JP3330968B2 - Subjective optometry device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a subjective optometric apparatus for performing a cross cylinder test, and more particularly to a subjective optometric apparatus for measuring visual acuity or visual function by arranging a plurality of lenses on a lens disk.

[0002]

2. Description of the Related Art Conventionally, a subjective optometry apparatus has been used for measuring a precision astigmatic axis and a precision astigmatic power of a subject. In this type of measurement, a method called a cross cylinder test has been conventionally employed, and a cylinder lens is presented in front of the subject's eye by presenting a visual target such as a character on a visual acuity chart. In that case, the subject must be presented with the same target in a state where the minus axis and the plus axis of the cylinder lens are alternately replaced. For this purpose, the measurer turns the lens unit to rotate the axis of the cylinder lens placed in front of the subject. Then, the subject was asked about the difference in the appearance of the optotype, and the answer was used to accurately measure the degree of astigmatism and its axial direction.

In this case, the subject memorizes the visual appearance of the optotype each time, and relies on his or her own memory to compare the visual appearance of the optotype presented next. Thus, a practically accurate measurement is not possible. In addition, the measurer repeatedly performs the same operation in the reversing set of the lens unit, which not only requires much time and labor but also places a great burden on the person to be measured.
Both increase fatigue.

[0004] Therefore, it has been considered to simplify the measurement by a subjective optometry apparatus having a built-in electric auto-cross mechanism. For example, according to Japanese Patent Application Laid-Open No. 64-32838, a method of performing a cross cylinder test by repeating normal rotation and reversal of a cross cylinder lens with respect to an astigmatism lens, and using a cross cylinder lens whose axes differ by 90 ° from a prism lens A method of performing a cross-cylinder test using a cross-cylinder test lens configured to enable simultaneous comparison of appearance by joining with a lens is shown.

[0005]

However, even when the above-mentioned cross cylinder test lens is used, two cross cylinder lenses are rotated with respect to the axis of the astigmatism lens in a state where the two cross cylinder lenses are joined to the prism lens. The target is presented to the subject. For this reason, at the time of the cross cylinder test, the measurer must always be aware of the separation direction of the image shown on the operation unit. Also, since the two images are always rotated according to the selection of the axis of the astigmatic lens, the subject also changes the positional relationship between the two images, making it difficult to compare the two images depending on how they are viewed. Therefore, in the subjective optometric apparatus, there is a problem that it is difficult to smoothly perform a dialog between the measurer and the subject due to consideration of the position of the image.

The present invention has been made in view of such a point, and an object of the present invention is to provide a subjective optometry apparatus in which two subjects can easily compare the appearance of two targets. Another object of the present invention is to link with an astigmatic lens,
To provide a subjective optometric apparatus in which the switching mechanism of the axis and the frequency is motorized to make it easy for the subject to compare, and for the measurer to simplify the measurement without considering the position of the image and to perform centralized control. That is.

Another object of the present invention is to provide a subjective optometric apparatus which can reduce the burden of astigmatism measurement by a cross cylinder lens unit and simplify the lens mechanism, and can be incorporated in the lens unit as an auto cross mechanism. With the goal.

[0008]

In order to solve the above-mentioned problems, the present invention provides left and right measurement lens units each having a measurement window for measuring the left and right eyes of a person to be measured. A motorized awareness having a left and right measurement lens unit having a configuration in which a plurality of lenses and the like used for performing the measurement are arranged in the measurement windows by controlling a plurality of lens disks on which a plurality of lenses and the like for measurement are arranged. An optometric apparatus, wherein one of the plurality of lens disks is provided with a rotatable astigmatic lens for astigmatism measurement, and the other one of the plurality of lens disks has A cross-cylinder lens unit for performing a cross-cylinder test, wherein two cylinder lenses having the same power have a minus axis of 90 ° with each other.
In a state where the lens is held in a positional relationship of intersecting with each other, the lens is arranged so as to be disposed between the cross cylinder unit rotatably juxtaposed in the same plane and the cross cylinder unit and the measurement eye of the subject. The two cross-cylinder lenses are mounted on a disc and form an oblique path so as to coincide with the optical axes of the two cross cylinder lenses on the target side and to coincide with the optical axis of the astigmatism lens on the measurement window side. One target is formed into two separated images in parallel via the lens so that the two separated target images do not move with respect to the rotation of the lens of the cross cylinder unit or the rotation of the astigmatic lens. and separation prism, is provided with a imaging function held in, in astigmatism measured
Are the cross cylinder lens unit and the astigmatism lens.
A subjective optometry apparatus, wherein the eyepiece is simultaneously arranged in the measurement window .

