The first basic understanding (on)
1. Optometry disc optometry, commonly known as the "bull's-eye", the main components, name and function as shown in Figure 1.
Figure 1
(1) the top frame is used to suspend the inspection disc.
(2) Fixed handwheel Used to adjust and fix the position of the inspection disk.
(3) Rotating handwheel is used to adjust the position of the disk relative to the subject's face.
(4) Horizontal handwheel is used to adjust the horizontal position of the optic aperture in relation to the subject's eyes.
(5) Horizontal Marker Indicates the horizontal tilt of the disc.
(6) Pupil distance scale Measures the distance between the pupils in mm.
(7) Pupil distance handwheel Used to adjust the relative position of the visual aperture and the pupil of the tested eye.
(8) Rotating prism Used to determine the hidden strabismus of the examined eye and the visual balance of both eyes.
(9) Rotating prism handwheel Used to adjust the base direction and prismaticity of the rotating prism.
(10) Auxiliary lenses handwheel is used to convert different auxiliary inspection lenses to complete a variety of visual function examination.
(11) Spherical Lens Focus Reading Window Displays the top focus of the spherical lens.
(12) Fine Focus Wheel Used to increase or decrease the O.25D spherical focal length.
(13) Coarse Focus Handwheel Used to increase or decrease 3.OOD spherical focal length.
(14) Cylindrical Lens Focus Readout Window Displays the cylindrical lens focus.
(15) Cylindrical Lens Handwheel Used to increase or decrease the focal length of an O.25D cylindrical lens.
(16) Cylindrical Lens Axis Handwheel Used to adjust the axis of the cylindrical lens.
(17) Cylindrical Axis Scale Displays the axis angle of the cylindrical lens.
(18) Crossed Cylindrical Lens Used to fine tune the axis position and focus of astigmatism.
(19) Flip Handwheel Used to change the axis orientation of the crossed cylindrical lens.
(20) Cylindrical Lens Axis Position Comparison Scale Used to compare with the axis position of the crossed cylindrical lens.
(21) Sight hole Placement of corrective lenses or auxiliary inspection lenses.
(22) Frontal handwheel Used to adjust the relative position of the examining disk to the eye under test.
(23) Frontal rest To facilitate tightening and fixation of the subject's forehead.
(24) The corneal position reading window is used to determine the distance of the corneal apex from the posterior apex of the corrected specimen.
(25) Cheek guard clip Used to hold the cheek guard.
(26) Gathering handpiece Used to adjust the degree of gathering of the two optometric discs.
(27) Close-up scale bar knob Used to secure the close-up scale bar.
(28) Nearby Scale Rod Notch Used to hold the head end of the near scale rod.
2. Auxiliary Lens Rotate the auxiliary lens handwheel (Fig. 2) to align the auxiliary lens with the aperture as required. The names and functions of the auxiliary lenses are as follows.
O, ō No lens or flat lens.
OC Black lens.
R Retinal detector film, a ten 1.5 OD lens for detector examinations at a working distance of 67 mm.
+.12 Spherical lens with ten O.12 focal lengths.
PH 1mm small-aperture lens to verify that the eye under test is not refractive dysmetropia.
P Polarizing filters to verify that the optometry specimen is balanced for binocular correction.
±.50 Cross-cylindrical lens for the detection of old-vision photometry.
RL Red lens for simultaneous vision and fusion testing.
GL Green lens, same as red lens.
RMV Red vertical malleable rod for detection of occult strabismus.
RMH Red horizontal Mars bar, same function as above.
WMV White vertical Mars bar, same function as above.
WMH White horizontal Mars bar, same function as above.
6 U 6 Bottom-up prism, works in conjunction with the rotating prism to detect horizontal occult strabismus.
1O 1 10 Bottom inward trigonometry, in conjunction with a rotating prism to detect vertical occult strabismus.
a right handwheel b left handwheel
Figure 2 Auxiliary piece of handwheel
Second lecture on the basics (below)
3. Visual standard
(1) visual standard projector using light projection will be the optometric visual standard display in the visual standard panel, its illuminance, brightness, contrast, clarity and monochromatic wavelengths are required to be reliable and standardized. The main question is shown in Figure 3.
