GB2114406A - Systems for the study and computation of visual fields - Google Patents

Abstract

To study and measure visual fields, a CRT displays to a patient fixation points anywhere in the field and a test stimulus movable and with brightness adjustable over 10000:1; background brightness also adjustable. Characters and graphics can also be displayed. A second CRT is provided as the practitioner's monitor. Main components of the central processor controlling the display are microprocessor (1), RAM (2) and EPROM (3) holding program, instruction decoder (4) and buffers (5, 6). Other components not shown are 9 video generator including character patterns stored in an EPROM, character memory and a clock locked to the one in the microprocessor (1); a video mixer including fixation point generator and D/A converters passing signals for setting the brightness of the best stimulus and background; and a video output amplifier combining the test stimulus, fixation point and background signals together with facilities for erasure. <IMAGE>

Description

SPECIFICATION Systems for the study and computation of visual fields The present application for Patent of Invention relates to a system for the study and calculation of the visual field, which has basic novelty features as well as considerable advantages over the actual known means, used for this same purpose.

The system of the invention (or campimeter) has been designed and constructed in a totally original manner, based on preliminary clinical studies, in which the microprocessor and clinical technology of the Medical Sciences have been applied.

Its field of application includes those medical specialities in which the visual organ is involved, such as Ophthalmology, Neurology and Neurophysiology. Its use comprises neuro-ophthalmological exploration for diagnosis purposes and experimental clinical research for scientific purposes.

The orginality of the system of the invention is due both to its concept as a physical structure and to its functionality, without any apparatus of similar characteristics existing at present.

The basic idea consists in the use of a wide surface cathode ray tube (CRT) as a campometric screen, so as to generate the background and luminous stimuli capable of provoking the positive response of the subject explored.

An original system of generation and amplification of the video signal also allows presenting, simultaneously, a background of variable luminosity which fills up the surface of the screen, the test luminous stimuli also with variable luminosity and situation, as well as the points necessary to maintain the fixation, in function of the type of exploration to be performed. This is obtained by means of a triple excitation of the cathode ray tube cathode, through an output amplifier specially designed for this purpose.

The background and test stimuli luminosity cover, independently, a range of discreet values, in a scale which allows a great resolution, ranging from a maximum to minimum light flux linear raticiof 10,000:1, enough to encompass the practical totality of the peripheric explorations.

One of the advantages derived from the use of the CRT as a campimetric screen and the video electro nix system of the invention is that it permits obtaining a great angular resolution of up to 0.2 degrees. A similar original procedure for siting the fixation points at different places of the CRT expior- able area permits extending the exploration field to peripheric areas.

The extension of this field reaches 60 horizontal and 48 vertical degrees, with a tube of ?0 diagonal inches, situating the eye of the patient 30 centi meters from the screen. For said peripherical exploration, four fixation points are sited sequentially in the angles of the screen. The subsequent composition of the explored quadrants is done automatically by programming.

Lastly, the use of a cathode ray tube as a generator of luminous stimuli permits undertaking, in an original manner, a set of exploratory techniques, such as the following: 1) Perimetry techniques 2) Acumetrytechniques 3) Optokinetics techniques ., 4) Fusion critical frequency techniques.

The achromatic and chromatic absolute threshold of the retinal sensitivity, and its topographic distribution, is determined by means of the perimetry techniques. For this purpose, on a background of zero luminosity appears the stimulus, the luminosity of which is varied from the zero level in positive increments, until it is perceived by the patient. The parameters used are the following: - Luminosity of the background: Zero value.

- Luminosity of the test stimulus: From zero until it is perceived, in discreet program-selected positive increments of value.

- Dimensions of the test stimulus: Variable, with shape and size according to program.

- Color of the test stimulus: Selectable by program.

- Point of fixation.

a) Number: 1 in 5 different positions, in function of the retina area to be explored. 4 in pericentral position for the study of the macular area.

b) Luminosity: Invariable during exploration.

The perimetry techniques also permit determining the achromatic or chromatic differential threshold, for which, on a defined background luminosity the test stimulus luminosity is varied until it is perceived due to its contrast on the background. For a given level of background luminosity, the luminosity increment of the test stimulus may be either positive or negative.

Up to the present, only thresholds for positive increments have been established. However, with the use of the CRT, according to the invention, it is possible to measure the differential thresholds with negative increments of the test stimulus, establishing in this manner a new perimetry technique.

The parameters used are the following: - Background luminosity: Adjustable between 00 and 1000 apostilbs. Program performed.

- Fixation Similar to the preceding paragraph.

- Stimulus luminosity: Variable at discreet positive or negative intervals, beginning with the value of the background luminosity, by program.

- Stimulus dimensions: Variable by program from a minimum of 0.2 square degrees.

- Stimulus color: Selectable by program.

