GB2457735A

GB2457735A - Method and system for the measurement of visual distortion by deformation of a pattern

Info

Publication number: GB2457735A
Application number: GB0803380A
Authority: GB
Inventors: Eddie Doyle
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-02-25
Filing date: 2008-02-25
Publication date: 2009-08-26
Also published as: GB0803380D0

Abstract

An system 30 for the evaluation of visual distortion comprising a display 34, a controller 32 and a user input device 48, the controller 32 being configured to generate a pattern 40 on the display 34 observable by the user and to deform the pattern (figures 4, 4A) according to a user defined input using the user input device 48, wherein the controller 32 is adapted to repeatedly generate a pattern 40 of predetermined dimensions for each use of the system 30, independent of the settings of the display 34. The pattern may preferably comprise a regular grid array 40, such as an Amsler grid, which may preferably be deformed in a non-linear manner (figure 4A) by said user. The repeatedly generated pattern of predetermined dimensions may preferably be achieved using anti-aliasing graphical techniques. A second independent claim specifies a system wherein a pattern comprises a plurality of user selectable points (used for the pattern deformation), whilst a third independent system claim specifies that more than one of a plurality of user selectable points may be selected at a time by the user to deform the pattern. Three independent method claims specify that use of a computer system to perform tests using the systems as specified.

Description

Method and apparatus for evaluating visual distortion

Technical field

The invention relates to a method and apparatus for evaluating and preferably quantitatively testing and measuring the extent of visual distortion in a subject.

Background to the invention

It is known to test for visual distortion, such as macular disease and metamorphosia, in a subject by making the subject observe a pattern suitable for testing for the disease and noting the perceived distortion of the pattern as observed by the subject. An example of a known suitable pattern is an Amsier grid 10 as shown in figure 1. The Amsler grid is an array that consists of a plurality of horizontal 14 and vertical 16 orthogonal axes which intersect at intersection points 12. There is a focus point 18 substantially in the centre of the pattern.

Stevens in US 5,892,570 describes an electronic interface to enable a subject to deform the Amsier grid by selecting points in the pattern that appear distorted and manipulating them until the distortion is substantially neutralised to the subject -ie the grid appears substantially orthogonal. In Figure 2, there is an example of a suitable pattern that has been distorted to nullify the distortion as seen by a subject. There is shown the grid 10, the focus point 18, the original position of a user selected point 20 the user defined position of said point 22, the dotted line 24 represents the original position and solid line 26 the user defined position of the vertical line. The user selects a point 20, which the subject perceives to be distorted and defines a new position for the point 22, so that it no longer appears distorted to the subject.

This manipulation deforms the pattern and redefines the axis from an original configuration 24 to the user defined configuration 26. The polygons defined by the axes that form the Amsier grid 10, have changed from being square to including trapezoids about the user manipulated point 20. The selection and manipulation of the individual distorted points 20, continues until such time that the pattern 10 appears substantially regular to the subject.

The manipulation of the individual points according to Stevens is time consuming and is tedious for the subject and may produce disjointed lines. Furthermore the method of recording the distortion of the array used to test for visual distortion is unsatisfactory when comparing the results between tests for a subject, or when comparing the results of a test between subjects.

Summary of the invention

To address the above and other problems of the prior art the present invention seeks to provide an improved method and/or system for determining the extent of visual distortion and in one aspect provides a method and apparatus which improves the test for visual distortion by providing a standardised measure of the distortion in the subject's eye which can be readily compared to previous results of the test and means for implementing such a test. The test is beneficially standardised in such a way that the test is identical irrespective of the display device used. In the preferred embodiment, the apparatus includes a computer system which generates and displays the pattern which can test for visual distortion, a display device that is configured to show the pattern, an input device (such as a computer mouse) that is configured by the computer system to allow the user to selectively deform sections of the pattern until such time that the subject is able to neutralise the distortions caused by the visual distortion, a form of recordable memory that records the pattern and a program that is enabled to quantitatively calculate the extent of the distortion.

A pattern with a fixation point, such as an array defining an Amsler grid, is generated by the computer, the physical size of which as displayed on the display device can be adjusted and then is set which allows for standardisation of the pattern between tests, and therefore standardisation of the test. The setting of the array size allows for the test occurring on different display devices which may be of different sizes. In preferred embodiments the setting of the scale of the array is done via user intervention though an automated scaling process may be used. The subject, focuses onto the fixation point and if the subject suffers from visual distortion the pattern will appear distorted.