Figure 3 visual projector
①top cover ② projector ③ remote sensor ④ focusing handwheel ⑤ power switch ③ chassis
(2) visual remote control can be based on the need for refractive examination snap different function keys, so as to choose a different visual standard, the main function keys as shown in Figure 4.
Figure 4 Remote control of the reticle
1) The emitter uses infrared technology to transmit the command information to the reticle projector.
2) The key of the viewport is usually labeled with the category of the viewport displayed by the key above the key of the viewport, and the inner space will be described in the following.
3) The on/off key (Light) is used to turn on the power of the remote control, and usually displays the O.1 vision scale when it is turned on.
4) Reset key (Reset) If the remote control has been programmed, press the Reset key to return the check step to the initial display.
5）Program △ key (△ ) to display the programmed steps forward. (
6) Program ▽ key displays the programmed inspection steps in reverse order.
7) Selection key selectively displays part of the reticle on the projection of the whole frame according to the need, such as selecting to display a row, a line or a single optic table reticle.
8) Replace key according to the direction of the key to replace the display of the immediate neighboring cursor. For example, it replaces the display of an adjacent row, row, or single vision meter cursor.
9) Red and green keys Display a red and green background that is equal in size to the left and right behind the whole frame of the projected cursor.
(3) Commonly Used Retinoscopes
1) Logarithmic E-retinoscopic and logarithmic circular retinoscopic retinoscopes retinoscopes (Fig. 5)
Mounting table lenses Spherical and cylindrical lenses optometry test pieces.
Testing method Often monocular, occasionally binocular.
Purpose of the test To determine the visual acuity of the naked eye and to evaluate the refractive correction of the tested eye with corrective lenses.
Figure 5 Visual acuity scale
2) Radial astigmatism test scale (Figure 6)
Fitted with lenses Cylindrical lens optometry test piece.
Test method Monocular test.
Purpose of test To evaluate whether the eye under test still has uncorrected astigmatism after wearing corrective lenses.
Figure 6 Radiographic astigmatism test reticle Figure 7 Specular astigmatism test reticle
3) Specular astigmatism test reticle (Figure 7)
Compatible lenses Crossed cylindrical lens.
Test method Monocular test.
Purpose of test To assess whether the tested eye still has uncorrected astigmatism after wearing corrective test lenses.
4) Red-green test reticle (Figure 8)
Fitting lenses Spherical lens optometry test piece.
Test method Monocular test.
Purpose of the test To evaluate the degree of spherical refractive correction in the tested eye after wearing corrective test lenses.
5) Polarized red-green test reticle (Figure 9)
Fitting lenses Polarized lenses combined with spherical lens optometry test piece.
Method of test volume Binocular test.
Purpose of the test To assess whether the refractive state of the eye is balanced in both eyes after wearing an optometric test piece.
Figure 8 Red-green test reticle Figure 9 Polarized red-green test reticle
6) Binocular Equilibrium Test Reticle (Figure 10)
Fitting Lens Polarizing Auxiliary Lens Spherical Lens Optometry Test Lens.
Test Method Binocular test.
Purpose of the test To assess whether the refractive state of the tested eye is balanced after wearing an optometric test piece.
7) Worth four-dot test reticle (Figure 11)
Complementary lenses The right eye wears a red lens and the left eye wears a green lens.
Test method: Binocular test.
Purpose of the test: To assess binocular simultaneous visual function and fusion in the tested eye.
Figure 10 Binocular Equilibrium Test Scale Figure 11 Worth Four Points Test Scale
8) Stereopsis Test Scale (Figure 12)
Fitting Lenses Polarizing Auxiliary Lens.
Test method Binocular test.
Purpose of the test: To assess the fusion and stereoscopic function of the tested eye and to diagnose occult strabismus.
Figure 12 Stereopsis test reticle Figure 13 Mars bar test reticle
9) Mars bar test reticle (Figure 13)
Complementary lenses Vertical or horizontal Mars bar aids combined with a rotating prism.
Mode of test Binocular test.
Purpose of test Determination of occult strabismus.
10) Cross-ring test reticle (Fig. 14)
Complementary lenses Red and green auxiliary lenses in combination with a rotating prism.
Mode of test Binocular test.
Purpose of test To assess the simultaneous visual function of the tested eye and to determine occult strabismus.
