vision tester
By designing a vision testing instrument with adjustable lens groups, the issues of convenience and economy in vision testing in home and school settings have been solved, realizing portable and low-cost vision testing, which is suitable for continuous vision monitoring of teenagers.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- BOE YIYUN (ZHENGZHOU) TECH CO LTD
- Filing Date
- 2025-01-20
- Publication Date
- 2026-06-16
AI Technical Summary
Existing vision testing methods are difficult to implement in a convenient and efficient manner for continuous monitoring in home or school settings. Traditional vision chart tests require fixed locations and assistants, and professional optometry equipment is expensive and not portable.
A vision tester including an imaging lens group is designed. The lens group consists of a first lens and a second lens. The lens spacing is adjustable. The lens group is located inside an outer box. The open end face of the outer box can be close to the periorbital area to shield external light. The refractive power is detected by observing the optotype by adjusting the lens distance.
It enables convenient and economical vision testing in home or school environments, shields against external light interference, ensures test accuracy, has a simple structure, low cost, and is suitable for continuous vision monitoring of teenagers.
Smart Images
Figure CN224357586U_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of vision testing equipment technology, and in particular to a vision testing instrument. Background Technology
[0002] In recent years, the myopia rate among Chinese teenagers has remained high, especially among students. The increase in online classes and prolonged close-range use of the eyes have exacerbated this problem. Therefore, it is particularly important to conduct regular vision screenings for students and to track their eye health.
[0003] Currently, vision tests are typically conducted using eye charts, but this method has several limitations. Eye chart tests require a fixed location, with the chart placed at least 5 meters away from the test subject. This necessitates sufficient space and at least one assistant, making the entire process relatively cumbersome. Furthermore, this traditional vision testing method is difficult to conduct frequently in everyday settings such as homes or schools, thus failing to meet the need for continuous monitoring of adolescents' vision.
[0004] On the other hand, professional optometry equipment is mainly concentrated in optical shops or eye hospitals. This equipment is bulky and expensive, making it difficult to deploy in home or school settings. Therefore, existing technologies are significantly insufficient in providing convenient and efficient vision screening and tracking solutions for home and school environments. To improve this situation, developing a portable, easy-to-use, and economical vision testing tool is urgently needed. Utility Model Content
[0005] The purpose of this invention is to provide a vision testing device to meet the need for continuous monitoring of adolescents' vision at home or school to a certain extent.
[0006] This utility model provides a vision testing instrument, including an outer box and an imaging lens group;
[0007] The imaging lens group includes a first lens and a second lens, which are arranged sequentially along the optical axis of the imaging lens group. The second lens has positive optical power, and the first lens has negative optical power.
[0008] The second lens is directed toward the eye of the test subject, who can observe a target at a predetermined distance in front of them through the imaging lens group, and the distance between the first lens and the second lens along the optical axis is adjustable;
[0009] The imaging lens group is disposed inside the outer box. The length direction of the outer box is along the optical axis of the imaging lens group. Both ends of the length direction of the outer box are through. A limiting segment is formed between the end face of the outer box facing the eye of the test subject and the optical center of the second lens. The length of the limiting segment is a, 1.2cm≤a≤1.5cm.
[0010] Furthermore, the range of the refractive power X of the test subject's eye that can be detected by the vision tester satisfies: -7D≤X≤4D.
[0011] Furthermore, the distance between the optical centers of the first lens and the second lens is d, where 0 < d ≤ 250 mm.
[0012] Furthermore, when X = -7D, d = d min When X = 4D, d = d max ;d max -d min ≥150mm.
[0013] Furthermore, the outer casing includes a first casing and a second casing;
[0014] Both ends of the first box and the second box are through, and one end of the first box is retractably inserted into the second box from one end of the second box.
[0015] The first lens is disposed inside the first housing, and the second lens is disposed inside the second housing at the end away from the first housing.
[0016] Furthermore, the first box body and the second box body are fitted with a clearance fit;
[0017] Alternatively, both the first and second boxes are cylindrical. The inner wall of the second box away from the second lens is provided with an internal threaded connection part, and the outer wall of the end of the first box inserted into the second box is provided with an external threaded connection part. The external threaded connection part is adapted to be screwed into the internal threaded connection part.
