WO2006108246A1 - An ophthalmoscope - Google Patents

An ophthalmoscope

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Publication number
WO2006108246A1
WO2006108246A1 PCT/AU2006/000523 AU2006000523W WO2006108246A1 WO 2006108246 A1 WO2006108246 A1 WO 2006108246A1 AU 2006000523 W AU2006000523 W AU 2006000523W WO 2006108246 A1 WO2006108246 A1 WO 2006108246A1
Authority
WO
Grant status
Application
Patent type
Prior art keywords
light
ophthalmoscope
light source
focusing lens
path
Prior art date
Application number
PCT/AU2006/000523
Other languages
French (fr)
Inventor
Gabriel Rajmund Suplewski
Matthew David Spark
Original Assignee
Visiomed Group Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date

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Classifications

    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B3/00Apparatus for testing the eyes; Instruments for examining the eyes
    • A61B3/10Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions
    • A61B3/12Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions for looking at the eye fundus, e.g. ophthalmoscopes

Abstract

An ophthalmoscope (10) is disclosed which comprises a real or apparent point light source (12), at least one focusing lens (20) and imaging optics (24). The point light source (12) is arranged to illuminate a non-central portion (27) of the focusing lens (20). Each focusing lens (20) is arranged such that during use light from the point light source (12) passes through each focusing lens (20) and illuminates a fundus portion (14) of a patient's eye (16) when the patient's eye is disposed at a predetermined location relative to the ophthalmoscope (10). The imaging optics (24) are arranged such that during use only light reflected from a fundus portion (14) of a patient's eye (16) and passing through the non-central portion of each focusing lens (20) is focused at a predetermined observation location. The point light source (12) and each focusing lens (20) are disposed relative to each other such that light illuminating the non-central portion (27) of each focusing lens (20) and reflected from each focusing lens (20) is not directed towards the imaging optics (24). The point light source (12) is disposed such that during use light from the point light source (12) and reflected light from a fundus portion (14) of a patient's eye form a relatively small angle.

Description

AN OPHTHAIJyIOSCOPE

Field of the Invention

The present invention relates to an ophthalmoscope and, in particular, to a portable ophthalmoscope.

Background of the Invention

It is known to provide ophthalmoscopes of direct or indirect configuration for observing and in some cases imaging a fundus portion of a patient's eye.

With a direct ophthalmoscope, a light source is used to directly illuminate a patient's eye. Light which is reflected from a fundus portion of the patient' s eye passes through a focusing lens and the focusing lens generates a real, inverted image of the patient's retina which is viewable by the observer. Since the optics required for producing the image of the retina and the optics required for focusing the light source are separate, unwanted reflections from the focusing lens are avoided.

With an indirect ophthalmoscope, light from a light source passes through a focusing lens to illuminate the fundus portion of a patient's eye. Reflected light from the fundus portion passes back through the focusing lens which generates a real, inverted image of the patient's retina viewable by the observer. An indirect ophthalmoscope is generally more complex and has a wider field of view than a direct ophthalmoscope.

However, because the same focusing lens is used for both outward and return ray paths, an indirect ophthalmoscope often produces undesired reflections from the focusing lens which are seen as "spots" by the observer. Summary of the Invention

In accordance with a first aspect of the present invention, there is provided an ophthalmoscope comprising: a real or apparent point light source; at least one focusing lens; and imaging optics; said point light source being arranged to illuminate a non-central portion of the focusing lens; the or each focusing lens being arranged such that during use light from the point light source passes through the or each focusing lens and illuminates a fundus portion of a patient's eye when the patient's eye is disposed at a predetermined location relative to the ophthalmoscope; the imaging optics being arranged such that during use only light reflected from a fundus portion of a patient's eye and passing through the non-central portion of the or each focusing lens is focused at a predetermined observation location; said point light source and the or each focusing lens being disposed relative to each other such that light illuminating the non-central portion of the or each focusing lens and reflected from the or each focusing lens is not directed towards the imaging optics; and said point light source being disposed such that during use light from said point light source and reflected light from a fundus portion of a patient' s eye form a relatively small angle.

In one arrangement, one focusing lens is provided.

