Abstract: take a + 10.0ds lens from the audition disc. Draw a red dot on a piece of white paper as the observation target. The target moves slowly in all directions about 10cm away from the lens, and the moving direction and speed of the target imaging in the lens are observed through the lens. In this experiment, the lens is used to represent the total refractive power of the refractive system of the tested eye.
this chapter will introduce ophthalmoscopy, ophthalmoscopy, keratometer to measure corneal curvature, automatic optometry, X-ray to measure eye axis, ultrasonic to measure eye axis, laser holography to measure eye diopter and proctor’s plate to measure corneal surface curvature. Among them, the detection method is the focus.
section I retinoscopy
retinoscopy, referred to as retinoscopy, was accidentally discovered by willanam in 1859. When he examined the astigmatic eye with ophthalmoscope, he found a special moving reflection. It was not used clinically by cuignet until the afternoon of 1873. In 1884, Smith suggested using the term censorship. The term retinoscopy was proposed by parent in 1881. In fact, it is not used to check the retina.
in order to enable beginners to understand some optical phenomena encountered in photographing and eliminate the mystery of photographing, this paper introduces a simple demonstration method.
take a + 10.0ds lens from the audition disc. Draw a red dot on a piece of white paper as the observation target. The target moves slowly in all directions about 10cm away from the lens, and the moving direction and speed of the target imaging in the lens are observed through the lens. In this experiment, the lens is used to represent the total refractive power of the refractive system of the tested eye. The red dot represents the spot formed by the projection light of the ophthalmoscope on the retina of the tested eye. Change the distance between the red dot and the lens to simulate the length of the eye axis of the tested eye, that is, the position of the main focus behind the tested eye. When the distance between the red dot and the mirror is less than 10cm, the movement direction of the red dot seen is the same as its real movement direction, which shows the refractive state of hyperopia, which is called forward movement. When the distance between the red dot and the mirror is greater than 10cm, the light emitted by the target is collective light, forming a focus between the observation eye and the lens. The light seen by the observer is emitted by the false light source (focus). This is the refraction of myopia. The movement direction of the red dot is opposite to the real movement direction, which is called reverse movement. When the red dot and the observation eye are just at the coaxial focus of the lens, the light seen flashes past, which is called the reversal point, neutralization point or the far point of the inspected eye. From the above experiments, it can be seen that some phenomena encountered in the examination can be demonstrated by simple models, which are not profound. Moreover, what we see in this test is only the reflection of the object, and there is no shadow in the movement. The shadow seen during examination is formed by the pupil of the tested eye covering part of the light. As mentioned earlier in
, any eye has a distal point, which represents the point where the refractive system of the eye becomes the conjugate focus with the fovea of the eye when it is at rest. Retinoscopy is to find the far point of the tested eye and convert it into the diopter of the eye according to the far point distance. When the distal point is behind or before the peephole of the ophthalmoscope, it shows forward or reverse movement. When neutralizing or reaching the reversal point, the far point just falls at the peephole. If the far point does not fall at the peephole, pull the far point back to the peephole with a lens, which is the general goal of retinoscopy. Because this method is to find the far point, which exists only in static refraction, the accurate results can be found only by relaxing the regulation with drugs or making the subject look at the far target. However, the latter can only be used for those who can relax when looking far.
II. Equipment and lighting system of the photographing method
before applying the photographing method, it is necessary to understand the equipment required for the photographing. First, optical conditions are the most important. The examination room should be half dark. In order to enable patients to relax and adjust, the room should be larger. In cases without cycloplegia, it is difficult to check the diopter at the macula, because when the spot falls on the macula, the pupil shrinks and the line of sight is covered by reflection. For this reason, the examination method of mild paracentral part is often adopted to make the patient look at the distance behind the examiner’s head from the examiner’s ear. Theoretically, in order to measure the refraction of the macular area as much as possible, the smaller the illumination area is, the less it deviates from the fovea. On the other hand, we should also relax the regulation. In order to achieve the above two purposes, it is best to install two small light spots on the opposite wall at a distance of 6m to keep the patient’s eyes fixed in an appropriate direction and distance. Or just install a light spot and gently move the examiner’s head to the side when examining the other eye.
in short, the light from the ophthalmoscope to the inspected eye is called the lighting system. It can be adjusted to parallel, spread and collect three different beams. Where the display light source s’ is located between the tested eye and the ophthalmoscope, the spot on the fundus of the tested eye is reverse motion, and others are forward motion. The characteristics of anterograde and inverse movement have nothing to do with the refractive properties of the affected eye.