[0018] Furthermore, the second housing has a limiting segment of a predetermined length between one end of the second lens and the second lens to limit the distance between the subject's eye and the second lens.
[0019] Furthermore, a diopter scale is provided on the outer wall of the first box along the length of the first box;
[0020] The second housing has a viewing window on its side wall, and a pointer is provided at the viewing window. The refractive power represented by the scale aligned with the pointer on the refractive power scale can be read through the viewing window.
[0021] Furthermore, the smallest division of the diopter scale is 0.25D.
[0022] Furthermore, the target is an image with a target graphic, the target graphic including a ring and multiple isosceles triangles, the multiple isosceles triangles being evenly spaced around the ring with the ring as their base;
[0023] The color of the target graphic is different from that of the main body of the image.
[0024] Furthermore, the image is surrounded by a ring-shaped filled area, the color of which is different from the color of the main body of the image;
[0025] or,
[0026] The image has multiple strip-shaped color blocks evenly spaced around the target graphic. The length direction of each strip-shaped color block is set along the radial direction of its circumference. The angle between two adjacent strip-shaped color blocks is 15° to 30°. The ends of the strip-shaped color blocks away from the target graphic are sequentially marked with natural numbers starting from 1.
[0027] The color of the striped color block is different from the color of the main part of the image.
[0028] Compared with the prior art, the beneficial effects of this utility model are as follows:
[0029] The vision testing instrument provided by this utility model includes an imaging lens group, which includes a first lens and a second lens. The first lens is a concave lens with negative optical power, and the second lens is a convex lens with positive optical power. The first and second lenses are spaced apart along the optical axis of the imaging lens group, and the distance between the first and second lenses along the optical axis is adjustable. The imaging lens group is located inside an outer box, the length of which extends along the optical axis of the imaging lens group, and both ends of the outer box are open. During vision testing, the test subject holds the outer box with the end containing the second lens 2 (convex lens) facing the test subject's eyes. The test subject then observes a target at a predetermined distance through the imaging lens group and adjusts the distance between the first and second lenses until the test subject can clearly see the target.
[0030] The outer casing, with its end facing the test subject's eye, forms a limiting segment between itself and the optical center of the second lens. The length of this limiting segment is 'a', which satisfies the condition: 1.2cm ≤ a ≤ 1.5cm. During testing, the end of the outer casing with the second lens can gently rest against the test subject's eye. The limiting segment maintains a distance 'a' between the second lens and the test subject's eye, simulating the distance between the eye and the lens when wearing glasses. Simultaneously, the limiting segment, positioned between the test subject's eye and the second lens, effectively shields the test from ambient light interference, ensuring accurate results. Furthermore, the limiting segment prevents the surface of the second lens from being directly exposed to the external environment, avoiding scratches that could affect the accuracy of the test results.
[0031] When the first and second lenses are brought closer together, and the visual target is just clearly visible to the human eye, the image distance of the second lens is the far point distance of the tested eye, and the reciprocal of the image distance of the second lens is the refractive power of the tested eye. Given the focal lengths of the first and second lenses, the image distance of the second lens, and thus the refractive power of the tested eye, can be calculated from the distance between the first and second lenses. Therefore, the imaging lens group of the vision testing instrument of this application can be used for vision testing, and its overall structure is simple and low-cost, making it easy to integrate into home or school environments, thereby meeting the need for continuous monitoring of the vision of teenagers. Furthermore, by using a combination of concave and convex lenses, the image formed is upright, without any inversion (up, down, left, or right), making it easier to view the visual target. Attached Figure Description
[0032] To more clearly illustrate the specific embodiments of this utility model or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this utility model. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.
[0033] Figure 1 A schematic diagram of the imaging lens group of the vision testing instrument provided in an embodiment of this utility model;
[0034] Figure 2 This is a schematic diagram of the structure of the vision testing instrument provided in an embodiment of the present utility model;
[0035] Figure 3 A schematic diagram of the optotype of the vision tester provided in an embodiment of this utility model;
[0036] Figure 4 Another schematic diagram of the visual target of the vision tester provided in this embodiment of the present invention.