The point light source may comprises at least one LED which may be disposed immediately adjacent the imaging optics . In one arrangement, the or each focusing lens is disposed such that a central axis of the or each focusing lens is not coincident with a central axis of the imaging optics.

In one embodiment, the or each focusing lens is tilted relative to the imaging optics .

The ophthalmoscope may further comprise an iris disposed in a first path of light from the point light source to the fundus portion and disposed in a second path of reflected light from the fundus portion to the imaging optics, the iris defining an aperture. The diameter of the aperture may be adjustable.

In one arrangement, the iris is disposed in a plane which is non-normal to the path of light from the point light source to the fundus portion. The iris may be disposed in a plane which subtends an iris angle with the path of light from the point light source to the fundus portion and the iris angle may be adjustable.

In one embodiment, the ophthalmoscope further comprises an at least partially light diffusive reflective element disposed in a path of light from the light source to the or each focusing lens such that at least part of the light from the light source is diffused and reflected towards the imaging optics. The diffusive reflective element may comprise the iris.

In one arrangement, the ophthalmoscope further comprises an image capture device which may include a CCD. The image capture device may comprise automatic gain control arranged to apply a gain to a captured image focused on the image capture device which is dependent on the light intensity of the captured image. In one arrangement, the diffusive reflective element is disposed in a plane which subtends an element angle with the path of light from the point light source to the or each focusing lens, and the element angle is selected so as to thereby select the gain of the image capture device. The element angle may be adjustable so as to thereby adjust the gain of the image capture device.

The gain of the image capture device may be selected by selecting the light reflective and/or light diffusive properties of said diffusive reflective element.

In one arrangement, the ophthalmoscope further comprises configuration means arranged to facilitate configuration of the ophthalmoscope for a particular patient, the configuration means being arranged to direct a beam of infra red light along a path generally coincident with the path ordinarily traveled by visible light produced by the light source, and to capture infra red light reflected from a fundus portion of a patient's eye along a path generally coincident with the return light path ordinarily traveled by visible light.

The configuration means may further comprise a mirror movable into and out of the light path ordinarily traveled by visible light from the light source, an infra red light source arranged to direct light onto the mirror and thereby along a path generally coincident with the path ordinarily traveled by visible light produced by the light source, an infra red image capture device, and an infra red imaging lens arranged to direct infra red light reflected from a fundus portion of a patient's eye and passing along a path generally coincident with the return light path ordinarily traveled by visible light to the infra red image capture device. In one embodiment, the point light source is arranged to generate pulsed light. The light pulses produced by the point light source may be synchronised with the image capture device.

The focusing lens may be an ophthalmic lens of between 2OD and 60D.

The aperture defined by the iris may be circular, ovular, rectangular, or any other suitable shape.

The ophthalmoscope may include a further iris disposed adjacent the imaging optics and arranged to mask light emanating from an edge portion of the ophthalmic lens and thereby improve sharpness and reduce chromatic aberration in the image produced by the imaging optics.

In accordance with an alternative aspect of the present invention, there is provided an ophthalmoscope comprising: a light source; at least one focusing lens; imaging optics; the light source being arranged to illuminate the or each focusing lens, the or each focusing lens being arranged such that during use light from the light source passes through the or each focusing lens and illuminates a fundus portion of a patient's eye when the patient's eye is disposed at a predetermined location relative to the ophthalmoscope, and the imaging optics being arranged such that during use light reflected from a fundus portion of a patient's eye passes through the or each focusing lens and is focused at a predetermined observation location; and an at least partially light diffusive reflective element disposed in a path of light from the light source such that at least part of the light from the light source is diffused and reflected towards the imaging optics; the arrangement being such that when an image capture device comprising automatic gain control arranged to apply a gain which is dependent on the light intensity of the captured image is disposed at the observation location, the gain applied by the image capture device is dependent on a selected degree of light incident on the imaging optics from said reflective element.

Brief Description of the Drawings

The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a schematic diagram of a fundus imaging system of an ophthalmoscope in accordance with an embodiment of the present invention;

Figure 2 is a schematic diagram of part of the fundus imaging system shown in Figure 1; and

Figure 3 is a schematic diagram of an alternative fundus imaging system of an alternative embodiment of an ophthalmoscope in accordance with the present invention.

