Color vision characteristic correction filter and color vision examination method

Abstract

Provided is a correction filter for changing the spectrum of light to be transmitted. The correction filter changes the spectrum of light in a wavelength band including at least one of an absorption maximum wavelength λL at which the absorption spectrum of L cone cells of a person reaches a peak and an absorption maximum wavelength λM at which the absorption spectrum of M cone cells reaches a peak. The correction filter is set so that the transmittance increases from a wavelength XC between λL and λM toward a wavelength XL which is a longer wavelength than the wavelength λL, when changing the spectrum of light in a wavelength band including λL, and is set so that the transmittance increases from the wavelength XC toward a wavelength XS2 which is a shorter wavelength than λM, when changing the spectrum of light in a wavelength band including λM.

Description

Color vision characteristic correction filter and color vision testing method

[0001] The present invention relates to a color vision characteristic correction filter and a color vision testing method.

[0002] Known disorders related to human color vision include color blindness and color weakness, which are conditions in which sensitivity to light in specific wavelength bands is low, and photosensitivity, which is a condition in which light of specific wavelengths is perceived as dazzling. An example of photosensitivity is Aaron syndrome. These color vision disorders occur when the sensitivity of the three cone cells (S cones, M cones, and L cones) and rod cells on the retina of a patient is higher or lower than that of a healthy individual. A known method for correcting the color vision of patients with color vision disorders is to use optical filters whose light transmission characteristics are tailored to each individual. By having the patient wear glasses with optical filters with tailored characteristics, the patient's color vision deficiency is alleviated.

[0003] To create optical filters tailored to each patient, it is necessary to test the patient's color vision characteristics (sensitivity) to various colors of light. However, because there are countless combinations of sensitivity to various colors of light, it is difficult to determine the characteristics of an optical filter that is appropriate for each patient.

[0004] Methods for producing optical filters tailored to patients have been known for some time. For example, Patent Document 1 (US Patent Application Publication No. 20230016452) discloses a method for correcting a patient's color vision characteristics using an optical filter that significantly reduces the transmittance of light in the yellow wavelength band, which is the wavelength band between red and green.

[0005] U.S. Patent Application Publication No. 20230016452

[0006] The optical filter described in Patent Document 1 significantly reduces the transmittance of the yellow wavelength band, which can cause a problem in that even if the patient's color vision characteristics are corrected, the patient will not be able to perceive the color of yellow objects.

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a correction filter and a color vision testing method that correct the color vision characteristics appropriate for each patient in accordance with the patient's color vision characteristics without significantly reducing the intensity of light in a specific wavelength band.

[0008] A correction filter according to one embodiment of the present invention is a correction filter that changes the spectrum of light that is transmitted, and changes the spectrum of light in a wavelength band that includes at least one of the maximum absorption wavelength λL at which the absorption spectrum of human L cone cells reaches its peak, and the maximum absorption wavelength λM at which the absorption spectrum of human M cone cells reaches its peak.

[0009] With this configuration, color vision defects caused by a shift in the absorption maximum wavelength at which the absorption spectrum of a person's L cone cells or M cone cells peaks can be corrected by changing the spectrum of light incident on the person's eye. Furthermore, because the correction filter according to one embodiment of the present invention does not significantly reduce the intensity of light in a specific wavelength band, it is possible to prevent the problem of patients being unable to recognize specific colors.

[0010] Furthermore, the correction filter according to one embodiment of the present invention is set so that the transmittance increases from the wavelength XC between the maximum absorption wavelength λL and the maximum absorption wavelength λM toward the wavelength XL, which is longer than the maximum absorption wavelength λL.

[0011] With this configuration, the light in the red wavelength band that enters the human eye changes so that its intensity increases toward the longer wavelength side, thereby correcting type 1 color vision, which occurs when the maximum absorption wavelength of L cone cells shifts toward the shorter wavelength side.

[0012] Furthermore, the correction filter according to one embodiment of the present invention is set so that the transmittance increases from the wavelength XC between the maximum absorption wavelength λL and the maximum absorption wavelength λM toward the wavelength XS2 that is shorter than the maximum absorption wavelength λM.

[0013] With this configuration, the light in the green wavelength band that enters the human eye changes so that its intensity increases toward the shorter wavelength side, thereby correcting type-2 color vision, which occurs when the maximum absorption wavelength of M cone cells shifts toward the longer wavelength side.

[0014] A color vision testing method according to one embodiment of the present invention is a color vision testing method using a correction filter, and includes a determination step of determining whether a test image satisfies a predetermined condition when viewed by a subject through the correction filter.

[0015] This configuration makes it possible to test for color vision defects caused by a shift in the maximum absorption wavelength at which the absorption spectrum of a person's L cone cells or M cone cells peaks.

[0016] According to an embodiment of the present invention, an optical filter is provided that corrects the visual characteristics of each patient in a manner appropriate for that patient, without significantly reducing the intensity of light in a specific wavelength band.

[0017] Figure 1 shows the absorption spectra of each cone and rod cell in a person. Figure 2 shows the exons contained in the human red opsin gene and the exons contained in the human green opsin gene. Figure 3 shows the absorption maximum wavelengths of red opsin and green opsin. Figure 4 shows the relative absorption spectra of L and M cone cells in a person with normal color vision. Figure 5 shows the relative absorption spectra of L and M cone cells in a person with mild protanopia. Figure 6 shows the relative absorption spectra of L and M cone cells in a person with mild deuteranopia. Figure 7 shows the relative absorption spectra of L and M cone cells in a person with mild mixed protanopia. Figure 8 shows the transmittance of a correction filter for correcting protanopia. Figure 9 shows the relative absorption spectra of corrected L and M cone cells in a person with mild protanopia. Figure 10 shows the transmittance of a correction filter for correcting protanopia. FIG. 11 shows the transmittance of a correction filter for correcting protanopia. FIG. 12 shows the transmittance of a correction filter for correcting protanopia. FIG. 13 shows the transmittance of a correction filter for correcting deuteranopia. FIG. 14 shows the relative absorption spectra of corrected L and M cones in a person with mild deuteranopia. FIG. 15 shows the transmittance of a correction filter for correcting deuteranopia. FIG. 16 shows the transmittance of a correction filter for correcting deuteranopia. FIG. 17 shows the transmittance of a correction filter for correcting deuteranopia. FIG. 18 shows the transmittance of a correction filter for correcting protanopia. FIG. 19 shows the relative absorption spectra of corrected L and M cones in a person with mild deuteranopia. FIG. 20 shows the transmittance of five correction filters for correcting protanopia. FIG. 21 shows the transmittance of five correction filters for correcting protanopia. Fig. 22 shows the transmittance of a correction filter that corrects protanopia. Fig. 23 shows the transmittance of five correction filters that correct deuteranopia. Fig. 24 shows the transmittance of five correction filters that correct deuteranopia. Fig. 25 shows the transmittance of five correction filters that correct protanopia and deuteranopia. Fig. 26 shows the transmittance of five correction filters that correct protanopia and deuteranopia.

