Field of the invention
The invention relates in general to medical devices for eye diagnostics,
in particular, to illuminating means for examining the eyes.
The technical problem solved by the present invention is to design
a light source in a diagnostic lamp for slit illumination to provide a uniform illumination
across the entire slit surface. Besides, when regulating the intensity of the illumination,
the light source shall not change its colour. In addition, the solution of the illumination
shall ensure that the consumption of electric energy is small and that heating of
the slit illuminator is as small as possible. The design of a light source should
be such as to allow building-in into portable slit lamps.
Background to the disclosure
Slit lamps are devices for eyes examination. A slit lamp produces
an illuminating slit with adjustable width to enable the ophthalmologist to observe
parts of the eye selectively. It is very important that the illumination is even
across the entire surface of the slit and that the intensity of the illumination
can be regulated. The ophthalmologist watches the illuminated part of the eye through
a binocular stereomicroscope with an up to 40 times magnification. The change of
colour of the illuminating light, which is needed in some examinations, can be achieved
by different colour filters.
In known solutions of slit lamps, the slit is illuminated predominantly
by a filament bulb, mostly by a halogen illuminant. Due to high consumption of electric
energy, such illuminants warm themselves, and their transportability is limited,
as well. Besides, they are sensitive and due to warming they have a short lifespan,
even less than 100 hours. As the current through the filament controls the intensity
of the illumination, the filament temperature is changing with the intensity, causing
the colour of the light to vary, that can be very disturbing for the user of the
slit lamp. For examination of eyes mostly a slightly bluish light is desired, that
is produced by the filament at a high temperature, which means at high intensity
of the light.
A uniform illumination of individual parts of the eye can be achieved
by a Koehler illumination technique, using condenser optics to image the filament
through a slit onto a rear objective, where an image of the filament appears. The
rear objective images the light slit onto the eye. To protect the eye against heat
injury that can be caused by the infrared light, an infrared filter is built-in
after the slit.
In the patent US 4,699,482, the illumination using optical fibers
is described. The illumination by means of modulators of light composed of chip
components with liquid crystals is described in the patent US 5,943,118. By the
solution from US 4,699,482 a sufficient evenness of illumination cannot be achieved,
while in the solution according to US 5,943,118, a halogen bulb or a similar light
source is used. According to patent US 6,409,346 the illumination of the slit is
solved by several diodes or diode chips, which do not enable a satisfactory uniformity
of the slit illumination.
Beside white light, colour light is also used in slit lamps, especially
blue and green light, which is produced by inserting adequate filters into the illuminating
light beam. The colour is determined by the type of filter or by several filters,
which complicates the construction as well as the use of the device.
Description of the invention
The essential feature of the slit lamp with a light emitting diode
(LED) according to the invention is in that the control circuit 8 controls the light
source 1, the light source being either a white LED or a LED with adjustable colour
that lights through condenser optics 2, a slit 3, and a rear objective 4, and through
a prism or a mirror 6 onto the eye, where a slit image 7 is produced. The control
circuit 8 enables regulation of the intensity of the light emitted by the LED and
ensures a correct ratio between the voltage across the LED and the current flowing
through the LED.
A slit lamp with light emitting diode according to the invention is
explained in detail by means of figures showing:
- Figure 1 -
- a block diagram of the slit lamp with a white LED
- Figure 2 -
- a block diagram of the slit lamp incorporating a white LED with integrated condenser
The light source 1 in the slit lamp according to present invention
(Figure 1) is a white LED that is controlled by the control circuit 8. The patient's
eye is illumined by a white illuminating slit that is produced as an image 7 of
the slit 3 by means of Koehler illumination technique. This means that the phosphorescent
surface of the LED is projected through the condenser optics 2 onto the rear objective
4 that makes an image of the slit 3 through a prism or a mirror 6 onto the eye.
In this way an evenly illuminated image 7 of the slit 3 is formed on the inspected
A white LED is a small impedance load therefore small changes of voltage
across the LED can cause big changes of the current flowing through it. Consequently,
the current must be regulated precisely across the whole range of the operation
of the LED. In the slit lamp according to the invention a correct ratio between
the voltage across the LED and the current flowing through the LED is ensured by
means of the control circuit 8, which also takes care for the desired changing of
the light intensity. The intensity of the light emitted by the phosphorescent surface
of the LED is regulated by means of the pulse width of the current that has a fixed
frequency and amplitude, and can be adjusted in the range from 0 to 100 % of the
maximum intensity. The colour of the light does not vary with the intensity of the
In the second embodiment of the invention, the light source of the
slit lamp is a white LED 11 having the condenser optics integrated in the LED 11.
In the third embodiment of the invention, the light source of the
slit lamp is a LED emitting simultaneously a red, a green, and a blue light. By
adjusting the intensity of individual light components, optional colour of the slit
image 7 can be produced on the eye. So, for coloured illumination of the eye, the
colour filters, which must otherwise be inserted into a white illuminating beam,
are not needed.
With the slit lamp according to the invention incorporating a white
LED, the examination of the eye is improved and facilitated as the illuminating
slit on the eye is white and has even distribution of light across its surface,
and because the colour of the light beam does not change with the light intensity.
The advantage of the slit lamp according to the invention is also in a prolonged
time between maintenance procedures as the lifespan of a LED is much longer than
the lifespan of a halogen bulb. Besides, due to lower energy consumption the slit
lamp according to the invention is suited for portable construction.
By applying light emitting diodes as light sources in slit lamps,
the time between maintenance procedures can be extended considerably, even up to
1000 times. An important consideration is also several times lower energy consumption
as compared to halogen light sources. Smaller energy consumption also means that
the heating, which is generally not wanted, is smaller too.
A LED light source in the slit lamp has some other advantages as compared
to filament bulbs or halogen illuminants. No special filters are necessary for infrared
radiation as in the case of a hot filament bulb. The LEDs are cheaper than special
halogen illuminants that must be applied in slit lamps, therefore the devices with
LEDs are cheaper and require lower maintenance costs. As the energy consumption
of the LEDs is low, the portable slit lamps can be used for longer periods of time
without intermediate charging, which is an important gain for the fieldwork.