Petitioner: Haag-Streit AG
`Petitioner: Haag-Streit AG
`
`Ex. 100(cid:24)
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`EX. 1005
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`(mUK Patent Application WGB m, 2 077 946 A
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`(54) Indirect ophthalmoscope
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`(57) An indirect ophthalmoscope
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`a light source 5, collimating lens 6,
`and a beam Splitter 7 reflecting the
`light through a lens 8 serving as a
`projection lens and a viewing lens. The
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`user views the aerial image produced
`by the lens 8, through a viewing
`window 13 close to the image plane.
`The light source and collimating lens
`are mounted in a handle 4. The
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`ophthalmoscope can be used with an
`infra—red image converter for infra—red
`examination.
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`s.
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`(21)
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`(3Q)
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`Application No 8118189
`Date of filing 12 Jun 1981
`Pri?');)’2:ata
`80 1
`9
`12 Jun 1980
`United Kingdom (GB)
`Application published
`23 Dec 1981
`INT CL3
`A61 B 3/1 2
`Domestic classification
`GZJ 13A5
`Documents cited
`GB 1 401664
`Field of search
`GZJ
`Applicants
`Robin Devonshire.
`87, Hallam Grange
`Crescent, Fullwood,
`Sheffield $10 433.
`Gholam Ali Peyman,
`535 North Michigan,
`Chicago. Illinois 60611 .
`United States of America,
`Robert L. Epstein.
`912, Pawnee Road,
`Wilmette, Illinois 60091.
`United States of America
`Inventors
`Robin Devonshire,
`Gholam Ali Peyman,
`Robert L. Epstein
`Agents
`Marks Er Clerk.
`
`57—60 Lincoln’s Inn
`Fields, London WC2A 3LS
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`SPECIFICATION
`Indirect ophthalmoscope
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`This Invention relates to Indirect
`ophthalmoscopes.
`Conventional indirect ophthalmoscopes
`comprise a head band which carries a light—
`projection system and viewing optics, usually a
`binocular eye piece. The projection system forms a
`beam of light which is directed into the eye of a
`patient by way of a hand—held condensing lens,
`and the retina thus illuminated is viewed through
`the same condensing lens, and the viewing
`optics. Such instruments are widely used but have
`a number of disadvantages. The light projector
`and viewing optics are quite heavy, and a power
`supply lead for the light source must be provided.
`The head band is consequently awkward and
`uncomfortable. It takes a substantial amount of
`practice, to learn to use such an instrument
`effectively. Careful co—ordination is needed to
`position correctly the hand—held lens and the
`observer’s eye. There is usually a large amount of
`stray light which impairs the clarity of the image
`seen by the observer, and this makes it necessary
`to use relatively intense illumination, which may
`be uncomfortable or even dangerous for the
`patient. Because of the difficulty in eliminating
`stray light, inconvenient corneal reflexes may be
`produced.
`According to the present invention, the light
`projection system, and a converging lens used to
`form an aerial image of the fundus of the eye
`illuminated by the projection system, are
`combined in a single unit, which can be designed
`to be hand—held. The viewing line of sight and the
`axis of the light beam are made substantially
`coincident, for example by the use of a beam
`splitter. With such an instrument, the aerial image
`formed can be viewed directly, or through auxiliary
`optics for example a binocular eye piece. Because 105
`the light source and the viewing and image—
`forming lens are combined in a single unit,
`accurate alignment of the light beam axis and the
`line of sight is ensured and the amount of stray
`light is very much less than in the case of a
`conventional indirect ophthalmoscope using a
`separate hand—held lens. The present instrument is
`therefore much easier to use than a conventional
`indirect ophthalmoscope, requiring little practice to
`secure a clear and well illuminated image, and the 115
`accurate control of the illuminating beam which it
`makes possible greatly reduces discomfort of the
`patient, both directly and because it becomes
`possible to use less intense illumination than in a
`conventional indirect ophthalmoscope.
`In a preferred arrangement, the converging lens
`is placed in the light path from the light source to
`the patient as well as in the line of sight between
`the patient and the observer, so that this lens
`serves both to direct the light into the eye of the
`patient and to form an aerial image of the fundus,
`in a manner analogous to the hand—held lens of a
`conventional indirect ophthalmoscope.
`Preferably, the aerial image is formed
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`substantially at a viewing aperture of the
`instrument. This makes it possible to place
`graticules and other optical elements. in or near
`the image plane, for measuring or mapping
`features of the retina.