The system of the invention automatically performs, at an optimum time, the perimetric exploration, determining the differential thresholds, of the visual field. Varying, by selection, the position of the point of fixation, the area of the visual field to be explored is selected, namely, in the middle of the screen for the central field, or in the four extreme angles for the peripheric fields.

When the central field is explored, the perimetry can be limited to a certain meridian, which is selected by convenience, depending on clinical or scientific requirements. The threshold values obtained are compared with a table of normal values stored in the computer, informing the operator of the correlation obtained.

The angular resolution can be modified at will, so as to obtain greater or lesser information of a defined area of the visual field. In cases of loss of retinal sensitivity due to pathological processes, the resolution increases at the edges of the scotoma to facilitate its delimitation.

The graphical representation is obtained in the console monitor, or by means of the printer, in the form of densities map, according to a grewy scale which represents the degree of sensitivity of the different points of a meridian or parallel.

With regard to the acumetry techniques, the system of the invention determines, automatically and interactively with the patient, the angular visual acuity of the same, using the separable minimum method. For this reason, luminous stimuli appear on the screen, the separation of which increases or decreases, until the patient sees them as a double or single stimulus, in which case the pulsator is pressed, replaying its response to the computer. This measurement of the visual acuity can be performed in any exploratory area of the visual field at will, or it can be limited to a certain meridian.

Having finished the exploration, the graph of the visual sharpness value, and its retinal topographic distribution by areas or by meridians, is obtained in the console monitor (or in the printer).

The results obtained are compared with a table of normal values stored in the computer, so as to have a statistical criterion of normality.

As to the adaptometry techniques, the system of the invention determines the values of local adaptation to light, and their retinal topographic distribution.

Using a background fixed supraumbral luminosity during a certain time produces the adjustment of the retinal photoreceptors. The readjustment of the photoreceptors to progressively decreasing luminosity stimuli determines, in time, the positive response of the patient and accumulates the value of the stimulus perceived in function of time. Adaptometry is performed by areas or by meridians, and the results appear on the screen, or on the printer, as in the other exploratory techniques, comparing them with a table of normal values.

In relation to the optokinetics techniques, the system of the invention generates on the screeen luminous fringes of variable angular separation and width which, in producing a horizontal, vertical or oblique movement sensation, release in the patient observing them the so-called optokinetics nystagmus, the positive response of which is detected visually by the reflex movement of the eyeball. An additional detection of the electro-oculographic response can be carried out from the microprocessor and periphery, permitting the valuation and registry of the ocular movements.

Lastly, as to the fusion critical frequency, the system of the invention generates on the screen intermittent stimuli of shape, size, luminosity, color and frequency controlled by programming, which measure the fusion critical frequency value in the different areas of the retina or in certain meridians, also selectable by programming. The results appear on the screeen of the monitor or on the printer, comparing them automatically, in each case, with the table of normal values.

The system offers the additional advantage of handling ease, so that the operator assisting the patient has at his disposal, in a lateral console, a video monitor and an alphanumeric manual which permits dialogue with the computer, selecting the different available options in function of the exploratory technique to be used, and observing at the same time the development of the exploratory process.

The results of any exploration appear on the screen of the console monitor in graphic or alphanumeric form, according to the previously established options.

The aforesaid console will be provided with a paper printer, which permits drawing graphs or alphanumeric characters corresponding to the data of the patient, or to the results of the exploration.

The following detailed description of the invention is read in conjunction with the accompanying drawings, which illustrate the invention merely as an example and therefore without any limitative nature.

Figure 1 is a diagram of blocks of the Central Process Unit (CPU).

Figure 2 is a diagram of blocks of a video generator circuit.

Figure 3 is a diagram of blocks of the video mixer set.

Figure 4 is an electrical diagram of the video output amplifier of the invention.

Referring initially to Figure 1 of the drawings, shown therein is a diagram of the blocks of the Central Process Unit (CPU). Said Figure shows the microprocessor -1-, the RAM -2- and EPROM -3memory modules and the instructions decoder -4-.

The monitoring, data and control channels have been buffered by means of built-in modules -5- and -6-.

As experts on the subject will understand, the microprocessor -1 - will handle the performance of the programs contained in any of the memories -2and -3-. The RAM memory-2- provides a capacity of 4 Kbytes whereas the EPROM memory -3- will have a capacity of 8 Kbytes.

The Central Process Unit will contain, in addition, the logic for the monitoring of both memory modules, decoder -4-, and the necessary doors that will allow itto operate under distributed timing with the video circuit (machine cycle fractionation of the microprocessor).