11) Polarization cross test reticle (Figure 15)
Mounted lenses Polarization cochlear combined rotating prism.
Test method Binocular test.
Purpose of the test To assess the simultaneous visual function of the tested eye and to determine occult strabismus.
Figure 14 Cruciform test reticle Figure 15 Polarized cruciform test reticle
12) Polarized cruciform fixation test reticle (Figure 16)
Complementary lenses Polarizing auxiliary lenses combined with rotating prisms.
Test Method Binocular test.
Purpose of the test To assess the simultaneous visual function of the tested eyes and to diagnose occult strabismus with peripheral fusion.
13) Vertical alignment test reticle (Jail 17)
Fitting lenses Polarizing auxiliary lenses in combination with a rotating prism.
Test method Binocular test.
Purpose of the test is to assess the simultaneous visual function of the tested eyes and to quantify binocular image inequality and vertical esotropia.
Figure 16 Polarized cross fixation test visual field Figure 17 Vertical alignment test visual field
14) Horizontal alignment test visual field (Figure 18)
Complementary lenses Polarized attachment lens combined with a rotating prism.
Test method Binocular test.
Purpose of the test is to assess the simultaneous visual function of the tested eyes and to quantify binocular image inequality and horizontal esotropia.
Figure 18 Horizontal alignment test reticle
Preparation
1. Turn on the power: Turn on the power switch and check whether the projector video reticle, the near reading lamp, the detector mirror, and the seat brake switch are connected to the power.
2. The aperture test piece back to "O": Check the reading window of the spherical lens and cylindrical lens of the aperture test piece of the test disc, and carefully return the spherical lens test piece and the cylindrical lens test piece to "O" carefully. Because if the myopic eye is mistakenly used to observe the distance and near vision markers with the over-corrected negative lens, it will induce accommodation, thus affecting the measurement results. Therefore, at the end of each optometry should be in a timely manner after the visual aperture test piece back to "O".
3. Adjust the position of the tested eye: the test subject is asked to take a comfortable posture on the test chair, lift the height of the seat, usually large enough to cause the midpoint of the tested eye and the opposite side of the wall hanging on the polarization of the coordinate of the standard plate relative to the midpoint.
Figure 19: Adjustment of the comprehensive optometry accessories
4. Adjust the length of the top bar: loosen the fixing bolts (39), a small amount of adjustment of the length of the top bar (1), the amount of adjustment depends on the location of the seat to be detected, adjusted that is, after the completion of the tightening of the fixing bolts, usually as long as the seat of the test
position is fixed and unchanged, after the completion of debugging is not often modified (Figure 19).
5. Adjustment of the horizontal axial handwheel: loosen the horizontal axial handwheel (2), the top bar can be rotated along the horizontal axis. Usually adjusted so that the disc is perpendicular to the ground plane, tighten the horizontal axial handwheel after the adjustment is completed, if in the process of optometry need to be tested when the eye looks above or below the optic standard, it can be adjusted at any time.
6. Adjustment of the vertical axis handwheel: loosen the vertical axis handwheel (3), the optical disk can be rotated along the vertical axis, usually used to adjust the relative position of the optical disk and the coronal plane of the eye being tested, after the adjustment is completed, tighten the vertical axis handwheel.
7. Adjustment of the balance handwheel: rotate the balance handwheel (4), observe the tested eyes from the viewports, and adjust the relative position of the center of the viewports and the pupil of the tested eyes in the vertical direction. Usually centering the bubble in the equilibrium calibration tube. In case of vertical ocular deviation complicated by forced head position or primary head deviation, the degree of horizontal tilt of the test disc can be adjusted appropriately to the extent that the tested eye feels comfortable.
8. Adjustment of the pupil distance handwheel: rotate the pupil distance handwheel (7), observe both eyes from the optic aperture, and adjust the horizontal position of the center of the optic aperture and the pupil of the eye under test. Usually, the distance between the optical centers of the double-aperture lenses is equal to the distance between the pupil centers of the tested eyes when looking at the distance vision mark. When the adjustment is completed, the pupil distance reading window (6) can be read directly from the pupil distance of the eye under test in mm.
9. Adjustment of mirror eye distance: When the eye under test observes the optic standard from the center of the optic aperture at the same time, the frontal part of the subject is in stable contact with the frontal support (23), and the tester can observe the position of the corneal apex of the eye under test from the mirror eye distance reading window (24), and the distance of the observation is about 20mm.
