WO2008012649A2

WO2008012649A2 - Apparatus for measuring the visual acuity of a person

Info

Publication number: WO2008012649A2
Application number: PCT/IB2007/002110
Authority: WO
Inventors: Alessandro Foggi; Paolo Pasquini
Original assignee: Hesp Technology Srl
Priority date: 2006-07-25
Filing date: 2007-07-25
Publication date: 2008-01-31
Also published as: ITPI20060094A1; WO2008012649A3

Abstract

An apparatus for measuring the visual acuity of a patient comprising: - a front display surface; - at least one liquid crystal screen comprising a plurality of liquid crystal cells arranged adjacent to one another in order to provide a matrix, the cells having electric contacts for applying an electric field to the liquid crystal; - a control circuit for operating singularly the cells; - a light source adapted to backlight the screen opposite to the surface. The control circuit produces a first group of images at a first portion of the surface and a second group of images at a second portion of the surface. Furthermore, at least one polarized film is arranged between the screen and the surface only at the second portion, whereby the second group of images appears on the display surface at the second portion in polarized conditions for visual acuity tests. This way, it is possible to have high performances of the liquid crystal screen for first portion, obtaining the same quality of image achieved in case of optometric examinations not involving polarized images, reaching in the meantime a maximum quality also for the second portion that in case of optometric examinations involves polarized images. The apparatus is thus highly flexible for carrying out a wide variety of optometric examinations.

Description

TITLE

APPARATUS FOR MEASURING THE VISUAL ACUITY OF A PERSON

DESCRIPTION

Field of the invention

The present invention relates to the field of optometry and, in particular, it relates to an apparatus for measuring the visual acuity of a patient, in particular, using polarized images.

Background of the invention

As well known, a variety exists of types of ophthalmological examinations adapted to determine quantitatively the visual acuity of a patient. Such examinations allow measuring the visual performance and the amount of refractive correction necessary for optimizing the functionality of the visual system of the patient .

Usually, the steps of measuring the visual acuity are carried out through the recognition of signs or symbols, so called optotypes. A measure of the recognition ability is a value that is an inverse of the minimum visual angle that looks at two points at a distance from which the two points start to be not distinguishable any more. The symbols to be distinguished can be displayed on illuminated charts or on back-illuminated boards; alternatively, it is possible to use an opaque screen on which the optotypes are projected. Usually the symbols to be distinguished are black on bright background and can comprise capital letters, numbers, or other standard symbols such as "Albini's E" and "Landolt C", suitable for patients incapable of reading and writing, such as small children. It is also known that visual acuity is strongly influenced by photometric contrast existing between an object and its background. More in detail, if the contrast is strong, responsive to the lighting differences on the retina, even small objects can be distinguished. If, instead, the contrast is low even large objects cannot produce on the retina enough contrast to distinguish them.

The test for determining visual acuity at high contrast then involves quantifying the ability of the eye to discriminate the details of the objects. The measure is responsive to the angle under which the objects are seen at a standard distance of observation (minimum resolution angle) .

The apparatus normally comprises a projector, which allows automatically to adjust the size of the projected image versus the distance from the screen of the projector, maintaining a correct proportion responsive to the distance of the patient from the screen. This type of equipment, however, is particularly cumbersome and requires an appropriate kit of charts.

Alternatively, for displaying the visual acuity test it is possible to use a LCD screen interfaced to a personal computer that, with a suitable software, loads the frames of the visual acuity test, with the size of the symbols being suitably proportioned via software according to the distance of the patient from the test.

A problem arises with the use of a LCD display of prior art, when representing a polarized test according to a polarization standard at 45° and 135° (necessary for tests carried out with widespread computerized phoropters) . In fact, the LCD display adopts a specific polarization and the application of different polarization angles reduces both its brightness that its contrast sensitivity. In DE 19947775 an LCD display is described that adopts a line polarization method showing even lines to one eye and the lines odd to the other eye. Even if this polarization method of the LCD display allows a high flexibility, when carrying out the visual acuity test, however it shows reduced brightness and contrast, as well as the resolution of the LCD display in the polarized tests .

Summary of the invention It is therefore a feature of the invention to provide an apparatus for measuring the visual acuity of a patient, having high performances of the liquid crystal screen both in case of optometric examinations not involving polarized images and in case of optometric examinations involving polarized images.