[0037] Figure label:
[0038] 1-First lens, 2-Second lens, 3-Second housing, 4-First housing, 5-Pointer, 6-Diopter scale, 7-Limiting segment, 8-Viewing window. Detailed Implementation
[0039] The technical solution of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of this utility model, but not all embodiments.
[0040] The components of the present invention embodiments described and shown in the accompanying drawings can typically be arranged and designed in a variety of different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention.
[0041] Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this utility model.
[0042] In the description of this utility model, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the accompanying drawings and are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this utility model. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.
[0043] In the description of this utility model, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.
[0044] The following reference Figures 1 to 4 This application describes a vision testing device according to some embodiments.
[0045] This application provides a vision testing device, such as... Figure 1As shown, the vision testing instrument includes an outer box and an imaging lens group. The imaging lens group includes a first lens 1 and a second lens 2. The first lens 1 is a concave lens with negative optical power, and the second lens 2 is a convex lens with positive optical power. The first lens 1 and the second lens 2 are spaced apart along the optical axis of the imaging lens group, and the distance between the first lens 1 and the second lens 2 along the optical axis is adjustable.
[0046] The imaging lens group is located inside the outer box. The length of the outer box extends along the optical axis of the imaging lens group, and both ends of the length of the outer box are open. When testing vision, the test subject can hold the outer box with the end of the outer box containing the second lens 2 (convex lens) facing the test subject's eyes. Then, the test subject observes the target at a predetermined distance in front through the imaging lens group and adjusts the distance between the first lens 1 and the second lens 2 until the test subject can just clearly see the target.
[0047] In this design, a limiting segment 7 is formed between the end face of the outer box facing the test subject's eye and the optical center of the second lens 2. The length of the limiting segment 7 is 'a', which satisfies the condition: 1.2cm ≤ a ≤ 1.5cm. During testing, the end face of the outer box with the second lens 2 can gently rest against the test subject's eye. The limiting segment 7 maintains a distance 'a' between the second lens 2 and the test subject's eye, simulating the distance between the eye and the lens when wearing glasses. Simultaneously, during visual acuity testing, the limiting segment 7, positioned between the test subject's eye and the second lens 2, effectively shields the test process from interference from ambient light, ensuring the accuracy of the test results. Furthermore, the limiting segment 7 prevents the second lens 2 from being directly exposed to the external environment, avoiding scratches on its surface that could affect the accuracy of the test results.
[0048] When the first and second lenses are brought closer together, and the target is just clearly visible to the human eye, the image distance of the second lens 2 is the far point distance of the tested eye, and the reciprocal of the image distance of the second lens 2 is the refractive power of the tested eye. Given the focal lengths of the first lens 1 and the second lens 2, the image distance of the second lens 2 can be calculated from the distance between the first lens 1 and the second lens 2, thus obtaining the refractive power of the tested eye.
[0049] For example, the refractive power of the test subject's eye is X, the focal length of the first lens 1 is f1, and the focal length of the second lens 2 is f2. When the test subject's eye clearly sees the target, the distance between the optical centers of the first lens 1 and the second lens 2 is d, the object distance of the first lens 1 is u1, the image distance of the first lens 1 is v1, and the object distance of the second lens 2 is u2. The image distance of the first lens 1 is the distance between the optical center of the first lens 1 and the image formed by the first lens 1, and the object distance of the second lens 2 is the distance between the image formed by the first lens 1 and the optical center of the second lens 2. Therefore, u2 = d - v1.
[0050] For the first lens 1, according to the Gaussian imaging formula, 1 / u1 + 1 / v1 = 1 / f1;
[0051] For the second lens 2, according to the Gaussian imaging formula, 1 / (d-v1)+X=1 / f2;
[0052] From the above two formulas, the relationship between the refractive power X of the tested human eye and the distance d between the optical centers of the two lenses can be derived: The object distance u1 of the first lens 1 is the distance between the visual target and the optical center of the first lens 1. Since the distance between the visual target and the test subject is much greater than the length of the visual acuity tester, the object distance of the first lens 1 can be approximated as the distance between the test subject and the visual target, that is, u1 is also known.
