Petitioner: Haag-Streit AG
`Petitioner: Haag-Streit AG
`
`Ex. 10(cid:20)(cid:21)
`
`EX. 1012
`
`

`

`United States Patent
`
`[19]
`
`[11] Patent Number:
`
`4,682,866
`
`Jul. 28, 1987
`Volk
`[45] Date of Patent:
`
`[54] HEAD-BORNE BINOCULAR INDIRECT
`OPHTHALMOSCOPE WITH INTEGRATED
`TELESCOPE
`
`[76]
`
`Inventor:
`
`David Volk, 3336 Kersdale Rd.,
`Pepper Pike, Ohio 44124
`
`[21] Appl. No.: 669,345
`
`[22] Filed:
`
`Nov. 8, 1984
`
`
`
`A61B 3/10
`[51]
`Int. Cl.4 ...............................
`
`[52] US. Cl. .......................................... 351/205
`[58] Field of Search ............... 351/205, 216, 217, 218;
`350/516
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`.............................. 351/205
`3,475,082 10/1969 Strietzel
`3,582,191
`6/1971 Cohen et al.
`..
`.. 351/205
`3,963,329
`6/1976 Stumpf et al,
`.
`351/205
`4,056,310 11/1977 Shimizu .........
`351/205
`4,449,797
`5/1984 Kocher et a1.
`...................... 351/205
`
`
`
`Primary Examiner—Rodney B. Bovernick
`Attorney, Agent, or Firm-Baldwin, Egan & Fetzer
`
`[57]
`
`ABSTRACT
`
`There is presented an improved head-borne binocular
`
`indirect ophthalmoscope for viewing the aerial image of
`the fundus of the eye, having the unique feature that it
`incorporates within each of its two observing portions 3
`two-lens telescope of low magnifying power which
`magnifies said aerial image of the fundus. The telescope
`incorporated into the ophthalmoscope differs from the
`usual coaxial type in that the optical axis of the high
`powered objective lens and that of the high powered
`ocular lens of said telescope are caused to intersect each
`other at an angle of about 94" at the surface of a laterally
`positioned oblique front surface mirror, said lenses and
`said mirror being in a fixed relationship to each other
`within a transversely movable mounting as a fixed tele-
`scope unit such that the reflected secondary focus of the
`objective lens falls at the primary focus of the ocular
`lens, said unit being attached to a slide which is trans—
`versely movable along ways toward and away from a
`medially positioned oblique
`front
`surface mirror
`whereby adjustments can be made within the ophthal—
`moscope to accommodate the interpupillary distance of
`the observer without affecting the relative position of
`the elements of said telescope unit.
`
`13 Claims, 12 Drawing Figures
`
`RIGHT OBJECTIVE
`LENS
`
`RIGHT
`OCULAR LENS
`G
`
`b
`
`1 w
`
`
`LEFT
`0' OBJECTlVE
`LENS
`
`
`
`
` .
`
`

`

`US. Patent
`
`Jul. 28, 1987
`
`Sheet 1 of 6
`
`4,682,866
`
`PRIOR ART
`
`
`
`
`

`

`U.S. Patent
`
`Jul. 28, 1987
`
`Sheet 2 of 6
`
`4,682,866
`
`
`
`PMAGNIFICATIW.—
`
`POWER IN DIOPTERS
`
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`
`

`

`US. Patent
`
`Jul. 28, 1937
`
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`US. Patent
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`Jul. 28, 1987
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`Sheet 4 of 6
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`4,682,866
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`

`US. Patent
`
`Jul. 28, 1987
`
`Sheet6of6
`
`4,682,866
`
`63ficcuma LENS
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`ID
`
`LEFT OBJECTIVE
`LENS
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`

