Optics: eye examining – vision testing and correcting – Eye examining or testing instrument – Objective type
Reexamination Certificate
2000-11-29
2001-10-09
Manuel, George (Department: 3737)
Optics: eye examining, vision testing and correcting
Eye examining or testing instrument
Objective type
Reexamination Certificate
active
06299310
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a luminous intensity detection and control system for slit lamps and slit lamp projectors.
PRIOR ART
Slit lamps or slit lamp projectors have become known which consist of a microscope and a pivotable illuminating system, which generates a slit image. They serve the purpose of an enlarged observation of the eye and its environment. Inter alia such solutions have become known in which the optical system of the slit image projector is, so to speak, an improvement of the slit image projects so far common. There the attempt was made for the first time to merge the optical condenser system with the optical lens system so as to form a highly efficient unit. The condenser serves the purpose of projecting the image of the bulb filament onto the lens or the exit prism, respectively. It is the function of the lens of the lamp to project the slit and iris diaphragm into the axis of rotation of the device, i.e. onto the eye. Furthermore, these devices comprise the following components: the lens with reflecting prism for projecting the slit and iris diaphragm, a variable aperture stop, certain variable filter systems, compensating glass flat as well as the body and the mechanical adjusting system.
The objective of the developments of slit lamps has so far been characterised by the achievement of the following properties in application:
excellent imaging quality,
accommodation-free observation,
several magnifying stages,
slit lengths suitable for optical change-over,
series-produced eyepieces for spectacle wearers,
excellent slit images on account of carefully matched aperture and light conditions,
high illuminating intensity and constant luminance,
survey viewing at diffuse illumination with a ground or frosted glass adapted to be pivoted in front of the system,
pin-sharp slit images from the front surface of the cornea up to the rear surface of the lens due to an exchangeable prism head with a variable aperture.
From the German Patent DE 195 39 371 A1 an imaging optical device is known which serves the purpose of providing a novel enlarging or reducing optical device displaying improved characteristics, which, even in observation through turbid media, creates an image of the object which is as contrasty and non-glaring as possible so that-individual details will become visible. The luminous intensity of the device and the resolution achieved with the device are very high. A device for preventing the eye under examination and to be exposed to an excessively high load by an excessive light radiation and for signalling such a condition is not envisaged.
From the German Patent DE 42 27 942 C2 a slit lamp illuminating device is known which serves to project a slit diaphragm into a target plane and which comprises the following constituents:
a light source, preferably with a high intensity, which a fibre-optical light conductor disposed downstream,
a slit diaphragm downstream of the exit surface of the light conductor at a small spacing therefrom, without optical elements connected therebetween,
an imaging means connected downstream of the slit diaphragm and comprising at least two optical systems producing each a converging optical effect,
whereof the first one is so dimensioned that an image of the exit surface of the light conductor is created in a plane located between the target plane and the principal plane of the optical system next to the image, and wherein a collimation of the optical path for slit diaphragm imaging takes place simultaneously with the first optical system,
whilst the second optical system causes the collimated optical path for slit diaphragm imaging to be focussed into the target plane, which results in a complete exploitation of the numerical aperture of the fibre-optical light conductor by the imaging means.
A means for avoiding overload with the illuminating light and for signalling this condition is not envisaged here either.
The European standard DIN EN ISO 10939 regulates, inter alia, the demands on slit lamps and slit lamp projectors. In Section 4 of that standard specifies the requirements and Section 4.4 defines particularly the demands in terms of a hazard created by optical radiation in slit lamps. There threshold levels are defined and in Section 4.4.4 the following requirement is determined specifically: “The manufacturer must provide the user with a graph which shows the relative spectral radiation intensity emitted by the slit lamp in the range from 305 nm to 1,100 nm for the case that the instrument will be operated at maximum luminous intensity and at a maximum aperture value. The emitted spectral radiation intensity must be specified for the cone of light rays after the latter's exit from the instrument.
The manufacturer is bound to specify to the user the values of the spectrally weighted photo-chemical radiant intensity and of the source of radiation for both the phakic eye L
B
and the aphakic eye L
A
. These values must be determined in the cone of light rays leaving the instrument in the event that the instrument is operated at maximum luminous intensity and maximum aperture.”
Pursuant to this DIN standard the manufacturer is moreover required to hand out to the user accompanying documents such as directions for use which must comply also with the requirements pursuant to Section 4.4.4 of DIN EN ISO 10939, inter alia. In practical operation it is now common practice to attach appropriate diagrams which reflect, for instance, the radiation intensity versus the applied voltage. In such an approach short-term overstrain on the eye to be examined cannot be precluded. The simplest solution were a general reduction of the illuminating intensity of the slit lamps, however with the high luminous intensity of the slit projector being the main argument in particular in the application of the slit lamps.
Even though the presently applied methods and means for determining and influencing the luminous intensity on slit lamps and slit lamp projectors satisfy the requirements specified in the DIN standard, for instance, a short-term overstraining of the eye under examination as a result of an excessively high light load cannot be precluded.
The present invention is therefore based on the problem of developing a solution which permits, on the one hand, the work on the eye under examination with a high illumination level, whilst, on the other hand, damage to the patient's eye under examination with application of the slit lamp is prevented, without a general reduction of the maximum level of the luminous intensity of the slit lamp.
REFERENCES:
patent: 5098426 (1992-03-01), Sklar et al.
G. Rodenstock Instrumente GmbH
Manuel George
St. Onge Steward Johnston & Reens LLC
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