RU2207039C2 - Method for predicting pathology of retina and optic nerve - Google Patents

Abstract

FIELD: medicine, ophthalmology. SUBSTANCE: it is necessary to increase area of affecting light impulses R_i against radius of central stimulus R₀ proportionally to the decrease of light sensitivity of normally functioning eye as removing from the center of vision area. One should measure the values of threshold contrast c_i of affecting light stimuli in different parts of vision area. One should calculate possible conformity P₀ in function of distributing the value of threshold contrast along vision area F₀(c) function of normal distribution Fn₀(c^-,σ). One should calculate possible conformity P_j function F_j(c) function of normal distribution Fn₀(c^-,σ) at successive exclusion of maximum values of threshold contrast c_max out of area to determine function F₀(c). Pathology is diagnosed when maximum possibility in conformity of compared functions is reached at excluding values of threshold contrast out of area to determine F₀(c). EFFECT: higher sensitivity of diagnostics. 4 dwg

Description

 The invention relates to medicine, namely to ophthalmology, and can be used to diagnose the initial stages of the development of the pathological process in the retina and optic nerve, as well as to evaluate the effectiveness of treatment by examining the visual fields.

 The earlier is the kinetic perimetry method, with which the boundaries of the visual fields are determined. As test stimuli, light spots of a certain size and intensity moving from the periphery to the center of the field of view are used.

 In the framework of kinetic perimetry, a method for assessing the state of the retina based on an assessment of the ability to spatial summation was proposed. Using equal-energy stimuli (the product of the stimulus brightness and the area — constant value), isopters — the boundaries of the same spatial summation — were determined. With equal energy perimetry, the diagnostic criterion is the coincidence or mismatch of boundaries during repeated studies. The standards for equal-energy perimetry were determined by S. B. Polyak (see Polyak, S. B. Methods of standardizing quantitative perimetry for clinical purposes // Ophthalmological Journal, 1968, v. 23, 3, pp. 212-216) [1]. The method is not widely used in clinical practice due to the duration of each study.

 To assess contrast sensitivity in different parts of the field of view and identify cattle (areas with reduced sensitivity), the static perimetry method is used. With this method of examination, the test object is not moved or changed in size, but is presented at specified points in the field of view with variable brightness.

The most common are subthreshold methods of static perimetry. To detect visual pathology by the method of static perimetry, the principle of comparing the light sensitivity of the tested portion of the field of view with the standard is used. Standards for static perimetry in different age groups were developed by R. Brenton and C. Phelps (see Brenton RS, Phelps CD The normal visual field on the Humphrey field analyzer // Ophthalmologica. 1986. V.193, 1-2, p. 56 -74) [2]. With an increase in eccentricity along different meridians, the decrease in sensitivity is approximately the same. Since photosensitivity decreases uniformly over the entire field of view with age, the relief of sensitivity remains constant. In standard static-perimetric examinations (background brightness 10 abs, test size 12 arc s, test presentation time 1 s), the threshold sensitivity in the center of the field of view is about 1 abs, and at 20 ^o from the center about 10 abs (see Petkova N Age-related changes in the visual-functional ability of a healthy eye, established using static-perimetric studies // In the book: Actual problems of ophthalmology. M., Medicine. 1981. S.13-21) [3].

 The development of the method of suprathreshold static perimetry was the creation of automatic perimeters. Examples include the Humphrey field of view analyzer, the Torsop Computerized Perimeter SBS-2020 and Perikom computer perimeters (see Vagin B.I., Bakshinsky P.P., Baurina O.I. . and others. Automatic static perimeter "Pericom" in the clinical practice of an ophthalmologist // Methodological recommendations. M., 1998, 29 S.) [4]. According to the passport data for the indicated devices, the procedure for testing the visual fields is carried out in the above-threshold mode: the brightness of the test stimuli is set at 5-6 dB above the threshold values that characterize the norm. Such a significant increase in test intensity (3-4 times higher than the threshold) is necessary in order to exclude distortion of the result due to the high variability of individual indicators of light sensitivity. As a result, modern computer perimeters are used only to detect pronounced changes in the fields of view: cattle of varying degrees of depth (usually 2-3 gradations are used). At the same time, the initial stages of the pathological process, which are characterized by a significantly smaller decrease in light sensitivity, are not detected by existing methods.