[0018] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0019] (Human Color Vision Deficiency) First, the mechanism by which color vision deficiency occurs in humans will be explained. A person's color vision characteristics are determined based on the characteristics of their photoreceptor cells. Photoreceptor cells include three types of cone cells and one type of rod cell. Photoreceptor cells such as cone cells and rod cells are cells located on the human retina. Each type of photoreceptor cell is sensitive to a different wavelength band of light, allowing humans to recognize light of various colors.

[0020] Cone cells include three types: S cone cells, M cone cells, and L cone cells. Figure 1 shows an example of the absorption spectra of each cone cell and rod cell. The horizontal axis of Figure 1 represents the wavelength of light, and the vertical axis represents the absorption spectrum of each cone cell and rod cell. The absorption spectra shown in Figure 1 are normalized by the maximum absorptance. The higher the absorptance of each cone cell and rod cell, the higher its sensitivity (susceptibility) to that light. S cone cells have maximum sensitivity around a wavelength of 420 nm. M cone cells have maximum sensitivity around a wavelength of 534 nm. L cone cells have maximum sensitivity around a wavelength of 563 nm. Rod cells have maximum sensitivity around a wavelength of 498 nm. Note that the wavelengths at which each cone cell and rod cell is most sensitive vary from person to person.

[0021] Human color vision disorders can occur when the sensitivity of these cone cells and rod cells is lower or higher than that of a normal person. For example, when the sensitivity of L cone cells to red light is low, it is called protanopia, and when the sensitivity of M cone cells to green light is low, it is called deuteranopia. In this embodiment, color vision that has characteristics of both protanopia and deuteranopia is called mixed protanopia.

[0022] Color vision deficiencies such as protanopia and deuteranopia are innate color vision conditions determined by whether or not genes express the visual pigments involved in the synthesis of cone cells. Visual pigments are complexes of visual pigment proteins (opsins) and vitamin A derivatives (retinal). Opsins include rhodopsin, which makes up rod cells, and red, green, and blue opsins, which make up L, M, and S cone cells, respectively.

[0023] Both rhodopsin and blue opsin consist of 348 amino acids. The gene encoding rhodopsin (rhodopsin gene) is located on human chromosome 3, and the gene encoding blue opsin (blue opsin gene) is located on human chromosome 7.

[0024] Red and green opsins consist of 364 amino acids, and the genes encoding red opsins (red opsin genes) and green opsins (green opsin genes) differ in 15 of the 364 amino acids. Both the red and green opsin genes are located on the long arm of the X chromosome (Xq28) in humans, and normally, only the red opsin gene is expressed in L cone cells, and only the green opsin gene is expressed in M ​​cone cells.

[0025] Because the red and green opsin genes have similar gene sequences and are located adjacent to each other, homologous recombination between the genes can occur. This homologous recombination can result in abnormalities such as gene deletion (partial deletion of the opsin gene), gene duplication (partial duplication of the red and green opsin gene sequences), and the formation of hybrid genes containing both red and green opsin gene sequences. These gene sequence abnormalities cause color vision deficiencies.

[0026] For example, if a portion of the red opsin gene is replaced by a sequence from the green opsin gene through homologous recombination, it will result in type 1 color vision, and if a portion of the green opsin gene is replaced by a sequence from the red opsin gene, it will result in type 2 color vision. The degree of color vision deficiency will depend on the extent to which the gene sequence replacement occurs.

[0027] Figure 2 shows the exons contained in the red opsin gene and the green opsin gene. Exons are regions of a gene sequence involved in amino acid synthesis. Both the red and green opsin genes contain six exons, exons 1 to 6. Of the amino acids synthesized by these exons, the 65th, 180th, 230th, 233rd, 277th, 285th, and 309th amino acids are involved in the spectral absorption characteristics of opsin. The 180th amino acid is synthesized by exon 3, and the 277th and 285th amino acids are synthesized by exon 5.

[0028] If homologous recombination does not occur between the exons and red and green opsins are synthesized normally, humans will have normal red and green color vision. However, if homologous recombination of the genes results in the formation of a hybrid gene, the spectral absorption characteristics of the opsins will change.

[0029] Figure 3 shows the change in the wavelength at which red opsin absorbs most (maximum absorption wavelength) when the red opsin gene becomes a hybrid gene, and the change in the wavelength at which green opsin absorbs most (maximum absorption wavelength) when the green opsin gene becomes a hybrid gene. In Figure 3, "normal" indicates a normal gene sequence, and "homologous recombination" indicates when an exon of the red opsin gene is replaced with a green opsin gene, or when an exon of the green opsin gene is replaced with a red opsin gene.

[0030] Of the two absorption maximum wavelengths shown in Figure 3, absorption maximum wavelength 1 is based on the research of Merbs et al. (Merbs SL, et al: Science (1992) 258: 464-466), and absorption maximum wavelength 2 is based on the research of Asenjo et al. (Asenjo AB, et al: Neuron (1994) 12: 1131-1138). Due to individual differences and measurement errors in absorption maximum wavelengths, there is a difference of several nm between absorption maximum wavelength 1 and absorption maximum wavelength 2.

[0031] When homologous recombination does not occur in the red opsin gene, the maximum absorption wavelength of red opsin is approximately 560 nm. When homologous recombination occurs in an exon of the red opsin gene, resulting in the exon sequence of the green opsin gene, i.e., in the case of protanopia, the maximum absorption wavelength shifts from approximately 560 nm to shorter wavelengths. The greater the number of exons that undergo homologous recombination, the greater the shift in the maximum absorption wavelength.