[0053] Therefore, the imaging lens group of the vision testing instrument of this application can be used for vision testing, and the overall structure is simple and low in cost, so as to be popularized in home or school environments, thereby meeting the needs of continuous monitoring of the vision of teenagers; at the same time, by using concave and convex lenses together, the image formed is an upright image, and there will be no upside down or left and right reversal, which is more conducive to viewing the visual target.
[0054] In one embodiment of this application, preferably, the testing range of the vision tester, that is, the range of values of the refractive power X of the human eye that it can detect, satisfies: -7D≤X≤4D, so as to meet most vision measurement requirements.
[0055] In this embodiment, preferably, under the premise of satisfying the above-mentioned test range, the distance d between the optical centers of the first lens 1 and the second lens 2 satisfies: 0 < d ≤ 250 mm. This ensures that the distance between the first lens 1 and the second lens 2 is neither too short, resulting in low measurement accuracy, nor too long, causing inconvenience in testing.
[0056] More preferably, when X = -7D, the distance d between the optical centers of the first lens 1 and the second lens 2 is d = d min When X = 4D, the distance d between the optical centers of the first lens 1 and the second lens 2 is d = d max d max -d min The travel is ≥150mm, which ensures that the first lens 1 has a suitable stroke relative to the second lens 2 while meeting the refractive power measurement range, thereby guaranteeing test accuracy, improving test precision, and enhancing the convenience of operation during the test.
[0057] Next, a vision testing device based on a specific example will be described. In this example, the focal length of the first lens 1 is f1 = -0.05m, the focal length of the second lens 2 is f2 = 0.125m, and the visual target is fixed at a position 3m in front of the test subject during the test. The relationship between X and d is shown in Table 1 below.
[0058] Table 1
[0059]
[0060] As shown in Table 1, when the refractive power X of the tested human eye is -7D, the distance d between the optical centers of the first lens 1 and the second lens 2 is the smallest, i.e., d min The distance d between the optical centers of the first lens 1 and the second lens 2 is the largest when the refractive power X of the tested eye is 4, which is 17.49 mm. max The value is 200.82 mm; d satisfies: 0 < d ≤ 250 mm, and at the same time, d max -d min =183.33mm, satisfying d max -d min ≥150mm.
[0061] In one embodiment of this application, preferably, as Figure 2 As shown, the outer box includes a first box body 4 and a second box body 3. Both ends of the first box body 4 and the second box body 3 are open. One end of the first box body 4 is retractably inserted into the interior of the second box body 3 through one end of the second box body 3. That is, the first box body 4 can move towards the outside of the second box body 3 and also towards the inside of the second box body 3.
[0062] The first lens 1 is disposed inside the first housing 4, and the second lens 2 is disposed at the end of the second housing 3 away from the first housing 4. Therefore, when performing a vision test using the vision testing instrument of this application, the end of the second housing 3 with the second lens 2 is directed toward the eyes of the test subject, and then the first housing 4 is moved to adjust the distance between the first lens 1 inside the first housing 4 and the second lens 2 inside the second housing 3. Specifically, by moving the first housing 4 toward the inside of the second housing 3, the distance between the first lens 1 and the second lens 2 can be reduced, and by moving the first housing 4 toward the outside of the second housing 3, the distance between the first lens 1 and the second lens 2 can be increased.
[0063] In this embodiment, preferably, as follows: Figure 2 As shown, the first housing 4 and the second housing 3 are fitted together with a clearance, allowing the first housing 4 to be inserted precisely into the second housing 3 and to extend or retract relative to the second housing 3. When it is necessary to reduce the distance between the first lens 1 and the second lens 2, simply push the first housing 4 into the second housing 3; when it is necessary to increase the distance between the first lens 1 and the second lens 2, simply pull the first housing 4 outward from the second housing 3.
[0064] In this embodiment, the cross-sections of the first box 4 and the second box 3 can be circular or square.
