ITPD20110307A1 - KIT FOR THE DETERMINATION OF THE CURVE OF THE SENSITIVITY TO THE CONTRAST OF AN INDIVIDUAL - Google Patents

Description

TITLE

KIT FOR DETERMINING THE CURVE OF THE

SENSITIVITY TO THE CONTRAST OF AN INDIVIDUAL

DESCRIPTION

This patent relates to optotypes or optotype tables for the diagnosis of vision defects and in particular concerns a new kit for determining the contrast sensitivity curve of an individual, comprising at least one optotype and at least one graph, table or card. evaluation related to said optotype.

When we talk about vision or sight measurement, we usually immediately think of "visual acuity or visus" which is measured in tenths using tables with black symbols on a white background (letters of the alphabet, numbers, figures, animals, etc.)

These tables are commonly called optotypes, meaning by optotype a graphic representation of symbols such as letters, numbers, objects or other. These tables give information on the central vision of an individual in conditions of maximum contrast, but do not allow to understand the spatial relationships between objects or the visual functionality in situations where the contrast or luminance between objects changes.

This implies that sometimes, even in the presence of perfectly normal visual acuity, the visual function can be considerably compromised precisely due to a poor ability to recognize adjacent objects whose brightness difference is reduced.

The contrast expresses the difference in brightness between two contiguous objects, the sensitivity to contrast is the inverse of the contrast and is the ability to perceive this difference in brightness.

The measure of "Contrast Sensitivity" quantifies the ability to recognize objects in situations of low contrast, that is the ability of an individual's eye to perceive the smallest difference in brightness between two adjacent regions of the visual field, or between a object and the background of the object or between two objects.

The smaller the difference in brightness that the eye can perceive, the greater the sensitivity to contrast.

To determine and evaluate the sensitivity to contrast in a subject there are various methodologies, but mainly two methods of investigation are used.

The first methodology uses optotypes showing symbols or characters of constant size, for example letters, drawn on a support or table, which present a progressively decreasing contrast with respect to the background of the table.

The minimum contrast value at which a symbol is perceived by the subject measures the sensitivity to contrast.

The second method, more precise and accurate, involves the use of sophisticated computerized equipment, which uses grids usually formed by light and dark bars.

The various lattices are distinguished from each other by:

1- the different spatial frequency, i.e. for the different number of bars included in a degree of visual angle, in relation to the size of the stimulus and the distance between the subject and the stimulus and

2- for a different contrast.

Since the ability to perceive a certain minimum contrast value varies according to the angular dimensions of the stimulus, i.e. according to the size of the bars, the sensitivity to contrast of a subject cannot be expressed with a single value, but through a series of values that can only be represented by a curve.

This curve, therefore, called the contrast sensitivity curve, shows the different values of the minimum perceived contrast, according to the different dimensions of the bars that make up the stimulus and marks the boundary line between the perceived and non-perceived symbols.

Therefore, the optotypes of the first methodology currently in use are not sufficient for a precise determination of the contrast sensitivity, since the contrast varies in them but not the size of the stimuli.

On the contrary, the equipment used in the second methodology, which can determine the contrast sensitivity curve with high precision, because they take into account both the contrast and the size of the stimuli, are very expensive. Therefore, such equipment is not widely used because it is uneconomical, especially for smaller medical or ophthalmology offices.

The fact that doctors' offices in ophthalmology, general medicine and various medical-surgical specialties do not have suitable equipment for measuring contrast sensitivity is to the detriment of the patient, given the importance of the contrast sensitivity curve for diagnostic purposes and therapeutic not only for eye diseases, but also for those of general medicine, neurology, psychiatry, endocrinology, neurosurgery, etc.,

To overcome the aforementioned drawbacks, a new kit has been studied and created to determine the contrast sensitivity curve of an individual.

The main aim of the present invention has been that of realizing an optotype which considers both the contrast and the spatial frequency of the symbols, in order to be able to provide the contrast sensitivity curve of an individual.

Another object of the present invention is that of not requiring expensive or complex equipment for its operation, being therefore economical, but also easy to use and consult.