A user (such as a technician, specialist or the subject) has an input device with which they can select the sections of the pattern which appear distorted and deforms the pattern until it no longer appears distorted to the subject. In the preferred embodiment the input device is a computer mouse, which selects the nearest intersection point on the grid on clicking the mouse button. The selected intersection can then be moved by holding down the mouse button and dragging the mouse. The process can be repeated for any number of other intersections until the individual vertices appear substantially regular to the subject.

In order to simplify the test for the user the number of visible lines can be reduced. This reduces the number of intersections that can be selected. There will be subpoints along the visible lines and also invisible subpoints in the spaces between lines. The movement of a visible intersection by the user can additionally cause the displacement of the surrounding subpoints by an amount less than but proportional to the movement of the main intersection and inversely proportional to the distance of the subpoint from the main intersection. Thus the movement of a visible intersection will result in a curve in the visible line. This reduces the number of deformations required by the user to substantially neutralise the visual distortion as seen by the subject thus reducing the time taken for an individual test.

Once the pattern has been sufficiently manipulated so that it appears regular to the subject, the pattern is confirmed to the computer system. If desired, the system may then display the displacement of the points. The preferred method of display, is a line to show the displacement of each intersection and a dot to show the original position, though other representations may be used. In order to quantify the visual distortion, the displacement of every point from the original configuration is calculated, which may include the displacement of subpoints both on visible lines and between them as a vector. Preferably the magnitudes of the individual vectors are then summed to produce a single figure which gives a quantifiable measure of the visual distortion, which is recorded onto the computer system, for comparison with other tests.

For validation purposes the resulting pattern may be stored and displayed to a subject who does not suffer from visual distortion. The subject would complete the test in the manner described above by neutralising any distortion seen by deforming the pattern. This would allow normal subjects to be tested for intra-and inter-subject variability in response.

Other aspects and features of the invention will become apparent from the appended claims.

Brief Descrrntion of the Drawings Further aspects, features and advantages of the present invention will be apparent from the following description of preferred embodiments, presented by way of example only, and by reference to the accompanying drawings, and wherein: Figure 1 is an example of an Amsier grid; Figure 2 is a representation of the user selected deformation of the Amsier grid in the prior art; Figure 3 is a schematic of the apparatus according to the invention used for testing visual distortion; Figure 4 is a representation of the manipulation of a single point in the invention; Figure 4a is magnified image of a section of figure 4 showing the manipulation of a single point; Figure 5 is a schematic of the method for calculating the displacement of a singular point; Figure 6 is an example of the simplified version of the Amsler grid with number of gridlines visible to the subject reduced; and Figure 7 is a schematic of the method for calculating the displacement of the sub-points.

Description of the Embodiment

Figure 3 is a schematic drawing of the apparatus 30 according to the invention as described below, though this invention can be applied to all types of computer, for example though not limited to a portable personal computer, a network of computers. There is shown a desktop computer 32, with a display unit 34, displaying a form of the visual distortion test 40, a keyboard 50, a computer mouse 48, a connection 38 to the internet 36. The desktop computer 32 generates a pattern 10, which has a fixation point 18, which is suitable for detection of visual distortion in a subject. An array such as an Amsler grid is the standard pattern used when testing for visual distortion, and therefore is shown as the preferred embodiment, though other patterns that are suitable for detecting visual distortion, may be used. Figure 1 shows an example of an Amsler grid. The Amsier grid 10 consists of a plurality of horizontal 14 and vertical 16 orthogonal lines, that are equally spaced, and intersect at points 12. The preferred configuration of an Amsler grid consists of 25 horizontal 14 and vertical 16 lines, thereby forming a grid of 24 x 24 (or 576) boxes of equal size, though different sized arrays may be used. The Amsler grid 10 has a central fixation point 18, which in the preferred form is smaller than the size of the individual boxes formed by the Amsler grid 10.

In order to meaningfully compare results of the test between patients or successive tests, the tests is preferably standardised. A way of standardising the test is to ensure that the pattern displayed 40 must be of the same physical dimensions independent of the diplay or device.

The pattern 40 displayed is generated by a program which preferably scales the Amsier grid by taking into account the settings of the display unit 34, such as size and resolution, to ensure the pattern displayed 40 is of the required physical dimensions. Preferably, the program uses anti-aliasing graphical rendering techniques when generating the Amsler grid to ensure that the lines appear smooth and unpixelated. Other techniques to scale and render the pattern displayed 40 on the display unit 34 may also be used.