III. optical principle of observation system
this is the optical system from the light reflected from the fundus of the affected eye to the observation eye, that is, the part demonstrated with convex lens in the previous overview. Light is reflected from the retinal pigment cells of the affected eye and the choroid behind it, so it has orange color. The light is emitted from the tested eye and moves forward to finally form the far point of the eye. The light divergence represents the refractive property of the tested eye. The collective light is emitted by myopia, the scattered light is emitted by hyperopia, and the parallel light is emitted by emmetropia. After entering the peephole of the ophthalmoscope, some light is imaged on the omentum of the examination eye. This image is projected to the pupil of the examination eye, and the change of the pupil becomes the focus of the examiner in the examination process. Because the tested eye is a high-power refractive body, the examiner cannot see the fundus of the tested eye, and can only judge the refractive nature of the eye through the change of light reflected from the pupil.
if the astigmatism of the projection light of the ophthalmoscope is just focused on the pupil plane of the affected eye, the pupil of the affected eye is full of input light. At this time, the pupil of the affected eye is either completely bright or completely black, that is, there is no movement. At this time, no shadow movement can be seen in any refractive state. At this time, it seems to be neutralization. In fact, it is generated by the projected light of the lighting system, not by the light emitted from the affected eye, so it is called projected light neutralization or false neutralization. HereIn the case of false neutralization, the bright area of light moves very fast. It is calculated that the speed of this movement is infinite. When the cornea or lens is turbid, a dark shadow can be seen on the background of uniform red light.
in a word, when the ophthalmoscope is used, three situations can be seen: forward motion, reverse motion and neutralization. The nature of its motion depends on the divergence of the light emitted from the tested eye, that is, it changes with the refractive state of the tested eye. When using scattered light, parallel light or collective light less than 1.0d to detect at 1m, only myopia higher than – 1.0d is reverse- Myopia of 1.0d was neutral. The rest are clockwise. When the collective light greater than 1.0d is used for detection, the above shadow movement phenomenon is completely opposite, that is, the myopia is forward movement and the hyperopia is reverse movement. Therefore, when checking high myopia, if you can see the forward movement with high collective light, it is easier to distinguish than the reverse movement.
IV. operation of retinoscopy
the subject sits opposite the examiner 1m away, so that the subject can look at the fixed light in the distance to relax the adjustment. The examiner holds a plane ophthalmoscope to throw light into the pupil of the affected eye, gently rotate the mirror, and pay attention to the performance and movement direction of light and shadow in the pupil area of the affected eye.
in addition to the motion size of the image, pay attention to the motion direction of the lighting area. If it moves in the same direction with the mirror, it may be myopia, emmetropia and hyperopia below – 1.0d; If you move in the opposite direction, you have a higher myopia than – 1.0d. When checking, try the horizontal meridian first and try the vertical meridian again. If it moves along with the mirror, gradually increase the degree of the convex lens on the mirror frame until the shadow disappears; If + 0.25D lens is added, the shadow will turn into reverse motion, indicating excessive correction, including the existence of neutralization point. When there is no shadow movement, that is, the refraction on this meridian has been neutralized. The neutralized eye happens to be -1.0d myopia. Finally, minus – 1.0d from the total diopter of the lens added to the frame is the diopter on the meridian.
if the reversal points on all meridians are the same, this refractive error is spherical. If the reversal points on different meridians are different, it indicates that there is an astigmatism component. The diopter on each meridian should be corrected separately to determine the degree and nature of astigmatism. When the axis of astigmatism is vertical or horizontal, the edge of the illumination area in the pupil should also be vertical or horizontal. During examination, the rotation direction of the mirror shall be perpendicular to the edge of the light column in the pupil area, and neutralized with a suitable lens until it does not move. If the motion on the two meridians is both positive and negative, it may be mixed astigmatism. If the astigmatism axis is oblique, the light residence in the pupil area is also oblique. The deflection of the edge of
illumination area depends on the astigmatism axis of the eye and has little to do with the swing direction of the mirror. As shown in figure 14-9, AB represents an inclined ruler. When the ruler slides horizontally in the direction of C at the opening of a cylinder, if viewed from the opening, it will not be considered that the ruler moves in the direction of C, but in the direction of D, that is, in the direction perpendicular to the edge of the ruler. This sensed movement direction is formed by the vision of the eye, which shows that when checking astigmatism with the retinoscopy method, although it is required that the mirror movement direction should be perpendicular to the edge of the optical axis of astigmatism as far as possible, it does not matter much if there is a slight deflection.