The new optotypes can be used by anyone, even without specific skills on the subject, in a simple way.

Another purpose of the present invention is to give an immediate and easily consultable and interpretable result.

These and other direct and complementary purposes are achieved by the new kit for the determination of the contrast sensitivity curve of an individual, comprising at least one optotype and at least one graph or table or correlated evaluation sheet, designed to report the sensitivity curve to the contrast of an individual.

The new optotype comprises a table or support on which a sequence of frames of predetermined dimensions, described and claimed below, is reported.

Each square comprises a grid formed by a succession of pairs of alternating light and dark colored strips or bars, parallel to each other.

Said gratings preferably have a rectangular shape, and can form flags or other graphic symbols composed of bars.

Different lattices have pairs of bars differently oriented, for example vertical or inclined to the right or to the left.

The number of pairs of said light and dark bars present in each grating determines the spatial frequency. The difference in brightness between each light bar and each adjacent dark bar instead defines the contrast. Each of said grids is therefore characterized by a certain spatial frequency value, a certain contrast value and a certain orientation of the bars.

In the preferred solution, said grids are arranged on said optotypes according to a matrix, where the grids aligned for example on the same column have bars with constant spatial frequency.

This spatial frequency decreases passing from one column to another, for example from left to right and the value is preferably indicated in correspondence with each column of lattices, for example at the bottom of the abscissa line.

The gratings aligned on the same line, on the other hand, have bars with constant contrast, which varies line by line, for example decreasing from bottom to top.

This contrast is preferably indicated in correspondence of each row, for example on the right on the ordinate line.

The sensitivity to the contrast is indicated on the left ordinates and increases from the bottom to the top.

Therefore in a given column for a constant spatial frequency, the contrast varies, for example decreasing from bottom to top, while sensitivity to contrast increases from bottom to top.

Instead at constant contrast, the spatial frequency varies in each row, for example increasing from left to right.

Each lattice is appropriately numbered or in any case identified with a number, letter or other.

For example, these grids are numbered from 1 to n, starting from the lower left grating, with lower spatial frequency and greater contrast, then continuing along the first column, rising from the bottom upwards, and then to the subsequent columns with frequency gradually increasing.

The orientation of the bars of the different lattices is instead preferably ordered randomly.

The optotype, similarly to the optotype tables of the type known for the assessment of visual acuity, must be placed at a certain distance from the subject, as there is a relationship between the distance of the patient's eye from the optotype and the size of the stimuli used, as described below.

The subject must have the best correction for distance vision, so as not to influence the evaluation of contrast sensitivity.

The examination can be performed monocularly or binocularly.

The subject must identify both the presence of the bars and the orientation of the bars contained in the gratings present on the optotypes, preferably starting from the first column on the left, with lower frequency, and from the lower grid with greater contrast.

the reading of the chart must then continue along the column at constant spatial frequency, towards the grids with less contrast up to the last grating of which the subject is able to identify the presence of the bars and their orientation. This grating therefore represents the minimum limit contrast value or contrast threshold for that specific spatial frequency and the corresponding contrast sensitivity, which is the inverse of the contrast expressed by the formula S = 1 / C.

The reading then continues to the next column, having a higher spatial frequency value and the operation is repeated for all subsequent columns, evaluating in each column, which is indicative of the spatial frequency, the value of the minimum perceived contrast, whose inverse It is the contrast sensitivity.

This optotype is associated with at least one graph, table and / or evaluation sheet, which shows for example:

in abscissa the values of the spatial frequency, for example values increasing from left to right, in ordinate, for example on the right the contrast values, for example decreasing from bottom to top, and on the left the corresponding values of contrast sensitivity, increasing bottom up.

In said evaluation form, at the points of intersection between lines with constant spatial frequency and lines with constant contrast, the numbers are indicated which, by position and order, correspond to the same numbers present near the grids of the chart.

