GB2310051A

GB2310051A - Aligning the condensing lens and eyepiece of a binocular indirect ophthalmoscope

Info

Publication number: GB2310051A
Application number: GB9602385A
Authority: GB
Inventors: Bertil Damato
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-02-06
Filing date: 1996-02-06
Publication date: 1997-08-13
Also published as: GB9602385D0

Abstract

A hollow body 3 of a binocular ophthalmoscope holds the condensing lens 1 and eyepiece or eyepieces 2 in alignment. The hollow body 3 may also house a light source (4, fig 5) which is placed as near as possible to the examiners visual axis and may be reflected into the patients eye by a tiltable mirror (not shown). The light source (4, fig 5) can be controlled by a switch 5 and a rheostat 6. The condensing lens 1 may be attached to the body 3 at two points and have a protruding lever 8 so that it may be tilted. The body 3 may be variable in length in a telescopic fashion. The ophthalmoscope may have a beamsplitter (not shown) so that a second observer may examiner the patient's eye simultaneously.

Description

A tubular binocular indirect ophthalmoscope Ophthalmoscopes have allowed visual examination of the back of the living eye through the pupil for well over a century, facilitating diagnosis, treatment, and monitoring of a wide range of conditions of the eye and brain.

The direct ophthalmoscope is merely a hand-held light source shone very close to the examiner's direction of gaze, so as to illuminate the back of the patient's eye, and this ophthalmoscope is generally provided with a set of tiny viewing lenses that are interchanged by the examiner dialling a knob on the ophthalmoscope so that the examiner can obtain a focused view of the back of the eye. The direct ophthalmoscope, which is held very close to the patient's eye, provides only a limited field of view, and because the view is monocular there is no depth perception.

The binocular indirect ophthalmoscope consists of a light source, which is held by means of a spectacle frame near the examiner's eyes, as close to the examiner's visual axis as possible, and shone towards the patient's eye to illuminate the back of the eye. Unlike direct ophthalmoscopy, the examiner focuses not on the back of the eye itself, but on an aerial image in space, which is created by means of a condensing lens held by the examiner at the correct distance from the patient's eye, this distance normally being about five centimetres for a lens having a dioptre of 20 dioptres. In addition to holding the light source, the spectacle frame of the binocular indirect ophthalmoscope holds two eyepieces, one for each eye, which are connected to prisms that approximate the visual axes of the examiner's eyes to each other. It is usually possible to adjust the spacing between the prisms to fit the inter-pupillary distance, which varies from person to person. The image of the back of the eye provided by an indirect ophthalmoscope is stereoscopic ar.d has a wider field of view than that of the direct ophthalmoscope, but the image is inverted.

Conventional binocular indirect ophthalmoscopy is difficult to learn, because the examiner must align in space the patient's eye, the condensing lens and the examiner's eyes along one axis. Furthermore, this alignment must be maintained when the examiner moves his or her head from side to side and up and down to look at different parts of the back of the eye. The task of aligning the patient's eye, the condensing lens, and the examiner's eyes is complicated by the fact that the image is inverted and made even more difficult when the patient looks in different directions so as to reduce the amount by which the examiner's head needs to be moved. For these reasons, considerable practice is required before an examiner is able to examine the back of an eye adequately with a conventional binocular indirect ophthalmoscope.

Because of the skill required to perform conventional binocular indirect ophthalmoscopy, this examination is not widely performed, except by ophthalmologists in developed countries and some optometrists. As a result, many workers, such as optometrists, family doctors, physicians, lay volunteers, and ophthalmologists in under-developed countries are unable to examine the back of the eye properly.