when astigmatism is found, a bright light band appears. The movement direction of the mirror shall be perpendicular to the edge of the light band. The meridian closer to the front view should be corrected first, and then the meridian at right angles to it, that is, the axis with higher refractive error, should be corrected. When the refraction on the first meridian is indeed corrected, the illumination area of the pupil will be banded. When the mirror is swung parallel to the strip-shaped illumination area, it can be found that a shadow is generated on both sides of the pupil, and soon converges in the center of the pupil to form a shadow in the center of the pupil, and both sides become the illumination area. This phenomenon shows that the ametropia on the meridian consistent with the light band has been accurately corrected. This is because the retinal image is reversed into a linear shape during mirror movement. The diopter of
astigmatism shall be calculated the same as that of the sphere, and each meridian shall be measured separately. If the reversal point of one meridian is + 4.0d and the other is + 6.0d, subtract 1.0d from each, and the result is + 3.0d / + 2.0dc.
if the correction results of the two meridians are + 2.0D and -2.0d respectively, subtract 1.0d from each, that is + 1.0d Od and -3.0d are + 1.0d / – 4.0dc or -3.0dc / + 4.0dc, and the latter prescription axis is at right angles to the former. Which of the two prescriptions is better should be determined according to the astigmatism axis of the other eye, so as to make the astigmatism axis of the two eyes consistent as far as possible.
if the axes of the two main meridians do not form a right angle, but cross obliquely, the diopter of the two main meridians should be found out by general methods, but this kind of oblique cross column mirror group can not be used to correct astigmatism, so it should be converted into the equivalent of two mirror pieces with right angles. Thompson introduces a clever drawing method; When the refractive power of the two meridians and the angle between them have been found, such as F1 θ 1/F2 θ 2, (the smaller value in the direction of column axis is determined as F1, θ 2- θ 1 ≠ 90 °), according to figure 14-10, OA and ob respectively represent the degrees of the two main meridional lines, expressed in scale, ∠ AOB is twice the included angle between the two axes, i.e. ∠ AOB = 2 α ( α=θ 2- θ 1)。 After drawing the parallelogram, the diagonal OC is the diopter of the synthetic cylindrical mirror. The positive value of convex mirror is expressed by OA and ob, the negative value of concave mirror is drawn in the opposite direction, and the diopter value can be measured by ruler side, ∠ c0a = 2 θ， Finally, the direction of column axis is θ+θ 1。 The examples of
are as follows: it is assumed that the two main meridional lines are inclined in refractive examination, such as F1 is + 4.0d, which is located on the axis of 20 °; F2 is + 2.0D, which is located on the axis of 60 °. Use a ruler to draw OA equal to 4. OB equals 2. The included angle between the two shafts is 60 ° – 20 ° = 40 °, so 40 ° × 2 = 80 ° is the included angle between QA and ob, drawn as a parallelogram, connected with its diagonal OC, measured at the same scale, OC = 4.77, which represents the mirror degree of the synthesized column, and ∠ COA is 24 °, i.e. 2 θ= 24°， θ= 12 °, soFinally, the axial position of the synthetic cylindrical mirror is 12 ° + 20 ° = 32 ° (i.e. + 4.77dc) × 32)。
this cylindrical mirror must be combined with a spherical mirror, and its degree is represented by s, and the degree of cylindrical mirror is represented by C. Therefore, in the lens combination, the curvature on the meridian of the minimum refractive power is SD and the maximum refractive power is (s + C) d. Because the sum of the new combined forces must be equal to the sum of the original two diopters. Therefore, the value of spherical mirror can be obtained by the following formula.
s + (s + C) = F1 + F2
2S + C = F1 + F2
s = (F1 + f2-c) / 2 = (4 + 2-4.77) / 2 = 0.615d
, i.e. + 0.62d / + 4.77dc × 32
if you do not need to draw, you can also use the formula designed by Thompson to calculate the diopter and axis position of the cylindrical mirror. with α Represents the angle between two meridians, θ Represents the angle between the axis of F1 and the synthetic cylindrical mirror (c).