[0009]

The two cylinder lenses rotate without changing the positional relationship with the separation prism, while maintaining the positional relationship where the minus axes intersect at 90 ° with each other. Therefore, the cross cylinder lens unit itself does not rotate within the field of view of the person to be measured, and the target can be imaged as if the other cylinder lens was obliquely inverted with respect to one cylinder lens. .

[0010]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a front view showing the overall configuration of the subjective optometry apparatus. This subjective optometric apparatus includes a measuring head unit 1 having a visual function including near and far vision, and a visual acuity measuring mechanism.
It comprises a measurement head support 2 for instructing the measurement head 1 to move up and down and rotate horizontally, an optometry table 3, and a base 4 supporting these parts 1 to 3. The measuring head unit 1 includes a measuring lens unit unit 5 and a PD mechanism unit 6. The present invention is characterized in that the left and right unit portions 5a and 5b have a built-in electric auto-cross mechanism as described later.

FIG. 2 is a control block diagram showing a main part of a control mechanism of the subjective optometry apparatus. The main control board 110 includes an interface circuit 111, a processor (CPU) 112, a ROM 113, a RAM 114, an RS232C interface 115, and the like.

The CPU 112 controls the main control board 11 based on a control program stored in the ROM 113.
0 overall control. The ROM 113 stores a plurality of screen data to be displayed on the EL display 111 when the visual function or the visual acuity is measured. Note that RAM1
An SRAM or the like is used as the storage 14 and various data such as objective measurement data required for subjective measurement of visual function or visual acuity are stored as measurement information. Input devices such as a mouse 101 and an EL display 102 are connected to the interface circuit 111. RS232C interface 1
Reference numeral 15 denotes a PD head substrate 12 built in the PD mechanism unit 6.
0, and functions as an interface circuit for performing data communication between the main control board 110 and the PD head board 120.

The PD head substrate 120 has a function of controlling left and right head substrates, which will be described later, and a target control substrate, and includes a processor (CPU) 122 and a ROM 12.
3, RAM124, and RS232C interface 1
25.

FIG. 3 is a view showing the front appearance of the measuring head unit 1. The measuring head unit 1 includes a measuring lens unit 5 and a PD mechanism 6. Here, the subject is located in the front direction of the measurement head unit 1. The measurement lens unit 5 includes left and right unit units 5a and 5b, and various measurement lenses for visual function measurement such as spherical measurement, astigmatism measurement, astigmatism axis measurement, and prism measurement of the eye of the person to be measured. Lenses are accommodated, and various visual field states are created by combining these lens groups, so that optometry can be performed. Measurement lens unit 5
Is suspended from the PD mechanism 6, and the PD mechanism 6 sets the distance between the unit 5a for the left eye and the unit 5b for the right eye of the measurement lens unit 5 as the distance between the pupils of the subject ( A mechanism for adjusting according to PD) is built in.

The left and right eye units 5a and 5b of the measurement lens unit 5 have measurement windows 5c and 5d, respectively, so that the eye can be examined while allowing the subject to look through the measurement windows 5c and 5d with both eyes. At the time of this optometry, in addition to the adjustment of the interpupillary distance described above, the vertical direction in which the optical axis of the measurement lens installed in the measurement windows 5c and 5d also coincides with the visual axis of the eye of the subject in the vertical direction. Adjustment and the distance between the measurement lens and the corneal vertex of the subject's eye (generally, this is called "vertex"
Is adjusted to a predetermined value, for example, 12 mm.

A supporting member 7 of a head supporting device is fixed to the PD mechanism 6, and a fore-and-aft moving device, an up-and-down moving device 9, and a forehead abutment member for contacting the forehead of the subject with the supporting member 7 10 and the like are provided. The fore-and-aft movement device is a device for moving the forehead abutment member 10 in the fore-and-aft direction of the subject to adjust the vertex to a predetermined value, and the up-and-down moving device 9 moves the optical axis of the measuring lens to the eye of the subject. It is a device that matches the visual axis of the vertical direction.