Observation can try to change the observation angle, make sure that the long line in the reading window falls exactly on the reading window frame in the center of the protruding angle of the line. If the anterior corneal apex of the measured eye is tangent to the long line scale in the center of the reading window, then the distance between the lens and the eye is 13.75mm (Figure 2O). On the ocular side of the long scale there are three short scales, each spaced at 2 mm intervals. if the anterior corneal apex is tangent to the first short line, the specular eye distance is 15.75 mm, and so on.
Figure 20 Lens Eye Distance Viewing Chart
The size of the lens eye distance affects the focal force produced by the optometric specimen on the eye being measured. With reference to the average distance from the back vertex of the frame glasses to the eye, the lens eye distance is usually 13.75mm for the standard lens eye distance, and because of the low bridge of the nose in China, it is set at 12mm for the standard lens eye distance, and once the lens eye distance is determined, the focal length of the optometry test piece must be converted into the actual focal length of the prescription according to the standard lens eye distance, and the calculation method is as shown in Equation 1.
D′=D± (Equation 1)
1000-LD
Where D is the measured focal length, D' is the actual focal length, and L is the difference between the lens eye distance of the optometric specimen and the standard lens eye distance. Positive lens specimen focal length with the lens eye distance monks and increase, so the formula of the measured focal length must be added to correct the focal length; negative lens specimen focal length with the lens eye distance increases and decreases, so the formula of the measured focal length must be reduced to correct the focal length.
Example 1 It is known that the measured focal length D=1O.OO D
Lens-eye distance difference L=2mm
Seek the actual focal length of the optometric specimen D'
Solution D′=D± =10.20 D
1000-LD
Example 2 It is known that the measured focal length D=-1O.OO D
Lens-eye distance difference L = 2 mm
Find the actual focal length of the optometric specimen D'
Solution D′ = D± = -9.80 D
1000-LD
For the convenience of conversion, a table of lens-eye distance conversions has been developed for the determination of focal lengths on positive lens specimens and for the determination of focal lengths on negative lens specimens
Swiveling of the frontal handwheel (22) controls the spacing of the eye to the posterior vertex of the eye-contact test specimen (Fig. 21) and the distance between the eye and the posterior vertex of the aperture specimen (Fig. 21). The distance between the measured eye and the posterior vertex of the aperture specimen is controlled by rotating the frontal handwheel (22) (Fig. 21).
Figure 21 Adjusting the distance between the eye and the lens with the frontal handwheel
The fourth session on fogging
The use of an optical lens to shift the focus (or line of focus) of a parallel ray of light incident on the subject's eye to the anterior aspect of the retina, thus easing the tonus of the subject's eye, is called fogging.
I. Principle
1. Adjustment tension in refractive error eyes
(1) When a farsighted eye is looking at a distant target, the blurred image on the retina as a visual-motor stimulus induces the ciliary muscle to contract, leading to lens accommodation. The hyperopic eye, when looking at a near target, in addition to maintaining the accommodation paid for when looking at a distance, causes further lens accommodation due to the near reflex. Since the hyperopic eye has to exert a certain degree of accommodation both when looking away and when looking closer, a certain amount of accommodation is produced over time. Over time, a certain amount of accommodation tension is created, which cannot be relaxed within a short period of time, even after the factors causing the accommodation are removed.
(2) When a myopic eye looks at a distant target, the object falls in front of the retina, and because the adjustment can make the object even more blurred, the myopic eye cannot be adjusted when looking at a distance. When myopic eyes look at a near target, if they do not wear corrective eyeglasses, when the target is far away, they still do not need to be adjusted; if they wear corrective negative lenses, they have to pay for the adjustments corresponding to the orthoptic eyes when looking at a near target. As myopic eyes do not wear corrective lenses to see far and near do not need to adjust, over time the ciliary muscle is thin and weak, when wearing corrective lenses near reading time is too long or reading too close to the target, the ciliary muscle is prone to spasmodic regulation of tension, even if the stop near reading operations, the regulation of tension in a short period of time can not be relaxed.
