Crowding phenomenon of amblyopic eye

Introduction One of the signs of amblyopia is that the ability to recognize a single font is much higher than that of a font of the same size but arranged in a row. This phenomenon is called crowding.

Cause

Causes

At present, the classification of von Noorden is used, which divides amblyopia into the following five types: strabismic amblyopia, refractive amblyopia, anisometropic amblyopia, form deprivation amblyopia and congenital amblyopia. Dale suggests that amblyopia caused by visual developmental disorders that occur during the sensitive period of visual development from birth to age 6 is called developmental amblyopia. Developmental amblyopia includes strabismus, refractive error, anisometropia, form deprivation amblyopia, excluding congenital amblyopia (Figure 1).

1. Strabismic amblyopia

After strabismus occurs, the two eyes cannot simultaneously gaze at the specified target, and the object image of the same object cannot fall at the corresponding point of the retina of both eyes at the same time, thereby causing double vision. In addition, when strabismus occurs, the bilateral macula gaze at different targets. Due to the fusion function, the brain center overlaps the two distinct targets that the two eyes are looking at, which is confusing. The diplopia and confusion caused by strabismus cause extreme discomfort to the patient, and the visual center actively suppresses the visual impulse of the erythema yellow spot input. When the macula is in a suppressed state for a long time, it will lead to the occurrence of strabismic amblyopia.

Monocular strabismus is prone to amblyopia, while alternating strabismus has alternating gaze and alternating inhibition in both eyes, and its inhibition is temporary, so it is difficult to form amblyopia.

The incidence of esotropia is earlier, often occurs before the formation of binocular monocular function, so amblyopia is easy to occur. External strabismus generally has a late onset, and the erythema of the strabismus is less severe. Once the strabismus is corrected, it is easy to restore the binocular monocular function.

This amblyopia is a consequence of strabismus, secondary, functional, and thus reversible, with a good prognosis. However, the earlier the strabismus occurs, the deeper the degree of amblyopia. If it is not treated in time, the possibility of cure is small.

Strabismus amblyopia has the following four points of waiting:

(1) Esotropia has a higher incidence of amblyopia than exotropia.

(2) Constant strabismus has a higher incidence of amblyopia than intermittent strabismus.

(3) The incidence of amblyopia is high when strabismus occurs before the age of 3, and amblyopia is not easy to cure.

(4) The longer the duration of monocular strabismus, the deeper the degree of amblyopia.

2. refractive amblyopia (ametmpic amhlyopia)

Refractive amblyopia is more common in mid-height hyperopia and astigmatism. Since the key period of visual development (born to 3 years old) and sensitive period (before 6 years old), the correct optometry is not given, the image on the retina is always Unclear, the brain center accepts this vague stimulus for a long time, and it can form amblyopia for a long time. This kind of amblyopia is equal or close to the two eyes, there is no binocular fusion disorder, and does not cause deep inhibition of the macula. Therefore, after wearing appropriate glasses, the visual acuity of both eyes will be improved, which is the best kind of amblyopia treatment effect.

The reason why astigmatism causes amblyopia is that the corneal curvature radii of the two meridians perpendicular to each other are not equal, and the image of the external object passes through the refractive system of the eye, especially the cornea, and cannot form a focal point on the retina but forms a focal line, regardless of the eye. How to adjust, the retina can not always form a clear image, and the so-called meridian linear amblyopia will form in a long time.

3. anisometropic amblyopia

The diopter of both eyes is called anisometropia. Most of them are farsightedness, the difference between binocular mirrors is 1.50D, and the difference between cylinders is 1.0D. Because the anisometropia is too large, the image clarity and image size of the retina on both eyes are different (the difference between the diopter of each eye is 1.0D, the size of the binocular image is 2%), and the center of the eye is easy to accept the image. At the glance of visual conduction, the object image from the eyeball with a large refractive error is suppressed, and the image of the eye with a higher degree of diopter is suppressed to form amblyopia. Even if the refractive errors of the two eyes are completely corrected, the size of the objects formed on the retinas of the two eyes is not equal. When the difference between the size of the objects exceeds 5%, it is difficult for the visual center to fuse the large and small objects into one. . Therefore, the formation of anisometropic amblyopia is the result of the retinal image of the two eyes, and the active inhibition of the refractive error of the central fusion is the result of the higher image of the eye.

Myopic anisometropia is not easy to form amblyopia, because the patient often uses a lighter eye for a long-sighted vision, and a near-sighted one with a higher degree of myopia. Their gaze nature is generally central gaze or paracentral gaze. After refractive correction, the visual acuity can be improved. However, if the anisometropia is too large, the eyes will have obvious unequal vision, and it is difficult for the visual center to fuse the retinal images of both eyes. Can not form a single eye, then a more serious degree of myopia forms amblyopia.

As early as 1932, Ames determined the binocular inequalities theoretically and clinically as an independent field. Lancaster conducted a systematic study of image inequalities. At present, there are many instruments for examining binocular images in foreign countries. At present, the inequality check chart designed by Su Shihan is widely used, but it can only check the aberration on the retina of both eyes, and can not determine the threshold of maintaining fusion and stereoscopic vision. The purpose of the binocular inconsistency check is to determine the threshold of binocular disparity allowed to maintain the binocular single vision function. China's Liu Yannian and Yan Shaoming applied binocular vision into the first-class simultaneous view, two-level fusion, three-dimensional stereoscopic classic theory and the red-green complementary principle designed and developed "Double-eye image inequality check chart" to solve three items at the same time. The problem of the aberration function is the retinal aberration function, the binocular fusion aberration function, and the stereoscopic binocular aberration function.