Figure 2 shows the diagram of blocks of a video generator set. Shown in said Figure is the layout of the built-in circuit -7- which is used as controller of the cathode ray tube, and which therefore has horizontal and vertical synchronism outlets. The aforesaid Figure shows, surrounding said controller circuit -7-, all the additional servicing logic thereof, among which are: - Control clock -8-, formed by a phase locked loop (PLL) and a frequency divider chain, to generate signals which are synchronized with the microprocessor clock -1-, allowing in this manner a multiplexed use of the memory gap, or space, with the latter.In this manner, without any delays or interrup tionsforthe microprocessor -1-, the CRT controller -7- acts transparently (the machine cycle of the microprocessor is divided into two parts, oneforthe microporcessor -1- and the otherforthe reading activity of the controller -7-).

- Logic of times, which configures the controller -7-, together with an initialization by prog ram of the desired scanning. Graphically, it is configured with a resolution of 340 x246 points. The set of characters necessary for the alphanumeric sweep is engraved in an EPROM memory -9-, and further contains the additional logic -10- necessary in carrying out the graphic and alphanumeric video mix for output to a second monitor, as well as the set of doors which take care of generating erase signals, graphic and alphanumeric video outputs, as well as inverse video, for two monitors, with independent control signals.

- Alphanumeric memory -11-, which provides sufficient memory space, or gap, for the programmed alphanumeric configuration.

- Various three-state "drivers" -12-and -13-, which are necessary in order to perform reading of the alphanumeric and graphic memories from the CRT controller -7-. They also permit, thanks to the distribution of the aforementioned machine cycle, reading and writing of the same memory spaces from the microprocessor -1-. The "enable" outputs of the aforesaid drivers are controlled by the video clock and by the reading/writing line.

- Lastly, the corresponding instructions decoder -14- has also been foreseen.

Figure 3 shows the diagram of blocks of a video mixer set, which handles the generating and conditioning of the different video signals for the exploration monitor of the patient. Among these signals are the following: - Generation of fixation points: This function is performed by means of the built-in circuit -15-. The fixation points generated can be freely sited at any point of the exploration area, and they are furth ermorevariable in presentation modality, thus providing the monitor the capacity for central and peripheric exploration. A special generation modality of four points sited at the edges of a square in the center of the screen permits observing scotomas in the same center of the exploration area. The modal itycontrol and presence of these points are performed by programming.

- Variation of the test stimulus luminosity: The combination of a digital/analog converter -16- and the tube response permit an excursion of the light flux of this stimulus upwards of 10,000:1. By programming, 40 points of different luminosity can be gaged between all of these values and adjusted to a logarithmic scale from 0.1 to 1,000 apostilbs. These values can, furthermore superimpose themselves on the background brightness.

- Control of background brightness: This is also performed by programming, and by means of a digital/analog converter -17-, thus permitting adjustment of a certain value of the background brightness accurately.

- Buffering: By means of the built-in circuit -18-, buffering of the horizontal and vertical synchronism impulses is carried out, as well as by the graphic video signal of the exploration monitor of the patient.

Figure 4 shows the electrical diagram of the video output amplifier. In this case, due to the special characteristics of said amplifier, we have preferred to represent a concrete performance of the same.

By means of said amplifier, electrical excitation of the exploration monitor tube cathode is carried out, and it has the capacity to convert a set of currents, suitably added up, into a cathode signal. Said currents are added up in the transistor -19-. In said amplifier can be distinguished four well-defined sections, which are the following: - Amplifier of the test stimulus: It is formed by a set of transistors -20-, -21 - and -22-. This amplifier set receives two different signals, namely, the first consisting of a voltage emanating from the test stimulus digital/analog converter -16-, which attacks the transistor -22- and is converted into a current proportional to said voltage, so that the current is injected into the transistor -21-, and commutes to the exploration graphic video speed the current produced in the aforesaid stage.

- Amplifier of the fixation point impulse: This amplifier consists of the transistor -23-, injecting maximum current to the transistor -19- when the fixation impulse appears.

- Amplifier of the background current: It is formed by the operational amplifier -24- and the vertical FET type transistor -25-. When the non-inverse input of the operational amplifier -24- receives a signal originating in the digital/analog converter -17-, a current proportional to said signal, which is injected into the transistor -19-, is generated.

- Erase transistor: It consists of the transistor -26-, and its function is to displace the current injection into the transistor -19- in the presence of the erase impulses.

The above-described set has a series of advantages over the heretofore-known systems, among which the following stand out: - Interactivity between patient and doctor: For this purpose, it will have an adequate keyboard, or manual, preferably with 24 keys, with a high level functional allocation, as well as two cthode raytubes so as to establish dialogue with the doctor and the exploration work in the patient. The doctor's monitor can showsimultaneouslythe data in an alphanumeric and graphic manner, whereas the patient's moni torwill operate preferably in a graphic manner.

- Simple to operate: It is determined principally by the aforesaid work routine and direct programming to the keyboard, or manual, and by automatic monitoring of the patient's response. Once the work procedure has been selected, intervention of the doctor is practically unnecessary.