It is another feature of the present invention to provide an apparatus for measuring the visual acuity of a patient that is highly flexible and can be used for carrying out a wide variety of optometric examinations. These and other features are accomplished with one exemplary apparatus, according to the invention, for measuring the visual acuity of a patient comprising:

- a front display surface;

- at least one liquid crystal screen comprising a plurality of liquid crystal cells arranged adjacent to one another in order to provide a matrix, said cells having electric contacts for applying an electric field to said liquid crystal cells;

- a control circuit for operating . singularly said cells;

- a light source adapted to backlight said screen from a side opposite to said surface; whose main feature is that said control circuit produce a first group of images at a first portion of said surface and a second group of images at a second portion of said surface, and that at least one polarized film is arranged between said screen and said surface only at said second portion, whereby only said second group of images appears on said display surface at said second portion in polarized conditions for visual acuity tests.

In particular, the front display surface can be obtained approaching at least two liquid crystal screens.

In this case, the first portion can for example be determined at the first liquid crystal screen and the second portion at the second liquid crystal screen.

Furthermore, each liquid crystal screen can be operated independently by the control circuit.

Advantageously, the second , group of images is effected by a measured combination of films having different polarization, whereby according to the type of polarization to which the light is subject before crossing the surface, a part of the second group of images is visible to the only right eye of the patient, a par is visible to the only left eye and a further part -to both eyes. In general, the combination of polarized films and the group of images are chosen responsive to the type of visual acuity test to carry out.

For example, the apparatus above described can be advantageously used for making examinations for measuring the visual acuity of a patient, such as polarized and dichromatic binocular balance, binocular balance, test of coincidence for aniseikonia, polarized test for phoria, test for fixation disparity, stereo test, etc.

Advantageously, the control circuit is operated remotely by a remote drive, for example by means of infrared transmission, via radio transmission, etc. Advantageously, the second portion has substantially rectangular shape with longer side double the shorter side.

In particular, the display surface and the second portion have both a rectangular shape, with the second portion that has larger side equal to the shorter side of the display surface and shorter side equal to the half of it.

Advantageously, the liquid crystal screen may be selected from the group comprised of:

- screen with 16:9 format;

- screen with 16:10 format.

Preferably, the portion adapted to display not polarized images may have square shape having a side equal to the shorter side of the original rectangular surface. Alternatively, the portion adapted to display not polarized images may have a ratio 4:3 between its sides, with lower side equal to the shorter side of the original rectangular surface. Brief description of the drawings

The invention will be now shown with the following description of an exemplary embodiment thereof, exemplifying but not limitative, with reference to the attached drawings wherein: - Figure 1 shows diagrammatically in an exploded view an elevational side view of an apparatus for measuring the visual acuity of an patient, according to the invention;

Figure 2 shows diagrammatically an elevational front view of an element of the apparatus of figure 1; - Figures from 3 to 13 show diagrammatically some possible frames obtainable with the apparatus of figure 1 to carry out optometric examinations of a patient;

Figure 14 shows diagrammatically an elevational front view of an exemplary embodiment of the apparatus of figures 3-13;

Figure 15 finally shows a possible polarization filter used by the apparatus of figure 1. Description of preferred exemplary embodiments

In figure 1 the main elements are diagrammatically shown in an exploded view involved with an apparatus 1, according to the invention, for measuring the visual acuity of a patient 20. It comprises essentially a front display surface 10 on which different images are in turn projected depending on the type of analysis to carry out. The display surface 10 can correspond to the surface of a LCD screen of known type, or alternatively, it is obtained by approaching two or more LCD screens, for example 17 inch screens. As well known, an LCD screen comprises a liquid enclosed in a plurality of cells 2a-2n arranged adjacent to one another in order to form a matrix (figure 2) . Each cell 2a-2n has electric contacts, not shown in the figure, in order to apply a determined electric field to the liquid that it contains. Cells 2a-2n are contained between two glass sheets 3 and 4. Behind glass sheet 3 a backlighting source is arranged adapted to cross the matrix of cells 2a-2n with white light, for example a fluorescent lamp 5. Cells 2a-2n are operated singularly by a control circuit 15, which for example can be operated remotely by a remote drive 40, in order to display on surface 10 a wide variety of high resolution images after having crossed at least one polarized film 50. Through control circuit 15 a first group of images 101 at a first portion 11 of surface 10 and a second group of images 102 at a second portion 12 of surface 10 same (figures from 3 to 9) are produced. More in detail, film 50 for example polarized at 45 or 135 degrees, is arranged only at portion 12, so that only in this portion it is possible to display polarized images 102, whereas the other portion 11 of surface 10 can be used for displaying not polarized images 101. This way it is possible to carry out on a same liquid crystal screen both diagnostic tests of traditional type, which do not require the use of polarized images, and diagnostic tests, such as monitoring binocular functions, for which instead it is necessary to use polarized images, without affecting minimally the optical resolution of the liquid crystal screen versus potentiality of brightness and contrast in portion 11 adapted to receive not polarized images 101. If surface 10 is obtained by approaching two or more LCD screens, control circuit 15 can operate each screen independently.