Description of an Embodiment of the Present Invention

Referring to Figures 1 and 2 of the drawings, there is shown a fundus imaging system 10 which forms part of an ophthalmoscope, in this example of a type which is readily portable. Some features of the fundus imaging system 10 are omitted from Figure 2 for clarity purposes.

The fundus imaging system 10 includes a point light source 12, in this example in the form of a white LED. Light from the LED 12 is directed by system optics onto a fundus portion 14 of a patient's eye 16, and light reflected from the fundus portion 14 is focused by the system optics at an observation location which may correspond with an observer's eye, or an image capture device 18 as is the case with the present example.

The point light source 12, in this example a white LED, is disposed immediately adjacent the image capture device 18 so as to minimize distortion in the final image captured by the image capture device 18. In this regard, it will be appreciated that by using a point light source, it is possible to position the light source relatively close to the image capture device 18 and thereby obtain optimum minimization of distortion.

As an alternative to disposing a point light source adjacent the image capture device 18, the system may be arranged so as to produce an effective point light source adjacent the image capture device 18, for example by disposing a light source perpendicular to the image capture device and focusing light from the light source using a suitable lens arrangement and beam splitter in order to form an apparent point light source adjacent the image capture device 18, or by using optical fibres to direct light to a position adjacent the image capture device 18.

The system optics include a focusing lens 20 and an imaging lens 24 arranged so that light passing through the focusing lens 20 from the fundus portion 14 is focused at an observation location. In this example, a CCD device 26 is disposed at the observation location so that an image of the fundus portion is digitally captured. The CCD device 26 forms part of the image capture device 18. As an alternative, the image capture device may include a CMOS digital image capturing element instead of a CCD device .

The system optics may also include an LED lens (not shown) arranged to concentrate light from the LED 12 onto the focusing lens 20. With LEDs, a focusing component is ordinarily incorporated into the LED itself and in this case the LED 12 may be used with or without an additional focusing component.

In this example, the focusing lens 20 is a 2OD or 4OD ophthalmic lens and the imaging lens 24 is a 12mm or Iβmm imaging lens, although it will be understood that other suitable focusing and imaging lenses are envisaged.

The LED 12 produces a narrow spherical beam of about 20° or less and an output of at least 20000 mcd constant light. In order to successfully operate with such a liught source, a CCD device 26 with board lenses and a minimum light requirement of 0.5 lux or less is required.

As can be seen in Figure 1, the focusing lens 20 and the image capture device 18 are disposed relative to each other and arranged such that light reflected from the fundus portion 14 and passing through a specific predetermined non-central region 27 of the focusing lens 20 is focused at the observation location and thereby captured by the CCD device 26.

In particular, it can be seen that the image capture device 18 and the LED 12 are tilted relative to the focusing lens 20 such that central axes 28, 29 of the image capture device 18 and the LED 12 respectively are non-parallel to the central axis 30 of the focusing lens 20. As indicated in Figure 1, the central axis 28 of the imaging capture device 18 defines an angle α with the central axis 30 of the focusing lens 20, and the central axis 29 of the LED 12 defines an angle β with the central axis 30 of the focusing lens 20. The image capture device 18 and the LED 12 are also translated relative to the central axis 30 of the focusing lens 20, as indicated by translation distance d in Figure 1. It can also be seen that the angle θ between the central axes 28, 29 of the image capture device 18 and the LED 12 is small, which is significant since in this way distortion in the final image captured by the image capture device 18 is small.

As shown more particularly in Figure 2, it can also be seen that by tilting the image capture device 18 and the LED 12 relative to the focusing lens 20, light from the light source 12 which is reflected from the focusing lens 20 at the predetermined region 27 of the ophthalmic lens 20 will not be directed towards the imaging lens 24.

As a consequence of configuring the fundus imaging system 10 in this way, light from the LED 12 which is reflected by the focusing lens 20 is not focused at the observation location and is not captured by the CCD device 26 and capture of undesired ophthalmic lens reflections by the CCD device 26 are avoided without the need for cumbersome and complex optics.