A pattern is displayed on display unit 34, and the subject focuses on the central fixation point 18. The regularity of the Amsier grid 10 appears distorted, to the subject who suffers from visual distortion and hence the user is able to resolve the apparent distortion through displacement of one or more points on the Amsler grid 10. Figures 4 and 4a show the affect of the selection and displacement of a single point on the Amsier grid 10. There is shown the Amsier grid 10, the selected and manipulated point 54, the surrounding affected array of points 52, and the original location of the selected point 56.

A user, who may be the subject or another person instructed by the subject, has an input device such as computer mouse 48, which is configured by the computer to move a selector 42, to select a point 54 on the Amsier grid 10 that appears distorted, which in the preferred embodiment is an intersection point 12. The user places the selected point 54 in a position so that it and the plurality of chords that form the affected intersection point 58, 60, 62, 64, appear substantially straight to the subject. The extent of the deformation of the chords is calculated to provide a smooth continuous function to better accord with and model the effect of the distortion.

Figure 5 shows the relationship between the displacement of a user selected point 70 and the affected points in the vicinity of the user selected point 70. In the preferred embodiment the movement of a single intersection point affects the points in a 5x5 sub-array around it though the size of the box may be increased or decreased. In Figure 5 there is the initial position of the user selected point 72, the user defined position of the selected point 70, the displacement in the x direction (dx) between the initial and final position of the user defined point 76 and the displacement in the y direction (dy) between the initial and final position of the user defined point 74. The initial position of the intersection point immediately adjacent to the user defined point 80, and its final position 78 as determined by the displacement of the user defined point 70. The displacement of the point in the x direction (&i) 84, and the y direction (y) 82. The initial position of the second closest point in the x direction 88, its subsequent position 86 due to the manipulation of the user defined point, the displacement of the point in the x direction (X2) 92 and the y direction (y2) 90. The affected intersection points are bounded by the dotted line box 71. Intersection points 12 beyond the 5x5 sub-array (outside the dotted line box) are unaffected.

The user selects an intersection point 12 which has an initial position 72 and displaces the point to the user-defined position 70 so that the local distortion of the array as seen by the subject is substantially neutralised. The displacement of the user-selected point is described as dx 76 and dy 74. The surrounding points in a 5x5 array (including the user selected point) are preferentially displaced according to the following rules. The points move in the same direction as the displacement of the user selected point. The magnitude of the displacement of the points is determined by the position in the 5x5 array in relation to the central user-selected point. In the preferred embodiment the displacement of each point is calculated according to the formula ml/[(I (x2 + y))* 1.3], where ml is the magnitude of displacement of the user selected point, x is the number of points away from the user selected point in the x axis (to the left or the right) and y is the number of points away from the centre in the y axis (above and below). In Figure 5 the first adjacent point 78 to the user displaced point 70 in the x-axis would have a value of x=l and y=0, therefore the displacement would be given as m1/[(J (12 +02))*l.3] In a second embodiment the displacement of the user selected point is geometrical described as dx 76 and dy 74. The calculation of the non-user selected intersection point displacement for n points, where n is the number of intersection points along the chords that form the intersection point 58, 60, 62, 64 that are displaced, is as follows. If the original displacement of the intersection in the x-axis is dx 76, the initial position of the intersection point immediately adjacent to the user defined point 80, its displacement in the x direction (x) 84 is given by Lx= dxlv1, similarly the displacement of the intersection point immediately adjacent to the user defined point 70 in the y direction (Ay) 82 is given by Yi= dy/vs.

Similarly for the displacement of the second nearest intersection point from its initial position 88 to its subsequent position 86 due to the manipulation of the user defined intersection point 70, the displacement of the point in the x direction (1X2) 92 is given by tX2= dx/v2 and the y direction (Y2) 90 is given by 1y2= dy/v2. For the nth nearest intersection point along a chord from the user selected intersection point the displacement in the x axis of the point is Lx dxJv. For the function to be smooth the values of v must satisfy vI<v2< In the preferred embodiment there are two affected intersection points along the chords that form the intersection point 58, 60, 62, 64 that are displaced.

Figure 6 is an example of the variation of the number of horizontal 14 and vertical 16 orthogonal lines that form the Amsier grid 10. There is shown the Amsier grid 10 with a central fixation point 18, which consists of nine horizontal 14 and vertical 16 orthogonal lines forming a 8x8 Amsier grid 10, though other sized Arnsler grids 10 may also be produced.