FIG. 4 is a sectional view taken along line AA of FIG. With reference to this sectional view, the configuration of the electric auto-cross mechanism built in the unit 5b will be described. Since the left and right measurement lens systems are symmetrical in the internal configuration, only the measurement lens system of one unit will be described here.

In FIG. 4, the measurement window 5 of the unit 5b
The base plate 11 is fixed at a position orthogonal to the optical axis of the lens system from d to the target. This base plate 1
Reference numeral 1 supports the measurement lens system and the drive system in the unit section 5b. The auto cross disk 12 is rotatably supported by a support shaft 13 provided in parallel with the base plate 11 and on the target side.

The auto cross disk 12 is provided with a measuring window 5d.
The prism 14 and the prism lens 1 correspond to
5a and 15b and through holes (not shown) are arranged.
The cross cylinder lens unit 16 composed of two cross cylinder lenses 16a and 16b is provided at a predetermined rotation angle position of the auto cross disk 12 same as the separation prism 14 by a unit support not shown. A support shaft 17 parallel to the optical axis of the lens system is also provided on the measurement window 5 d side of the base plate 11, and the support shaft 17 allows the four spherical lens disks 18 a to 18 a to 1.
8d is rotatably supported.

In the unit 5b, a base plate 19 is further arranged in parallel with the base plate 11, and a pulse motor 141 is provided here. This pulse motor 141
Is a switching motor for rotating the auto-cross disc 12, and a drive gear 20 attached to a drive shaft thereof meshes with a gear on the peripheral surface of the auto-cross disc 12. The pulse motor 1 is provided on the base plate 11.
A drive gear 21 is mounted on the drive shaft. The drive gear 21 is connected to the base plate 1.
The gear 9 is meshed with an intermediate gear 22 provided on the gear 9, and the sun gear 23 can be rotated via the intermediate gear 22.

That is, the pulse motor 142 rotates the sun gear 23 around the support shaft 13 and
3, the prism lens 15a and the cross cylinder lenses 16a and 16b are simultaneously rotated. Therefore, hereinafter, this pulse motor 142 is referred to as an auto cross motor. The sun gear 25 that rotates around the support shaft 13 via the intermediate gear 24 by a prism motor (not shown) has another prism lens 15b,
The prism lens 15a is configured to rotate independently.

The two astigmatic lenses 26 and 27 are independently rotatably arranged on a lens disk (not shown), and are positioned between the auto-cross disk 12 and the spherical lens disk 18a.

FIG. 5 is a plan view showing the positional relationship between the auto cross disk 12 and the respective drive mechanisms of the lens system. A cross cylinder lens unit 16 composed of cylinder lenses having the same power coincides with the measurement window 5d. The auto cross disk 12 is shown in the state.

The auto cross disks 12 are separated from each other by a rotation angle position of 60 °, respectively, at a prism lens 15a (in FIG. 5, the prism lens 15b is on the lower surface of the prism lens 15a and is not visible),
A support 31 that rotatably supports the through-hole 30 and the cross cylinder lenses 16a and 16b is disposed. Further, the auto cross disc 12 is provided with a switching sensor 151. The two lenses 16 a and 16 b of the cross cylinder lens unit 16 are separated from the separation prism 14 on the auto cross disk 12 by the support 30.
Are fixed in a fixed positional relationship with respect to. Each lens frame 31a of these cross cylinder lenses 16a, 16b,
31b have the same diameter, and a gear meshing with the intermediate gear 31c is formed on the peripheral surface thereof. The lens frame 32 of the prism lens 15a meshes with the sun gear 23. And this sun gear 23
The intermediate gear 22 meshing with the
2 are provided.

Here, when the auto cross disc 12 is rotated by the switching motor 141, the rotation position is detected by the switching sensor 151. When the sun gear 23 is rotated by the auto cross motor 142 via the drive gear 21 and the intermediate gear 22, the rotation position is detected by the auto cross sensor 152. Therefore, by rotating the lens frame 31b meshed with the sun gear 23 on the support base 31, this intermediate gear 31
c, the two cross cylinder lenses 16a, 16b
Are rotated in the same direction while maintaining the positional relationship where the minus axes intersect at 90 °. Also, when the sun gear 23 rotates via the intermediate gear 22, the prism lens 15a is also rotated corresponding to the two lenses 16a and 16b of the cross cylinder lens unit 16.