[0032] When homologous recombination does not occur in the green opsin gene, the maximum absorption wavelength of green opsin is approximately 530 nm. When homologous recombination occurs in an exon of the green opsin gene, resulting in the exon sequence of the red opsin gene, i.e., in the case of deuteranopia, the maximum absorption wavelength shifts from approximately 530 nm to longer wavelengths. The greater the number of exons that undergo homologous recombination, the greater the shift in the maximum absorption wavelength.

[0033] In mixed protanopia (i-di-type color vision), both homologous recombination of the red opsin gene and homologous recombination of the green opsin gene occur, resulting in a shift in the absorption maximum wavelength of both red and green opsin.

[0034] In mild protanopia, homologous recombination occurs at most in exons 1 to 4, shifting the absorption maximum wavelength of L cone cells to approximately 550 nm. However, because there is a difference between the shifted absorption maximum wavelength of L cone cells (approximately 550 nm) and the absorption maximum wavelength of M cone cells (approximately 530 nm), protanopia can be corrected (bringing the color vision characteristics closer to those of a normal person) by changing the spectrum of light entering the human eye to correct this shift in the absorption maximum wavelength of L cone cells. On the other hand, in severe protanopia, homologous recombination occurs in exons 1 to 5 of the red opsin gene. In this case, the absorption maximum wavelength of L cone cells shifts to approximately 530 nm, making L cone cells most sensitive to green light. In other words, in this condition, L cone cells and M cone cells have nearly identical characteristics, making it difficult to correct severe protanopia simply by changing the spectrum of light entering the human eye.

[0035] Similarly, in mild deuteranopia, homologous recombination occurs at most in exons 1 to 4, shifting the absorption maximum wavelength of green opsin to approximately 535 nm. However, because there is a difference between the shifted absorption maximum wavelength of M cone cells (approximately 535 nm) and the absorption maximum wavelength of L cone cells (approximately 560 nm), deuteranopia can be corrected (bringing the color vision characteristics closer to those of a normal person) by changing the spectrum of light entering the human eye to compensate for this shift in the absorption maximum wavelength of M cone cells. On the other hand, in severe deuteranopia, homologous recombination occurs in exons 1 to 5 of the green opsin gene. In this case, the absorption maximum wavelength of M cone cells shifts to approximately 560 nm, making M cone cells most sensitive to red light. In other words, in this condition, M cone cells and L cone cells have nearly identical characteristics, making it difficult to correct severe deuteranopia simply by changing the spectrum of light entering the human eye.

[0036] Next, we will explain the characteristics of human color vision. Human L-cone cells and M-cone cells output signals corresponding to the intensity of the light they receive. According to Stell et al.'s hypothesis (Stell WK, Lightfoot DO, Wheeler TG, Leeper HF (1975) Goldfish retina: Functional polarization of cone horizontal cell dendrites and synapses. Science 190: 989-990), the output from L-cone cells is input to H-type horizontal cells, which then input to M-cone cells. M-cone cells output signals corresponding to the intensity of the received light and the signals input from L-type horizontal cells to R / G-type horizontal cells. The output from R / G-type horizontal cells is the difference between the outputs from L-cone cells and M-cone cells—in other words, the difference between the intensity of red light and the intensity of green light. The output from H-type and R / G-type horizontal cells is then sent to the visual cortex via retinal ganglion cells (aquamarine cells, bipolar cells, etc.), resulting in color vision.

[0037] That is, according to the hypothesis of Stell et al., it is presumed that red and green are not perceived as a direct correspondence between the outputs of L cone cells and M cone cells, but are perceived based on the output of L cone cells and the difference in output between L cone cells and M cone cells. Therefore, when correcting light intensity with a correction filter, it is presumed that color vision deficiency can be corrected by correcting the intensity of red light to which L cone cells are sensitive and the difference between the intensity of red light and the intensity of green light to which M cone cells are sensitive.

[0038] Figure 4 shows the relative absorption spectra of L and M cone cells in a person with normal color vision. While Figure 1 normalizes the absorption spectrum of each cone cell by its maximum value, Figure 4 shows the relative absorption spectrum of the L cone cell, using the maximum value of the absorption spectrum of the M cone cell as the reference. Figure 4 also shows the difference between the absorption spectra of the M and L cone cells (the absorption spectrum of the M cone cell minus the absorption spectrum of the L cone cell). This difference corresponds to the output from the R / G horizontal cells.

[0039] Humans generally perceive light with a single wavelength of approximately 546 nm as green and light with a single wavelength of approximately 580 nm as yellow. The relative absorption spectra of L cone cells and M cone cells shown in Figure 4 are estimated based on the assumption that the wavelength of green light is approximately 546 nm and the wavelength of yellow light is approximately 580 nm. When green light and red light are mixed at equal intensities, yellow light results. Therefore, it is inferred that the sensitivity of L cone cells and M cone cells are equal at the wavelength of yellow light (approximately 580 nm). Furthermore, humans perceive green light based on the output of R / G horizontal cells, which corresponds to the difference between the intensity of red light and the intensity of green light. Therefore, it is inferred that at the wavelength of green light (546 nm), the intensity of red light relative to the output of R / G horizontal cells becomes zero, i.e., the sensitivity of M cone cells is twice that of L cone cells. The relative absorption spectra of L cone cells and M cone cells shown in Figure 4 are based on these assumptions.

[0040] According to the hypothesis of Stell et al., humans perceive red light according to the output from L cone cells and green light according to the output from R / G horizontal cells. Therefore, in Figure 4, it is inferred that light with wavelengths longer than the wavelength XC (approximately 546 nm in healthy individuals), where the output from R / G horizontal cells (the absorption spectrum of M cone cells minus the absorption spectrum of L cone cells) intersects with the absorption spectrum of L cone cells, is perceived as reddish, and light with wavelengths shorter than wavelength XC is perceived as greenish.

[0041] Figure 5 shows the relative absorption spectra of L cone cells and M cone cells in a person with mild protanopia. The horizontal axis of Figure 5 represents the wavelength of light, and the vertical axis represents the absorption spectra of L cone cells and M cone cells. Figure 5 also shows the difference between the absorption spectra of M cone cells and L cone cells (the absorption spectrum of M cone cells minus the absorption spectrum of L cone cells). Figure 5 shows an example in which exons 1 to 4 of the red opsin gene are replaced with exons 1 to 4 of the green opsin gene, respectively, resulting in a shift in the maximum absorption wavelength of L cone cells from approximately 560 nm to approximately 550 nm.