is replaced by θ Represents the angle between the required column mirror and F1, then
TG2 θ= F2sin2 α/ (F2+F1cos2 α)
according to the above example, F1 = 4, F2 = 2, α= 40°
tg2 θ= (2 × 0.9848)/(4+2 × 0.1736)=0.453
θ= 14 ° 15 ′
substitute 4.77 into
according to the formula for s, and obtain that s is 0.615, i.e. 0.62d.
original cross cylindrical lens formula of oblique astigmatism:
+ 4.0dc × 20/+2.0DC × The optical equivalent of 60 shall be:
+ 0.62ds / + 4.75dc × 32
the ball column combined lens can be ground. In order to improve vision and wear comfort, try again before prescribing glasses for the patient, and slightly correct the axis of the column mirror and the degree of the ball mirror according to the actual feeling of the patient. In order to avoid complex formula calculation, someone later designed calculators and tables, which is omitted.
v. correction of detection results
when correcting astigmatism, the axial degree of the cylindrical mirror can be measured very accurately with the help of the direction between the illumination area and the shadow junction. If the suitable spherical lens and cylindrical mirror are placed on the frame and then the shadow is observed, the astigmatism can be measured more accurately. It is valuable to use this method to correct the measured force of cylindrical mirror. It is assumed that the refractive power at 90 ° meridian is + 3.0d and the other at 180 ° meridian is + 7.0d, if a + 3.0ds lens and a + 4.0dc lens are used × 90 lens is placed on the frame, and there should be no influence in any direction. Another commonly used method to identify the joint strength of lenses is to observe the influence by increasing or reducing the inspection distance. If the light emitted from the fovea of the tested eye is imaged at 1m, that is, its distal point is 1m. Because the distal point coincides with the examiner’s eye, there is no shadow formation, which is the ideal result required by the retinoscopy. The examiner bends forward gently to reduce the examination distance to 75cm, and the far point falls behind the examiner’s head, and the shadow is smooth movement; The examiner tilts back slightly to increase the distance to 125cm, and the far point falls between the examiner and the patient, which is a reverse motion. Therefore, when moving forward and backward, the above situation does not occur on both meridians, indicating that the spherical correction lens is incorrect; If the movement of one direction changes and the other remains unchanged, the column mirror correction is incorrect.
illustrate the above inspection. If the inspected eye is a hyperopia eye of + 3.0d, the inspection result is also + 3.0d (excluding the correction value of detection spacing). When wearing this lens for inspection, the examiner tilts forward and tilts back in different axial positions, which shows that the lens degree is correct. If + 3.25ds is placed in front of the tested person, due to over correction, the manual distance moves between the examiner and the patient, so there is no forward movement when leaning forward, and it is still reverse movement when leaning back, which proves over correction. In case of simple astigmatism, if the tested eye is + 3.0dc × 90. Different from the above, it is assumed that the refraction on the 180 ° axis is correct, so only the light band of astigmatism is corrected. If the lens used is correct, the forward tilt is forward and the backward tilt is reverse. If + 3.0dc is wrongly changed to + 3.25dc or + 2.75dc, only the axis position of astigmatism shall be corrected by the above method. If it is a + 3.0d / + 1.0dc × 90, which is actually a + 3.0dc × 180 and + 4.0dc × 90 composite refractive system. At this time, two light bands shall be made separately for correction. The low degree represents the spherical part, and the high degree represents the astigmatism part. According to Duke elder’s book, if this method can be correctly applied, the accuracy of correction can be reduced to & plusmn; Within 0.25D.
can also change the speed of reflective movement after checking the change of distance. If the observer moves closer to the far point plane, the motion speed will increase; On the contrary, when it is away from the far point plane, the reflective motion speed can be reduced. In the change of observation distance, on the one hand, when the reversal point has been reached, a small amount of distance can be changed to judge the accuracy of diopter from false “forward movement” and “reverse movement”. On the other hand, in cases of high ametropia, the initial movement can be slow to an illegible degree before adding any lens, The method of changing distance can also be used as the qualitative basis of ametropia. Because the examiner moves forward a certain distance, the motion speed of the shadow will increase. This change is the same whether in myopia or hyperopia. When the movement speed increases, it is easier to identify the movement direction. According to the movement direction, put the lens close to enough correction, return to the customary inspection distance, and then carefully look for the reversal point.