In figures from 3 to 11, the liquid crystal screen has rectangular shape and precisely has a 16:9 format. In this case portion 11 adapted to display not polarized images may have square shape having a side equal to the shorter side of original rectangular surface 10. Alternatively, portion 11 may have a ratio 4:3 between its sides, with shorter side equal the shorter side of original rectangular surface 10. The first group of images 101, for example a plurality of "Albini's E" with different orientations (figure 3), is given at portion 11. Instead, as diagrammatically shown in figures from 4 to the 11, group of polarized images 102 is displayed in portion 12 of surface 10. Depending on the type of polarization, at 45° or 135°, of films 50 and on the different combination chosen, on portion 12 zones are made that are displayed only to the right eye, dashed lies in figures, zones are made that are displayed only to the left eye, continuous lines in the figures, and zones displayed to both eyes.

In figure 15 for example a polarization filter 200 is shown that can be used in the apparatus 1 in combination with determined templates in order to provide different polarized images according to the type of analysis to carry out. In particular, polarization filter 200 has areas 210 displayed to the only right eye, areas 220 displayed to the only left eye and areas 230 involving both eyes. This way, with a single filter it is possible to carry out a high number of known tests for optometry simply changing the images 102 and 103 to display, as described hereafter with reference to the examples from 1 to 8 where some among possible tests for evaluating the visual acuity of a patient operable with the apparatus according to the invention are described in a not limitative way.

Example 1

With reference to figure 4, a polarized and dichromatic binocular balance test is made as described hereafter. To the right eye of a patient 50 a rhombus 111 with number 9 and a rhombus 112 with number 6 are displayed, whereas to the left eye a rhombus 113 with number 3 and a rhombus 114 with number 5 are displayed. To both eyes a not polarized frame 115 is instead visible. This has the function of fusional recollection because the test is very dissociating and it allows to align better the visual axes on the sights. In this way a binocular monitoring is carried out and an accommodation effect is avoided. An- ophthalmologist will apply a correction on the right eye and on the left eye up to when both eyes see with the same clarity the vertical and horizontal numbers. Example 2 With reference to figure 5, a binocular balance test for analysis of the final balancing of the binocular refraction is made as described below. The right eye is capable of displaying a first line of letters 116, whereas the left eye displays a second line 117. By using the polarization the patient looks at the same time at the two lines but one with the right eye and one with the left eye in order to carry out a simultaneous comparison between the images displayed separately from the two eyes. In these conditions the ability of the visual system to determine minimum differences of clearness is very high. The presence of a possible central not polarized line allows an examination in binocular conditions bringing the images to melt . Example 3

With reference to figures 6 and 7, a test for evaluating aniseikonia, i.e. the difference of size or shape between the two ocular images of which the visual system has conscience, can be carried out as described hereafter. The patient 20 looks with an eye at a semi perimeter 118 of figure 102, with the other eye at the other half 119 and with both eyes a point of fixation 120 that is a strong attraction for fusion. In case of aniseikonia the patient 20 sees a semi perimeter larger than the other. Aniseikonia can be determined quantitatively with suitable lenses. Example 4

With reference to figure 8, a test for .measuring dissociated phoria provides an image 102 comprising vertical lines 123 and 124 displayed to the right eye and horizontal lines 121 and 122 displayed to the left eye of a patient 20. Patient 20, in case of etherophoria sees a full cross with aligned arms. If, instead, the patient 20 looks at vertical arm 123-124 of the arrow of the arrow displaced on the right side (esophoria) or left side (exophoria) with respect to the horizontal reference centre, a horizontal phoria is seen. If, instead, the patient 20 looks at horizontal arm 121-122 of the arrow displaced up (hyperphoria) or below (ipophoria) with respect to the horizontal reference centre sees a vertical phoria. Example 5

With reference to figure 9, a test for measuring an associated phoria, or fixation disparity, provides an image 102 comprising a vertical rod 124 and a horizontal rod 125 displayed to the right eye and a vertical rod 126 land a horizontal rod 127 displayed to the left eye of the patient 20. Both eyes, furthermore, look at a central not polarized point 130. Central point 130 is seen binocularly and represents a fusional central attraction whereby the test is not dissociative. The patient 20 sees the bars of the cross perfectly aligned in case of orthodisparity, otherwise the classification of the fixation disparity is carried out in esodisparity and exodisparity according to the movement in the horizontal plane, hyperdisparity or hypodisparity in- the vertical plane .