`1
`
`4,682,866
`
`HEAD-BORNE BINOCULAR INDIRECT
`OPHTHALMOSCOPE WITH INTEGRATED
`TELESCOPE
`
`indirect ophthalmoscopes
`Head—borne binocular
`presently commercially available subserve two func-
`tions: (1) They provide a light source which, in con—
`junction with a hand-held indirect ophthalmoscopy
`condensing lens, illuminates the interior of the eye, and
`(2) they provide a binocular viewing system of the ae-
`rial image of the fundus of the eye produced by said
`condensing lens, said aerial image being an inverted real
`image formed of light emerging from the eye and re-
`fracted by said condensing lens.
`PRIOR ART
`
`Monocular indirect ophthalmoscopy utilizing a sepa-
`rate light source to one side and at a distance behind the
`subject and utilizing a head-borne mirror with a central
`aperture in front of the examiner’s eye and a hand-held
`+ 13.00 diopter spherical condensing and image form-
`ing lens, was first used in the mid 19th century. By the
`early 20th century, Gullstrand had designed a large
`table-model binocular indirect ophthalmoscope. The
`large size and complexity of the Gullstrand apparatus as
`well as the inability of the examiner to view the periph-
`cry of the retina with it prevented its wide acceptance.
`In 1947 Dr. Charles Schepens developed a small
`head-borne binocular indirect ophthalmoscope incorpo—
`rating a high intensity illuminating system and two pairs
`of oblique mirrors for directing the light rays from the
`aerial image of the fundus to each eye of the examiner.
`Said aerial image is formed by a hand-held condensing
`and image forming indirect ophthalmoscopy lens, said
`lens being separate and distinct from the head-bome
`indirect ophthalmoscope. The power of the indirect
`ophthalmoscopy lens may be varied to suit the examiner
`and its tilt and position may be modified to enhance the
`viewing of the fundus of the eye. The Schepens head-
`borne binocular indirect ophthalmoscope greatly in-
`creased the ability of the examiner to observe details of
`the fundus, especially the peripheral portions.
`Since Schepens introduced his binocular head—borne
`indirect ophthalmoscope, several other similar head-
`borne ophthalmoscopes identical
`in principle to the
`Schepens instrument have become commercially avail-
`able. The inverted aerial
`image of the fundus when
`viewed by means of the Schepens ophthalmoscope and
`similar ophthalmoscopes remains inverted and essen-
`tially not magnified. In learning to use the head—borne
`binocular indirect ophthalmoscope, the examiner must
`take into account the fact that the image he is observing
`is inverted and diametrically opposed to the actual posi-
`tion of points in the fundus. Also, when the hand-held
`indirect ophthalmoscopy lens is of strong dioptric
`power, the aerial image of the fundus is less magnified
`although the area of the fundus included in the aerial
`image is increased.
`BRIEF DESCRIPTION OF PREFERRED
`EMBODIMENTS
`
`Briefly, this invention relates to a new and improved
`head-borne binocular
`indirect ophthalmoscope for
`viewing the aerial image of the fundus of the eye, hav-
`ing the unique feature that it incorporates within each of
`its two observing portions a two-lens telescope of low
`magnifying power which magnifies said aerial image of
`
`10
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`
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`
`60
`
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`
`2
`the fundus. The telescope incoprated into the ophthal-
`moscope differs from the usual coaxial type in that the
`optical axis of the high powered objective lens and that
`of the high powered ocular lens of said telescope are
`caused to intersect each other at an angle of about 94° at
`the surface of a laterally positioned oblique front sur—
`face mirror, said lenses and said mirror being in a fixed
`relationship to each other within a transversely mov—
`able mounting as a fixed telescope unit such that the
`reflected secondary focus of the objective lens falls at
`the primary focus of the ocular lens, said unit being
`attached to a slide which is transversely movable along
`ways toward and away from a medially positioned
`oblique front surface mirror whereby adjustments can
`be made within the ophthalmoscope to accommodate
`the interpupillary distance of the observer without af-
`fecting the relative position of the elements of said tele-
`scope unit. A single low-powered columnating lens
`whose primary focus is at the usual working distance in
`performing indirect ophthalmoscopy,
`is fixed in posi-
`tion in front of both of the medially positioned oblique
`mirrors. Since the telescope and mirror unit is a fixed
`unit and since the light reflected from said medially
`positioned oblique mirror and incident upon said tele-
`scope objective lens of said unit is columnated, move-
`ment of said unit toward and away from said medially
`positioned oblique mirror along the direction of the
`incident columnated light rays requires no relative ad-
`justment of said telescope when it is moved transversely
`to accommodate the observer’s interpupillary distance.
`The incorporation of aberration correcting aspherical
`objective and ocular lenses within said unit of the indi-
`rect ophthalmoscope of this invention and the use of the
`columnating lens provides to the observer viewing the
`aerial
`image of the fundus binocularly a magnified,
`stereoscopic clear image of the aerial image of the fun-
`dus of the eye.
`Two types of telescopes are used in this invention: a
`Galilean telescope wherein the objective lens is of
`strong positive power and wherein the ocular lens is of
`strong negative power and the image is seen as clear,
`enlarged, and inverted, and; an astronomical telescope
`wherein the objective lens is of strong positive power
`and the ocular lens is of strong positive power and the
`image is reinverted and is seen as clear, enlarged, and
`upright.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a schematic representation of the illuminat-
`ing system for illuminating the fundus of the eye utiliz-
`ing the hand-held indirect ophthalmoscopy lens as a
`condensing lens.
`FIG. 2 is a schematic representation of the formation
`of the inverted aerial image of the fundus of the eye by
`the hand-held indirect ophthalmoscopy lens.
`FIG. 3 is a schematic representation of the formation
`of the inverted aerial image of the fundus of the eye and
`the binocular indirect ophthalmoscope of the prior art
`for viewing said inverted aerial image.
`FIG. 4 is a schematic drawing of a section through
`one embodiment of the binocular indirect ophthalmo-
`scope of this invention showing the columnating lens
`and the positive objective and positive ocular lenses of
`the included astronomical telescope.
`FIG. 5 is a graph of the dioptric power of the colum-
`nating lens versus magnification of the aerial
`image
`produced by the columnating lens.
`
`