2. Analysis of the implementation of the fog vision method
Refractive error of the eye's regulation of tension, because it is difficult to quantify and active and variable, so the refractive quantitative analysis of the eye constitutes an important interfering factors. It usually makes the results of myopic eyes darker and the results of hyperopic eyes lighter.
In the absence of ciliary muscle paralyzing agents for normal refractive error, the fog method can be used to relieve the ciliary muscle tension. The method is in accordance with the "negative plus positive" principle of adjusting the test lens in front of the eye under test, so that the eye under test is in sufficient myopia, and asked to recognize the distance vision mark 5m away, at this time the eye can not be adjusted theoretically, because the adjustment can be made to further deepen the degree of myopia, resulting in a decline in the clarity of the vision mark. In order to see the distant visual target clearly, the fixating eye is forced to gradually relax the original adjustment tension to minimize the interference of the adjustment tension on the refractive error.
3. Fog vision method of attention
(1) the principle of fog vision method is to make the measured eye in a sufficient "myopic state", but not the use of any focal length of the positive lens, and can not be used on all the measured eye with the same focal length of the fog vision lens. It is known that in the case of excessive fogging, stimulus accommodation occurs because the eye is not looking at the target and lacks the effort to see the target clearly.
(2) The focal length of the fogging lens must be selected according to the different refractive states of the tested eyes, because the adjustment of both eyes is synchronized, and if the adjustment of one eye is not sufficiently relaxed, both eyes will not be able to achieve fogging since.
(3) the use of the trial lens box to implement the fog vision method, must comply with the "first after the change" principle of operation, i.e., when changing the focal length of the fog lens, the first plus a new fog lens, and then remove the original fog lens, to avoid the loss of the fog effect in the separate removal of the original fog lens intervals. This is often due to the iterative addition of fog vision lenses, so that the focal length of fog vision lenses greatly increased and decreased, affecting the effect of fog vision. The use of integrated optometry to control the fog lens gradient is not only smooth and stable, and the operation is much easier.
(4) The use of fog vision to relieve accommodation in the eye under test is not as complete and reliable as ciliary muscle paralyzers. It is recommended that the use of fog vision to control accommodation in the subject's eye be abandoned in the following cases.
1) Poor or variable corrected visual acuity.
2) Unstable results of primary or secondary refraction.
3) Small pupils, especially if due to internal strabismus or internal occult strabismus.
Figure 22 Adjustment of fine spherical lens focus handwheel
① Fine spherical lens focus handwheel ② Spherical lens focus reading window
Figure 23 Spherical lens focus handwheel
a Negative spherical lens focus reading window b Positive spherical lens focus reading window
II. Operation
1. Adjustment of Spherical Lens Focus
(1) Adjust the sight hole auxiliary piece to "O" or " Ω".
(2) Rotate the fine spherical lens focal length handwheel ① (Fig. 22) according to the need of refractive determination, and observe the spherical lens focal length reading window ②. Negative lens reads red, the right clockwise rotation of the handwheel, the focal length from flat light to -19.OOD according to -O.25D increment, counterclockwise rotation of the handwheel is decreasing (Figure 23-a); left counterclockwise rotation of the handwheel, the focal length from flat light to -19.OOD according to -O.25D increment, clockwise rotation of the handwheel is decreasing. Positive lens reads black, the right counterclockwise rotation of the handwheel, the focal length from flat light to +16.0OD according to +O.25D increment, clockwise rotation of the handwheel is decreasing (Figure 23-b); the left clockwise rotation of the handwheel, the focal length from flat light to +16.0OD according to +O.25D increment, counterclockwise rotation of the handwheel is decreasing. Usually there is no decimal point between the integer value and the decimal value.
(3) More than ±3.OOD focus increment, in order to avoid frequent adjustment of fine spherical lens focus handwheel, can be changed to adjust the coarse spherical lens focus handwheel (Figure 24). When adjusting the negative lens, turn the handwheel counterclockwise on the right side to increase the focal length by -3.OOD, and turn the handwheel clockwise to decrease it; turn the handwheel clockwise on the left side to increase the focal length by -3.OOD, and turn the handwheel counterclockwise to decrease it. When adjusting the positive lens, turn the handwheel clockwise on the right side to increase the focal length by +3.OOD, and turn the handwheel counterclockwise to decrease it; turn the handwheel counterclockwise on the left side to increase the focal length by +3.OOD, and turn the handwheel clockwise to decrease it.