[0065] Regarding the telescoping fit between the first housing 4 and the second housing 3, in another embodiment, preferably, both the first housing 4 and the second housing 3 are cylindrical. The inner wall of the end of the second housing 3 away from the second lens 2 has an internal thread connection, and the outer wall of the end of the first housing 4 inserted into the second housing 3 has an external thread connection. The external thread connection matches the internal thread connection, allowing the first housing 4 to be screwed onto the second housing 3. Furthermore, by rotating the first housing 4, it can be moved towards the inside or outside of the second housing 3. For example, rotating the first housing 4 clockwise allows it to extend outwards from the second housing 3, increasing the distance between the first lens 1 and the second lens 2; rotating the first housing 4 counterclockwise allows it to move towards the inside of the second housing 3, decreasing the distance between the first lens 1 and the second lens 2. The threaded connection method is used to adjust the optical center distance between the two lenses. min No requirements, d max It still needs to meet the requirement of ≤250mm.
[0066] In one embodiment of this application, preferably, as Figure 2 As shown, for a vision testing instrument in which the first housing 4 moves linearly to adjust the distance between the first lens 1 and the second lens 2, according to the relationship between the diopter X and the distance d between the optical centers of the two lenses, a diopter scale 6 is set on the outer wall of the first housing 4 along the length of the first housing 4. The scale value of the diopter scale 6 near the second lens 2 is 4D, and the scale value away from the second lens 2 is -7D. At the same time, the minimum scale of the diopter scale 6 is 0.25D.
[0067] The second housing 3 is provided with a window 8 at a position opposite to the diopter scale 6, and a pointer 5 is provided at the window 8. When the first housing 4 moves to the predetermined position, the scale value of the diopter scale 6 aligned with the pointer 5 can be read through the window 8. This scale value is the diopter X corresponding to the distance d between the optical centers of the first lens 1 and the second lens 2 at this time.
[0068] During the vision test, firstly, pull the first box 4 outwards towards the second box 3 so that the scale value corresponding to the pointer 5 at the viewing window 8 is +4D. Then, slowly push the first box 4 inwards towards the second box 3 until the subject's eye clearly opens to the target for the first time. Then, read the scale value corresponding to the pointer 5 at the viewing window 8, which is the refractive power of the subject's eye.
[0069] In one embodiment of this application, preferably, as Figure 3 As shown, a visual symbol is an image with a visual symbol graphic, and the color of the visual symbol graphic is different from the color of the main body of the image; for example, if the main body of the image is white, the visual symbol graphic is red or black, that is, the visual symbol is a white background with a red symbol or a white background with a black symbol.
[0070] The target graphic includes a circular ring and multiple isosceles triangles. The circular ring is located in the center of the image, and the multiple isosceles triangles are evenly spaced around the circular ring, with the apex angle of each triangle ranging from 15° to 40°. Preferably, the target is a square image measuring 23.4cm x 23.4cm, with four isosceles triangles, each with a apex angle of 30°. During testing, two isosceles triangles are positioned opposite each other horizontally, and the other two are positioned opposite each other vertically.
[0071] The isosceles triangle with a small apex angle requires high resolution. At the same time, setting four isosceles triangles opposite each other horizontally and vertically can eliminate the influence of astigmatism on human eye resolution, thereby improving the accuracy of vision tests to a certain extent when using this optotype.
[0072] In one embodiment of this application, preferably, as Figure 3 As shown, the image is surrounded by a ring-shaped filled area. For example, if the image is square, this filled area will be a square ring. The color of this filled area is different from the color of the image itself; it can be the same as the color of the test image. For example, if the image itself is white, both the test image and the filled area can be red or black. By setting this filled area, the visual acuity marker is made more prominent, thus reminding the test subject of its location during vision tests.
[0073] In one embodiment of this application, preferably, as Figure 4 As shown, the target image has multiple strip-shaped color blocks evenly distributed around it in a circle. The length of each strip-shaped color block is along the radial direction of the circle it belongs to. The angle between two adjacent strip-shaped color blocks is 15 to 30 degrees. The color of the strip-shaped color blocks is different from the color of the image body. For example, if the color of the image body is white, the color of the strip-shaped color blocks is the same as the color of the target image, which is red or black.
[0074] During a vision test, if the test subject sees different clarity of the striped color blocks in different directions while adjusting the distance between the first and second lenses, it indicates that the test subject has astigmatism.