[0042] Figure 6 shows the relative absorption spectra of L cone cells and M cone cells in a person with mild deuteranopia. The horizontal axis of Figure 6 represents the wavelength of light, and the vertical axis represents the absorption spectra of L cone cells and M cone cells. Figure 6 also shows the difference between the absorption spectra of M cone cells and L cone cells (the absorption spectrum of M cone cells minus the absorption spectrum of L cone cells). Figure 6 shows an example in which exons 1 to 4 of the green opsin gene are replaced with exons 1 to 4 of the red opsin gene, respectively, resulting in a shift in the maximum absorption wavelength of M cone cells from approximately 530 nm to approximately 535 nm.

[0043] Figure 7 shows the relative absorption spectra of L cone cells and M cone cells in a person with both mild protanopia and mild deuteranopia, i.e., a mixed protanopia. The horizontal axis of Figure 7 represents the wavelength of light, and the vertical axis represents the absorption spectra of L cone cells and M cone cells. Figure 7 also shows the difference between the absorption spectra of M cone cells and L cone cells (the absorption spectrum of M cone cells minus the absorption spectrum of L cone cells). A person with mixed protanopia has characteristics of both protanopia and deuteranopia, so the maximum absorption wavelength of L cone cells is approximately 550 nm, and the maximum absorption wavelength of M cone cells is approximately 535 nm.

[0044] Protanopia, deuteranopia, or mixed protanopia can be corrected by changing the spectrum of light incident on a person's eye so that the absorption spectra of the L and M cone cells shown in Figures 6 and 7 approach the absorption spectra of the L and M cone cells of a normal person shown in Figure 5. In other words, color vision can be corrected by matching the shifted absorption maximum wavelength to the absorption maximum wavelength of a normal person and by matching the relative sensitivity of the L and M cone cells to that of a normal person.

[0045] The correction filter in this embodiment performs correction based on the color vision characteristics of the subject, such as protanopia, deuteranopia, or mixed protanopia and deuteranopia, to bring the shifted maximum absorption wavelength of the L or M cone cells closer to the maximum absorption wavelength of a healthy subject, and to adjust the intensity ratio of red and green light.

[0046] (Correction Filter) Next, a correction filter for correcting mild protanopia, mild deuteranopia, or mixed protanopia and deuteranopia will be described. The correction filter corrects the color vision of the subject and is intended to be worn on the subject's eyes. For example, the correction filter may be worn by the subject, like glasses or contact lenses. Alternatively, the correction filter may be attached to a television or monitor screen used by the subject to adjust the colors of the television or monitor screen.

[0047] Fig. 8 shows the transmittance of a correction filter for correcting protanopia. The horizontal axis of Fig. 8 represents the wavelength of light, and the vertical axis represents the transmittance of the correction filter. The correction filter shown in Fig. 8 is a filter that brings the maximum absorption wavelength of L cone cells in people with protanopia closer to the maximum absorption wavelength of L cone cells in a normal person, and adjusts the difference or ratio between the intensity of red light and the intensity of green light.

[0048] The correction filter shown in FIG. 8 is set so that its transmittance increases from a wavelength XC at which the output from the R / G horizontal cell intersects with the absorption spectrum of the L cone cell, between the maximum absorption wavelength λM of the M cone cell of type 1 color vision and the maximum absorption wavelength λL of the L cone cell, toward a wavelength XL that is longer than the maximum absorption wavelength λL of the L cone cell.

[0049] Because the transmittance of the compensation filter is graded so that it increases from wavelength XC to wavelength XL, the intensity of light passing through the compensation filter near the maximum absorption wavelength λL of the L cone cells is reduced, and the intensity of light on the longer wavelength side than wavelength λL is relatively increased. Therefore, when a subject with protanopia wears this compensation filter, the peak of the absorption spectrum of the subject's L cone cells is shifted to the longer wavelength side. This allows the peak sensitivity of the L cone cells, which is shifted to the shorter wavelength side in protanopia, to be closer to the peak sensitivity of the L cone cells of a normal person.

[0050] The wavelength XL may be set to a wavelength that humans perceive as yellow for light of a single wavelength. For example, the wavelength XL is approximately 580 nm. This reduces the reduction in the intensity of yellow light caused by the correction filter, thereby preventing the correction filter from changing humans' color vision for yellow light.

[0051] 8 is set so that its transmittance increases from wavelength XC toward wavelengths shorter than wavelength XS1, which is shorter than the maximum absorption wavelength λM of M cone cells. As a result, the intensity of green light transmitted through the compensation filter decreases. This is because the transmittance of green light is reduced in accordance with the reduction in the transmittance of the compensation filter for light with wavelengths between wavelengths XC and XL (i.e., red light), thereby balancing the intensities of red light and green light.

[0052] The wavelength XS1 may be set to 498 nm, which is the maximum absorption wavelength of rod cells, thereby suppressing a reduction in the intensity of light received by the rod cells due to the correction filter.

[0053] (Correction of protanopia) Figure 9 shows the corrected absorption spectra of L cone cells and M cone cells when a subject with protanopia shown in Figure 5 wears the correction filter shown in Figure 8. The horizontal axis of Figure 9 represents the wavelength of light, and the vertical axis represents the absorption spectra of L cone cells and M cone cells. The difference between the absorption spectrum of M cone cells and the absorption spectrum of L cone cells, which corresponds to the output of R / G horizontal cells, is also shown. In Figure 9, the solid line represents the absorption spectrum before the correction filter was worn, and the dotted line represents the absorption spectrum corrected with the correction filter. The corrected absorption spectrum is obtained by multiplying the absorption spectra of L cone cells and M cone cells by the transmittance of the correction filter shown in Figure 8 at each wavelength.

[0054] In people with protanopia type 1, the maximum absorption wavelength of L cone cells shifts from approximately 560 nm in normal people to approximately 550 nm. In response, a correction filter changes the spectrum of light entering the human eye, returning the maximum absorption wavelength of L cone cells to approximately 560 nm. This makes it possible to correct the characteristics of L cone cells in people with protanopia type 1. Furthermore, this correction filter reduces the intensity of light in the green band that is transmitted. This makes it possible to correct the balance between the intensity of red and green light that is changed by the reduction in the intensity of red light when correcting the characteristics of L cone cells.