 In order to increase the sensitivity of static perimetry, the method of threshold perimetry was proposed (in contrast to the previously considered above-threshold perimetry). This method is implemented, in particular, on a Humphrey field of view analyzer (USA) (see Brenton RS, Phelps CD The normal visual field on the Humphrey field analyzer // Ophthalmologica. 1986. V.193, 1-2, p. 56-74) [2], (see Brenton RS, Argus WA Fluctuations on the Humphrey and Octopus perimeter // Invest. Ophthalmol. 1987. V.28, 5, p. 767-771) [5]. First, light sensitivity is measured in various parts of the patient’s field of vision. Then, the average threshold value over the entire field of view is calculated. The diagnosis is made on the basis of the deviation of the individual average light sensitivity from the indicator of the age-related population norm. A certain development of the threshold perimetry method was the development protected by US patents (see Jonson CA, Shapiro LR Visual testing method and apparatus // Patent US 5050983, 1991) [6], (see Gonzales De La Rosa M. Method of determining the perimeter of the visual field of the human eye // Patent US 5864385, 1999) [7].

 The method and apparatus for the dynamic and static perimetry of the human eye, protected by a US patent, are also based on the assessment of threshold sensitivity values for light sensitivity (see Gelius S. Process and apparatus for the dynamic of static perimetry of the eye // Patent US 4349250, 1982) [8 ] and implemented in the perimeters of the company "Rodenstock". This method is the closest to the implementation of the claimed method and is taken by us as a prototype.

 According to this method, the threshold contrast sensitivity is determined independently for different parts of the field of view. Then the obtained values are compared with the normative indicators for each tested section of the field of view. The standard is defined as the average value of the sensitivity of a given section of the field of view when measured on a large number of subjects (population norm) and can be determined independently for different age groups. A comparison of the standard values with the values obtained as a result of the examination indicates the presence of deviations in the light sensitivity in a particular area of the field of view.

 The threshold perimetry method was developed to increase the sensitivity of the above-threshold static perimetry method in order to detect relatively small changes in light sensitivity, reflecting the initial stages of the development of pathology. However, the method is not without drawbacks. So, individual light sensitivity is a fairly variable indicator and, in addition to age, depends on the general functional state of the patient, his emotional state, level of visual fatigue, etc. It is known that in different patients with normal vision the threshold brightness of the stimuli can vary by 4-5 dB (see Brenton RS, Phelps CD The normal visual field on the Humphrey field analyzer // Ophthalmologica. 1986. V.193, 1-2, p. 56-74) [2], (see Brenton RS, Argus WA Fluctuations on the Humphrey and Octopus perimeter // Invest. Ophthalmol. 1987. V.28, 5, p. 767-771) [5]. Thus, deviations of light sensitivity from the norm, which can be confidently identified as a sign of pathology, are detected only with significant increases in the threshold brightness of stimuli (of the order of 5 dB) in most of the tested sections of the field of view. The use of population norm indicators as a diagnostic criterion reduces the sensitivity of the method, which does not allow diagnosing diseases of the retina and optic nerve in the early stages.

 The technical result of the invention is to increase the sensitivity of the diagnosis of pathology of the retina and optic nerve.

вычисляют вероятности соответствия P_j функции F_j(c) функции нормального распределения Fn_j

при последовательном исключении максимальных значений порогового контраста с_max из области определения функции F₀(с), и патологию диагностируют, когда максимальная вероятность соответствия сравниваемых функций достигается при исключении значений порогового контраста из области определения F₀(c).The technical result is achieved by the fact that in the method for diagnosing pathology of the retina and optic nerve, including measuring the threshold contrast of the acting light stimuli at predetermined points of the field of view, according to the invention, the area of the acting light stimuli R _{i is} increased relative to the radius of the central stimulus R _{0 in} proportion to the decrease in the light sensitivity of a normally functioning eye as you move away from the center of the field of view, measure the values of the threshold contrast with _i acting light stimuli in different parts of the field of view, calculate the probability of matching P ₀ the distribution function of the threshold contrast value over the field of view F ₀ (c) of the normal distribution function Fn ₀

calculate the probability of matching P _j functions F _j (c) the normal distribution function Fn _j

with successive exclusion of the maximum values of the threshold contrast with _max from the domain of definition of the function F ₀ (s), and pathology is diagnosed when the maximum probability of correspondence of the compared functions is achieved by excluding the values of the threshold contrast from the domain of definition of F ₀ (c).