[0075] During astigmatism testing, the subject slowly decreases the distance between the first and second lenses. When the subject's eye sees a stripe in a certain direction as just clear, the test stops. The reading at this point, where the diopter scale 6 at window 8 aligns with the pointer 5, is recorded. Then, the subject continues to slowly decrease the distance between the first and second lenses until the subject's eye sees a stripe in another direction perpendicular to the aforementioned direction as just changing from blurry to clear. The reading at this point, where the diopter scale 6 at window 8 aligns with the pointer 5, is recorded. The astigmatism is the difference between the two recorded readings.
[0076] Preferably, the number of bar blocks is even, and the ends of the multiple bar blocks furthest from the target graphic are sequentially marked with natural numbers starting from 1, so as to indicate the direction of the bar blocks by numbers.
[0077] for example, Figure 4 The target shown has 12 colored bars. Bar 3 and bar 9 are in the same direction, and bar 6 and bar 12 are in the same direction, and these two directions are perpendicular to each other.
[0078] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this utility model, and are not intended to limit it. Although the utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this utility model.
Claims
1. A vision testing instrument, characterized in that, Includes the outer casing and imaging lens group; The imaging lens group includes a first lens and a second lens, which are arranged sequentially along the optical axis of the imaging lens group. The second lens has positive optical power, and the first lens has negative optical power. The second lens is directed toward the eye of the test subject, who can observe a target at a predetermined distance in front of them through the imaging lens group, and the distance between the first lens and the second lens along the optical axis is adjustable; The imaging lens group is disposed inside the outer box. The length direction of the outer box is along the optical axis of the imaging lens group. Both ends of the length direction of the outer box are open. A limiting segment is formed between the end face of the outer box facing the eye of the test subject and the optical center of the second lens. The length of the limiting segment is a, 1.2cm≤a≤1.5cm.
2. The vision testing instrument according to claim 1, characterized in that, The range of refractive power X of the human eye that the vision testing instrument can detect satisfies the following condition: -7D≤X≤4D.
3. The vision testing instrument according to claim 2, characterized in that, The distance between the optical centers of the first lens and the second lens is d, where 0 < d ≤ 250 mm.
4. The vision testing instrument according to claim 3, characterized in that, When X = -7D, d = d min When X = 4D, d = d max ;d max -d min ≥150mm.
5. The vision testing instrument according to claim 1, characterized in that, The outer box includes a first box body and a second box body; Both ends of the first box and the second box are through, and one end of the first box is retractably inserted into the second box from one end of the second box. The first lens is disposed inside the first housing, and the second lens is disposed inside the second housing at the end away from the first housing.
6. The vision testing device according to claim 5, characterized in that, The first box body and the second box body are fitted with a clearance. or, Both the first box and the second box are cylindrical. The inner side wall of the end of the second box away from the second lens is provided with an internal threaded connection part, and the outer side wall of the end of the first box inserted into the second box is provided with an external threaded connection part. The external threaded connection part is adapted to be screwed into the internal threaded connection part.
7. The vision testing instrument according to claim 5, characterized in that, A diopter scale is provided on the outer wall of the first box along the length of the first box; The second housing has a viewing window on its side wall, and a pointer is provided at the viewing window. The refractive power represented by the scale aligned with the pointer on the refractive power scale can be read through the viewing window.
8. The vision testing instrument according to claim 7, characterized in that, The smallest division of the diopter scale is 0.25D.
9. The vision testing instrument according to claim 1, characterized in that, The target is an image with a target graphic, which includes a ring and multiple isosceles triangles. The multiple isosceles triangles are evenly spaced around the ring with the ring as their base, and the vertex angle of each isosceles triangle is 15° to 40°. The color of the target graphic is different from that of the main body of the image.
10. The vision testing instrument according to claim 9, characterized in that, The image is surrounded by a ring-shaped filled area, the color of which is different from the color of the main body of the image. or, The image has multiple strip-shaped color blocks evenly spaced around the target graphic. The length direction of each strip-shaped color block is set along the radial direction of its circumference. The angle between two adjacent strip-shaped color blocks is 15° to 30°. The ends of the strip-shaped color blocks away from the target graphic are sequentially marked with natural numbers starting from 1. The color of the striped color block is different from the color of the main part of the image.