Further, a driving gear 33 of a driving shaft of the prism motor 143 is attached.
Meshes with an intermediate gear 24 provided on the base plate 11 facing the intermediate gear 22. This intermediate gear 24
Is a prism lens 15a via a sun gear 25 (in FIG. 5, on the lower surface of the sun gear 23 and not visible).
Is to rotate the prism lens 15b on the lower surface of the lens. Therefore, the rotational position of the prism lens 15b is controlled by the prism sensor 153.

FIG. 6 is an enlarged view for explaining a lens system arranged in the measurement window 5d at the time of precise astigmatism measurement. Base plate 1
1, an intermediate gear 34 is disposed around an axis 35, and the intermediate gear 34 is rotated by an astigmatic lens motor (not shown). A gear formed on the peripheral surface of the lens frame 27a of the astigmatism lens 27 meshes with the intermediate gear 34, and the base direction of the astigmatism lens 27 can be controlled to a predetermined rotation angle.
Similarly, the base direction of the astigmatism lens 26 supported by the lens frame 26a of the astigmatism lens 26 is controlled to a predetermined rotation angle by another astigmatism motor (not shown).

The separating prism 14 has an oblique optical path that coincides with the optical axis of the two cross cylinder lenses 16a and 16b on the target side and coincides with the optical axis of the astigmatic lens 26 on the measurement window 5d side. Is formed. Two images of the same target, which are incident from each of the cross cylinder lenses 16a and 16b, are formed in parallel on the astigmatic lens 26 at a predetermined interval through the obliquely traveling optical path.
Therefore, even if each lens 16a, 16b of the cross cylinder lens unit 16 rotates with respect to the measurement eye, or the base direction of the astigmatism lenses 26, 27 rotates, 2
The left and right positional relationship is always maintained in the images of the two separated targets.

FIG. 7 is a control block diagram showing a control mechanism of the lens disk. The left head substrate 130 includes an interface circuit 131 and a drive circuit 132, and is connected to the PD head substrate 120 via the interface circuit 131. The interface circuit 131 is connected to a switching sensor 151, an auto-cross sensor 152, a prism sensor 153, an astigmatic lens sensor 154, and a spherical lens sensor 155. The drive circuit 132 is connected to a switching motor 141, an autocross motor 142, a prism motor 143, an astigmatic lens motor 144, and a spherical lens motor 145.

FIG. 8 is a diagram showing the rotational position of the auto cross disk 12 at the time of spherical measurement or astigmatism measurement. The through hole 30 is provided between the prism lenses 15a and 15b and the cross cylinder lenses 16a and 16
b. Therefore, the lens system can be built in the unit section 5b compactly, and the measurement can be easily switched by operating one switching motor 141 with respect to the measurement window 5d.

FIG. 9 is a diagram showing the rotational position of the auto cross disk 12 during the prism measurement. In the prism measurement, the two prism lenses 15a and 15b are independently rotated by the auto cross motor 142 and the prism motor 143 to create a desired frequency of the combined prism values. Therefore, unlike the conventional prism measurement, there is no need to prepare and place prism lenses having various powers in advance, so that the lens disk rotation mechanism is easily configured.

FIG. 10 is a schematic diagram for explaining the operation of the lens system for precision astigmatism measurement. When a cross cylinder test is performed, the Stokes astigmatism lens 26,2
7 is the four spherical lens disks 1 before the eye 40 to be measured.
They are arranged via lenses 41a to 41d arranged in 8a to 18d. The astigmatic lenses 26 and 27 can set the combined astigmatic axis direction and astigmatic power by rotating their axes. When the astigmatic power and the astigmatic axis are changed by the astigmatic lenses 26 and 27, if the rotational positions of the four spherical lens disks 18a to 18d are controlled, the correction of the spheric power is performed at the same time. Here, the lens system constituted by the lenses 41a to 41d can be switched in steps with a spherical power of 0.125 (D).