Figure 24 Handwheel for adjusting the focal length of the coarse spherical lens
2. Steps for the fog vision method
(1) Adjust the right eye's optic-hole cochlear lens to "O" or "Ω", and the left eye to " OC".
(2) Display the single-row O.2 vision chart reticle.
(3) Follow the principle of "minus and plus" to gradually adjust the focal length of the spherical lens of the right eye's optic hole until the eye under test can not distinguish the direction of the visual standard.
(4) The left eye was also treated for foggy vision as described above.
(5) Both eyes were adjusted to "O" or "Ω", and both eyes were instructed to look at and try to differentiate the foggy visual field for 3-5 min.
(6) If the subject eye could clearly differentiate the foggy visual field during foggy visualization, then O.25D-O.5OD fogging lens can be added to both eyes at the same time as appropriate, always maintaining the fogging optic in a blurred state.
The fifth session of retinal projection optometry
From an objective point of view, according to the characteristics of the light reflected by the retina of the tested eye to determine its refractive state, known as retinal projection. The working lens on the comprehensive optometrist is specially set up for retinal shadowgraphy.
I. Evaluation
1. Advantages:
(1) in the adoption of other subjective and objective refractive methods can not be measured or difficult to accurately determine the refractive state of the eye under test, retinal imaging methods can be used to obtain further subjective determination of the information.
(2) Objective refraction for young children or adults who are unable to express their visual perception.
(3) Observation of the transparency of the refractive interstices such as the energy source, the lens, and the vitreous body by adjusting the focus of the projected light of the retinal microscope.
2. Disadvantages:
(1) Normal retinoscopy is greatly affected by the eye's adjustment, and the results of the retinoscopy show a darker myopia and a lighter hyperopia.
(2) The retinal reflection is not bright enough, which makes it difficult to determine the result.
(3) Over-reliance on the experience and skill of the examiner.
(4) The working distance and the focal meridian orientation suggested by the movement of the reflected light are not precise values.
(5) The results still need to be verified by subjective refractometry.
II. Principle
1. Basic principle The basic structure of the retinal reflector is a parallel adjustment of the sine wave light source, through the 45 ° inclined plane mirror reflected to the pupil of the eye being measured, the fundus retina of the eye being measured is illuminated, it will emit orange-red reflected light. There is a round hole on the plane mirror for the tester to see the reflected light in the pupil of the tested eye. With a spot projected light detector, the reflected light is in the form of a speck, called a reflective spot. With a banded light microscope, the reflected light is in the form of a band of light, called a band of reflected light.
Reflected light passes through the refractive interstitium of the eye to be measured, and is affected by its refraction, inevitably focusing at the far point of the eye to be measured, with convergence occurring in the myopic eye, dispersion occurring in the hyperopic eye, and parallelism in the orthopic eye.
Moving the light source emitted by the retinal detector and causing the reflected light to move. If you look at the eye to be measured as an unknown lens, observe the characteristics of the reflected light and the relative movement of the eye to be measured, you can roughly determine the range of the far point of the eye to be measured, the far point of the eye is located in the eye to be measured and the retinal detector, the two occur in the reverse direction of the movement, known as retrograde; the far point of the eye is located in the eye to be measured after the eye or after the detector, the two occur in the same direction of the movement, known as the paracentric movement (Figure 25). The known lens was also used to adjust its distal point to either position where the retinal detector lens was located. The refractive state of the eye under test is determined by quantitative analysis of the additional known lens.
Figure 25 The position of the far point of the eye and the pattern of reflected light moving forward or backward
Backward movement is seen when the far point is located between the eye and the retinal detector, and forward movement is seen when the far point is located after the eye or after the detector
2. Principle of movement of reflected light The basic principle of movement of reflected light has already been described above, but it would be more plausible to explain the phenomenon of movement of reflected light that occurs in actual operation as follows. Do the following explanation is more plausible.
(1) smooth movement when the tested eye for farsightedness, orthokeratology, or far distance is greater than the detection of the working distance of the myopic eye, then the reflected light of the tested eye without a real focus or focus falls behind the detector of the observation of the eye. At this time, the plane mirror of the detector mirror tilted downward, the reflected light in the measured eye above the upper edge of the hole in the plane mirror cover black, seems to form the phenomenon of reflected light downward (Figure 26-a), because the direction of the reflected light moves in the same direction as the plane mirror tilted, so it is known as the smooth movement.