Example 6

With reference to figure 10, a test for checking the presence of stereopsis, for determining the perception of the three-dimensionality of objects in space, provides an image 102 comprising a couple of bars 131 and 134 displayed to the right eye and a couple of bars 132 and 133 displayed to the left eye. A central not polarized dot 135 is then present having the function of sight of fixation. The principle on which the test is based is to project on the retina, with respect to the point of fixation 135, images similar but with a slight disparity, whereby, if they are displayed separately, but at the same time to both eyes both eyes and are then fused, they are displayed distant in the spaces with respect to the point of fixation. If the stereoscopic monitoring is correct the patient sees up a single bar displaced forward with respect to the point of fixation 135 and sees down a bar displaced back with respect to the point of fixation. Example 7

With reference to figure 12, a test for checking the "fixation disparity of type one", also called "Zeigertest", provides an image 102 that resembles a clock face and that comprises four bars, two vertical bars 141 and 143 and two horizontal bars 142 and 144, displayed to the right eye and four groups of segments of different lengths 151-154 arranged at hour 12, hour 3, hour 6 and hour 9, displayed to the left eye. A central element is then present, for example a dot or a ring 140 not polarized that represent a strong fusional attraction. The patient with fixation disparity of type one sees a shifting between the rods 141-144 and the groups of segments 151-154 corresponding. Example 8

With reference to figure 1,3, a further test for checking the binocular balancing, known as Cowen test, can be made through image 102 comprising four frames, two green 163 and 164 displayed to the left eye and two red 161 and 162 displayed to the right eye, on each of which two concentric rings 171 and 172 are provided.

The foregoing description of a specific embodiment will so fully reveal the invention according to the conceptual point of view, so that others, by applying current knowledge, will be able to modify and/or adapt for various applications such an embodiment without further research and without parting from the invention, and it is therefore to be understood that such adaptations and modifications will have to be considered as equivalent to the specific embodiment. The means and the materials to realise the different functions described herein could have a different nature without, for this reason, departing from the field of the invention. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

Claims

1. Apparatus for measuring the visual acuity of a patient comprising:

- a front display surface; - at least one liquid crystal screen comprising a plurality of liquid crystal cells arranged adjacent to one another in order to provide a matrix, said cells having electric contacts for applying an electric field to said liquid crystal cells; - a control circuit for operating singularly said cells;

- a light source adapted to backlight said screen from a side opposite to said surface; characterised, in that said control circuit produces a first group of images at a first portion of said surface and a second group of images at a second portion of said surface, and that at least one polarized film is arranged between said screen and said surface only at said second portion, whereby only said second group of images appears on said display surface at said second portion in polarized conditions for visual acuity tests.

2. Apparatus, according to claim 1, wherein said second group of images is displayed by a measured combination of films having different polarization.

3. Apparatus, according to claim 1, wherein, said front display surface is obtained approaching at least two liquid crystal screens.

4. Apparatus, according to claim 3, wherein each of said liquid crystal screens is operated independently by said control circuit.

5. Apparatus, according to claim 1, wherein said at least one film has a polarization selected from the group comprised of: - at 45 degrees;

- at 135 degrees;

- a combination thereof.

6. Apparatus, according to claim 1, wherein said control circuit is operated remotely by a remote drive, in particular, by means of infrared transmission.

7. Apparatus, according to claim 1, wherein said second portion has substantially rectangular shape with longer side double the shorter side.

8. Apparatus, according to claims 1 and 7, wherein said display surface and said second portion have rectangular shape, said second portion having larger side equal to the shorter side of said second portion and the shorter side equal to half of it.

9. Apparatus, according to claim 1, wherein said liquid crystal screen is selected from the group comprised of:

- screen with 16:9 format;

- screen with 16:10 format.

10. Apparatus, according to claim 1, wherein said liquid crystal screen has a portion adapted to display not polarized images with shape selected from the group comprised of:

- square shape having a side equal to the shorter side of the original rectangular surface; - rectangular shape with ratio 4:3 between its sides, with shorter side equal to the shorter side of the original rectangular surface.