[0055] 8 is set so that the transmittance increases from wavelength XC to wavelength XL, and so that the transmittance increases from wavelength XC to the shorter wavelength side, so that the transmittance is set to a minimum value near wavelength XC. However, in this embodiment, the correction filter for correcting protanopia is not limited to this setting.

[0056] In this embodiment, for example, as shown in Fig. 10, the transmittance may be constant in the wavelength band from wavelength XC to wavelength XS1, which is shorter than the maximum absorption wavelength λM of M cone cells. Even in this configuration, the difference or ratio between the intensities of red light and green light can be adjusted.

[0057] Furthermore, the correction filter does not have to be a single filter. For example, the two correction filters shown in FIGS. 11 and 12 may be combined. The correction filter shown in FIG. 11 is set so that its transmittance increases from wavelength XC to wavelength XL, and is set so that the transmittance of the correction filter is high (for example, almost 100%) in the wavelength band from wavelength XC to wavelength XS1. The correction filter shown in FIG. 12 is set so that its transmittance increases from wavelength XC to wavelength XS1, and is set so that the transmittance of the correction filter is high (for example, almost 100%) in the wavelength band from wavelength XC to wavelength XL. By combining the two filters in this way, it is possible to adjust the difference or ratio between the intensities of red light and green light and simultaneously correct protanopia.

[0058] Fig. 13 shows the transmittance of an example of a correction filter for correcting deuteranopia. The horizontal axis of Fig. 13 represents the wavelength of light, and the vertical axis represents the transmittance of the correction filter. The correction filter shown in Fig. 13 is a filter that brings the maximum absorption wavelength of M cone cells in deuteranopia closer to the maximum absorption wavelength of M cone cells in a healthy individual.

[0059] The correction filter shown in Figure 13 is set so that its transmittance increases from wavelength XC, at which the output from the R / G horizontal cell intersects with the absorption spectrum of the L cone cell, to wavelength XS2, which is longer than the maximum absorption wavelength λM of the M cone cell in deuteranopia, and the maximum absorption wavelength λL of the L cone cell.

[0060] Because the transmittance of the compensation filter is graded so that it increases from wavelength XC to wavelength XM, the intensity of light passing through the compensation filter near the maximum absorption wavelength λM of the M cone cells is reduced, and the intensity of light on the shorter wavelength side than wavelength λM is relatively increased. Therefore, when a subject with deuteranopia wears this compensation filter, the compensation filter acts to shift the peak of the absorption spectrum of the subject's M cone cells to the shorter wavelength side. This allows the peak sensitivity of the M cone cells, which is shifted to the longer wavelength side in deuteranopia, to approach the peak sensitivity of the M cone cells of a normal person.

[0061] 13 is set so that its transmittance is low on the wavelength side longer than wavelength XC. As a result, the intensity of red light passing through the compensation filter is reduced. This is because the transmittance of red light is reduced in accordance with the reduction in the transmittance of the compensation filter for light of wavelengths between wavelength XC and wavelength XS2 (i.e., green light), thereby balancing the intensities of red light and green light.

[0062] The wavelength XS2 may be set to a wavelength that humans perceive as blue for light of a single wavelength. For example, the wavelength XS2 is approximately 450 nm. This reduces the reduction in the intensity of blue light caused by the correction filter, thereby preventing the correction filter from changing humans' color vision for blue light.

[0063] (Correction of Deuteranopia) Figure 14 shows the corrected absorption spectra of L cone cells and M cone cells when a subject with deuteranopia shown in Figure 6 wears the correction filter shown in Figure 13. The horizontal axis of Figure 14 represents the wavelength of light, and the vertical axis represents the absorption spectra of L cone cells and M cone cells. The difference between the absorption spectrum of M cone cells and the absorption spectrum of L cone cells, which corresponds to the output of R / G horizontal cells, is also shown. In Figure 14, the solid line represents the absorption spectrum before the correction filter was worn, and the dotted line represents the absorption spectrum corrected with the correction filter. The corrected absorption spectrum is obtained by multiplying the absorption spectra of L cone cells and M cone cells by the transmittance of the correction filter shown in Figure 13 at each wavelength.

[0064] In people with deuteranopia, the maximum absorption wavelength of M cone cells shifts from approximately 530 nm in normal people to approximately 535 nm. In response, a correction filter changes the spectrum of light entering the human eye, returning the maximum absorption wavelength of M cone cells to approximately 530 nm. This allows the characteristics of M cone cells in people with deuteranopia to be corrected. Furthermore, this correction filter reduces the intensity of light in the red band that is transmitted. This allows the balance between the intensity of red and green light, which has changed due to the reduction in the intensity of green light, to be corrected when correcting the characteristics of M cone cells.

[0065] 13 has a constant transmittance on the wavelength side longer than wavelength XC, but in this embodiment, the correction filter for correcting deuteranopia is not limited to this setting. For example, as shown in FIG. 15, the transmittance may be set to increase from wavelength XC toward wavelength XL, which is longer than the maximum absorption wavelength λL of L cone cells. Even with this configuration, the difference or ratio between the intensity of red light and the intensity of green light can be adjusted.

[0066] Furthermore, the correction filter does not have to be a single filter. For example, the two correction filters shown in FIGS. 16 and 17 may be combined. In the correction filter shown in FIG. 16, the transmittance is set to increase from wavelength XC to wavelength XS2, and the transmittance of other wavelength bands is set to be high (for example, approximately 100%). In the correction filter shown in FIG. 17, the transmittance of wavelength bands longer than wavelength XC is set to be lower than the other wavelength bands. By combining the two filters in this way, it is possible to adjust the difference or ratio between the intensity of red light and the intensity of green light and simultaneously correct deuteranopia.

[0067] Fig. 18 shows the transmittance of an example of a correction filter for correcting protanopia and deuteranopia. The horizontal axis of Fig. 18 represents the wavelength of light, and the vertical axis represents the transmittance of the correction filter. The correction filter shown in Fig. 18 has characteristics that combine those of a correction filter for correcting protanopia and a correction filter for correcting deuteranopia.

[0068] The correction filter shown in Figure 18 is set so that its transmittance increases from wavelength XC, at which the output from the R / G horizontal cell intersects with the absorption spectrum of the L cone cell, to wavelength XL, which is longer than the maximum absorption wavelength λL of the L cone cell, between the maximum absorption wavelength λM of the M cone cell of protanopia and the maximum absorption wavelength λL of the L cone cell.