 This leads to the alignment of the threshold contrast values for the field of view of a normally functioning eye, which allows us to compare the sensitivity of different parts of the field of view of one individual and use not the population norm, as in the prototype, but the individual norm obtained as a result of the indicated action. This leads to an increase in the sensitivity of the method and, therefore, to the possibility of diagnosing pathology in the early stages of the disease. An additional advantage of this method is a 25-fold reduction in the working range of brightness of test stimuli, which makes it possible to use a computer monitor as a stimulator.

 Figure 1 presents the block diagram of the implementation of the method.

 In FIG. 2 presents the results of computer campimetry, characterizing the norm. A is a map of the field of view, B is a histogram of the distribution of threshold contrast values over the field of view. Dotted lines indicate: on the left is the value of the threshold contrast in the center of the field of view, on the right is the normal spread of threshold values from the average level (the boundary of the individual norm).

 In FIG. 3 presents the results of computer campimetry, characterizing the initial stage of development of the pathological process. The designations are the same.

 In FIG. 4 presents the results of computer campimetry characterizing a far-reaching pathological process.

 The method was implemented by the campimetry method using a personal computer (Pentium, a video card of at least 4 MB, a 15 '' monitor). During the examination, the patient’s head is in the frontal-chin rest at a distance of 35 cm from the monitor, which is used as the campimeter screen. Testing is monocular. The patient fixes his gaze in the center of the crosshairs, the image of which is formed on the screen. Test stimuli appear in different parts of the screen. The patient responds to the stimulus by pressing a key on the computer keyboard.

 The method can be implemented in the same way as the method of static threshold perimetry.

 During the examination, actions are carried out in the sequence 1-11 in accordance with the block diagram depicted in figure 1.

1. Increase the radius of the acting light stimuli R _i relative to the central stimulus R _{0 in} proportion to the decrease in the light sensitivity of a normally functioning eye as it moves away from the center of the field of view (with an increase in eccentricity). In a specific case, in addition to the central one, 48 test positions are used (i∈ {0 ... 48}).

Functions extend the range of stimuli were determined on a group of subjects with normal vision to each of the principal meridians of the field of view when backlight 150-200 cd / m ² screen.

For the temporal meridian:
R = (4, l3 • 10 ^-4 • S ³ -1.92 • 10 ^-2 • S ² + 3.4 • 10 ^-1 • S + 1) • R ₀ ;
for dorsal meridian:
R = (1.25 • 10 ^-3 • S ³ -3.62 • 10 ^-2 • S ² + 5 • 10 ^-1 • S + 0.95) • R ₀ ;
for the nasal meridian:
R = (4.41 • 10 ^-4 • S ³ -1.61 • 10 ^-2 • S ² + 3.09 • 10 ^-1 • S + 1.02) • R ₀ ;
for ventral meridian:
R = (1.16 • 10 ^-3 • S ³ -3.42 • 10 ^-2 • S ² + 5.06 • 10 ^-1 • S + 1.03) • R ₀ ,
where R is the radius of the stimulus (ang. min),
S - eccentricity of the stimulus (ang. Hail.), (S≤30),
R ₀ is the radius of the central stimulus (ang. Min.), (R ₀ = 5).

 For test positions located on diagonal meridians, the stimulus radii were calculated by linear interpolation of the above functions.

2. Using the ladder method, determine the threshold contrast in the center of the patient’s field of view c ₀ . The step of changing the contrast is 0.1 log. units The obtained contrast value is taken as the initial value for all test stimuli.

3. Similarly determine the threshold contrast with _i in different parts of the field of view for all test stimuli.

4. Calculate the histogram of the distribution of threshold contrast values over the field of view F _j (c), where с∈С, and С = {c _min ... c _max }.

5. Count the number of classes in the histogram N _c at j = 0. Calculate j _max = N _c -3.

и б) дисперсию σ. На основании полученных значений рассчитывают функцию нормального распределения Рn_j

7. Сравнивают экспериментальную (п. 4) и расчетную (п.6) функции. В конкретном случае по критерию хи-квадрат вычисляют вероятность соответствия сравниваемых функций P_j.6. For the current set C calculate: a) the average value of the threshold contrast

and b) the variance of σ. Based on the obtained values, the normal distribution function Pn _{j is} calculated

7. Compare the experimental (p. 4) and calculated (p. 6) functions. In a specific case, the chi-square test calculates the probability of matching the compared functions P _j .