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`The light source is preferably a light-emitting
`diode or similar source, or a fibre optic light guide.
`The accompanying drawing show, in section,
`an indirect ophthalmoscope embodying the
`present invention. The eye of a patient is shown
`schematically at l.
`The instrument has a housing 2 which is
`generally T—shaped and comprises a cylindrical
`tube 3 mounted across the wider end of a tapered
`tube 4. The tube 4 has at its narrow end a fibre
`optic light guide 5 which illuminates a piano—
`convex lens 6 to form a parallel beam of light
`which is projected into the tube 3. In the latter is a
`partly reflecting and partly transmitting plate 7
`mounted obliquely so as to reflect the incident
`light along the tube 3 onto a piano-convex lens 8
`at one end of the tube 3. This lens forms an image
`of the fibre optic light source, of unit
`magnification, and this image in use is made to
`coincide with the iris of the patient’s eye. The lens
`8 also forms an image of the fundus of the eye
`thus illuminated, in a plane 9 at the opposite end
`of the tube 3.
`A filter wheel 10 is mounted on the outer end
`of the light source tube 4, so that different filters
`and graticules carried by the wheel can be moved
`into the path of the light from the fibre optic light
`guide 5. The light guide is longitudinally adjustable
`for focusing.
`'
`On the output side of the lens 6 is a polariser
`1 1, and another polariser 12 is mounted in the
`viewing window 13 at the end of the tube 3, close
`to the image plane 9. The polarisers are to
`eliminate unwanted reflections.
`In use, the instrument is held by the observer or
`examiner, so that the light beam is focused at the
`iris of the patient's eye. The examiner observes the
`aerial image formed at the image plane 9. This
`image can be viewed directly or by way of further
`optics for example a binocular optical system (for
`stereoscopic viewing) mounted on a headband or
`on a spectacle frame. The instrument is very easy
`to use. It is only necessary to ensure that the light
`beam is accurately placed in the patient's iris. The
`optical system will then be necessarily correctly
`aligned to produce the desired aerial image, which
`is easily found by the examiner.
`An important advantage of the instrument is
`the accurate imaging of the light source onto the
`desired position in the eye (usually the plane of the
`pupil). The object-image relation is one to one in
`the case of the lenses 6 and 8 being of the same
`power.
`The lens 8 may be mounted so that lenses of
`different powers can be fitted. In this case, a dust
`plate consisting of an optically clear disc is
`provided behind the interchangeable lens 8.
`Typically, a set of lenses of powers 16D, 20D, 30D
`and BBB is provided. The lenses 8 preferably have
`projecting hoods, which when the lens is attached
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`to the body of the instrument projects forwards
`towards the patient. The hoods preferably have
`lengths which are in inverse relation to the lens
`power. This serves to identify the particular lens,
`and to establish an appropriate viewing distance
`from the instrument to the patient’s head.
`The instrument can be held by the user in
`whatever way is convenient for example by the
`tube 4 or by means of the region containing the
`lens 8 or a lens hood. Holding the instrument by
`the lens hood or lens—containing region has the
`advantage that the user's fingers, other than the
`index finger and thumb which grip the instrument,
`are free to rest against the forehead of the patient
`in order to steady the instrument.
`The tube 4 may be attached to or form part of a
`hand grip which can contain a lamp bulb and
`. battery, and optionally, a dimmer control.
`Alternatively, light may be conducted from a
`remote lamp by the light guide.
`Fibre optic light sources have excellent
`characteristics for use in the present instrument.
`The light output falls within a well defined cone
`which fills the aperture of the collimating lens 6
`and the resulting parallel beam can be focused to
`give a small image at the patient's iris. For
`example, a 2 mm diameterfibre bundle, with an
`optical system of unit magnification, produces an
`image of 2 mm diameter which results in very
`efficient and uniformly distributed illumination of
`the fundus. Because of the small size of the beam
`image, the eye can be examined with a small
`pupil. There is very little stray light in the focal
`plane of the fibre optic source, with the result that
`the reflex from the cornea is spatially well defined 100
`and can be easily avoided by the examiner.
`The position of the light source is adjustable
`towards and away from the lens 6, so that the
`effective focal length of the illumination system
`can be continuously varied whereas the focal
`length for viewing remains unchanged. The
`instrument is normally set for viewing an eye with
`a "standard" iris-retina distance. To view an object
`closer to the front of the eye, the viewing lens 8
`must be moved away from the eye. This would
`increase the diameter of the light beam at the iris,
`reducing the illumination with the eye and causing
`reflexes. By adjustment of the light source towards
`the lens 6, the narrowest part of the beam can be
`moved to coincide with the iris. Such focusing
`adjustment is also desirable to compensate for
`changes in the focal length of the lens when the
`instrument is used in different regions of the
`spectrum, for example by means of filters in the
`filter wheel 10.