in order to confirm whether the position of the cylindrical lens axis is accurate, use the correct spherical lens and slightly corrected cylindrical lens on the test stand, for example, change + 3.0d / + 4.0dc to + 3.0d / + 3.5dc. In this case, when the mirror is rotated in a direction perpendicular to the cylindrical mirror axis, a shadow representing uncorrected + 0.5dc will appear, which moves in a direction accurately at right angles to the cylindrical mirror axis. If the axis of the cylindrical mirror is not placed in the correct direction, the shadow does not move at right angles to the axis of the cylindrical mirror, but is inclined, and the direction of deflection is quite different× 180 mirrors. When + 7.0ds is placed on the frame, the vertical light band has not moved, indicating that the hyperopia diopter on the 180 ° meridian has been neutralized. Turn the light band to horizontal, the horizontal light band is dark and wide, and the forward speed is also slow, indicating the existence of high astigmatism. Pull down the push plate slowly until the light band in the pupil becomes the narrowest and brightest. It is found that the skin light band of the eyelid is completely parallel to the forward moving light band of the pupil at 18O °, which is the narrowest and brightest. Thus, it is determined that the astigmatism axis should be 180 °. After the axis positions of
are determined, push the push plate to the highest position again and gradually increase the degree of convex spherical mirror. The + 10.0ds lens to be used is placed on the mirror frame. It can be seen that the horizontal light band has not moved, so it is known that the astigmatism is + 10.0ds – (+ 7.0ds) = + 3.0ds. The degree of wearing lens is 6.0ds / + 3.0dc × 180。
(4) high myopia: when taking concave mirror examination for high myopia, because the push plate is at the highest position, the light band in the pupil is too dark and wide, the shadow movement is too slow, and the boundary of the reverse light band is not clear. Therefore, the push plate shall be pulled down to the lowest position to produce the detection effect of concave mirror, so as to turn the reverse light band into forward, brighten and narrow it, so as to find the astigmatism axis position and reversal point. The method is to place a concave spherical mirror on the mirror frame and neutralize the moving light band. When the neutralization point is reached, subtract + 1.0d (i.e. add – 1.0ds) from the concave ball mirror degree on the mirror frame to be the lens degree to be worn.
2. Points for attention in operation
(1) those who have mastered the general detection method can master the strip light detection method with a little practice. When it is necessary to exclude ametropia for some patients in the outpatient service, it can be examined by row mirror at a distance of 2 / 3M. If the vertical and horizontal anterograde light bands can be neutralized with + 1.5ds, it is estimated that there will be no ametropia. If the light and shadow are irregular, pay attention to whether there is corneal facet or opacity, and whether there is opacity in lens and vitreous. In
(2) and the diopters on the two principal meridian lines at right angles to each other, a spherical mirror is used instead of a cylindrical mirror. Because most of the axis positions seen in the detection are estimates, if the axis position of the cylindrical mirror is slightly misplaced, it will cause human errors in the axis position and degree. There is no such disadvantage when the ball mirror is used in the middle and.
(3) generally, the push plate always takes the highest position in the process of forward or reverse motion. The push plate moves down only for the following two cases: ① when determining the forward motion position of high hyperopia astigmatism, the push plate should move down partially; ② When the concave mirror is used for the examination of high myopia or myopic astigmatism, the push plate shall be pulled down.
(4) in order to further determine the “reversal point”, it can be carefully corrected in combination with the method of slightly changing the distance in paragraph 5 of this section.
VII. Dynamic retinoscopy
dynamic retinoscopy was first introduced by cross in 1911 to measure the diopter of the eye in the dynamic refractive state. General retinoscopy requires the subject to look at the infinite distance as far as possible to relax the adjustment, so as to check the static refractive state. Dynamic retinoscopy is to make both eyes fixedly see the near target, that is, the adjustment and collection of both eyes are in an active state, so it can measure the adjustment degree of both eyes and objectively measure the near point of adjustment. This method can be competent only if it has more skilled technology than static radiography. The
dynamic ophthalmoscope is an additional fixation target under the ophthalmoscope to attract the focus of the subject’s two eyes. If there is no special dynamic ophthalmoscope, a simple font or visual mark can be pasted next to the reflector of the general ophthalmoscope as the fixation target, so that the subject’s eyes can carefully focus on the nearby target. During the examination, the subject wears corrective lenses for remote viewing, and both eyes are not covered. Pay attention to observe whether the corneal reflection of both eyes is in the center to determine whether the two eyes are in the assembled state.