Due to a double convex shape of the focusing lens and tilting of the image capture device 18 and the LED 12, light will reflect off the focusing lens 20 at such an angle that prevents capture by the image capture device 18. Translating the image capture device 18 away from the central axis of the focusing lens 20 resolves lens reflection problems but exacerbates image distortion and chromatic aberration due to the use of a periphery of lens for removing reflections. However, this distortion is minimised because the translation is supported by tilting the camera optics and light source such that the off centre translation is closer to the focusing lens centre than to its periphery. A small amount of increased chromatic aberration is reduced by the retina itself because the retina is highly absorptive of all colours of the white light spectrum except red, which is reflected back and collected by the camera for retina image projection.

In this example, the image capture device 18 and the LED 12 are tilted relative to the central axis 30 of the focusing lens 20 by an angle of approximately 8°.

As shown in Figure 1 but omitted from Figure 2 for clarity, the fundus imaging system 10 also includes an iris 32, in this example disposed adjacent the focusing lens 20 at the focal point of the image capture device 18. The purpose of the iris 32 is to minimize the amount of light reflected from the patient's cornea which reaches the CCD device 26. It will be understood that the size of the aperture defined by the iris 32 may be adjustable so as to correspond with the size of the patient's pupil, a relatively large pupil necessitating a relatively large iris aperture and a relatively small pupil necessitating a relatively small iris aperture.

The iris 32 also serves to limit the amount of corneal reflection by minimising incidence on the cornea of rays impinging on the cornea at relatively large angles. In this way, the CCD device 26 is forced to react to the true retina image rather then an image mixed with anterior reflection.

It will be appreciated that since the function of the iris 32 is to shield light reflected from a portion of the patient's cornea, it is possible to locate the controllable iris 32 at different positions in the fundus imaging system 10. For example, the iris 32 may be disposed at an opposite side of the focusing lens 20, or between the CCD device 26 and the imaging lens 24.

The controllable iris 32 may define an aperture of any suitable shape such as circular, ovular or rectangular and may be arranged so that it may be tilted relative to the CCD device 26 so as to vary the camera gain.

For an image capture device 18 comprising automatic gain control arranged to apply a gain which is dependent on the light intensity of the captured image, the iris 32 may additionally be used to control the gain of the image capture device 18. The gain is controlled by configuring the iris 32 so as to be at least partially light dispersive and by tilting the iris 32. Because light from the LED 32 is reflected off the aperture and is imaged by the CCD device 26, depending on the degree of tilt and the size of the aperture, the CCD device 26 will receive more or less light and adjust its gain lower or higher respectively. In general, a small pupil (i.e. <2.5mm) requires greater camera gain and therefore, less light reflection from the iris 32. The light passing to and reflected back from retina through a small pupil is lower than that from a large pupil and thus requires a higher camera gain for signal amplification. A higher gain can be attained by tilting light reflected from the iris 32 away from the camera sensor.

As an alternative to providing an iris which is at least partially light dispersive, an iris and a separate light dispersive element may be provided, the light dispersive element being at least partially light transmissive and at least partially light dispersive and light reflective. The light dispersive element may be disposed at an angle relative to the central axis of the LED 12 which is selected so as to provide the required image capture device gain, and the tilt angle may be adjustable so that the gain is adjustable during use.

In addition, the light dispersive properties of the light dispersive element may be chosen so as to provide a desired degree of light reflection and dispersion during use and thereby the required image capture device gain.

A further consequence of using a portion of only half of the focusing lens 20 is that a phenomenon occurs whereby dispersion of light into individual wavelengths with visible red, green and blue displacement occurs, in particular adjacent the edge of the focusing lens 20. This is known as chromatic aberration. In order to minimize capture of chromatic aberration by the CCD device 26, a further controllable iris (not shown) may be disposed adjacent the imaging lens 24, the further controllable iris functioning to mask light emanating from an edge portion of the ophthalmic lens 20 and thereby improve sharpness and reduce chromatic aberration in the image captured by the CCD 26.

Although problems associated with using a portion of only half of the focusing lens 20 are minimized in the present example by appropriate positioning of the focusing lens 20 and by using controllable irises, it will be understood that other arrangements are possible. For example, distortion and chromatic aberration in the image captured by the CCD device 26 could be removed using a suitable computing device and appropriate software, or by using achromatic lenses.

