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`«» UK Patent Application .»GB «. 2077 946 A
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`Application No 81187189
`Date of filing 12 Jun 1981
`Priority data
`80/19259
`12 Jun 1980
`United Kingdom (GB)
`Application published
`23 Dec 1981
`INT CL?
`AGIB 3/12
`Domestic classification
`G20 13A5
`Documents cited
`GB 1401664
`Field of search
`G2J
`Applicants
`Robin Devonshire,
`87, Hallam Grange
`Crescent, Fullwacd,
`Sheffield $10 4BB,
`Gholam Ali Peyman,
`535 North Michigan,
`Chicago,IHinois 60671,
`United States of America,
`Robert L. Epstein,
`912, Pawnee Road,
`Wilmette, Illinois 60091,
`United States of America
`Inventors
`Robin Devonshire,
`Gholam Ali Peyman,
`Robart L. Epstein
`Agents
`Marks & Cterk,
`57-60 Lincoln's Inn
`Fields, London WC24 3L5
`
`
`
`(54) Indirect aphthalmescope
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`(57) An indirect ophthalmoscope
`consists of a single unit incorporating
`a light source §, 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
`ophthalmoscope can be used with an
`infra-red image converterfor infra-red
`examination.
`
`7
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`okidandeaak
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`V976LL0Z4D
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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 aye piege. 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 thusilluminated is viewed through
`the same condensinglens, and the viewing
`optics. Such instruments are widely used but have
`a numberof disadvantages. Thelight 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 ammountof
`practice, to learn to use such an instrument
`effectively. Careful co-ordination is needed to
`position correctly the hand-held fens and the
`observer's eye. There is usually a large amount of
`stray light which impairs the clarity of the image
`seen by the obsarver, and this makes it necessary
`to use relatively intense illumination, which may
`be uncomfortable or even dangerousfor the
`patient. Because of the difficulty in eliminating
`stray light, inconvenient corneal reflexes may be
`produced.
`According to the presentinvention, tha fight
`projection system, and a converging lens used to
`form an aerial image of the fundus of the eye
`illuminated by the projection system, are
`combinedin a single unit, which can be designed
`to be hand-held. The viewing line of sight andthe
`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 combinedin 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 muchless than in the case ofa
`conventional indirect ophthalmoscope using a
`separate hand-held lens. The present instrumentis
`therefore much easier to use than a conventional
`indirect ophthalmoscope,requiring little practice to
`secure a clear and well iNuminated image, andthe 115
`accurate controlof the illuminating beam whichit
`makes possible greatly reduces discomfort of the
`patient, both directly and because it becomes
`possible to use less Intenseillumination than ina
`conventionalindirect ophthalmoscope.
`Ina preferred arrangement, the converging lens
`is placed in the light path fram the light source to
`the patient as wall as in theline of sight between
`the patient and the observer, so that this lens
`serves both to direct the light into the eye ofthe
`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 aarial 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 elaments in or near
`the image plane, for measuring or mapping
`features of the retina.
`The light sourceis 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 1.
`The instrument has a housing 2 whichis
`generally T-shaped and comprises a cylindrical
`tube 3 mountedacross the wider end of 2 tapered
`tube 4. The tube 4 has at its narrow end a fibre
`optic light guide 5 which illuminates a plano-
`convex Isns 6 to form a parallel beam oflight
`whichis 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 plano-convexlens 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 fitter wheel 10 is mounted on the outer end
`of the light source tube 4, so thatdifferentfilters
`and graticules carried by the wheel can be moved
`into the path of the light from the fibre optic fight
`guide 5. The light guideis longitudinally adjustable
`for focusing.
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`On the output side of the lens 6 is a polariser
`11, and another polariser 12 is mounted in the
`viewing window 13 at the end of the tube 3, close
`ta 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 instrumentis very easy
`to use. It is only necessary to ensure that thelight
`beam {s 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 advantageof the instrumentis
`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 onein
`the case of the lenses 6 and 8 being of the same
`power.
`The iens 8 may be mounted so that lenses of
`different powers can be fitted. In this case, 4 dust
`plate consisting of an optically clear disc is
`provided behind the interchangeable lens 8.
`Typically, a set of lenses of powers 16D, 20D, 300
`and 36D is provided. The lenses 8 preferably have
`projecting hoods, which whenthelens is attached
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`to the body of the instrumant projects forwards
`towards the patient. Tha hoods preferably have
`Jengths which are in inverse relation to the tens
`power. This serves to identify the particular lens,
`and to establish an appropriate viewing distance
`from the instrumentto the patient's head.
`The instrument can be held by the userin
`whatever wayis convenient for example by the
`tube 4 or by meansof 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 famp bulb and
`- battery, and optionally, a dimmercontrol,
`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 outputfalls within a well defined cone
`whichfills the aperture of the collimating lans 6
`andthe resulting parallel beam can be focused to
`give a smail imags 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 awayfrom the lens 6, so that the
`effective focal length of the illumination system
`can be continuously varied whereas the focal
`length for viewing temains unchanged. The
`instrumentis 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 awayfrom the eye. This would
`increase the diameter of the light beam attheiris,
`reducing theillumination with the eye and causing
`reflexes. By adjustment ofthe light saurce towards
`the lens 6, the narrowest part of the beam can be
`moved to coincide withtheiris. Such focusing
`adjustmentis also desirable to compensate for
`changesin the focal length of the lens when the
`instrument is used in different regionsof the
`spectrum, for example by meansof filters in the
`filter wheel 10.
`Thefibre optic bundle may have the simplest
`end profile namely a circle, or other bundle end
`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 &. 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 have.the advantage thatthe lightis directed-,
`forwards, Incandescentlight sources are inferior,
`because they radiatelight in all directions, and aré
`therefore inefficient and cause straylight.