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`The fibre optic bundle may have the simplest
`end profile namely a circle, or other bundle and
`profiles can be used for example further to
`alleviate problems of reflexes originating at
`refractive index boundaries on the surface of or
`within the eye. Any desired bundle end profile can
`be selected for example a rectangular or “slit"
`profile forming a corresponding image which can
`be rotated about the axis of the eye by rotation of
`the fibre optic bundle 5. Two or more fibre optic
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`bundles may be provided to give a desired light
`distribution in the eye.
`Alternative light sources are solid state
`emitters, for example of gallium arsenide. These ;
`also havethe advantage that the light is directed;
`forwards. Incandescent light sources are inferior,
`because they radiate light in all directions, and are
`therefore inefficient and cause stray light.
`Conveniently, the collimating lens 6 is an
`aspheric lens of plastics material which is well
`corrected and has good optical transmission
`throughout the visible and near infra red regions of
`the spectrum.
`The dual-function lens 8 can also be a plastics
`aspheric lens, but the optical layout enables a
`wide variety of lenses to be used. This lens should
`exhibit no birefringence. Since it is illuminated by
`parallel light, substitution of a lens of different
`power does not require any other changes in the
`system. The illuminating light will still be brought
`to a focus close to the plane of the iris, and will
`illuminate a larger or smaller area of the fundus as
`the power of the lens is increased or decreased. If
`the lens 8 is a high—power, small—aperture lens,
`light could be scattered from the lens mount or
`retaining ring which would cause a halo around
`the observed image. To eliminate this, the
`instrument may include an adjustable aperture 14
`so that the illuminating beam can be stopped
`down so as just to fill the lens 8.
`The polarisers are also to reduce stray light. The
`first polariser 1 1 preferably has its plane of
`polarisation perpendicular to the plane of
`incidence of the partial reflector 7. The second
`polariser 12 has its plane of polarisation set to
`give minimum transmission to the examiner of
`light reflected from the surface of the cornea and
`from the lens 8. The instrument described has a
`very low aura of stray light. The only significant
`light outside the instrument is that in the
`converging forward beam, which can be made to
`pass wholly through the iris of the patient as
`already described. The high background
`illumination typical of conventional indirect
`ophthalmoscopes is eliminated and the image
`quality is therefore greatly improved. It istherefore
`possible considerably to reduce the level of
`illumination of the retina without any loss of
`subjective brightness in the image compared with
`a conventional indirect ophthalmoscope.
`The partial reflector plate 7 has a reflectivity
`chosen to maximise the brightness of the
`observed image. if the rear surface of the plate has
`an anti—reflection coating, the front surface should
`have a reflectance of 50%. If there is no coating;
`the front surface should have a reflectance'of
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`approximately 47%.‘The plate will in general be at
`45° to the axis of the tube 3, providing a fixed
`lens/light source angle of zero. it may be
`advantageous to have a small fixed angle between
`the lens and light source, for example by mounting
`the reflector plate at 46° to the tube axis. The
`viewing/illumination angle is continuously variable
`from zero upwards, in contrast to conventional
`indirect ophthalmoscopes in which the angle is
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`The instrument can be used, with an
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`appropriate accessory, for fluorescence
`angiography, with visible radiation (using for
`example fluorescein) or infra-red (using
`cardiogreen), using suitable filters and, in the case
`of infra—red, an image converter as already
`mentioned, preferably mounted on the examiner's
`head by means of a head band. The fluorescence
`excitation wavelength is selected by an
`appropriate filter in the filter wheel 10, and the
`fluorescence emission is selected by a filter for
`example clipped over the output face of the
`instrument.
`The instrument described combines the ease of
`use of a direct ophthalmoscope, with the wider
`field of view, better illumination and possibility of
`stereoscopic vision, of an indirect
`ophthalmoscope, and has substantial advantages
`not found in either form of conventional
`instrument.
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`CLAIMS
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`1. An indirect ophthalmoscope comprising a
`light projection system for projecting a beam of
`light, and a converging lens arranged to form an
`aerial image of the region illuminated by the light
`projection system, the said light projection system
`and converging lens being combined in a single
`unit in which the viewing line of sight through the
`lens is substantially coincident with the axis of the
`projected light beam.