`

`4,682,866
`
`3
`FIG. 6 is a partial schematic drawing to scale of a
`section through another embodiment of the binocular
`indirect ophthalmoscope of this invention showing the
`columnating lens and the positive objectives with nega-
`tive ocular lenses of the included Galilean telescope.
`FIG. 7 is a schematic drawing of a portion of the
`indirect ophthalmoscope of this invention showing the
`positions and angular relationships of the essential com—
`ponents of the ophthalmoscope.
`FIG. 8, drawn to scale, is an enlarged detailed view
`of the arrangement of the front surface mirrors and the
`included Galilean telescope of the left half of the binoc-
`ular indirect ophthalmoscope of this invention as shown
`in FIG. 6 showing the columnating lens, front surface
`mirrors, and the included positive objective and nega-
`tive ocular lenses of said Galilean telescope in their
`respective positions affixed to the housing of the lateral
`front surface mirror. Also included in FIG. 8 in its
`proper position for viewing, is a drawing of a section
`through the eye of the observer.
`FIG. 9, drawn to scale, is an enlarged detailed view
`of the arrangement of the front surface mirrors and the
`included astronomical telescope of the left half of the
`binocular indirect ophthalmoscope of this invention
`analogous to FIG. 8 showing the columnating lens,
`front surface mirrors, and the included positive objec-
`tive and positive ocular lenses of said astronomical tele-
`scope in their respective positions affixed to the housing
`(“of the lateral oblique front surface mirror. Also in-
`Ircluded in FIG. 9 in its proper position for viewing is a
`drawing of a section through the eye of the observer.
`FIG. 10 is an exploded perspective View of the head-
`borne ophthalmoscope of this invention showing the
`apparatus for mounting on the head of the user.
`FIG. 10A is a perspective view showing the slide
`assembly for the lateral front surface mirrors; and,
`, FIG. 11 is a perspective view of the ophthalmoscope
`fof this invention shown mounted on the head of the
`user.
`
`”
`
`In FIG. 1, I have shown schematically the optical
`system for illuminating the fundus of the eye. Light
`source S sends light to condensing lens C] which in turn
`directs divergent light rays to oblique mirror M which
`redirects the divergent beam of light to indirect oph-
`thalmoscopy condensing lens C2, which converges the
`beam of light to form a real inverted image 8’ of light
`source S in the vicinity of the center of the pupil of the
`eye, I. The light rays then diverge to illuminate the
`fundus F. In FIG. 2 I have shown schematically light
`rays emerging from the illuminated eye I from points in
`the fundus F and passing through the pupil of the eye, to
`be incident upon the back surface of indirect ophthal-
`moscopy condensing lens C2 and refracted through lens
`C2 to form a real inverted aerial image i of the fundus F.
`Since the object points in the fundus are at different
`depths, aerial image i likewise has depth. The light rays
`from each point in the fundus passing through image i p
`then continue to the head-borne binocular ophthalmo—
`scope (see FIG. 3) where they impinge upon medial
`oblique mirrors a and a’ and after reflection, upon lat-
`eral oblique mirrors b and b’ which then direct the
`reflected light rays to the pupils o and o’ of the observ-
`er’s eyes e and e’. Oblique mirrors b and b’ are adjust-
`able towards or away from each other by means of
`slides and ways not shown in FIG. 3, to match the
`interpupillary distance of the observer. The observer is
`thus observing binocularly and stereoscopically in-
`verted aerial image i. Since aerial image i is at a fairly