Non-mydriatic capability may be achieved by generating pulsed light from the LED 12 and by synchronising the light pulses with the image capture device 18 so as to reduce the patient's exposure to the light. Alternatively, a single pulse is generated by the LED 12 and the intensity of light from the LED 12 is set to the minimum level required by the image capture device 18 for observation of the fundus. Upon activation of image capture, the image capture device 18 waits until the next optimum time for capturing an image, then sends a trigger signal to the LED 12 to generate a light pulse. The duration of the light pulse is dependent on the length of time required for the image capture device 18 to capture a good quality image, the upper boundary of which is restricted by the envelope frequency of the image capture device 18 (i.e. the maximum shutter time) as well as the contraction time of the patient's pupil.

A low intensity light pulse is initially used for alignment, and a high intensity light pulse from the same LED 12 is used for retina image capture. The pulse is set for milliseconds and this is long enough to capture the image, but not long enough for the iris muscles to react. Thus the pupil remains widely open, despite the flash. If desired, the LED can also be set for the fixed light level during aligning and during retina monitoring. This fixed light mode is used for examining dilated patients, because their muscles responsible for pupil movement are paralysed by drops.

Referring to Figure 3, there is shown an alternative fundus imaging system 40 arranged in non-mydriatic configuration. Like features are indicated with like reference numerals.

Operation of the fundus imaging system 40 is essentially the same as operation of the fundus imaging system 10 shown in Figures 1 and 2. However, with the alternative fundus imaging system 40 provision is provided for configuring the system using infra red light prior to capturing an image of the fundus portion 14 using visible light. This is useful because infra red light does not cause pupil dilation and as a consequence configuration of the system for a particular patient is much simpler than would be possible with visible light. The alternative fundus imaging system 40 includes an infra red point light source 42 which may be in the form of an infra red LED, an infra red image capture device 44, and an infra red imaging lens 46 arranged to focus infra red light onto an infra red CCD 48. The alternative fundus imaging system 40 also includes a mirror 50 arranged so that infra red light incident on the mirror 50 from the infra red LED 42 is directed along a path generally coincident with the path ordinarily traveled by visible light during use of the fundus imaging system. Infra red light reflected from the fundus portion 14 likewise passes along a path generally coincident with the return light path shown in Figure 1 and is directed by the mirror 50 through the infra red imaging lens 46 and onto the infra red CCD 48.

The arrangement is such that once appropriate configuration of the fundus imaging system 40 has occurred, the mirror 50 is moved out of the path of the outward and return rays, and the visible light LED 12 is energised so as to illuminate the fundus portion 14 and capture the image of the fundus portion 14 prior to dilation of the patient's pupil.

It will be appreciated that the fundus imaging system described above has the advantages of simplicity and compactness of conventional indirect ophthalmoscopes but without the problems associated with ophthalmic lens and anterior eye reflections.

It will also be appreciated that the compactness of the present ophthalmoscope is enhanced and distortion is minimized by using a point light source, in this example in the form of an LED. Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.