In the precise measurement of the astigmatic axis, the cross cylinder lenses 16a and 16b are set to have a positional relationship of 45 ° and 135 ° with respect to the minus axes of the astigmatic lenses 26 and 27, respectively. In the precise measurement of the astigmatic power, the minus axes of the cross cylinder lenses 16a and 16b are set at 90 ° and 180 ° with respect to the minus axes of the astigmatic lenses 26 and 27, respectively. The separation prism 14 is disposed between the cross cylinder lenses 16a and 16b and the two astigmatism lenses 26 and 27. As a result, the target presented to the subject is separated, and observed as two images formed by the measuring eye 40 via a lens system having a predetermined spherical power.

FIG. 11 is a diagram showing an example of an input screen of the subjective optometry apparatus. Conventionally, in an optometry apparatus with a display, a control box in which a number of switches are arranged has been used as a means for inputting optometry information displayed on a display. This requires the measurer to have knowledge of all switches, which is rather a burden.

In addition, since the measurer must measure while looking alternately at the three positions of the optometer, the display, and the control box, there is a problem in that the distance of movement of the eyes is large and the subject is easily tired.

Therefore, in the subjective optometry apparatus of the present invention, in order to maintain the visibility of the input screen and improve the operability,
Auto cross switches 201R and 201L are provided in a basic measurement screen 200 as shown in FIG. The basic measurement screen 200 corresponds to the EL display 10 shown in FIG.
2 is one of the screens displayed. The auto cross switches 201R and 201L are switches for opening a window 202 including switches required to execute an auto cross test for the right and left measurement eyes, respectively. FIG. 11 shows a state where the left window is opened.

On the basic measurement screen 200, in addition to the auto cross switches 201R and 201L, a prism measurement switch, a near measurement switch, an optotype switch, and the like are provided. These switches are arranged to open an operation menu necessary for the corresponding measurement and a display window including measurement information. In the measurement information display window 203, measurement information such as measurement results such as a spherical power and an astigmatic power is displayed. The standard optotype operation key group 204 is arranged slightly below the center of the screen, and only command keys for optotypes that are usually used frequently are displayed.

In the operation menu of the window 202, an astigmatic axis measuring switch (AX) 202a, axial direction adjusting switches 202b and 202c, and an astigmatic power measuring switch (CYL) 202d are arranged.

FIG. 12 and FIG. 13 are flow charts showing the procedure of precision astigmatic axis measurement and precision astigmatic power measurement, respectively. Here, after determining the precision astigmatism axis of FIG.
A precision astigmatism of 3 is determined. In the figure, a numerical value following S indicates a step number.

When one of the auto cross switches 201R and 201L is first selected from the basic measurement screen 200, one of the left and right measurement windows 5c and 5d is closed, and the auto cross test can be executed for each eye. (Step S1). Then, the measurement switch (AX) 20
If 2a is selected by clicking with the mouse 101, the basic measurement screen 200 changes to an auto-cross AX measurement screen (step S2). At this time, the rotation of the auto cross disk 12 is controlled by the switching motor 141 to the position shown in FIG. 5 (step S3), and at the same time, the corresponding astigmatic axis is calculated (step S4). Further, the auto cross motor 142 is driven (step S5), and the cross cylinder lenses 16a and 16b are positioned based on the previously measured value of the astigmatic axis. As the measurement value, for example, a measurement value by an objective measurement device performed prior to the subjective optometry is used, or a measurement value set by inputting data of the subject through an inquiry or the like can be used.

The axial direction of the astigmatic axis is adjusted by the axial direction adjusting switch 20.
2b or 202c, the subject is asked to answer whether or not the two optotypes match (step S6). According to the result of the left-right comparison, the measurer further moves the axial adjustment switch 202b,
By operating any one of 202c, the astigmatic axis is changed (step S7). The precision astigmatic axis is determined while adjusting according to the response of the subject until the axes match (step S).
8).

Further, when measuring the astigmatic power, if the measuring switch (CYL) 202d is selected (step S1).
1), the basic measurement screen 200 changes to an auto-cross CYL measurement screen. At this time, the auto cross motor 142 is controlled in accordance with the astigmatic power stored in the subjective optometer, whereby the cross cylinder lens 16a, 1
6b is set to a predetermined rotation angle position. Steps S11 to S17 in FIG. 13 correspond to steps S2 to S8 in FIG.