`2. An indirect ophthalmoscope as claimed in
`claim 1
`in which the light projection system
`includes a beam splitter and a light source, the
`beam splitter being arranged to direct light from
`the source along the said line of sight.
`3. An indirect ophthalmoscope as claimed in
`claim 2 having a generally T—shaped housing of
`which the stem portion contains the light source,
`and the cross piece is a viewing tube which
`contains the beam splitter and converging lens.
`4. An indirect ophthalmoscope as claimed in
`claim 1,2 or 3 in which the said lens is placed in
`the light path from the light source to the region
`illuminated by the light beam as well as in the line
`of sight from an observer to the said region.
`5. An indirect ophthalmoscope according to
`claim 1, 2, 3 or 4 having a viewing aperture and in
`which the lens is arranged to form the said aerial
`image substantially at the viewing aperture.
`7
`6. An indirect ophthalmoscope as claimed in
`any of claims 1 to 5 in the form of a hand—held
`instrument.
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`7. An indirect ophthalmoscope according to
`claim 6 having a handle which incorporates the
`light projection system.
`8. An indirect ophthalmoscope according to
`any of claims 1 to 7 in which the light projection
`system includes a fibre optic bundle constituting a
`light source.
`9. An indirect ophthalmoscope according to
`claim 8 in which the fibre optic bundle has a non—
`circular end profile.
`10. An indirect ophthalmoscope according to
`any of claims 1 to 7 in which the light projection
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`fixed at about 1° or 2°.-
`To enable several observers to view the image,
`a biprism or the like can be clipped or hinged to
`the instrument at the viewing window 13.
`The instrument described has parallel surfaces
`at opposite ends of the tube 3. These can be used
`for accurately known alignment or relative
`orientation of the axis of the instrument and the
`examiner’s eye, using graduation marks on the
`two surfaces. For example, a small reflecting or
`luminous point can be provided at the centre of
`the inner face of the viewing lens as a target, to be
`used in conjunction with a graticule of concentric
`rings.
`'
`The fact that the image is within the instrument
`makes it easier for the user to locate the image,
`without however restricting viewing, and makes
`the image accessible to viewing screens,
`graticules and other article devices, or the face
`plate of an image convertor or image intensifier. It
`should be noted that the image is not plane, and
`such auxiliary devices may have to be shaped
`accordingly to match the shape of the image.
`It is not necessary to use visible light. One of
`the advantages of the instrument described is
`that, since it is not necessary for the user to wear
`the usual heavy light projector and viewing
`system on a headband, he can wear other
`components on a headband, for example an image
`converter for viewing an'image produced by infra-
`red light. In another possible arrangement, an
`image converter may be placed at the viewing
`window 13.
`For infra—red use, a focusing target may be
`provided in or near the retinal image plane at the
`polariser 12. This target can for example be an
`illuminated ring, the illumination being channeled
`from the light source of the hand unit, whether a
`fibre optic bundle or a built—in source such as a
`gallium arsenide emitter.
`The image intensification properties of an infra— 105
`red image converter, used with the instrument,
`permit examination of interior portions of the eye
`at illumination levels significantly lower than those
`used at present in indirect ophthalmoscopy.
`Conventional illumination levels are being
`increasingly recognised as hazardous to patients.
`Because the image intensifier output depends on
`the properties of the screen phosphor, such
`devices are particularly suitable for low
`illumination level examination of the eye using
`monochromatic radiation of various wavelengths,
`infra—red or visible. The use of monochromatic
`radiation is a recognised technique in
`ophthalmoscopy but at present requires relatively
`high intensities of illumination. When the present 120
`instrument is used with an image intensification
`device, dilation of the pupil is not needed, which is
`an important practical advantage.
`It will be understood that if the instrument is
`intended for use with infra—red illumination, its
`optical components must be made of materials
`transparent to infra—red wavelengths and must be
`appropriately designed for operation at such
`wavelengths.
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`red radiation, and viewing means including an
`system includes a gallium arsenide light source.
`infra—red image converter.
`1 1. in combination, an indirect
`12. An indirect ophthalmoscope substantially,
`ophthalmoscope as claimed in any of claims 1 to
`as herein described with reference to the
`‘
`10 incorporating an infra—red light source and
`10 accompanying drawing.
`5 having optical components transparent to infra—
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`Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa. 1981. Published by the Patent Office,
`25 Southampton Buildings, London, WC2A 1AY. from which copies may be obtained.
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