Claims

CLAIMS :
1. An ophthalmoscope comprising: a real or apparent point light source; at least one focusing lens; and imaging optics; said point light source being arranged to illuminate a non-central portion of the focusing lens; the or each focusing lens being arranged such that during use light from the point light source passes through the or each focusing lens and illuminates a fundus portion of a patient's eye when the patient's eye is disposed at a predetermined location relative to the ophthalmoscope; the imaging optics being arranged such that during use only light reflected from a fundus portion of a patient' s eye and passing through the non-central portion of the or each focusing lens is focused at a predetermined observation location; said point light source and the or each focusing lens being disposed relative to each other such that light illuminating the non-central portion of the or each focusing lens and reflected from the or each focusing lens is not directed towards the imaging optics; and said point light source being disposed such that during use light from said point light source and reflected light from a fundus portion of a patient's eye form a relatively small angle.
2. An ophthalmoscope as claimed in claim 1, wherein one focusing lens is provided.
3. An ophthalmoscope as claimed in claim 1 or claim 2, wherein said point light source comprises at least one LED.
4. An ophthalmoscope as claimed in any one of the preceding claims, wherein said point light source is disposed immediately adjacent the imaging optics.
5. An ophthalmoscope as claimed in any one of the preceding claims, wherein the or each focusing lens is disposed such that a central axis of the or each focusing lens is not coincident with a central axis of the imaging optics .
6. An ophthalmoscope as claimed in claim 5, wherein the or each focusing lens is tilted relative to the imaging optics .
7. An ophthalmoscope as claimed in any one of the preceding claims, further comprising an iris disposed in a first path of light from the point light source to the fundus portion and disposed in a second path of reflected light from the fundus portion to the imaging optics, the iris defining an aperture.
8. An ophthalmoscope as claimed in claim 7, wherein the diameter of the aperture is adjustable.
9. An ophthalmoscope as claimed in claim 7 or claim 8, wherein the iris is disposed in a plane which is non- normal to the path of light from the point light source to the fundus portion.
10. An ophthalmoscope as claimed in any one of claims 7 to 9, wherein the iris is disposed in a plane which subtends an iris angle with the path of light from the point light source to the fundus portion and the iris angle is adjustable.
11. An ophthalmoscope as claimed in any one of the preceding claims, further comprising an at least partially light diffusive reflective element disposed in a path of light from the light source to the or each focusing lens such that at least part of the light from the light source is diffused and reflected towards the imaging optics.
12. An ophthalmoscope as claimed in claim 11 when dependent on any one of claims 7 to 10, wherein said diffusive reflective element comprises the iris.
13. An ophthalmoscope as claimed in any one of the preceding claims, further comprising an image capture device.
14. An ophthalmoscope as claimed in claim 13, wherein the image capture device comprises automatic gain control arranged to apply a gain to a captured image focused on the image capture device which is dependent on the light intensity of the captured image.
15. An ophthalmoscope as claimed in claim 14 when dependent on claim 11, wherein said diffusive reflective element is disposed in a plane which subtends an element angle with the path of light from the point light source' to the or each focusing lens, and the element angle is selected so as to thereby select the gain of the image capture device.
16. An ophthalmoscope as claimed in claim 15, wherein the element angle is adjustable so as to thereby adjust the gain of the image capture device.
17. An ophthalmoscope as claimed in claim 14 when dependent on claim 11, wherein the gain of the image capture device is selected by selecting the light reflective and/or light diffusive properties of said diffusive reflective element.
18. An ophthalmoscope as claimed in any one of the preceding claims, further comprising configuration means arranged to facilitate configuration of the ophthalmoscope for a particular patient, the configuration means being arranged to direct a beam of infra red light along a path generally coincident with the path ordinarily traveled by visible light produced by the light source, and to capture infra red light reflected from a fundus portion of a patient's eye along a path generally coincident with the return light path, ordinarily traveled by visible light so as to .
19. An ophthalmoscope as claimed in claim 18, wherein the configuration means comprises a mirror movable into and out of the light path ordinarily traveled by visible light from the light source, an infra red light source arranged to direct light onto the mirror and thereby along a path generally coincident with the path ordinarily traveled by visible light produced by the light source, an infra red image capture device, and an infra red imaging lens arranged to direct infra red light reflected from a fundus portion of a patient's eye and passing along a path generally coincident with the return light path ordinarily traveled by visible light to the infra red image capture device.
20. An ophthalmoscope as claimed in any one of the preceding claims, wherein said point light source is arranged to generate pulsed light.
21. An ophthalmoscope as claimed in claim 20 when dependent on claim 13, wherein light pulses produced by said point light source are synchronised with the image capture device.
