Optics: eye examining – vision testing and correcting – Eye examining or testing instrument – Objective type
Utility Patent
1999-09-10
2001-01-02
Manuel, George (Department: 3737)
Optics: eye examining, vision testing and correcting
Eye examining or testing instrument
Objective type
Utility Patent
active
06168274
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to ophthalmoscopes, in particular to an indirect ophthalmoscope which is used by an ophthalmologist in the observation of an image of the retina of an eye under examination. The invention also relates to an attachment for an ophthalmoscope.
BACKGROUND TO THE INVENTION
It is known to fit an indirect ophthalmoscope with a camera for detecting an image of the retina being observed, through a condenser lens, by the user of the ophthalmoscope. Such ophthalmoscopes are often used in the instruction of students or to inform patients and their relatives, since the image of the retina being observed by an ophthalmologist using the device can be displayed on a separate video display unit in real time. The image can also be recorded for subsequent analysis. It is also envisaged that, with the advent of improved telecommunications systems, a non-specialist could use the ophthalmoscope to provide an image which is transmitted to a specialist at a remote location so that the specialist can perform an examination without visiting the patient.
Typically, an indirect ophthalmoscope is a binocular device having viewing optics which have two central mirrors arranged to direct respective images to the left and right eye of the person using the ophthalmoscope. In one known arrangement, the camera detects an image reflected from an angled half-silvered mirror disposed immediately in front of the two mirrors.
A disadvantage of this arrangement is that the half-silvered mirror reduces the intensity of light which reaches the viewing optics. in addition, the intensity of light reaching the camera is less than would be the case pith a fully silvered mirror. Given that there is, in practice, an upper limit to the intensity of light which can be used to illuminate the eye under examination, the image is seen by the person using the ophthalmoscope and detected by the camera may be less bright than is desired.
In addition, since the image detected by the camera has been reflected from the mirror, it is inverted relative to the image seen by the wearer, who would therefore have to take this into account when explaining features of the eye under examination to students viewing a display of the image detected by the camera.
Another known type of camera attachment for an ophthalmoscope is produced by Litechnica, and comprises a fully silvered mirror which reflects light into a camera attached to the side of the ophthalmoscope. However, this gives rise to a lop-sided arrangement and the mirror partially obscures the user's view of the eye under examination. It is also known to provide an ophthalmoscope with a centrally mounted camera (The Video Omega
2
C produced by Heine Optotechnik) but in this case the images detected by the camera and seen by the user may become incongruent as a result of changes in the working distance of the ophthalmoscope.
SUMMARY OF THE INVENTION
According to a first aspect of the invention, there is provided an ophthalmoscope having viewing optics through which, in use, an eye under examination is viewed, the optics having at least one light receiving element via which light from an eye under examination is received by the viewing optics, the ophthalmoscope further comprising image detection apparatus for detecting an image of an eye under examination, wherein the image detection apparatus is substantially centrally positioned on the ophthalmoscope and is so positioned relative to the light receiving element that, in use, light from the eye under examination which is incident on the image detection means is received by the latter at a position which is laterally spaced from the paths of light from the eye to the light receiving element or through the viewing optics, wherein, said position is in the same horizontal plane as the light receiving element.
Thus, the image detection apparatus does not block the passage of any light from the eye to the light receiving element, and therefore does not reduce the intensity of the image viewed through the viewing optics. Similarly, the viewing optics do not affect the intensity of the image detected by the image detection apparatus. In addition, since the element and the position at which light is incident on the image detecting apparatus are at substantially the same level, the images seen by the user and detected by the apparatus are not displaced relative to each other by variations in the working distance of the ophthalmoscope.
Preferably, the image detection apparatus has a portion via which, in use, light from the eye under examination enters the image detection means, and which may be laterally spaced from the light receiving element.
Where the ophthalmoscope is a binocular instrument, having two spaced apart light receiving elements, the portion is preferably so situated that the elements are at least partially spaced in opposite lateral directions from the portion.
If the stereopsis of the ophthalmoscope is fixed, substantially all of each element is preferably laterally spaced from the portion. If, however, the separation of the elements is adjustable to adjust the stereopsis of the ophthalmoscope, substantially all of each element is preferably laterally spaced from the portion at least when the separation of the objectives is at its maximum.
Preferably, the portion is equidistant from the elements.
This helps to ensure that the image detected by the image detection system corresponds to that viewed through the viewing optics.
Preferably, the image detection apparatus comprises a camera, which is substantially centrally positioned on the ophthalmoscope, preferably in a position equidistant from the light receiving elements.
The substantially central mounting of the camera helps to reduce the effect that the camera has on the balance of the ophthalmoscope; the instrument is not lopsided, and is consequently easier to wear than the type of ophthalmoscope in which the camera is situated to one side of the viewing optics.
Said portion of the image detection means may comprise the objective of the camera.
Preferably, however, the portion comprises reflecting means which, in use, reflects the image of an eye under examination into the camera. Preferably the camera is positioned above the light receiving elements, and the reflecting means is at substantially the same level as said elements and reflects light up into the camera.
The reflecting means is conveniently so arranged as to cause two reflections of light from the eye under examination so as to eliminate any mirror inversion of the image detected by the camera.
The use of two reflections to avoid mirror inversions provides an effective and relatively cheap method of ensuring that the orientation of the image detected by the camera corresponds to that of the image seen through the viewing optics.
Conveniently, the reflecting means comprises a prism, preferably a pentagonal prism, for example a penta prism.
The pentagonal prism provides the double reflection and is particularly advantageous since the relative orientation of the prism surfaces which cause the two reflections is fixed and the prism provides is an efficient reflector of light.
Preferably, the prism and camera are carried by a frame adapted to be mounted on the front of the ophthalmoscope.
The invention also lies in an attachment for an ophthalmoscope, the viewing optics of which have at least one light receiving element via which light from an eye under examination enters the viewing optics, the attachment comprising retaining means for holding a camera and reflecting means operable to reflect light from an eye under examination into a camera held by the retaining means, the attachment further comprising mounting means for mounting the attachment on an ophthalmoscope, wherein the position of the reflecting means relative to the mounting means is such that, when mounted on an ophthalmoscope, the reflecting means is, in use, laterally spaced from, and at the same level as the light receiving element and the camera is substantially centrally positioned on the ophthalmoscope.
Keeler Limited
Lee, Mann, Smith McWilliams, Sweeney and Ohlson
Manuel George
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