(2) reverse movement when the eye under test for the distance less than the detection of myopia working distance, then the focus of the reflected light of the eye under test falls between the detector observation eye and the eye under test, at this time the plane mirror of the detector mirror tilted downward, the lower part of the reflected light in the eye under test by the plane mirror hole in the upper edge of the cover blackened, it seems to form the phenomenon of the reflected light upward (Figure 26-b), because the reflected light moves in the same direction as the direction of the reflected light, so it is called the phenomenon of reflected light downward (Figure 26-b), due to the movement of reflected light and the direction of the plane mirror tilted. b), because the reflected light moves in the direction opposite to the direction of the plane mirror tilt, so it is called inverse motion.
(3) Neutralization when the eye under test (or through the adjustment of a known lens) for the distance of the far point is equal to the detection of the working distance of myopic eyes, then the reflected light of the eye under test with a sharp focus falls on the circular aperture of the plane mirror, at this time will be tilted downward of the plane mirror of the detection mirror, the reflected light of the eye under test is unaffected, the performance of the pupil of the eye under test is full of the pupil of the eye, known as the neutralization (Fig. 26) -C).
Figure 26 Schematic diagram of retinal detector reflected light
III. Detection method
1. Determine the main meridian to the strip light detector, for example, the strip projected light must be scanned in the meridian orientation perpendicular to it to move, in order to determine the degree of focus. When scanning a meridian with a detector mirror, if the band projected light and reflected light band pointed to the same orientation, the two move the same meridian orientation, whether it is moving along or against the movement is called the consistency of the move (Figure 27 a), confirming that the scanning meridian for the principal meridian. When a principal meridian is identified, another principal meridian is 90° from it (perpendicular to each other).
When the meridian scanned by the strip of projected light is not the principal meridian of the eye being measured, the orientation of the strip of projected light and the reflected strip of light do not coincide, and if the retinal detector is scanned, the two do not move in the same direction, which is known as a noncoherent movement (Figure 27-b). Therefore, when determining the axial position of astigmatism in the eye under test, the first step is to analyze the consistency between the orientation of the strip projected light and that of the reflected strip at rest, and then to observe whether the meridional orientation of the scanning direction and that of the reflective strip's direction of movement are consistent in the dynamic direction when the strip is being scanned (whether it is moving in the direction of the motion or against the direction of the motion). If there is a non-consistent movement, then the orientation of the strip of projected light must be patiently rotated and adjusted to coincide with the pointing of the reflected light strip.
Figure 27 Comparison of coherent and non-coherent movement of the strip projected light and the reflected light band
2. Neutralizing the reflected light Comparing the smooth and counter moving reflected light (Figure 28), it can be seen that the transition of the reflected light from smooth to neutralized is easier to recognize. In order to utilize the paracentric reflected light to operate, usually according to the detection results of computerized automatic optometry, pre-corrected -O.50D a O.75D negative spherical lens to change the myopic eyes initially show the reverse motion. And make each clock face meridian reflected light are in the state of smooth movement. There is no need to worry that the adjustment brought about by the negative spherical lens may interfere with the test results, because the +0.5OD working lens preset for retinal detection using the IMD optometer has excellent fog vision. Fig. 28 Reflected light bands smooth movement, reverse movement and neutralization In the case of a banded light detector, for example, there are usually three evaluation criteria for the reflected light bands, i.e., brightness, speed of movement and width. When approaching neutralization, the reflected light band appears brighter, moves faster, and becomes wider. When neutralization is reached, the reflected band is brightest and its width occupies the entire pupil space. Therefore, seeing a faint, narrow, slow-moving band of reflected light suggests the need to increase or decrease the focal length of a larger specimen. When the reflected band becomes brighter, faster moving, and wider, a smaller focal length (O.25D) specimen should be changed each time. Since the reflective band is adjusted to move smoothly with a negative spherical lens beforehand, the focal length of the negative spherical lens is usually reduced.