- Versatility: Since the whole electronics of the equipment is modular and will be set up on plug-in cards, the equipment can perform different types of work and calculation simply by adding programming modules.

- High angular resolution: The graphic sweep furnishes within the exploration area 340 horizontal by 240 vertical points, which presuppose a total of approximately 87,000 points, implying a resolution limit of 0.2 square degrees.

- Printing of results: The result of the exploration, as well as the data required by the doctor, can be printed automatically and graphically at the end of said exploration.

- Communication capacity: It has the possibility of transmitting data or results to a central computer by means of an adequate interphase system.

- Low maintenance and repair cost: Since the whole electronics of the system is modular, replacement of a card is an easy and fast task. By means of a programming module with diagnosis routine, the damaged area or circuits can be easily identified. In many cases, technical assistance in the repair of certain breakdowns is not necessary.

Although certain preferred embodiments of the present Patent of Invention have been herein described in order to illustrate the principles of the invention, it will be understood that multiple detail variations, likewise protected, which might affect the parts of the set, type of components used, or any others, can be effected without departing from these principles.

Claims (4)

1. - A system for the study and computation of the visual field, applicable for purposes of diagnosis and experimental clinical research in the field of ophthalmology, neurology and neurophysiology, the system being characterized as including: - A Central Process Unit (CPU) provided with an appropriate microprocessor (1) for the performance of the programs contained in the memory modules of the RAM (2) and EPROM (3) types, an instructions decoder (4) and means (5,6) to buffer the monitoring, data and control channels.

- A video generator system, which comprises a built-in medium (7) for the control of a cathode ray tube, provided with outlets for horizontal and vertical synchronisms, and in which, as a servicing logic of said cathode ray tube controller, have been provided: a) a control clock (8), forming a phase locked loop (PLL) and a frequency divider chain, which generates signals synchronized with the microprocessor clock (1) of the CPU; b) times logic, which configures the aforesaid control medium (7), together with an initialization by programming in the desired scanning, or sweep, and which graphically is configured with a resolution of for example, 340 x 256 points, whereas in the alphanumeric sweep, or scanning, the necessary set of characters is engraved in a memory (9), for example of the EPROM type, having further to the additional logic necessary for the graphic and alphanumeric video and inverse video mixture, for two monitors, with independent control signals; c) alphanumeric memory (11) for the programmed alphanumeric configuration ; d) threestate drivers (12, 13) for reading of the alphanumeric and graphic memories from the controller medium (7) of the tube and for reading and writing of the same memory spaces from the microprocessor (1), and e) the necessary instructions decoder (14).

- A video mix set, in charge of generating and conditioning the different video signals for the exploration monitor of the patient, and capable of performing the following functions: a) generating points of fixation, by means of a built-in module (15), which can be freely sited at any point of the exploration area and variable as to the presentation modality; b) changing the luminosity of the test stimulus, permitting by means of the combination of a digital/analog converter (16) and the tube response, an excursion of the light flux value of the stimulus upwards of 10,000:1; c) controlling the background brightness, by programming, by means of a digital/analog converter (17), thereby permitting adjusting accurately a certain value of said background brightness, and d) buffering the horizontal and vertical synchronism impulses, as well as the graphic video signal of the patient's exploration monitor by means of a built-in module (18).

- a video output amplifier for electrical excitation of the aforesaid exploration monitor tube, which has the capacity to convert into a cathode signal a set of currents suitably added up by means of an adequate transistor (19).

2. - A system, as defined in claim 1, and further characterized since in the aforesaid video output amplifier have been provided four differential sections, the functions of which are as follows: i) Amplification of the test stimulus, for which have been provided a set of three transistors (20 to 22) which receive two different signals, the first one comprising a voltage originating in a digital/analog converter (16) which attacks a transistor (22) and is converted into a current proportional to the former, with this current injected into the adding transistor (19) thus determining the stimulus brightness, whereas the second signal attacks the emitter of another transistor (21) and commutes to the speed of the exploration graphic video the current produced by the first signal.

ii) Amplification of the point of fixation impulse, by means of a transistor (23), which injets maximum current into the excitation transistor (19) of the tube cathode.

iii) Amplification of the background current, by means of an operational amplifier (24) and a transistor (25) of the FET type, for which a signal emanating from a digital/anaiog converter 2/3(17) is converted into a current proportional to the former, which is injected into the excitatortransistor (19) of the tube cathode.

iv) Erase section, comprising a transistor (26) which displaces the current injected into the excitatortransistor (19) ofthetube cathode when erase impulses appear.

3. - A system, as defined in the preceding claims, and further characterized by an angular resolution limit of 0.2 square degrees.

4. - A system for the study and calculation of the visual field, the system substantially as herein described with reference to the accompanying drawings.