`
`4
`close distance from the observer’s eyes, it may be neces-
`sary to provide supplementary lenses 1 of about two
`diopters power in front of the observer’s eyes should
`the observer be presbyopic. The image seen by the
`observer is inverted and not enlarged, except for slight
`magnification which results from said two diopter
`lenses when used.
`
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`In the present invention, I have improved upon the
`prior art in two ways, (1) by utilizing a columnating lens
`c, centered in front of medial oblique mirrors a and a’
`(see FIG. 4) so that light rays in each bundle from each
`point in image i, after refaction by said columnating
`lens, proceed as a homocentric bundle of essentially
`parallel light rays toward oblique mirrors a and a’. In
`FIG. 4, I have shown divergent light rays from a cen-
`tral point in image i incident upon columnating lens C
`and refracted to a homocentric bundle of parallel light
`rays to each medial oblique mirror a and a'. Since image
`i has depth, the light rays in the homocentric bundle
`may be parallel or may be very slightly convergent or
`divergent. The power of the columnating lens is such
`that the aerial image i of the fundus lies at its anterior
`focal plane. I have determined that an anterior vertex
`power of 3.37 diopters for the anterior focal distance of
`29.674 centimeters for the columnating lens, represent-
`ing the distance between the aerial image i and said
`columnating lens, is satisfactory. In the actual practice
`of indirect ophthalmoscopy with a 20 diopter hand-held
`indirect ophthalmoscopy lens and the 3.37 diopter
`columnating lens, the distance between the hand-held
`indirect ophthalmoscopy lens and the observer’s eyes
`would be approximately 16 inches, which is a conve-
`nient and comfortable working distance. However,
`different observers may prefer working distances less
`than or greater than 16 inches, requiring columnating
`lenses stronger or weaker than 3.37 diopters respec-
`tively. The columnating lens, in addition to its effect
`with respect to the working distance of the observer,
`also has the effect of magnifying the aerial image, the
`stronger its power, the greater the magnification. FIG.
`5 is a graph of power of the columnating lens versus its
`magnification within a range of 1.143 to 1.332. The
`power of the columnating lens is seen to be in the range
`of 2.00 to 4.50 diopters and depends upon the preferred
`working distance of the observer,
`the stronger lens
`being used for shorter working distances. Working
`distance is the distance between the observer’s eyes and
`the hand-held indirect ophthalmoscopy lens. Note that
`at a power of 3.37 diopters, magnification of the colum-
`nating lens is approximately 1.25.
`Although FIG. 5 shows columnating lens dioptric
`powers from 2.00 to 4.50, said lens with powers of less
`than 2.00 diopters, for example 1.0 diopter, or greater
`than 4.50 diopters, for example 5.50 diopters, may be
`used.
`.
`‘
`A second improvement upon the prior art is the in-
`corporation of a pair of two-lens telescopes of low mag-
`nifying power within the indirect ophthalmoscope of
`this invention.
`FIG. 6, drawn to scale, is a schematic representation
`of the entire optical system of indirect ophthalmoscopy
`according to this invention from the formation of the
`aerial image of the illuminated fundus by means of the
`hand-held indirect ophthalmoscope of this invention
`which includes firstly the novel single element colum-
`nating lens c’ and secondly the novel pair of two-ele-
`ment Galilean telescopes each element of which is in-
`clined and fixed in position with respect to its respective
`
`