On this evaluation form, the number that represents the last grid of the optotype, of which the subject was able to correctly identify the presence of bars and their orientation for each column of spatial frequency, must be underlined. By joining the identified points, a line is obtained, which is the contrast sensitivity curve of the subject under examination. The sequence of minimum perceived contrast values for each series of reticles of the optotype at constant spatial frequency therefore defines the typical curve of the subject, which is drawn in a simple and immediate way. The ease of the system consists in the possibility to immediately report on the diagram the identification numbers of the last grids correctly identified on the optotype, for each spatial frequency and which, joined together, give the contrast sensitivity curve.

This curve is then compared with the curves of the maximum and minimum values of the contrast sensitivity which are considered normal.

The sensitivity to contrast can in fact vary, while remaining normal, according to the age and refractive defect of a patient, the brightness of the environment, the size of the pupil and other parameters.

If one or more points of the patient's typical curve go outside the area between the two curves, the curve must be considered pathological.

These minimum and maximum normality curves are preferably already plotted in said evaluation sheet, making consultation immediate and simple. The operator is therefore able to immediately define if the curve is within the normal limits or if it is altered and if, repeated over time, it shows changes. When it goes out of normalcy, based on the spatial frequencies involved, low, medium or high, it also provides more diagnostic information for existing or suspected pathologies.

The diagnosis of diseases, which can be ocular, neurological, endocrinological, psychiatric, or other, is very important and with the new optotype with correlated evaluation form, valuable information is obtained in a very simple and immediate way that sometimes precedes the manifestation of a pathology.

The assessment of contrast sensitivity can be repeated periodically to study the variations and thus have further information on the course of any pathologies in progress, on the efficacy and outcome of any therapies and on everything of medical interest.

Said new optotype can comprise a rigid or flexible support, for example a simple sheet of paper, cardboard, plastic or other, suitable for being hung on the wall, on a mobile blackboard or where said gratings can simply be printed or applied.

This new optotype can be used in ambient light or illuminated by suitable lamps.

Said support can also be opaque, therefore applicable to the wall like a poster, or in transparent or semi-transparent material, and backlit; it can be inserted into a projector and then projected onto a screen or blackboard or wall suitable for correctly displaying the gratings.

Alternatively, said support can be transparent and applied integrally to a structure with lighting devices that back-illuminate the support itself, thus making the gratings visible.

Said kit can include two types of said optotypes, described below, each with its related evaluation sheet to plot the contrast sensitivity curve. In particular, an optotype with square wave bars and an optotype with sine wave bars.

The characteristics of the new kit for the determination and evaluation of contrast sensitivity will be better clarified by the following description with reference to the drawing tables, attached as a non-limiting example.

Figure 1a shows an optotype (A) with gratings (Ca) with square wave bars.

Figure 1b shows an optotype (B) with gratings (Cb) with sinusoidal wave bars.

Figure 2a shows an evaluation sheet (Ga) correlated to the optotype (A) with gratings (Ca) with square wave bars.

Figure 2b shows an evaluation sheet (Gb) related to chart (B) with gratings (Cb) with sinusoidal wave bars.

Figures 3, 3a, 3b and 3c schematize the construction methods of a lattice (Ca), for example with square waves, with bars (C1, C2) inclined to the left (3a) or to the right (3b) or straight verticals (3c).

It is a new kit for the determination and evaluation of the contrast sensitivity of an individual, including at least one optotype (A, B) and at least one chart or table or evaluation sheet (Ga, Gb) related to said optotype (A, B ).

This optotype can be of two types: with gratings (Ca) with square wave bars or with gratings (Cb) with sinusoidal wave bars.

Said new optotype (A, B) comprises a table or support on which a matrix of lattices (Ca, Cb) of predetermined constant dimensions is shown, for example of a substantially rectangular shape for square waves (Ca) or of a substantially square shape for sine waves (Cb).

In the example of figure 1a 11b, said gratings (Ca, Cb) represent flags, but they can have any other graphic representation, without prejudice to the geometric proportions described below.

In the preferred solution, each of said grids (Ca, Cb), schematized in detail in Figures 3, 3a, 3b and 3c, is obtained starting from a square shape (MNTV) having the side (MN) determined as a function of the distance to which chart will be used.