[0069] The transmittance of the correction filter is sloped so that it increases from wavelength XC to wavelength XL, so that when a subject with protanopia (deuteranopia) wears this correction filter, the peak of the absorption spectrum of the subject's L cone cells is shifted to the longer wavelength side, thereby making it possible to bring the peak sensitivity of the L cone cells, which is shifted to the shorter wavelength side in protanopia (deuteranopia), closer to the peak sensitivity of the L cone cells of a normal person.

[0070] Furthermore, the correction filter shown in FIG. 18 is set so that its transmittance increases from a wavelength XC between the maximum absorption wavelength λM of the M cone cells of protanopia and the maximum absorption wavelength λL of the L cone cells toward a wavelength XS2 that is shorter than the maximum absorption wavelength λM of the M cone cells.

[0071] The transmittance of the correction filter is sloped so that it increases from wavelength XC to wavelength XM, so that when a subject with protanopia-deuteranopia wears this correction filter, the peak of the absorption spectrum of the subject's M cone cells is shifted to shorter wavelengths, thereby bringing the peak sensitivity of the M cone cells, which is shifted to longer wavelengths in deuteranopia, closer to the peak sensitivity of the M cone cells of a normal person.

[0072] (Correction of protanopia and deuteranopia) Figure 19 shows the corrected absorption spectra of the L cone cells and the M cone cells when a subject with protanopia and deuteranopia shown in Figure 7 wears the correction filter shown in Figure 18. The difference between the absorption spectrum of the M cone cells and the absorption spectrum of the L cone cells, which corresponds to the output of the R / G horizontal cells, is also shown. The horizontal axis of Figure 19 represents the wavelength of light, and the vertical axis represents the absorption spectra of the L cone cells and the M cone cells. In Figure 19, the solid line represents the absorption spectrum before the correction filter was worn, and the dotted line represents the absorption spectrum corrected with the correction filter. The corrected absorption spectrum is obtained by multiplying the absorption spectra of the L cone cells and the M cone cells by the transmittance of the correction filter shown in Figure 18 at each wavelength.

[0073] In people with protanopia and deuteranopia, the maximum absorption wavelength of L cone cells shifts from approximately 560 nm in healthy people to approximately 550 nm, and the maximum absorption wavelength of M cone cells shifts from approximately 530 nm in healthy people to approximately 535 nm. In contrast, the correction filter works by changing the spectrum of light incident on the human eye, returning the maximum absorption wavelength of L cone cells to around 560 nm and the maximum absorption wavelength of M cone cells to around 530 nm. This makes it possible to correct the characteristics of M cone cells in people with protanopia and deuteranopia.

[0074] The correction filter for correcting protanopia does not have to be configured by a single filter. For example, the correction filter for correcting protanopia may be configured by superimposing a correction filter for correcting protanopia and a correction filter for correcting deuteranopia.

[0075] (Method for Testing Color Vision) In the present embodiment, the correction filters are used to correct the color vision of subjects with protanopia, deuteranopia, mixed protanopia, etc., but the present embodiment is not limited to this configuration. For example, these correction filters may be used to test the color vision of subjects.

[0076] When conducting a color vision test, the subject wears a correction filter that corrects protanopia, deuteranopia, or mixed protanopia and deuteranopia, and observes the surrounding scenery and test images. The test image may be, for example, a diagram from the well-known Ishihara color vision test. Ishihara color vision test diagrams are commonly used in tests for color vision deficiencies. Ishihara color vision test diagrams are colored so that figures (e.g., letters such as numbers) can be recognized when color vision is normal or when color vision deficiencies have been appropriately corrected. Tests using Ishihara color vision test diagrams are well known to those skilled in the art, and therefore will not be described further in this specification.

[0077] The subject observes the test image through a correction filter while changing the type of correction filter worn and the degree of correction. Types of correction filters include filters that correct protanopia, deuteranopia, and mixed protanopia. The degree of correction is changed by changing the transmittance of the correction filter. The subject observes the test image while changing the correction filter worn and selects a correction filter that allows the subject to clearly recognize figures included in the test image, thereby testing the subject's color vision characteristics. Furthermore, a correction filter that allows the subject to clearly recognize figures included in the test image can be used as a filter that corrects the color vision characteristics of that subject. The conditions under which the subject can clearly recognize figures included in the test image are an example of the predetermined conditions of the present application.

[0078] Fig. 20 shows the transmittance of five correction filters 1 to 5 that correct type 1 color vision. The horizontal axis of Fig. 20 represents the wavelength of light, and the vertical axis represents the transmittance of the correction filter. The multiple correction filters 1 to 5 shown in Fig. 20 have the same wavelength XC at which the transmittance is minimal and the same wavelengths (wavelengths XS1 and XL) at which the transmittance begins to decrease toward wavelength XC, that is, the same wavelength bands with low transmittance, but have different transmittances.

[0079] Since people's color vision characteristics vary from person to person, for example, even if they have the same type 1 color vision, their sensitivity to red light and green light varies. This difference in sensitivity is caused by, for example, the number and abundance ratio of L cone cells and M cone cells. Therefore, as shown in Figure 20, by using multiple correction filters with different transmittances, it is possible to more accurately test the color vision characteristics of the subject.

[0080] Fig. 21 shows the transmittance of five correction filters 6 to 9 that correct type 1 color vision. The horizontal axis of Fig. 21 represents the wavelength of light, and the vertical axis represents the transmittance of the correction filter. The multiple correction filters 6 to 9 shown in Fig. 21 differ from one another in terms of wavelength XC at which the transmittance is minimal and wavelengths (wavelengths XS1 and XL) at which the transmittance begins to decrease toward wavelength XC, i.e., in terms of wavelength bands with low transmittance.

[0081] As described above, the maximum absorption wavelength of a human M cone cell shifts depending on the number of exon homologous recombinations that have occurred in the green opsin gene, and the maximum absorption wavelength of a human L cone cell shifts depending on the number of exon homologous recombinations that have occurred in the red opsin gene. Therefore, as shown in Figure 21, by using multiple correction filters with different wavelength ranges of low transmittance, it is possible to more accurately test the color vision characteristics of the subject.