`

`5
`lateral oblique flat front surface mirror and each tele-
`scope and said lateral oblique mirror comprising a unit
`u within the direct ophthalmoscope of this invention.
`Also shown in FIG. 6 is the position and convergence
`of the observer’s eyes. Said telescope units are designed
`and angled such that the optical axis of each ocular lens
`is directed toward the center of the apparent position of
`the aerial image of the fundus.
`In FIG. 7, I have shown in greater detail the positions
`and angular relationships of the mirrors and lenses de—
`picted in the lefthand portion of FIG. 6 along with the
`path of the axial chief ray which coincides with the
`optical axis of the telescope of said fixed unit.
`The angle between the two medial oblique front sur-
`face mirrors a and a’ is 90° so that each mirror makes an
`angle of 45° with respect to the center plane of symme-
`try of the right and left halves of the indirect ophthalv
`moscope of this invention. From a point at the center of
`the aerial image of the fundus which is at the primary
`focus of the columnating lens, light rays proceed as a
`homocentric bundle of divergent rays to said columnat-
`ing lens and are refracted as a homocentric bundle of
`columnated light rays parallel to said center plane of
`symmetry, to then intersect the medial oblique mirror at
`an angle of incidence of 45° and are then reflected at an
`angle of reflection of 45°. The reflected homocentric
`bundle of parallel light rays are thus perpendicular to
`said columnated light rays to be incident upon the ob-
`jective lens of the telescope of the indirect ophthalmo-
`scope of this invention. The optical axis of said objec-
`tive lens is parallel to said homocentric bundle of re-
`flected parallel incident light rays and that light ray
`coinciding with the optical axis of said objective lens is
`the axial chief ray which proceeds through said objec-
`tive lens undeviated to be incident upon the lateral
`oblique mirror which itself is at an angle of 47° with
`respect to said center plane of symmetry. The angle of
`incidence of said chief ray at said lateral oblique mirror
`is thus 47° as is the angle of reflection, measured with
`respect to a normal to said mirror at the point of reflec-
`tion. Said reflected chief ray at said lateral oblique mir-
`ror is thus inclined at an angle of 4° with respect to said
`center plane of symmetry as is the inclination of the
`optical axis of the ocular lens of said telescope which
`coincides with the reflected chief ray from said lateral
`. oblique mirror.
`Of importance is the fact that the extended optical
`axis and axial chief ray of the objective lens and those of
`the ocular lens intersect and are reflections of each
`other at the lateral oblique front surface mirror. Two
`lenses having a common straight line optical axis are
`said to be coaxial. In this specification I have extended
`the concept of coaxiality to include those situations in
`which a mirror is interposed between two lenses such
`that the optical axis of one of the lenses intersects the
`optical axis of the other at said mirror and the two axes
`and the normal to the mirror surface at their point of
`intersection all lie in the same plane, with the angle
`between the optical axis of the first of said lenses and the
`normal to the surface and that between the optical axis
`of the second of said lenses and the normal to the sur-
`face being equal. This, in essence, is the law of reflection
`substituting optical axes for light rays. The two lenses
`are still said to be coaxial and the two lenses and the
`interposed mirror comprise the coaxial movable tele-
`scope unit of the indirect ophthalmoscope of this inven-
`tion.
`
`25
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`4,682,866
`
`10
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`
`6
`Although 47° is a very useful angle between the lat-
`eral oblique mirrors and the center plane of symmetry,
`said angle may be less than 47° or greater than 47°,
`approximately 46° or 48°, for example,
`in accordance
`with a working distance for indirect ophthalmoscopy
`somewhat less or greater respectively than the usual
`working distance of 16 inches and in accordance with
`the interpupillary distance of the observer, a large inter-
`pupillary distance requiring a larger angle and a small
`interpupillary distance requiring a smaller angle.
`In adjusting the indirect ophthalmoscope of this in-
`vention for the interpupillary distance of the observer,
`the movement of said unit must be along ways perpen-
`dicular to said center plane of symmetry to maintain
`coincidence of the optical axis of said unit and said chief
`ray reflected from said medial oblique mirror. During
`such an adjustment the inclination of said lateral oblique
`mirror remains at 47° with respect to said center plane
`of symmetry. Also any adjustment of the ocular lens for
`0 focusing of the telescope is in the axial direction of the
`ocular lens of the telescope, thereby maintaining coaxi-
`ality of the unit.
`FIG. 8, drawn to scale, shows in detail for one-half of
`said first embodiment as shown in FIG. 6, of the indirect
`ophthalmoscope of this invention, the positioning and
`inclination of the positive objective lens and the nega-
`tive ocular lens with respect to the lateral flat oblique
`front surface mirror. The two lenses and said lateral
`oblique mirror comprise the fixed unit which can be
`moved transversely along ways without the necessity
`for change in the telescopic adjustment when adjusting
`the ophthalmoscope for interpupillary distance by mov-
`ing said unit toward and away from its respective me-
`dial flat oblique front surface mirror. The negative ocu-
`lar lens is held in an axially adjustable mounting with a
`screw thread for fine adjustment in the axial direction.
`The image of the aerial image of the fundus of the eye
`as seen through this embodiment of the invention re-
`mains inverted.
`FIG. 9, drawn to scale, is similar to FIG. 8 with the
`exception that the telescope incorporated in said fixed
`unit is an astronomical telescope wherein the ocular lens
`is a strong positive lens. The relative fixed positions of
`the objective and ocular lenses with respect to the lat-
`eral oblique mirror are shown. There is adequate dis—
`tance between the front surface of the objective lens
`and the medial oblique mirror to allow for adjustment
`of said ophthalmoscope for observers with small inter-
`pupillary distances. The image of the aerial image of the
`fundus as seen by an observer through this embodiment
`of the indirect ophthalmoscope of this invention is up-
`right.
`The objective lens of said incorporated telescope is a
`strong positive lens of homogeneous transparent optical
`glass or plastic. The objective lens of the astronomical
`telescope is considerably stronger than that of the Gali-
`lean telescope. I have included spherical objective and
`ocular lenses as elements of the telescope of this inven-
`tion; however, such lenses when very strong as in the
`astronomical telescope, can produce considerable aber-
`rations in the image formed through them and it is nec-
`essary with said strong lenses as in the incorporated
`astronomical telescope, that the lens elements of the
`telescope be aspheric, with one or both surfaces of the
`objective lens being aspheric and one or both surfaces
`of the ocular lens also being aspheric, if aberrations are
`to be reduced to a minimum. The use of aspheric objec-
`tive lenses, especially if both front and back surfaces are
`
`

