference to accompanying drawings in which: Figure 1 shows one schematic block diagram form of the invention.

Figure 2 and 3 show two possible arrangements of the invention, particularly suitable as bench mountable systems.

Figure 4 shows an example of one possible form of bench mount implementation approach relating to Figure 2.

Figure 5 shows one possible arrangement for positioning the head.

Figure 6 shows an example of the embodiment of the invention in the form of a headset.

Figure7 shows an example of typical controls built in the form of a hand-set. Referring to Figure 1, the system comprises a light source 1 and a shutter 2 (which could be mechanical, electro-mechanical or electronic type) for controlling exposure

time, means for controlling the intensity of light 3 (such as a variable slit, optically (cl) graded neutral filters, pair/s of polaroid'filters or electronic light control using liquid

crystals), means for selecting the colour composition of light (for example by using optical wavelength filters), an optional focusing means 5 to form a defined beam of light 6 (whose intensity may be monitored by an optional light sensor 12) to illuminate one or both eyes 13 using a partial reflector 7 acting as a beam splitter, through which the image of the pupil is captured by a video camera 8 or a chargecoupled-device (CCD) sensor; means of displaying the image on a screen 9 (e. g. by using a video monitor) and recording means for storage of data 10 (such as a video recorder or a solid state image storage device) and an optional processing system such as a personal computer or a Digital Signal Processing (DSP) device 11. There is also provided an infra-red source (14) (such as an infra-red light emitting diode) whose light has no effect on the response of the pupil, to observe the pupil under low light settings or in complete darkness. This IR source could be placed in a convenient position to illuminate the pupil e. g. close to the eye or mounted close to the image pick up device or even within the main lighting compartment. The specific ordering of the blocks or components within the system may vary as the physical implementation of the invention could take different forms as would be clear from the three examples now provided.

In Fig 2, a simple realisation of the system is shown (example 1). The light source 1 comprises a white or monochromatic light emitter with an optional condenser lens, focusing light onto a variable slit 3. The shutter 2 may be placed either onto the left or to the right of the slit 3. A Choice of colour filters 4 may be used, which are typically placed in the path of the beam as shown. The emerging beam is shaped using the lens arrangement 5 to form a suitable beam of light 6. This patch of light need not be collimated as long as it defines a patch of adequate uniformity across the required aperture. Means for defining the overall aperture of the light patch to illuminate one or both eyes as required may be easily introduced after the lens arrangement (not shown). The other components 7-14 are the same as that described under Fig 1.

Fig 3 shows another implementation where the light box, shutter and intensity control components are replaced by a standard slide projector arrangement (example 2). In this case the projectors internal shutter may be used with intensity control achieved by means of optically graded slides 3 placed in the carousel. Colour filters may also be used in the form of cascaded slides, but they are better placed outside to reduce the number of combinations of grey and colour filters required to make individual slides.

As above, the components 7-14 are the same as that described under Fig 1.

Further description of the items 8-14 are now given below to enable the choice of appropriate, but different combinations of components, using examples.

For example the image pickup device 8 could be a CCD image sensor in which case the image analysis and measurement may be carried out in near real-time using DSP electronics, and results are output to a screen and/or printed directly using a standard printing device.

Similarly a compact digital TV camera may be used as the pick up device 8 in which case the video footage may be transmitted directly in to a laptop computer for analysis and presentation. Back up storage in either case may be provided by any standard data storage technique.

The function of light intensity monitoring device 12 is to ensure that the input intensity is correct according to the settings and also for calibration of the system as and when necessary. During such calibrations, its position may be changed to the position of the eye 13.

The two examples given under Fig 2 & 3 above may be implemented as bench arrangements mounted on adjustable kinematic rails with three translational movements (x, y, z) for ease of positioning. Arrangements as in Fig 2 could be conveniently assembled within a box and mounted on suitable rails as shown in the representative illustration of Fig 4 (a).

In bench assemblies as above, it is also important to provide means of positioning the head stationary with respect to the optical assembly. This may be achieved using an arrangement similar, but not restricted to that shown in Fig 5, where a frame to position the head is shown. In Fig 5, a vertically adjustable section 15 provide means for positioning the forehead with respect to a chin-rest 16 in the lower part of the frame. The forehead-rest may have an attachment consisting of two blackened, hollow tubes 17 in the region of the eyes'position with adjustable means for aligning the tubes with the subject's eyes in order to couple to the optical system shown in Fig 4 (b).

The invention may also be implemented with the use of fibre optic cables replacing some of the optical components of the system, for example in carrying prescribed light stimuli to the eyes and/or capturing and transferring the image of the pupils to the image sensor.