[0082] 20, the transmittance at wavelength XC of correction filters 1 to 5 differs in increments of approximately 5%, but the configuration of this embodiment is not limited to this. The multiple correction filters may differ in transmittance at wavelength XC in smaller increments (for example, in increments of approximately 3%) in order to test the color vision characteristics of the subject more accurately. Alternatively, the transmittance may differ in larger increments (for example, in increments of approximately 10%) in order to perform the test more quickly.

[0083] 21, the wavelength bands of low transmittance differ in increments of approximately 5 nm, but the configuration of this embodiment is not limited to this. The wavelength bands of low transmittance of the multiple correction filters may differ in smaller increments (for example, in increments of approximately 3 nm) in order to more accurately test the color vision characteristics of the subject. Alternatively, the wavelength bands of low transmittance may differ in larger increments (for example, in increments of approximately 10 nm) in order to perform the test more quickly.

[0084] 20 shows the characteristics of a plurality of correction filters 1 to 5 that differ only in transmittance without changing the wavelength band in which the transmittance is low, and FIG. 21 shows the characteristics of a plurality of correction filters 6 to 9 that have the same transmittance but different wavelength bands in which the transmittance is low, but the characteristics of the correction filters in this embodiment are not limited to these. A plurality of correction filters that differ from each other in both the transmittance and the wavelength band in which the transmittance is low may be used to test or correct the color vision characteristics of a subject.

[0085] 20 and 21 have a transmittance of 1 (approximately 100%) on the wavelength side shorter than wavelength XS1 and on the wavelength side longer than wavelength XL, but the correction filter of this embodiment is not limited to this configuration. The transmittance on the wavelength side shorter than wavelength XS1 or on the wavelength side longer than wavelength XL may be a value smaller than 1. This reduces the intensity of light in the visible light band incident on the subject's eyes, making it easier to test the color vision characteristics of subjects with photosensitivity who are sensitive to light. Furthermore, a correction filter with a transmittance set to a value smaller than 1 on the wavelength side shorter than wavelength XS1 or on the wavelength side longer than wavelength XL may be used to correct the color vision characteristics of subjects with photosensitivity who are sensitive to light.

[0086] FIG. 22 is a diagram showing the transmittance of a correction filter according to another embodiment of the correction filter. The horizontal axis of FIG. 22 represents the wavelength of light, and the vertical axis represents the transmittance of the correction filter. The correction filter shown in FIG. 22 is obtained by offsetting the correction filter shown in FIG. 8 so that the transmittance is lower across the entire visible light band. Between wavelengths XS1 and XL, the transmittance is set lower on the shorter wavelength side than XS1 and on the longer wavelength side than XL. By lowering the transmittance across the entire visible light band in this manner, it becomes easier to test the color vision characteristics of subjects with photosensitivity who are sensitive to light. The offset of the transmittance is not limited to the example shown in FIG. 22 . For example, a test of the color vision characteristics of a subject may be performed using multiple correction filters with different offset amounts. Furthermore, a correction filter with an offset transmittance may be used to correct the color vision characteristics of subjects with photosensitivity who are sensitive to light.

[0087] 20 and 21 show the characteristics of a correction filter for testing or correcting the color vision characteristics of a subject with protanopia, but this embodiment is not limited to this configuration. By changing the transmittance of the correction filter or the area where the transmittance is low, it is possible to test or correct the color vision characteristics of a subject with deuteranopia or mixed protanopia.

[0088] Figures 23 and 24 show the characteristics of correction filters for testing the color vision characteristics of a subject with deuteranopia. The horizontal axis of Figures 23 and 24 represents the wavelength of light, and the vertical axis represents the transmittance of the correction filter. The multiple correction filters 11 to 15 shown in Figure 23 have the same wavelength XC at which the transmittance is minimal and the same wavelength (wavelength XS2) at which the transmittance begins to decrease toward wavelength XC, i.e., the same wavelength bands with low transmittance, but have different transmittances. The multiple correction filters 16 to 20 shown in Figure 24 have different wavelengths XC at which the transmittance is minimal and the same wavelength (wavelength XS2) at which the transmittance begins to decrease toward wavelength XC, i.e., different wavelength bands with low transmittance.

[0089] The subject observes the test image while changing the correction filters 11 to 20 they wear, and by selecting the correction filter that makes it easiest for the subject to recognize the characters in the test image, the subject's deuteranopia characteristics can be tested. In addition, the correction filter that enables the subject to clearly recognize the figures included in the test image can be used as the filter that corrects the subject's color vision characteristics.

[0090] Figures 25 and 26 show the characteristics of correction filters for testing the color vision characteristics of subjects with protanopia and deuteranopia. The horizontal axis of Figures 25 and 26 represents the wavelength of light, and the vertical axis represents the transmittance of the correction filter. The multiple correction filters 21 to 25 shown in Figure 25 have the same wavelength XC at which the transmittance is minimal and the same wavelengths (wavelengths XS2 and XL) at which the transmittance begins to decrease toward wavelength XC, i.e., the same wavelength bands with low transmittance, but have different transmittances. The multiple correction filters 26 to 30 shown in Figure 26 have different wavelengths XC at which the transmittance is minimal and the same wavelengths (wavelengths XS2 and XL) at which the transmittance begins to decrease toward wavelength XC, i.e., the same wavelength bands with low transmittance.

[0091] The subject observes the test image while changing the correction filters 21 to 30 they wear, and by selecting the correction filter that makes it easiest for the subject to recognize the characters in the test image, the subject's characteristics of protanopia and dianthus color vision can be tested. In addition, the correction filter that enables the subject to clearly recognize figures included in the test image can be used as the filter that corrects the subject's color vision characteristics.

[0092] Note that the correction filters 11 to 15 shown in Fig. 23 and the correction filters 21 to 25 shown in Fig. 25 have transmittances at wavelength XC that vary in increments of approximately 5%, but the configuration of this embodiment is not limited to this. The multiple correction filters may have transmittances at wavelength XC that vary in smaller increments (for example, in increments of approximately 3%) in order to test the color vision characteristics of the subject more accurately. Alternatively, the transmittances may vary in larger increments (for example, in increments of approximately 10%) in order to perform the test more quickly.