it is reasonable that when both eyes focus on the nearby target and the subject has strong regulatory power, the retina of the tested eye and the fixation target are the conjugate focus of each other, so it should be the neutral point during dynamic examination. But in fact, it is not the direct movement of neutralization and immobility; That is, the eye is in a state of insufficient adjustment or relative hyperopia. For example, when the image is detected at 33cm, the set is 3mA, and the adjustment should also produce 3.0d adjustment accordingly. However, according to the actual observation, the image is clockwise. Therefore, it is necessary to extend the distance or add + 0.5d ~ + 0.75D lens in front of your eyes to achieve neutralization. The neutralization point reached by the above lens is called the low neutralization point. This phenomenon represents that the regulation function lags behind the collection function. It is said that the occurrence of this phenomenon is related to the size of the pupil and the details of gazing at the target during examination, but its true meaning and explanation are still unclear. During static examination, when the neutralization point is reached, as long as a low convex lens in the audition disc is added, the neutralization can become reverse. However, during dynamic examination, when the low neutralization has been reached and the convex mirror is added, it does not immediately become reverse. It seems that there is a neutralization area at the low neutralization point. Therefore, it is necessary to add a higher (+ 0.5 ~ + 3.0d) lens to make it reverse. After adding the lens again, the inversion point reached is called the high neutralization point.
, a simple objective examination method, have attracted the attention of many scholars and used it to measure various ocular refractive states. However, in future practice, it is found that the above adjustment lags behind the set, that is, there is the phenomenon of low neutralization and high neutralization, so its original advantages are diluted and its application scope is reduced. The two methods of adjusting and distinguishing true and false myopia by dynamic retinoscopy are introduced as follows.
1. This method uses two eyes to look at the near visual target, uses the joint motion relationship between the adjustment and the set to make the adjustment produce varying degrees of adjustment with the change of the set, and uses the retinoscopy to determine the conjugate focus of the tested eye.
in this method, self luminous ophthalmoscope shall be used, and simple and easy to see small characters shall be pasted next to the reflector as the fixation target. Put on long-distance corrective lenses, keep both eyes uncovered, look at the small eye mark on the ophthalmoscope at the same time, and observe the motion state of the shadow. According to the corneal reflection of the tested eye, the examiner monitors whether the visual axes of the tested eye are assembled at the plane of the reflector. Slowly move the ophthalmoscope to the eye to be examined. When it reaches the adjustment near point, the shadow will not move, or it will move forward slightly near, and it will move backward slightly far, that is, the near point of the eye to be examined will move back and forth with the movement of the ophthalmoscope. The adjustment force can be calculated by measuring the distance at the reversal point. If the collection of subjects is unstable, make them stareTheir own fingers, as the target of gaze, are examined by ophthalmoscope with the movement of their fingers.
this method can also compare the adjustment of two eyes at the same time. According to the above principle of measurement and regulation, this method can also be used to determine the degree of residual regulation after cycloplegia. It is generally stipulated that the remaining regulation of 1.0d is the indicator of complete drug action. If it exceeds 1.0d, it is considered that ciliary muscle paralysis is incomplete.
2. In the work of dynamic retinoscopy, Wu xiecan found that the high and low degrees of mild myopia were generally about + 2.5D. If 33cm colonoscopy is performed without total refractive correction glasses, the reversal point of myopia is mostly below + 2.0D, and the higher the myopia is. The lower the degree of convex lens required to reach the inversion point. If the myopia is above – 3.0d, a concave lens is often used to obtain the inversion point. In emmetropia or mild hyperopia, although the high and middle degree is also about + 2.50d when 33cm in-situ dynamic retinoscopy is used, most of the reversal point degrees of all emmetropia or hyperopia eyes exceed + 2.50d when total refractive correction glasses are not worn. The higher the hyperopia, the higher the degree of convex lens required to reach the inversion point. Therefore, the inversion point degree of the same position dynamic retinoscopy can be considered to identify the type of refraction of the examined eye. True or false myopia can be distinguished by combining far vision and near vision. The instruments used in
Wu’s method are one lens frame and two + 2.25ds lenses. The No. 5 small character is pasted on the side under the reflector of the ophthalmoscope as the visual mark, and the slit light next to the ophthalmoscope is used as the lighting of the visual mark. First check the far vision and near vision, and those with poor far vision and normal near vision are the inspection objects. Put + 2.25ds lenses in front of both eyes on the frame. The subject’s eyes are fixed on the ophthalmoscope visual target, and the two eyes are subject to 33cm in-situ examination respectively. If all diameter lines are reversed, it indicates that the tested eye is true myopia; Each diameter line is anterograde, which is emmetropia or hyperopia, which proves that the myopia state shown in the visual examination is false. Mixed astigmatism occurs when one radial line moves or does not move and the other radial line moves backwards.