In Fig 6, a different approach for implementing the invention is shown (example 3).

In this case the optical assembly is made in the form of a"head-set". In this case the components 1-6 (as necessary) may be assembled in the form of a compact light box (not shown) and attached to the rear end of the head set by suitable means, such as a standard optical bayonet fitting 18. Alternatively, if an external light source is preferred, this may be coupled using fibre optic cables to the head set. Light entering the head-set is first split by means of the pairs of mirrors 19 and are directed to the front of the head-set by the mirrors 20,21 and 22,23. The partial reflectors 24,25 at the front of the head-set reflect light into each eye as before and the image of each pupil of the eye is received as shown by the path of the received light reaching the image sensor 8, using the mirror arrangements 26,27, 28,29. Alternatively to the use of mirrors, it is also possible to use fibre optic cables for image pickup.

The separate light beams are directed to the eye in a way such that there is no leakage from one part to the other, e. g. by using short tubes closer to the eye and shielding the space between the partial reflectors (not shown). The individual light beams may be switched on or off independently by placing shutters in individual paths.

The light box may also be permanently mounted either at the rear or on the top of the head-set without the need of a detachable fixing arrangement. In the case where the light box is mounted on the head-set, the paths of the input light beams would be arranged in a similar fashion to the method described above, or using fibre optic cables to direct light from the top of the head-set into the eyes, instead of from the rear. The IR source introduced for dark viewing may be conveniently placed near the image pick up device 8, sending infra red light in the opposite direction to the light reaching the image sensor, or at any other convenient location within the head-set optical arrangement (not shown).

The necessary settings and controls in this case (or in the case of previous examples) may be conveniently carried out remotely by the operator, using a hand-set with typical controls as that shown in Fig 7.

Some typical controls and facilities that may be provided to carry out both static and transient measurements are shown in Fig 7, where: 30-power on/off switch 31-power in socket for the whole system (e. g. low voltage AC or DC, 12V) 32-multi-function display for the display of settings and exposure timing 33-light intensity control 34-operates the left beam shutter 35-operates the right beam shutter 36-selects the type of source (white of monochromatic) 37-selection of filters 38-selection of light stimulus (e. g. continuos/step/pulse/sinusoidal) 39-exposure time control 40-on/off switch for the infra-red source (for dark viewing) 41-system calibration 42-resetting any function entered 43-starting the test and system command for acquiring data.

44-remote control cable It should be mentioned that the above functions and facilities are given only as an example and to aid the understanding of the functional features of a typical system. Such facilities and operation could be provided in many different ways to support the basic functions of the invention using different forms of electronic and other means.

Claims

CLAIMS 1. A system for the measurement of the autonomous response of the pupil of one or both eyes to light stimuli, comprising a monochromatic and/or white light source (with or without colour filters), means of controlling light intensity and exposure time, optical beam forming/focusing means to produce an adequately uniform patch of incident light to which the eye/s are exposed and means of observing, recording and/or measuring the response of the pupil to that incident light including means for observing, recording and/or measuring the response of the pupil of the eye/s in low light conditions (or in complete darkness within the eye's visible wavelength range of light).
2. A system for the measurement of the response of the pupil of one or both eyes to controlled light stimuli as claimed in Claim 1, wherein the assembly is provided in the form of a bench mountable system with means for positioning the eyes in correct alignment with the system.
3. A system for the measurement of the response of the pupil of one or both eyes to controlled light stimuli as claimed in claim 1, wherein the assembly of the system is provided in the form of a head-set with a detachable or fixed light source arrangement, providing required beam of light input to the eyes.
4. A system for the measurement of the response of the pupil of one or both eyes to controlled light stimuli as claimed in any preceding claim, wherein light beam to the eyes is provided by means of optical fibres.
5. A system for the measurement of the response of the pupil of one or both eyes to controlled light stimuli as claimed in any preceding claim, wherein the image of the pupil/s are captured and coupled to an image sensing device by means of optical fibres.
6. A system for the measurement of the response of the pupil of one or both eyes to controlled light stimuli as claimed in any preceding claim, wherein means for aligning the optical assembly and the eyes are provided.
7. A system for the measurement of the response of the pupil of one or both eyes to controlled light stimuli as claimed in any preceding claim, wherein the necessary control functions are provided in the form of a remote controlled handset.
8. A system for the measurement of the response of the pupil of one or both eyes to controlled light stimuli substantially as described herein with reference to Figures 1-7 of the accompanying drawings.