Optical stimulation of the human eye

According to the invention, the eye of the subject is lit with light from the non-visible spectrum (infrared light) in such a way that its image, taken with an infrared camera, is of sufficiently high-contrast for an evaluation, so that the actual line of sight can be calculated from the picture based on the characteristics of the eye and that, proceeding from the determined line of sight, the coordinates of the coming optical stimulation can be adjusted in such a way that the intended retinal area is stimulated.

FIELD OF THE INVENTION

The invention concerns a procedure and an arrangement for the optical stimulation of the human eye by projection of light patterns on the inside of a perimeter hemisphere.

BACKGROUND

Optical stimulation systems that use a spatially fixed coordinate system are known. In the known systems the viewer directs his gaze to a defined visible point in the coordinate system. Under this condition, light stimuli are presented in pre-defined spatial relation to the coordinate system, and the point of fixation. Visible stimuli are projected on a flat or spherical surface, or light sources integrated into the surface may be activated as testing stimuli.

It is known from eye physiology that spontaneous eye movement occurs even when the tested subject deliberately fixedly stares at a fixation point. The angular deviations from the fixation point arising from unintended eye movement can usually be ignored for diagnostic purposes because of their small size.

The current procedures have the disadvantage that testing stimuli are presented in a position relative to the fixation target and not relative to the actual point of fixation. The measured data may therefore be unusable and the examination process is delayed by the need to repeat test stimuli to which responses are deemed unreliable.

The reasons for poor fixation can be of a subjective or objective nature. A typical subjective reason is positive malingering, the simulation of an illness or an impairment by the examined person. Less frequent is negative malingering in which the examined person tries to hide an impairment of the visual field.

Most problems with poor fixation are due to objective reasons: The patients are either not cooperative (small children, psychically ill people, mentally impaired) or have visual field defects already (for example central scotoma), in which case central fixation is not possible. Such patients can therefore not be diagnosed with common methods of examination that are based on the use of a perimeter with fixed coordinates of the optical system.

DESCRIPTION OF THE INVENTION

The invention provides a procedure and arrangement that makes it possible to determine the actual line of sight of the examined person relative to the coordinates of the optical system in such a way that the intended retinal areas can be optically stimulated regardless of the eye movement.

According to the invention, it is intended that during the procedure for the optical stimulation of the human eye by the projection of light pattern on the inside of a perimeter hemisphere that

the test stimulus light pattern is projected on the perimeter hemisphere with the help of a light source, an aperture arrangement, a lens arrangement and a light distributor and

the position of the test stimulus light pattern on the perimeter hemisphere follows the line of sight of the eye.

In a preferred embodiment of the procedure the light patterns are computer controlled and generated and are adjustable in brightness, color, geometry and time.

In the procedure, according to the invention, the coordinate system of the perimeter constantly follows the actual line of sight of the viewer, so that the intended areas on the retina can always be optically simulated, regardless variations in fixation.

The invention prevents interruption of the perimeter examination due to poor fixation, and is thus an improvement over common methods.

The invention furthermore concerns an arrangement for the stimulation of the human eye by projection of light patterns on the inside of a perimeter hemisphere in which methods are available for the determination of the line of sight of the examined eye during the projection of the light patterns on the perimeter hemisphere.

A preferred method for the determination of the line of sight utilizes an infrared light source and an infrared sensitive camera with digital image processing.

In a further embodiment of the invention the light distributor includes a multi mirror device a D-ILA arrangement, a rotating scanner, a galvano mirror scanner or a combination of these principles.

In the arrangement according to the invention a flat or curved surface is positioned in the field of vision of the viewer. Optical stimuli are provided at pre-defined points with suitable light sources in such a way that they stimulate the intended areas on the retina in their optical projection. The eye movements are captured with a camera and the actual line of sight is determined from the information on the image. Proceeding from the actual line of sight the points of stimulation are then placed on the projection area in such a way that they are positioned relative to the actual point of fixation.

This has the advantage that because of the constant monitoring of the line of sight and the following of the optical system to the change in the line of sight, the desired retinal areas are always stimulated even with movements of the eye. This is an advantage, especially in regards to the reliability and objectivity of the method, even with cooperative patients that are willing to maintain fixation but are not able to do so for physiological reasons. The essential contribution can be seen in the fact that it is still possible to achieve useful diagnostic field results with patients who subjectively or objectively do not maintain fixation. All current methods that utilize a fixed fixation target fail in this area.

DETAILED DESCRIPTION OF THE DRAWINGS

As shown in FIG. 1 the patient sits in front of a perimeter hemisphere 1 , in which a stimulation pattern, generated by the computer 6 , is projected from a lighting system 2 . The lighted pattern produces responses, typically in the EEG of the examined person. The EEG is captured from the skin of the head of the patient with the help of an EEG electrode system 3 , amplified in an amplifier 4 and digitized with an analog-digital converter 5 . The EEG is analyzed and evaluated in the digital form in the computer 6 .

It is of crucial significance for the success of the examination, that only the desired retinal areas are stimulated at all times. As shown in FIG. 2 , the examined person must focus his view on the fixation point BR 1 , so that the light stimuli coming from the stimulation points SP 1 and SP 2 impinge upon the desired area on the retina. If the gaze is not fixated on BR 1 and the examined person changes the line of sight, the stimulation points SP 1 and SP 2 follow the actual line of sight (fixation point BR 2 ) in order to guarantee the desired stimulation parameter.

For this purpose the eye is illuminated with an infrared light source 7 in such a way that its picture, taken with an infrared camera 8 , is of sufficiently high-contrast for an evaluation. Following the digitization in a picture digitizer 9 , the picture is evaluated in the computer 6 and the actual line of sight is determined. Afterwards, the fixation point is brought from the initial (BR 1 ) to a new position (BR 2 ) and the stimulation points SP 1 and SP 2 are spatially moved accordingly (SP 1 and SP 2 ). That way it can be guaranteed that the planned retinal areas are always stimulated, even with eye movement.