`

`4,682,866
`
`7
`aspheric, insures that a homocentric bundle of light rays
`originating in the aerial image of the fundus, rendered
`parallel by said columnating lens, and reflected from
`said medial oblique mirror and incident upon said objec-
`tive lens, will be focused toward an essentially aberra—
`tion—free image at the secondary focal plane of said
`objective lens. It is of course necessary that the aerial
`image of the fundus is itself essentially flat and aberra-
`tion—free and the use of my double aspheric indirect
`ophthalmoscopy lens as described in the specification of
`my copending patent application, Lens For Indirect
`Ophthalmoscopy, Ser. No. 437,279, produces such an
`aerial image. Divergent homocentric bundles of light
`rays from said inverted aerial image of the fundus are
`incident upon the columnating lens of the indirect oph-
`thalmoscope of this invention which refracts said bun-
`dles to homocentric bundles of parallel light rays di-
`rected towards the medial oblique front surface mirror
`of said ophthalmoscope which in turn reflects the ho-
`mocentric bundles of parallel light rays to the front
`aspheric surface of the objective lens.
`When the incorporated telescope is an astronomical
`telescope, the homocentric bundles of light rays emerg-
`ing from the back aspheric surface of said objective lens
`are incident upon the lateral oblique front surface mir-
`ror and reflected to a real reinverted (upright) aerial
`image of the aerial image of the fundus in the secondary
`focal plane of said objective lens which is also the pri-
`“mary focal plane of the ocular lens of said astronomical
`:‘telescope. Said reinverted aerial image then becomes
`"the object for the ocular lens of said telescope. The
`ocular lens is so designed with both front and back
`surfaces aspheric that diverging homocentric bundles of
`light rays from points in said object plane, after refrac-
`tion by said ocular lens, proceed as homocentric bun—
`.dles of parallel light rays, with the chief ray of each
`bundle proceeding towards the back focus of said ocu-‘
`"lar lens. When the observer’s eye is positioned with the
`center of its entrance pupil at the back focus of the.
`ocular lens of said telescope, the imageof the fundus as
`seen by means of the indirect ophthalmoscope of this
`invention will be enlarged and upright.
`In the binocular indirect ophthalmoscope of this in-
`vention incorporating the astronomical telescope, the
`dioptric power of the objective lens may be as low as 40
`diopters or as high as 80 diopters, while the dioptric
`power of the ocular lens may likewise be a value be-
`tween 40 and 80 diopters. An objective lens of 60 diop—
`ters in combination with an ocular lens of 70 diopters is
`well suited for the incorporated astronomical telescope:
`it permits a full range of adjustability for the interpupil—
`lary distance of the observer, and because of the high
`dioptric powers of both the objective and the ocular
`lenses, the head-borne indirect ophthalmoscope of this
`invention can be made compact and used close to the
`observer’s eyes.
`The magnification produced by the incorporated
`astronomical telescope is a function of the ratio of the
`dioptric power of the ocular lens divided by the diop-
`tric power of the objective lens. Additional magnifica-
`tion is provided by the positive aspheric columnating
`lens. For example, if the power of the columnating lens
`is 3.37 diopters, the magnification produced by it is 1.25,
`and if the power of the objective lens of the telescope is
`60 diopters and that of the ocular lens is 70 diopters, the
`magnification of said telescope is 1.167. The total mag-
`nification of the indirect ophthalmoscope of this inven-
`tion is then 1.25>< 1.167: 1.46.
`
`>
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`6O
`
`65
`
`8