8. Change the domain for the function F _{j + 1} (c) by eliminating the maximum contrast value with _max . Repeat the operations described in paragraphs 4, 6 and 7 for j = j + 1, until the condition j> j _max is fulfilled.

9. Determine the maximum value of the probability of compliance of the compared functions P _max .

максимально соответствует исходная функция распределения значений порогового контраста по полю зрения F₀(c) (без исключения максимальных значений порогового контраста). То есть когда выполняется условие Р_max=P₀.10. The norm is diagnosed when the normal distribution functions Fn _j

the initial distribution function of the threshold contrast values over the field of view F ₀ (c) corresponds to the maximum (without exception, the maximum threshold contrast values). That is, when the condition P _max = P ₀ is satisfied.

 Figure 2 shows the result corresponding to the norm. The initial histogram of the distribution of threshold contrast values is close to the normal distribution.

11. Pathology is diagnosed when, to achieve maximum compliance of the compared functions, it was necessary to exclude c _max . That is, when the condition P _max ≠ P ₀ is satisfied. The values of the threshold contrast, which were excluded to achieve maximum compliance of the compared functions, are assessed as pathological.

 In FIG. 3 and 4 show the results corresponding to the pathology. In Fig. 3, the histogram of the distribution of threshold contrast values has an asymmetric form and reaches the maximum correspondence of the normal distribution function only after the six maximum values of the contrast threshold are excluded from the distribution. In FIG. 4, the histogram of the distribution of threshold contrast values has a bimodal character, which characterizes a far-reaching pathological process.

Sources of information
1. Pole S.B. Methods for standardizing quantitative perimetry for clinical purposes // Ophthalmological Journal, 1968, v. 23, 3, p. 212-216.

 2. Brenton R.S., Phelps C.D. The normal visual field on the Humphrey field analyzer // Ophthalmologica. 1986. V.193, 1-2, p. 56-74.

 3. Petkova N. Age-related changes in the visual-functional ability of a healthy eye, established using static-perimetric studies // In the book: Actual problems of ophthalmology. M., Medicine, 1981, p. 13-21.

 4. Vagin B. I., Bakshinsky P. P., Baurina O. I., Volosova N. P., Simonova S. V., Naumova M. V., Budnik V. M., Piryazev E. T. Automatic static perimeter "Pericom" in the clinical practice of an ophthalmologist // Methodical recommendations. M., 1998, 29 pp.

 5. Brenton R.S., Argus W.A. Fluctuations on the Humphrey and Octopus perimeter // Invest. Ophthalmol. 1987. V. 28, 5, p. 767-771.

 6. Jonson C.A., Shapiro L.R. Visual testing method and apparatus // Patent US 5050983, 1991-09-24, MKI A 61 V 3/02.

 7. Gonzales De La Rosa M. Method of determining the perimeter of the visual field of the human eye // Patent US 5864385, 1999-01-26. MKI A 61 B 3/00.

 8. Gelius S. Process and apparatus for the dynamic of static perimetry of the eye // Patent US 4349250, 1982-09-14. MKI A 61 B 3/06 - prototype.

Claims (1)

A method for diagnosing pathology of the retina and optic nerve, including measuring threshold contrast values of the affected light stimuli at predetermined points of the field of view, characterized in that the area of the affected light pulses R _{i is} increased relative to the radius of the central stimulus R _{0 in} proportion to the decrease in the light sensitivity of a normally functioning eye as it moves away from the center of the field of view, measure the threshold contrast with _i acting light stimuli in different parts of the field of view, calculating the probability of correspondence P ₀ to the distribution function of the threshold contrast value over the field of view F ₀ (c) of the normal distribution function Fn ₀

calculate the probability of matching P _j functions F _j (c) the normal distribution function Fn _j

with successive exclusion of the maximum values of the threshold contrast c _max from the domain of definition of the function F ₀ (c), pathology is diagnosed when the maximum likelihood of matching the compared functions is achieved by excluding the values of the threshold contrast from the domain of definition of F ₀ (c).

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