`Conveniently, the collimating lens 6 is an
`aspheric lens of plastics material which is well
`corrected and has good optical transmission
`throughout thevisible and near infra red regions of
`the spectrum.
`The dual-function liens 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 iluminated by
`parallel light, substitution of a lens ofdifferent
`power does not require any other changesin the
`system. The iHuminating light will stili be brought
`to a focus close to the plane of the iris, and will
`Hluminate 4 larger or smailer area of the fundus as
`the powerof the fens is increased or decreased.lf
`the lens 8 is a high-power, small-aperture lens,
`light could be scattered from the lens mountor
`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
`downso asjust to fill the lens 8.
`The polarisers are also to reduce stray light. The
`first polariser 11 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 examinerof
`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 instrumentis that in the
`converging forward beam, which can be made to
`pass wholly throughtheiris of the patient as
`already described. The high background
`illumination typical of conventional indirect
`ophthalmoscopesIs eliminated and the image
`quality is therefore greatly improved.It is therefore
`possible considerably to reduce the level of
`ilumination 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%. Hf there is no coating,
`the front surface should have areflectancecf
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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 ofzero. It may be
`advantageous to have a small fixed angie between
`the lens and light source, for example by mounting
`the reflector plate at 46° to the tube axis. The
`viewing/illummination angle is continuously variable
`from zero upwards, in contrast to conventional
`indirect ophthalmoscopesin which the angle is
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`fixed at about 1° or 2°:
`To enable severa! observers to view the image,
`a biprism orthelike can be clipped or hinged ta
`the instrument at the viewing window 13.
`The instrument described has parallel surfaces
`at opposite endsof the tube 3. These can be used
`for accurately known alignment orrelative
`orientation of the axis of the instrument and the
`examiner's eye, using graduation marks on the
`twosurfaces. For example, a smail reflecting or
`juminous point can be provided at the centre of
`the inner face of the viewing lens as a target, to ba
`used in conjunction with a graticule of concentric
`rings.
`‘
`The fact that the imageis within the instrument
`makes it easier for the user to locate the image,
`without howeverrestricting viewing, and makes
`the image accessible to viewing screens,
`graticules and otherarticle devices, or the face
`plate of an image convertor or image intensifier. it
`should be noted that the imageis not plane, and
`such auxiliary devices may have to be shaped
`accordingly to match the shape of the image.
`itis not necessary to use visibie light. One of
`the advantages of the instrument described is
`that, sinceit 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
`converterfor viewing an-image producedbyinfra-
`red light. In another possible arrangement, an
`image converter may be placed at the viewing
`window 73.
`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
`illuminatedring, 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 imageintensification properties of an infra- 105
`red image converter, used with the instrument,
`permit examinationof interior portions of the eye
`at Hlurmination lavels significantly lower than those
`used at presentin indirect ophthalmoscopy.
`Conventional illumination levels are being
`increasingly recognised as hazardousto 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 ittumination. When the present 120
`instrumentis used with an imageintensification
`device, dilation of the pupil is not needed, which Is
`an important practical advantage.
`it will be understood that if the instrumentis
`intended for use with infra-red illumination,its
`optical components must be made of materials
`transparentto infra-red wavelengths and must be
`appropriately designed for operation at such
`wavelengths.
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`The instrument can be used, with an
`appropriate accessory,for fluorescence
`angiography, with visible radiation (using for
`example fiuorescein) 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 meansof a head band.The fluorescence
`excitation wavelength Is selected by an
`appropriatefilter in the filter wheel 10, and the
`fluorescence emission is selected bya 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, betterillumination and possibility of
`stereoscopic vision, of an indirect
`ophthalmescope, and has substantial advantages
`not found in either form of conventional
`instrument.
`
`CLAIMS
`1. An indirect ophthalmoscope comprising a
`light projection system for projecting a beam af
`light, and a converging lens arranged te form an
`aerial image of the region illuminated by the light
`projection system, the said light projection system
`and converging lens belng 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 ophthalmoscopeas claimed in
`claim 1
`in which the light projection system
`includes a beam splitter and a light source, the
`beam splitter being arranged to directlight from
`the source along the saidline of sight.
`3. An Indirect ophthalmoscope as claimed in
`claim 2 having 2 generally T-shaped housing of
`which the stem portion contains the light source,
`and the cross pieceIs 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 jens 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 observerto 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.
`6. An indirect ophthalmoscope as claimed in
`any of claims 1 to 5 in the form of a hand-held
`instrument.
`7. An indirect ophthalmoscope according to
`elaim 6 having a handle which incorporates the
`light projection system.
`8. An indirect ophthalmoscope according to
`any of claims 1 to 7 in which thelight projection
`system includes a fibre optic bundle constituting a
`light source.
`9. An indirect ophthalmoscope according to
`claim 8 in which thefibre optic bundle has a non-
`circular end profile.
`10. An indirect ophthalmoscope according to
`any of claims 17 to 7 in which the light projection
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`ted radiation, and viewing means including an
`system includes a gallium arsenide light source.
`infra-red image converter.
`11. In combination, an Indirect
`12. An indirect ophthalmoscope substantiaily_
`ophthalmoscopeas claimed in any of clairns 1 to
`as herein described with reference to the
`.
`10 incorporating an infra-redlight source and
`10 accompanying drawing.
`5 having optical components transparentto infra-
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`5*
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`BGR277BABA
`4
`GR 2077 946A
`4
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`Printed for Her Majesty's Stationery Office by the Courler Press, Leamington Spa, 1981. Published by tha Patert Office,
`25 Southampton Buildings, London, WC2A (AY, from which coples may be obtained.
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