Therefore between the visible horizontal 14 and vertical 16 orthogonal lines there are one or more invisible to the user sub-points. The Ainsler grid 10 would still appear distorted to a subject who suffers from visual distortion. The reduction of the number of horizontal 14 and vertical 16 orthogonal lines presents the subject with a less complicated grid and is less time consuming. In the preferred embodiment manipulation of an intersection point 54 results in displacement of a 5x5 array of sub-points in the manner as described above, so that the lines appear smooth when the user manipulates an intersection point 12, though other sized arrays of sub-points are acceptable. Such manipulation also results in displacement of the invisible sub-points (between the visible lines). The amplitude of displacement of the intersections and sub-points (both visible and invisible) can be summed to produce a single figure that represents the magnitude of the subject's perceived visual distortion.

Figure 7 shows the sub-points 104 that are invisible to the subject and user, that are between each intersection point 12 visible to the subject and user. There is shown the visible intersection points 12, that form the array. Between each visible intersection point 12 there are one or more sub-points 104 that are invisible to the subject and user. These sub-points 104 define axes that are invisible to the user. There are further invisible to the user sub-points 118 that lie along the axes defined by the sub-points 104 between the visible intersection points 12. In the preferred embodiment these invisible to the user sub-points 118 define a 2x2 array between the visible intersection points 12. A visible intersection point is displaced from its original position 102 to a secondary position 100, its displacement along the x-axis dx 112. The affected sub-points 106, 108 between the displaced intersection point 102 and a stationary intersection point 12. The original position of the affected sub-points 110, the displacement of the nearest sub-point in the x-direction 114 and the displacement of the second nearest sub-point in the x-direction 116. In the preferred embodiment the surrounding sub-points in a 5x5 array (including the user selected point) are displaced according to the following rules. The points move in the same direction as the user selected point 100. The magnitude of the displacement of the points is determined by the position in the 5x5 array in relation to the central user-selected point. The displacement of each point is calculated according to the formula m1/[(I (x2 + ?))*1.3] where ml is the distanced moved by the user selected point, x is the number of points away from the user selected point in the x axis (to the left or the right) and y is the number of points away from the centre in the y axis (above and below). Thus for example a point one to the right and 2 above the centre in the array will move m1/[('I (12 + 22))*l.3] or m112.9.

The extent of the displacement of the sub-points along a chord having n sub-points is as follows. If the original displacement of the intersection in the x-axis 112, as defined by the user is dx, the displacement of the nearest sub-point 108 to the intersection point 100 is given as Xl= dx/s1, the displacement of the second closest sub-point 106 to the intersection point is Lx2= dxls2 and the nth sub-point is x= dx/s. For the function to be smooth the values of s must satisfy S,<S2< In this embodiment there are two sub-points on the line between the intersections and the values of s1 and S2 are 1.3 and 2.6 respectively, though other values for s and the number of sub-points may be used. The displacement for the points in the y direction follows the same formula. The visible chord passes through the intersection points 12, 100 and all sub points 106, 108.

The user, continues this process until such a time that all sections of the grid appear to the subject as straight and regular. The resulting pattern is confirmed by the user to the computer, the preferred manner for confirmation is depression of the spacebar on the keyboard 50, though other methods can be used. The pattern is saved to the computer memory 46. An image representing graphically the deformation is created by the computer CPU. The displacement of every point and sub-point, from its initial configuration to the user defined configuration is calculated as a vector describing the magnitude and direction of displacement. The values of the vectors describing the displacement of the points are combined to form a single value that can be used to quantitatively measure the progress of the visual distortion in the subject. In the preferred embodiment the magnitude of the vectors are summed though other methods for forming a single value for the vector may be used. This value is saved to the computer memory 46.