[0093] 23 and 24 have a transmittance set to 1 (approximately 100%) on the shorter wavelength side than the wavelength XS2, but the correction filter of this embodiment is not limited to this configuration. The transmittance on the shorter wavelength side than the wavelength XS2 may also be a value smaller than 1. Furthermore, the correction filters shown in FIGS. 23 and 24 may have a uniform offset in transmittance so that the transmittance is low across the entire visible light band.

[0094] Furthermore, the correction filters 16 to 20 shown in Fig. 24 and the correction filters 26 to 30 shown in Fig. 25 have wavelength bands with low transmittance that differ in increments of approximately 5 nm, but the configuration of this embodiment is not limited to this. The multiple correction filters may have wavelength bands with low transmittance that differ in smaller increments (for example, in increments of approximately 3 nm) in order to more accurately test the color vision characteristics of the subject. Alternatively, the wavelength bands with low transmittance that differ in larger increments (for example, in increments of approximately 10 nm) in order to perform the test more quickly.

[0095] 25 and 26 have a transmittance set to 1 (approximately 100%) on the wavelength side shorter than wavelength XS2 and on the wavelength side longer than wavelength XL, but the correction filter of this embodiment is not limited to this configuration. The transmittance on the wavelength side shorter than wavelength XS2 or on the wavelength side longer than wavelength XL may be a value smaller than 1. The correction filters shown in FIGS. 25 and 26 may have a uniform offset in transmittance so that the transmittance is low across the entire visible light band.

[0096] Furthermore, the correction filters 11 to 30 differ from one another in either the transmittance or the wavelength band in which the transmittance is low, but the configuration of this embodiment is not limited to this. A plurality of correction filters that differ from one another in both the transmittance and the wavelength band in which the transmittance is low may be used to test or correct the color vision characteristics of a subject.

[0097] In this way, by testing the color vision characteristics of a subject using a plurality of correction filters, it is possible to create a correction filter that corrects the color vision characteristics of the subject based on the test results.

[0098] In this embodiment, the testing and correction of protanopia, deuteranopia, and mixed protanopia and deuteranopia have been described, but the embodiments of the present invention are not limited to this configuration. For example, if the maximum absorption wavelength at which the absorption spectra of the S cone cells, rod cells, etc. of the subject peaks is different from that of a healthy person, the testing and correction of the subject's color vision may be performed using a correction filter that shifts this maximum absorption wavelength.

[0099] The above is a description of exemplary embodiments of the present invention. The embodiments of the present invention are not limited to those described above, and various modifications are possible within the scope of the technical concept of the present invention. For example, the embodiments of the present invention also include appropriate combinations of embodiments explicitly shown as examples in the specification or obvious embodiments.

Claims

1. A correction filter that changes the spectrum of light that is transmitted, and changes the spectrum of light in a wavelength band that includes at least one of the maximum absorption wavelength λL, at which the absorption spectrum of a human L cone cell peaks, and the maximum absorption wavelength λM, at which the absorption spectrum of a human M cone cell peaks.

2. The correction filter according to claim 1, wherein the transmittance is set to increase from a wavelength XC between the maximum absorption wavelength λL and the maximum absorption wavelength λM toward a wavelength XL longer than the maximum absorption wavelength λL.

3. The compensation filter according to claim 2, wherein the wavelength XC is set to a wavelength near a wavelength at which a difference spectrum obtained by subtracting the absorption spectrum of L cone cells from the absorption spectrum of M cone cells of a human intersects with the absorption spectrum of L cone cells.

4. The correction filter according to claim 3, wherein the wavelength XC is approximately 540 nm.

5. The correction filter according to any one of claims 2 to 4, wherein the wavelength XL is a wavelength that is recognized as yellow by humans with respect to light of a single wavelength of the wavelength XL.

6. The compensation filter according to claim 5, wherein the wavelength XL is approximately 580 nm.

7. The correction filter according to any one of claims 2 to 6, wherein the correction filter corrects the color vision characteristics of a subject, and changes the intensity of light in the wavelength band from the wavelength XC to the wavelength XL based on the color vision characteristics of the subject.

8. The correction filter according to any one of claims 2 to 7, wherein the transmittance is set to increase from the wavelength XC toward a wavelength XS1 that is shorter than the maximum absorption wavelength λM.

9. The compensation filter according to claim 8, wherein the wavelength XS1 is set to be in the vicinity of a maximum absorption wavelength λROD at which the absorption spectrum of human L cone cells reaches a peak.

10. The correction filter according to claim 8, wherein the wavelength XS1 is approximately 498 nm.

11. The correction filter according to claim 1, wherein the transmittance is set to increase from a wavelength XC between the maximum absorption wavelength λL and the maximum absorption wavelength λM toward a wavelength XS2 that is shorter than the maximum absorption wavelength λM.

12. The compensation filter according to claim 11, wherein the wavelength XC is set to a wavelength near the wavelength at which a difference spectrum obtained by subtracting the absorption spectrum of L cone cells from the absorption spectrum of M cone cells of a human intersects with the absorption spectrum of L cone cells.

13. The correction filter according to claim 12, wherein said wavelength XC is approximately 546 nm.

14. A correction filter according to any one of claims 11 to 13, wherein the wavelength XS2 is set to be in the vicinity of a wavelength at which the absorption spectrum of a human M cone cell and the absorption spectrum of a human S cone cell intersect.

15. A correction filter according to any one of claims 11 to 13, wherein the wavelength XS2 is approximately 450 nm.

16. The correction filter according to any one of claims 11 to 15, wherein the correction filter corrects the color vision characteristics of a subject, and changes the intensity of light in the wavelength band from the wavelength XC to the wavelength XS2 based on the color vision characteristics of the subject.

17. A correction filter as claimed in claim 1, wherein the transmittance is set to increase from a wavelength XC between the maximum absorption wavelength λL and the maximum absorption wavelength λM towards a wavelength XL longer than the maximum absorption wavelength λL, and the transmittance is set to increase from a wavelength XC between the maximum absorption wavelength λL and the maximum absorption wavelength λM towards a wavelength XS2 shorter than the maximum absorption wavelength λM.

18. A correction filter comprising a correction filter according to any one of claims 1 to 10 and a correction filter according to any one of claims 11 to 16 superimposed on each other.

19. A color vision testing method using a correction filter according to any one of claims 1 to 18, comprising a determination step of determining whether or not a test image satisfies a predetermined condition when viewed by a subject through the correction filter.

Images