According to the present invention, there is provided a binocular indirect ophthalmoscope comprising a condensing lens attached to the examiner's binocular eyepieces by means of a rigid tube, the body possibly being adapted to be telescopic so as to be of variable length, and containing within it, firstly, a light source, or a mirror reflecting a light source, held between and as close to the examiner's visual axes as possible, and secondly, a source of energy for the light source. Unlike conventional binocular indirect ophthalmoscopes, the examiners eyepieces are not fixed to the examiner's head by spectacle side-arms or cap, but attached to the ophthalmoscope body. As with conventional ophthalmoscopes, there may be an attachment containing a beam-splitter, that can be attached to the outside of the eyepiece end of. the body, to allow a second examiner to observe an image of the patient's eye simultaneously. The main advantage of the present ophthalmoscope over conventional devices is that the condensing lens and the examiner's eyepieces are held in alignment by the rigid tube, thereby making the examination easier to perform.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawing in which: Figure 1 shows in perspective the superior view of the ophthalmoscope; Figure 2 shows in perspective the inferior view of the ophthalmoscope; Figure 3 shows in perspective the examiner's eye view of the ophthalmoscope; Figure 4 shows in perspective the patient's eye view of the ophthalmoscope; Figure 5 illustrates a lateral cross section of the ophthalmoscope; Figure 6 illustrates a vertical cross section of the ophthalmoscope.

Referring to the Figures the ophthalmoscope comprises the condensing lens 1, the eyepieces 2, the body 3, the light source 4, the switch 5, the rheostat to vary light intensity 6, the energy source 7, the lever for tilting the condensing lens 8, the lever for tilting the light source 9, and the lever for tilting the eyepieces.

In order to examine a subject's eye, the examiner switches on the illumination, holds the condensing lens close to the patient's eye, with the patient's pupil visible at the centre, and while looking through the ophthalmoscope, moves the ophthalmoscope away from the patient's eye, keeping the pupil in the centre of the image until the image of the pupil is replaced by the image of the back of the eye. The examiner can then vary the brightness of the illumination, alter the angle of illuminating light beam by rotating the reflector, alter the angle of the condensing lens to remove any annoying reflections, reduce the distance between the condensing lens and eyepiece so as to magnify the image or increase the distance between the condensing lens and eyepiece so as to minify the image.

Claims

1. A hollow body for holding the condensing lens of a binocular indirect ophthalmoscope in alignment with the examiner's eyepiece or eyepieces of that ophthalmoscope.

2. A simple binocular indirect ophthalmoscope as claimed in Claim 1, wherein the body is of variable length in a telescopic fashion.

3. A simple binocular indirect ophthalmoscope as claimed in any preceding claim, wherein the condensing lens is attached to the body at two points and wherein the condensing lens has a protruding knob or lever so that the condensing lens can be tilted by the examiner to remove any reflections that might interfere with the examiner's view of the patient's eye.

4. A simple binocular indirect ophthalmoscope as claimed in any preceding claim, wherein the patient's eye is illuminated by a beam of light travelling as close as possible to the examiner's visual axes.

5. A simple binocular indirect ophthalmoscope as claimed in Claim 4, wherein the light source is placed as close as possible to the examiner's visual axes.

6. A simple binocular indirect ophthalmoscope as claimed in Claim 4, wherein the light source is reflected into the patient's eye by means of a mirror placed as close as possible to the examiner's visual axes.

7. A simple binocular indirect ophthalmoscope as claimed in Claim 6, wherein the mirror is tilted by means of two knobs extending from diametrically opposite edges of the mirror and through the body to protrude on either side of the body.

8. A simple binocular indirect ophthalmoscope as claimed in any preceding claim with the light source located between the condensing lens and the examiner's eyepieces, and as close to the eyepieces as possible.

9. A simple binocular indirect ophthalmoscope as claimed in Claims 1-7 with the light source or sources located between the condensing lens and the patient's eye.

10. A simple binocular indirect ophthalmoscope as claimed in any preceding claim, with one or more sources of illumination near the rim of the condensing lens, each of which source can independently be switched on to provide, for example, a slit of light, or diffuse light, on the front of the eye so that the front of the eye can be examined if desired.

11. A binocular indirect ophthalmoscope as claimed in any preceding claim, containing a separable attachment wherein a sheet of plain, transparent glass can be placed at an angle to the examiner's visual axes, so as to split the image of the patient's eye thereby allowing a second observer to examine the image of the patient's eye simultaneously.

12. A binocular indirect ophthalmoscope as claimed in any preceding claim, with a single magnifying lens instead of an eyepiece, the lens being wide enough to allow the image of the back of the eye to be viewed with both eyes simultaneously.