In a possible embodiment, said square has a side of 4.36 cm, ie equal to 1/10 of visual acuity at a distance of 3 m.

This length is therefore a function of the distance at which the optotypes are used. This distance has been programmed as 3 m, but it can obviously be less or more.

For the square wave optotype (A), each lattice (Ca), for example rectangular in shape, therefore has a long side of 4.36 cm, preferably horizontal (MN), and a short side preferably of 2.523 cm, preferably vertical (NT).

Said lattice (Ca) is included in a hypothetical rectangle (MNPQ), as illustrated in the figures, constructed as follows and for example with the following measures: width or long side (MN) of cm. 4.36 and height or short side (NP) of 2.523 cm, determined as illustrated below.

A square (MNTV) is constructed with a side (MN) of 4.36 cm, corresponding to the visual of 1/10 at a distance of m. 3.

With reference to Figure 3a, the grating with bars (C1, C2) inclined by 15 ° with respect to the vertical, to the left, is obtained as follows: the angle VMZ, of 15 °, is drawn. From the opposite vertex (N), the segment NR is drawn, such that NR = MN, and where said segment NR intersects the segment MZ at the point R and its extension intersects the side MV at the point Q.

The PQ side is obtained by drawing from the point Q the parallel to the MN side, defining the point P on the NT side.

The MZ segment intersects the PQ side at point S.

The MNPQ rectangle is the square that will contain the lattice (Ca) with inclined bars (C1, C2) of 15 ° to the left, which are parallel to the MS segment. Their number, counted on the MN side, corresponds to the spatial frequency, which includes cycles formed by a light bar (C1) and a dark bar (C2), therefore:

- at frequency 1 the cycle will be a light bar and a dark bar;

- at frequency 1,5: a light bar, a dark bar, 1/4 of a light bar, 1/4 of a dark bar,

- at frequency 3 there will be 6 bars: 3 light and 3 dark and so on.

With reference to figure 3b, the grating with bars (C1, C2) inclined by 15 ° with respect to the vertical, towards the right, is obtained as follows: the square MNTV is created; from the vertex N we trace the triangle TNZ of 15 °; the MR side is found which intersects NZ at the point R, such that MN = MR.

The extension of MR meets the NT side at point P. From point P I trace the parallel PQ to the MN side. The NR extension intersects the PQ side at the point S. The MNPQ rectangle will contain the right-oriented bar grating (C1, C2), parallel to the NS side, with spatial frequency determined as above. With reference to Figure 3c, the grating with straight vertical bars (C1, C2) is obtained in the same way as described above, with bars (C1, C2) parallel to the short sides (MQ) and with a spatial frequency determined as above.

To trace sine wave gratings (Cb), said gratings (Cb) are inserted in a hypothetical square with side cm. 4.36 and have the shape of a flag with the pole on the left, for example. Said gratings (Cb) may have straight vertical bars or 15 ° inclined to the left or to the right, constructed like the gratings (Ca) with square wave bars.

The contrast levels to be used for the study of contrast sensitivity have not been internationally standardized.

The following contrast levels have been chosen for the sine bars: 100-50-25-10-5-2.5-1.25-0.6, which correspond to the following values of contrast sensitivity, which corresponds to inverse of contrast: S = 1 / C; these values are: 1-2-4-10-20-40-80-166.

For square wave bars we prefer to use the Weber formula which gives us the following contrast levels: 100-66.6-40-18.1-9.5-4.87-2.46-1.19, which correspond to the following contrast sensitivity values: 1-1.5-2.5-5.5-10.5-20.5-40.6-84.

Between the two formulas (Michelson and Weber) there is a precise relationship whereby, even if the numerical values are different, the resulting contrast sensitivity curve has the same shape.

In conclusion, each of said lattices (Ca, Cb) is characterized by a certain spatial frequency value, i.e. by a certain number of pairs of said light (C1) and dark (C2) bars, by a certain contrast value and from a certain orientation of the bars.

It can be envisaged that said bars (C1, C2) are made with two different types of possible profiles: square wave, as shown in figures 3, 3a, 3b and 3c, or sinusoidal wave.