Claims

Claims 1. A system for evaluation of visual distortion comprising a display, a controller and a user input device, the controller being configured to generate a pattern observable by user on the display and to deform the pattern according to a user defined input using the user input device, wherein the controller is adapted to repeatedly generate a pattern of predetermined dimensions for each use of the system, independent of the settings (such as size or resolution) of the display at the time of use.
2. A system according to claim I wherein the pattern comprises a regular array of predetermined dimensions.
3. A system according to claim 1 or 2 wherein the pattern is substantially of an area between 100cm sq and 250cm sq, more preferably in the order of 225cm sq.
4. A system according to any preceding claim wherein the pattern comprises a grid of substantially horizontal and vertical lines and preferably 25 such horizontal and vertical lines.
5. A system according to any preceding claim wherein the pattern comprises an array of between 10 x 10 and 30 x 30 regular polygons and preferably 24 x 24 squares defined by intersecting horizontal and vertical lines.
6. A system according to any preceding claim wherein the controller is adapted to use anti-aliasing graphical techniques to ensure repeatable sizing of the pattern on the display.
7. A system according to any preceding claim wherein the pattern comprises a plurality of selectable points, such as intersection points on an array of horizontal and vertical lines and a controller is adapted to effect a non-linear deformation of the pattern around a user selected point in the pattern.
8. A system for evaluation of visual distortion comprising a display, a controller and a user input device, the controller being configured to generate a pattern observable by user on a display and to deform the pattern according to a user defined input using the user input device, wherein the pattern comprises a plurality of user selectable points, such as intersection points on a grid of horizontal and vertical lines, and the controller is adapted to effect a non linear deformation of the pattern around a user selected point in the pattern upon deformation of the pattern by the user through movement of the selected point using the input user device.
9. A system according to the claim 8 wherein the controller is adapted to define points intermediate intersection points within the pattern and to determine non linear deformation of the pattern through movement of the intermediate intersection point.
10. A system according to claim 8, 9 or 10 wherein the controller selects one or more intersection points beyond the user selected point and is adapted to move these to affect apparent deformation of the pattern for the user.
11. A system according to claim 10 wherein the controller is adapted to select a symmetrical array of points around the user selected point and to effect deformation of the pattern using the selected symmetrical array of points.
12. A system according to claim 11 wherein the controller is adapted to select an array of points in the order of 5 x 5 intersection points comprising the user selected points as the centre point within the array.
13. A system according to claim 12 wherein the pattern comprises an array of points each selectable by a user using a user input device and a controller being adapted to deform the pattern by movement of one or more points adjacent to a user selected point thereby to extend the region of deformation within the pattern caused by user moving the selected point to a point or points beyond the selected point.
14. A system for evaluation of visual distortion comprising a display, a controller and a user input device, the controller being configured to generate a pattern observable by user on a display and to deform the pattern according to a user defined input using the user input device, wherein the pattern comprises an array of points each selectable by a user using user input device and a controller being adapted to form a pattern by movement of one or more points adjacent to a user selected point thereby to extend the region of deformation within the pattern caused by a user moving a selected point, through deformation of the point or points beyond a selected point.
15. A system according to claim 13 or 14 wherein the pattern comprises an array symmetrical points and the controller is adapted to select a sub-array of points symmetrically positioned around the user selected point thereby to cause deformation of the pattern beyond the selected point.
16. A system according to claim 15 wherein the controller selects a sub-array of 5 x 5 points.
17. A system according to any preceding claim whereby the controller is adapted to quantify the extent of visual distortion through deformation of a pattern using vector analysis of the points moved through a direction with the user.
18. A system according to claim 17 where the vectors describe the displacement of one or more intersection points from their initial configuration to their final user defined configuration.
19. A system according to claims 17 and 18 where the vectors describe the displacements of one or more points visible and invisible of the array to the user from their initial configuration to their final user defined configuration.
20. A system according to claims 17-19 where the resultant vectors are combined to form a single value.
21. A method on a computer system of evaluating visual distortion comprising the steps of generating a pattern observable by user on a display and enabling deformation of the pattern according to a user defined input so as to correct for the perceived distortion by the user, and further enabling repeatable generation of the pattern of predetermined dimensions for each use of the computer system, independent of the settings of the display.
22. A method on a computer system of evaluating visual distortion comprising the steps of generating a pattern observable by user on a display and enabling deformation of the pattern according to a user defined input so as to correct for the perceived distortion by the user, wherein the pattern comprises a plurality of user selectable points, such as intersection points on a grid of horizontal and vertical lines, and the method enables non linear deformation of the pattern around a user selected point in the pattern upon deformation of the pattern by the user through movement of the selected point.
23. A method on a computer system of evaluating visual distortion comprising the steps of generating a pattern observable by user on a display and enabling deformation of the pattern according to a user defined input so as to correct for the perceived distortion by the user, wherein the pattern comprises an array of points each selectable by a user using a user input device and the method enables deformation of the pattern by movement of one or more points adjacent to a user selected point thereby to extend the region of deformation within the pattern caused by a user moving the selected point.
24. A computer program product having encoded thereon computer readable instructions which instructions when implemented by a computer system enable a method according to one or more of claims 21, 22 or 23.
25. A system according to any of the proceeding claims where the results of the test are stored on some form of writeable computer memory.
26. A system according to any preceding claim wherein the controller is adapted to communicate with one or more computers in a computer network, such as the internet.