this method has the advantages of simple equipment, simple operation, rapid inspection and no pupil dilation, so it has some worries that will not affect students’ learning. The correct rate of distinguishing true from false is as high as 91.25%. The diagnostic accuracy of pseudomyopia was 92.62%, that of pupillary examination was 5%, that of mydriasis was 24.4%, and that of simple fog method was 46.39%. Only simple myopia astigmatism and mixed astigmatism are difficult to distinguish, which may be due to children’s inability to adhere to fixation.
3. This method is developed by Shi Mingguang and consists of two parts: a spectroscopic optometry frame and a binocular spectroscopic simultaneous optometry device. Figure 14-14a shows the photos of the examiner during examination on the right side of the patient. Fig. 14-14b is the light path diagram of the input light and the light reflected from the examined eye to the examiner’s eye during examination.
1. The subject looks at the target in front of his eyes (i.e. the fixation plane) through the half lens; 2. The light of the ophthalmoscope is projected to the examined eye as shown by the solid arrow in the figure; 3. The light of the examined eye is projected to the semi reflective half lens as shown by the imaginary arrow A, and then the light is projected to the ophthalmoscope as shown by the imaginary arrow B, and then enters the
in the eye Both the left and right eyes of the frame have a half mirror half lens, so that the examined eye can see not only the target in front, but also the left and right sides. The examiner can see the light reflected from the examined eye on the side for examination. When two eyes observe the immediate target, the examiner can perform optometry on the side of one eye at the same time, so the dynamic diopter can be measured in this case. In this way, both AC / A and Ca / C of both eyes can be measured.
VIII. Difficulties in optometry
previously introduced the principles and methods of general optometry and strip light optometry, but this inspection method only depends on the description of books is not enough. Optometrists should practice repeatedly and experience carefully. It is easy to master the neutralization methods of forward and reverse motion, but to be fast, accurate and flexible, we need to make some efforts in basic theory and technical operation in order to be able to use them freely. Therefore, Whittington called refractive examination optometry art has a certain basis. The difficulty often encountered in
examination is that different diopters appear in different areas of the pupil. The most common is that the central part is different from the peripheral part, which is more prominent after pupil enlargement. Depending on whether the tested eye has a positive spherical difference or a negative spherical difference, the brightness of the reflection in the pupil area can be increased in the central part or in the peripheral part. Even under normal circumstances, this spherical difference may reach a degree that can not be ignored. However, in pathological cases, such as lens sclerosis, the refractive difference between the two areas can be as high as 14.0d. For the optical phenomena of these manifestations, please refer to the schematic diagram of
mixed anisometropia in Fig. 14-15, which is referred to as mixed anisometropia, that is, the pupil reflection of this half is different from that half. It is represented by two banded reflections moving towards and away from each other, so it is called silhouette. The optical explanation of this phenomenon is that one part of the refractive body in the pupil area is comparative myopia and the other part is comparative hyperopia (Fig. 14-16). This phenomenon can occur only when it is close to the reversal point. It can be caused by lens astigmatism, spherical aberration and mild corneal opacity. If it is caused by mild corneal opacity, the two strands of the silhouette point to the scar. In this case, the best way to approach correction is to find a lens that can make the two parts of the silhouette meet in the center of the pupil. During the examination, we should focus on the central part of the shadow and the peripheral part on the secondary part, because the formation of vision depends on the refractive system of the central part. The shadow of
keratoconus is often triangular, and its tip faces the center of the cone. The shadow rotates around the cone like a mirror. In irregular astigmatism, all kinds of deformed shadows can be seen. These shadows are fuzzy and can only be corrected by estimation. In most cases, only by subjective optometry, a fine gap lens is placed on the frame, rotated to the best position considered by the patient, and corrected with a spherical mirror on this meridian as much as possible. Then, the same correction is made at another 90 ° meridian. The results are used to form a prescription for glasses. In determining the refraction of these abnormal cases, the personal experience of the examiner is much more important than the classical provisions.