`It is understood that the dioptric powers of the objec—
`tive and ocular lenses of the astronomical telescope may
`be other than 60 and 70 diopters respectively and still be
`completely compatible with the dimensions and con-
`cepts of the indirect ophthalmoscope of this invention,
`thereby obtaining other magnifications. As an example,
`the objective lens of said telescope may have a dioptric
`power of 55 and the ocular lens may have a dioptric
`power of 75, and the columnating lens may be kept at a
`dioptric power of 3.37 whereby the magnification of the
`primary aerial image of the fundus of the eye will be
`1.36X1.25=1.70.
`If the dioptric power of both the objective lens and
`the ocular lens of the incorporated astronomical tele-
`scope are the same, magnification produced by means of
`the telescope will be 1.00 and the total magnification
`will be that produced by the columnating lens only,
`1.25, with the power of the columnating lens still at 3.37
`diopters. The image as seen by the observer will be
`enlarged and upright.
`‘
`When the incorporated telescope is a Galilean tele-
`scope (see FIG. 8), the homocentric bundles of con-
`verging light rays emerging from the back surface of
`the objective lens of the telescope are incident upon the
`lateral oblique flat front surface mirror, and after reflec-
`tion by said mirror are directed toward the repositioned
`secondary focal plane of said objective lens. The nega-
`tive ocular lens is coaxial with the redirected optical
`axis of said objective lens and is interposed between the
`lateral oblique mirror and said secondary focus of the
`objective lens, with its primary focal plane coinciding
`with the secondary focal plane of said objective lens.
`The image seen by the observer is inverted and en-
`larged. Magnification of said Galilean telescope is equal
`to the ratio of the dioptric power of the ocular lens
`divided by the dioptric power of the objective lens. As
`an example, if the power of the objective lens is 20
`diopters and that of the ocular lens is 30 diopters, mag-
`nification is then 1.50. If the magnification due to the
`columnating lens is 1.25, then the total magnification is
`then 1.50X 1.25: 1.88. As a second example, if the diop-
`tric powers of the objective and ocular lenses of the
`included Galilean telescope are 25 and 35 diopters re-
`spectively, then magnification by the telescope is 1.4. If
`the magnification due to the columnating lens is 1.25,
`then the total magnification is 1.4x 1.25: 1.75.
`In FIGS. 10 and 11, I have shown an ophthalmoscope
`unit which incorporates the lens and mirror assembly of
`the present invention as set forth herein in FIGS. 4—9.
`Specifically as seen in FIGS. 10, 10A and 11, a strap
`assembly 25 comprises a peripheral head part 25:: and an
`upwardly projecting crown part 25b adapted to lie
`around and over the user’s head as best seen in FIG. 11.
`A suitable light source S as referred to in FIG. 1 is
`mounted to the top wall of an elongated tubular housing
`h which is square in cross section.
`As seen in FIGS. 10 andlll, mirror M is rotationally
`adjustable about its axis by finger lever 11 to position the
`light beam from mirror M to condensing lens C2 held by
`the observer.
`
`The observing lens and mirror system of the ophthal-
`moscope is disposed within the housing h so as interact
`with the light source S and its associated light reflecting
`mirror M.
`
`The observing lens and mirror system incorporates
`the system as shown in FIGS. 6-9 and includes medial
`oblique flat front surface mirrors a and a’, lateral front
`
`

`

`9
`surface mirrors b and b', objective lens, and ocular lens
`as a unit “”.u
`As best seen in FIGS. 10 and 10A each lateral front
`surface mirror b and b’ is fixedly mounted on a boss 28
`disposed within an elongated recess 29 which is formed
`on the upper surface 30 of rectangular mou