The sine wave spatial profile is more valid because it takes into account the receptive fields of the visual system and therefore provides more complete answers for the localization of ocular and neurological pathologies.

The background of chart (A) with square wave gratings (Ca) is preferably white, while the background of chart (B) with sine wave gratings (Cb) is gray at 50% of the gray scale.

The spatial frequency is preferably determined by the following values: 1, 1.5; 3; 6; 12; 18; 24, for sine wave gratings; while for square wave gratings the values are preferably the following: 1, 1.5; 3; 6; 12; 24.

Both the gratings, the background color, the spatial frequency and contrast values and the angle of inclination can obviously be changed.

In the preferred solution, both for square waves and for sine waves, represented in Figures 1a and 1b, said gratings (Ca, Cb) are ordered on said optotypes (A, B) according to a matrix with rows (A1, B1) and columns (A2, B2), where the gratings aligned in one direction, for example on the same column (A2, B2), have a constant spatial frequency, while the gratings aligned in the horizontal direction, for example on the same row (A1, B1) , have constant contrast.

In a given column (A2, B2) at constant spatial frequency, the contrast varies, for example decreasing from bottom to top, while continuing from column to column, the spatial frequency varies, for example increasing from left to right. The orientation of the bars (C1, C2) of the different lattices is instead preferably ordered randomly in the optotypes (A, B).

Each lattice is preferably numbered or in any case identified with a number, letter or other (An, Bn).

The arrangement of gratings within the optotypes (A, B) can however be any different from that described, for example by inverting the columns with the rows.

These optotypes (A, B) are correlated by graphs or tables or evaluation sheets (Ga, Gb), which, for example, report the value of the spatial frequency in the abscissa (G1), increasing from left to right, and in the ordinate (G2) the contrast value, decreasing from bottom to top and the value of contrast sensitivity (G3), that is, they substantially report the frequency and contrast values according to the order present in the optotypes (A, B).

These evaluation sheets (Ga, Gb) also report the numbers or letters identifying (An, Bn) of each lattice (Ca, Cb), also indicated in the optotypes (A, B), corresponding to the exact coordinates (frequency, contrast) of the optotypes (A, B) themselves.

The points (Gn) corresponding to each minimum contrast value that the subject is able to identify for each spatial frequency column must be reported on said evaluation sheets (Ga, Gb), combining which the typical curve (Gt) of the contrast sensitivity of the subject.

To indicate these points (Gn), it is sufficient to identify the number or letter An, Bn) relating to the last lattice (Ca, Cb) identified on each column of the chart and find it in said evaluation sheets (Ga, Gb).

The sequence of points (Gn) drawn on the evaluation sheets (Ga, Gb) can therefore be used to immediately identify the patient's typical curve (Gt).

Furthermore, one or preferably two reference curves (Gmin, Gmax) of contrast sensitivity are also preferably plotted on said evaluation cards (Ga, Gb), i.e. the curves corresponding to the minimum (Gmin) and maximum (Gmax) contrast sensitivity for a subject considered normal.

In the example of figure 2a, the typical curve of the subject (Gt) is normal, being completely included between said normal curves (Gmin, Gmax). In the example of figure 2b, however, the topical curve (Gt) comes out with some points below the minimum curve (Gmin). In this case, the typical curve (Gp) must be considered pathological.

These are the schematic modalities sufficient for the skilled person to realize the invention, consequently, in concrete application there may be variations without prejudice to the substance of the innovative concept.

Therefore, with reference to the above description and the attached tables, the following claims are expressed.