3. Record and analyze the results of the check frame
(1) neutralization of the first meridian to determine the orientation of the principal meridian, carefully scanning and comparing the two principal meridians of the reflected light band, to find out the reflection of the band of light moving faster, brighter and wider of the principal meridian, as the principal meridian is close to the state of neutrality, so it is called the first meridian. Scan with the band of projected light in the orientation of this principal meridian, take the method of gradually reducing the negative spherical lens for neutralization (Figure 29-a, b). A line is drawn to record the first meridian bearing and the neutralization focal length is recorded at the end of the line (Fig. 29-C).
Fig. 29 Neutralization and recording of first meridian orientation and focal length
a, The reflected light bands of the two principal meridians are in paracentesis using the addition of a negative spherical lens, at which time both refractive focal lines of the eye under test are located posteriorly to the retina
b. Gradually decreasing the focal length of the negative spherical lens, the reflected light of the perpendicular principal meridian undergoes neutralization at which time the horizontal refractive focal lines are located retina
C. Record the orientation and refractive focus of the first principal meridian
(2) Neutralization of the second meridian Scan and neutralize another principal meridian perpendicular to the first principal meridian by the method described above (Fig. 3O-a). A line is drawn to record the orientation of the second meridian perpendicular to the first meridian and the neutralizing focal length is recorded at the end of the line (Fig. 3O-b). The graph that records the neutralizing focal lengths on the two principal meridians is called an optical cross chart.
Figure 3O Neutralization and recording of the orientation and focus of the second meridian
a. Reducing the negative spherical lens focus, neutralization of the reflected light from the horizontal principal meridian occurs, and the re-straightened refractive focus line is then located on the retina
b. Recording of the orientation and refractive focus of the second principal meridian
(3) Conversion of prescription Converting the optical crosshairs graphs obtained from the retinal examination to a refractive prescription. The optical cross-plot obtained by retinal inspection in FIG. 3O-b can be decomposed into the two optical cross-plots shown in FIG. 31, representing spherical lens focal length and cylindrical lens focal length, respectively. The prescription may be written as -3.00-1.00X180. note that the orientation pointed to by the O focal degree in the optical cross diagram representing the cylindrical lens focal degree is the fine orientation of the cylindrical lens of the prescription.
Figure 31 Converting an optical cross diagram to a refractive prescription
4. Conversion of working distances
(1) The principle of conversion is usually to place the synthesizer within the length of the operator's arm, so that the retinal detector can be controlled with one hand, and the lens before the eye under test can be replaced with the other. The distance from the principal point of the eye under test to the circular aperture of the detector lens is called the working distance. It is conceivable that, assuming a working distance of 1 m, when neutralization is reached, the far point of the eye under test is at 1 m, indicating a refractive state of 1.OOD myopia, so that no matter how much focal length the specimen in front of the eye under test is, -1.OOD must be added (or subtracted from +1.OOD), which is called the compensation of the working distance, and, after compensation, the far point of the eye under test is moved from 1 m to infinity. This is because the refractive equivalent created by the working distance must be subtracted from the test result (i.e., the value measured by the retinal detector) to convert to the true refractive error of the eye under test. This distance is usually chosen as an integer (e.g., 100 cm, 67 cm, or 50 cm) for ease of calculation. The effect of working distance on the detection result can be calculated by the following formula:
D=D r -1/d w (Equation 2)
In this formula, D is the prescription focal length and Dr is the detection focal length. d w is the working distance in meters.
From equation 2:
1) The working distance is 1m, then the neutralizing luminosity is minus +1.OOD or plus -1.OOD.
2) The working distance is 2/3m, then the neutralizing luminosity is minus +1.5OD or plus -1.5OD.
3) The working distance is 1/2m, then the neutralizing luminosity is minus +2.00D or plus-2.OOD.
3) The working distance is 1/2m, then the neutralizing luminosity is minus +2.OOD.
4) The neutralizing luminosity is minus +2.00D or plus -1.OOD.
5) The working distance is 2/3m.
(2) working lens Comprehensive optometrist's eyehole has a function labeled as R auxiliary piece (Figure 32), that is, for the pre-added +1.5OD positive spherical lens, in the 67cm for the detection of the shadow, the neutralization of the focal length that is the focal length of the prescription, which can save the trouble of the conversion of the working distance.
Figure 32 Adjustment of the working lens with the auxiliary film handwheel