22. An ophthalmoscope comprising: a light source; at least one focusing lens; imaging optics; the light source being arranged to illuminate the or each focusing lens, the or each focusing lens being arranged such that during use light from the light source passes through the or each focusing lens and illuminates a fundus portion of a patient's eye when the patient's eye is disposed at a predetermined location relative to the ophthalmoscope, and the imaging optics being arranged such that during use light reflected from a fundus portion of a patient's eye passes through the or each focusing lens and is focused at a predetermined observation location; and an at least partially light diffusive reflective element disposed in a path of light from the light source such that at least part of the light from the light source is diffused and reflected towards the imaging optics; the arrangement being such that when an image capture device comprising automatic gain control arranged to apply a gain which is dependent on the light intensity of the captured image is disposed at the observation location, the gain applied by the image capture device is dependent on a selected degree of light incident on the imaging optics from said reflective element.
23. An ophthalmoscope as claimed in claim 22, further comprising an iris disposed in a path of light from the point light source to the fundus portion, the iris defining an aperture.
24. An ophthalmoscope as claimed in claim 23, wherein the iris is disposed in a plane which is non-normal to the path of light from the point light source to the fundus portion.
25. An ophthalmoscope as claimed in claim 23 or claim 24, wherein said diffusive reflective element comprises the iris .
26. An ophthalmoscope as claimed in any one of claims 22 to 25, wherein the diameter of the aperture is adjustable.
27. An ophthalmoscope as claimed in any one of claims 22 to 26, further comprising an image capture device.
28. An ophthalmoscope as claimed in claim 27, wherein the image capture device comprises automatic gain control arranged to apply a gain to a captured image focused on the image capture device which is dependent on the light intensity of the captured image.
29. An ophthalmoscope as claimed in claim 28, wherein said diffusive reflective element is disposed in a plane which subtends an element angle with the path of light from the light source, the element angle being selected so as to thereby select the gain of the image capture device.
30. An ophthalmoscope as claimed in claim 29, wherein the element angle is adjustable so as to thereby vary the gain of the image capture device.
31. An ophthalmoscope as claimed in claim 28, wherein the gain of the image capture device is chosen by selecting the light reflective and/or light diffusive properties of said diffusive reflective element.
32. An ophthalmoscope as claimed in any one of claims 22 to 31, wherein one focusing lens is provided.
33. An ophthalmoscope as claimed in any one of claims 22 to 32, wherein the light source is a real or apparent point light source.
34. An ophthalmoscope as claimed in claim 33, wherein said point light source comprises at least one LED.
35. An ophthalmoscope as claimed in claim 32 or claim 34, wherein said point light source is disposed immediately adjacent the imaging optics.
36. An ophthalmoscope as claimed in any one of claims 22 to 35, wherein the or each focusing lens is tilted relative to the imaging optics.
37. An ophthalmoscope as claimed in any one of claims 22 to 36, wherein the light source is arranged to illuminate a non-central portion of the or each focusing lens, the imaging optics are arranged such that during use only light reflected from a fundus portion of a patient's eye and passing through the non-central portion of the or each focusing lens is focused at a predetermined observation location, and the light source and the or each focusing lens are disposed relative to each other such that light illuminating the non-central portion of the or each focusing lens and reflected from the or each focusing lens is not directed towards the imaging optics; and the light source being disposed such that during use light from the light source and reflected light from a fundus portion of a patient's eye form a relatively small angle.
38. An ophthalmoscope as claimed in any one of claims 22 to 37, further comprising configuration means arranged to facilitate configuration of the ophthalmoscope for a particular patient, the configuration means being arranged to direct a beam of infra red light along a path generally coincident with the path ordinarily traveled by visible light produced by the light source, and to capture infra red light reflected from a fundus portion of a patient's eye along a path generally coincident with the return light path ordinarily traveled by visible light so as to.
39. An ophthalmoscope as claimed in claim 38, wherein the configuration means comprises a mirror movable into and out of the light path ordinarily traveled by visible light from the light source, an infra red light source arranged to direct light onto the mirror and thereby along a path generally coincident with the path ordinarily traveled by visible light produced by the light source, an infra red image capture device, and an infra red imaging lens arranged to direct infra red light reflected from a fundus portion of a patient's eye and passing along a path generally coincident with the return light path ordinarily traveled by visible light to the infra red image capture device .
40. An ophthalmoscope as claimed in any one claims 22 to 39, wherein the light source is arranged to generate pulsed light.
41. An ophthalmoscope as claimed in claim 40 when dependent on any one of claims 27 to 31, wherein light pulses produced by the light source are synchronised with the image capture device.
PCT/AU2006/000523 2005-04-15 2006-04-18 An ophthalmoscope WO2006108246A1 (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2014129700A1 (en) * 2013-02-19 2014-08-28 연세대학교 원주산학협력단 Upright indirect ophthalmoscope

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