Claims (1)

CLAIMS 1.Kit for the determination and evaluation of the sensitivity to monocular or binocular contrast of a subject, characterized by the fact of including: â € ¢ at least one optotype (A, B), comprising a table or support on which a plurality of lattices (Ca, Cb) is shown where in each lattice (Ca, Cb) a succession of bars (C1, C2) alternating light-colored (C1) and dark-colored (C2), parallel to each other, each grating (Ca, Cb) having a certain spatial frequency value and a certain contrast value, and where said grating (Ca, Cb ) are ordered on said optotype (A, B) according to a matrix, where the gratings (Ca, Cb) aligned in one direction have constant spatial frequency and decreasing contrast, while the gratings (Ca, Cb) aligned in the orthogonal direction have constant contrast and increasing spatial frequency; â € ¢ at least one graph or table or evaluation sheet (Ga, Gb) related to said optotype (A, B) which substantially reports said frequency and contrast values according to the order of said optotype (A, B), and where on said evaluation sheet (Ga, Gb) the points (Gn) relating to the minimum contrast values (An, Bn) of the last grating (Ca, Cb) perceived by the subject for each series of grating (Ca, Cb) can be reported Cb) at constant frequency of the chart (A, B), thus drawing a typical curve (Gt, Gp) of the subject's sensitivity to contrast. 2.Kit as per claim 1, characterized by the fact that said optotype (A, B) comprises a plurality of columns (A2, B2) of said gratings (C) with constant frequency and decreasing contrast, upwards or downwards , and where the spatial frequency of the columns (A2, B2) increases to the right or to the left. 3.Kit as per claim 1, characterized by the fact that said evaluation card (Ga, Gb) includes in abscissa (G1) the spatial frequency, increasing to the right or to the left according to the order in said optotype (A, B), and in ordinate (G2, G3) the contrast, decreasing upwards or downwards according to the order in said optotype (A, B) and / or the contrast sensitivity, equal to the inverse of the contrast. 4.Kit as per the previous claims, characterized by the fact that said bars (C1, C2) of each lattice (Ca, Cb) are oriented vertically or inclined, to the right by 15 ° with respect to the vertical, or to the left by 15 ° with respect to the vertical, and where said orientation of the bars (C1, C2) of the different lattices (Ca, Cb) is randomly ordered in the chart (A, B). 5.Kit as per the previous claims, characterized by the fact that each of said grids (Ca, Cb) of the optotype (A, B) is marked with a number (An, Bn), a letter or other, and where said card evaluative (Ga, Gb) also reports the numbers or letters identifying (An, Bn) of each lattice (Ca, Cb) of the chart (A, B), corresponding to the exact frequency and contrast coordinates of the chart (A, B) itself, and where said numbers (An, Bn) can be used to trace said typical curve (Gt). 6.Kit as per the previous claims, characterized in that it comprises at least one of said optotypes (A) with square wave gratings (Ca) and with correlated evaluation card (Ga), and / or at least one of said optotypes (B) with grids (Cb) with sine wave and with correlated evaluation card (Gb). 7.Kit as per the previous claims, characterized by the fact that at least one, two or more normal reference curves (Gmin, Gmax) of contrast sensitivity are also drawn on said evaluation sheet (Ga, Gb), suitable for being directly compared with said typical curve (Gt, Gp) for the evaluation of pathological or normal conditions. 8.Kit as per the previous claim, characterized by the fact that said normal reference curves (Gmin, Gmax) include the curves corresponding to the minimum (Gmin) and maximum (Gmax) contrast sensitivity for a subject considered normal, and where a typical curve normal (Gt) must be completely included between said normal curves (Gmin, Gmax), while a typical pathological curve (Gp) emerges with one or more points from the surface identified between said curves (Gmin, Gmax). 9.Kit as per the previous claims, characterized by the fact that each of said gratings (Ca, Cb) has a shape obtained from a square shape having a side length equal to 1/10 of visual acuity depending on the distance of use of the chart ( TO), 10.Kit as per the preceding claims, characterized in that said support of said optotype (A, B) comprises a sheet or panel, rigid or flexible, on which said grids (Ca, Cb) of suitable dimensions for use in a certain distance. 11.Kit according to the preceding claims, characterized in that said support comprises a panel made of transparent or semitransparent material, capable of being backlit for viewing said gratings (Ca, Cb). 12.Kit as per the preceding claim, characterized in that said support also comprises a structure with lighting devices which backlight said panel, thus making said grids (Ca, Cb) visible.