In order to input a command from these operation menus, a mouse 101 shown in FIG. 2 is used to move a cursor called an “icon” displayed on the screen, and a predetermined command button Can be performed by pressing.

By the way, even if these operation windows are newly displayed in the basic measurement screen 200, the measurement information essential for the measurement remains displayed in the measurement information display window 203. Therefore, the rotation of the auto cross disk 12 is controlled while constantly monitoring the measurement information, thereby enabling the cross cylinder test. Therefore, in a subjective optometric apparatus that measures the visual function or visual acuity of the eye by interacting with the subject, a measurement information display window that displays the visual function or visual acuity measurement information and an operation window that displays a plurality of command keys The simultaneous use of an input screen not only simplifies measurement but also allows for centralized control.

[0045]

As described above, in the present invention, the target viewed by the subject through the cross cylinder lens is always observed at the same position. That is, for the subject, 2
Since there is no change in the positional relationship between the two images, it is sufficient to simply compare only how they look. Therefore, the accuracy of the measurement in the cross cylinder test can be improved, and the fatigue of the subject can be reduced.

Also, for the measurer, 2
Since it is not necessary to consider the positions of the two images, the burden of subjective optometry measurement is reduced, and in particular, it is possible to concentrate on the lens switching operation that is motorized in conjunction with the optotype operation, so that accurate measurement results can be easily obtained. be able to.

[Brief description of the drawings]

FIG. 1 is a front view showing the overall configuration of a subjective optometry apparatus of the present invention.

FIG. 2 is a control block diagram showing a main part of a control mechanism.

FIG. 3 is a diagram showing the front appearance of a measurement head unit.

FIG. 4 is a sectional view taken along line AA of FIG. 3;

FIG. 5 is a plan view showing a positional relationship between an auto cross disk and respective drive mechanisms of a lens system.

FIG. 6 is an enlarged view illustrating a lens system.

FIG. 7 is a control block diagram illustrating a control mechanism of the lens disk.

FIG. 8 is a diagram showing a rotational position of an auto-cross disk during spherical measurement or astigmatism measurement.

FIG. 9 is a diagram showing a rotation position of the auto cross disk 12 during prism measurement.

FIG. 10 is a schematic diagram illustrating the operation of a lens system for precision astigmatism measurement.

FIG. 11 is a diagram illustrating an example of an input screen of the subjective optometry apparatus.

FIG. 12 is a flowchart showing a procedure of precise astigmatic axis measurement.

FIG. 13 is a flowchart showing a procedure of precise astigmatic power measurement.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Measurement head part 5d Measurement window 12 Auto cross disk 14 Separation prism 16a, 16b Cross cylinder lens

──────────────────────────────────────────────────続 き Continued from the front page (56) References JP-A-64-20825 (JP, A) JP-A-49-46595 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) A61B 3/00-3/16

Claims (1)

(57) [Claims] 1. A left and right measurement lens unit each having a measurement window for measuring the left and right eyes of a subject, and a plurality of lens disks on which a plurality of lenses or the like for measuring visual acuity or visual function are arranged. A motorized subjective optometry apparatus having a left and right measurement lens unit having a configuration in which a lens and the like used for performing the measurement are respectively arranged in the measurement window by controlling the number of the lens disks. One is provided with a rotatable astigmatism lens for astigmatism measurement, and the other one of the plurality of lens disks is a cross cylinder lens unit for performing a cross cylinder test, With the two cylinder lenses of the power held in a positional relationship where the minus axis intersects at 90 ° with each other, they can rotate freely in the same plane. A cross cylinder unit disposed on the lens disk so as to be disposed between the cross cylinder unit and the eye to be measured of the subject, and one of the optical axes of the two cross cylinder lenses on the target side. In the measurement window side, an optical path obliquely formed so as to coincide with the optical axis of the astigmatism lens is formed, and one target is formed into two images separated in parallel through the two cross cylinder lenses, the rotation of the cross cylinder unit of the lens, or a separation prism having imaging action which the image of the two separate optotype with respect to the rotation of the astigmatic lens is held so as not to move, is provided, in astigmatism measured Is the cross cylinder lens unit
And the astigmatic lens are simultaneously placed in the measurement window.
Visual acuity testing apparatus, characterized in that.