4. Deprivation amblyopia

In the critical period of visual development of infants and young children (before 3 years old), amblyopia caused by keratopathy, congenital cataract, complete ptosis and eye disease is called form deprivation amblyopia. Because it occurs in the critical period of visual development of infants and young children, it will cause extremely serious damage to vision. Therefore, it is necessary to emphasize the early removal of deprivation factors and to treat amblyopia as soon as possible, otherwise this amblyopia will become irreversible. According to von Noorden, children over the age of 8 are basically mature in their vision and can resist the development of amblyopia without amblyopia.

5. Congenital amblyopia (congenital amblyopia)

The current pathogenesis is still unclear. Von Noorden speculated that neonatal retinal macular and visual pathway bleeding may occur due to acute labor, dystocia, midwifery, etc., which may affect the normal development of visual function and cause amblyopia, while the chestnut endurance clinical observation, follow-up, found neonatal retina Macular hemorrhage can be absorbed quickly and does not cause amblyopia.

Some congenital amblyopia is secondary to congenital microscopic nystagmus. This tremor frequency is high, the amplitude is small, and it is difficult to observe. It can only be found under the fundus microscope. Because the eyeball is often in a high frequency and small tremor state, the macular can not be fixed. And produce amblyopia.

The corn borer treats microtropia amblyopia as a separate type of amblyopia. Because the appearance of micro-squint is not easy to find, the time of visit is late, the fovea of the macula is in a state of inhibition for a long time, and it is most likely to cause a strong side-centered gaze. According to the anatomical and physiological characteristics of the retina, the fovea of the macula has the highest visual acuity, and the visual acuity decreases slightly from the fovea. If the paracentral gaze is used for a long time, the fovea is inhibited for a long time and causes amblyopia.

(two) pathogenesis

Visual deprivation

Wiesel and Hubel first published physiological changes in the visual cortex and histological changes in the lateral geniculate body caused by visual deprivation caused by suturing the eyelids of immature kittens. These experiments indicate that suturing unilateral eyelids within 12 weeks after birth can significantly reduce cortical cells that are stimulated by the deprived eye and that are connected to both eyes. Functional changes occur in the visual center, while histological changes occur in the outer geniculate nucleus at the cellular level that is deprived of ocular input. The cells that are deprived of the eye are significantly smaller than the normal eye. The work of Wiesel et al. has aroused widespread interest among scholars. The laboratories are eager to follow suit, but the results obtained are also inconsistent due to the different types of experimental animals.

2. Binocular interaction

Another important factor in the formation of amblyopia is the interaction of both eyes. Under normal conditions, the binocular cells located in the lateral geniculate or cortex are in equilibrium. When abnormal vision occurs early in life, the cells that are deprived of the eye are at a disadvantage in the competition between the two eyes, and thus growth is hindered. This occurs when the visual inputs of the two eyes are not equal, such as between a single-sided eyelid suture or a far-sighted anisometropia, a clear image of the non-deprived eye and a blurred image of the eye that is deprived of the eye or greater in diopter. Competition occurs. The image formed on the macula of the strabismus eye is also different from that on the macula of the gaze eye, which also causes competition. Animal experiments and clinical cases have shown that in the mechanism of amblyopia formation, binocular competition is also involved. Bilateral deprivation amblyopia is a result of bilateral congenital cataract, dense corneal opacity or uncorrected bilateral hyperopia; and unilateral amblyopia due to strabismus, anisometropia, unilateral cataract, and occult amblyopia It is formed by the combination of form deprivation and abnormal interaction of both eyes.

3. Active inhibition of the cortex

In recent years, some preliminary experimental reports in biology and pharmacology have confirmed the active inhibition of cerebral cortex in developmental amblyopia.

(1) Physiological proof: It is believed that the main eye of the animal has an active cortical inhibition effect on the unilateral developmental amblyopia. For example, Kratz reported that removal of the healthy eye after 5 months of visual deprivation allowed the deprived eye to be immediately increased from driving only 6% of the visual cortical cells to driving 31%. This indicates that the dominant eye inhibits the function of the driven cells that are deprived of the eye. After removing the main eye, the deprived eye quickly recovered its function, but it did not reach the original level.

(2) Pharmacological evidence: intravenous bicuculline in animals can respond to cerebral cortical cells that do not respond to deprivation of the eye, in order to reduce the inhibition of the visual system at all levels. The experimenter can restore 60% of the connection between the cerebral cortex and the deprived eye. Unfortunately, intravenous bicucul-line can cause convulsions. Intravenous naloxone in visually deprived animals can restore 45% to 50% of cortical cells to receive binocular visual input.

an examination

Light perception

The vast majority of patients see the eye chart through the dark glass, the vision is reduced by a few lines, but some amblyopia is not the case, the dark glass can not be seen in front of the amblyopia can see the same line of sight, sometimes the vision can even There is improvement. In dim and faint light, the visual acuity of the amblyopic eye does not change much. Von Noorden and Burian found that placing the density filter in front of the normal eye reduced vision by 3 to 4 lines, but placed the same density of filter in front of the strabismic amblyopic (covering the main eye), and the vision was unaffected or only slightly reduced. When the filter of the same density is placed in front of the eyes of organic amblyopia (central retinal disease and glaucoma, etc.), the visual acuity is reduced. Therefore, they believe that the use of neutral density filter can identify visual acuity caused by reversible amblyopia and organic lesions. Later, scholars found that some reversible amblyopia without organic lesions, like organic amblyopia, under the neutral density filter examination, vision is also highly reduced. The reason for this has been unclear until Hess examined the contrast sensitivity function (CSF) of strabismus and anisometropic amblyopia under low-light illumination, and found that the responses in the two groups were different. The CSF of strabismic amblyopia rises to the same level as the normal eye under low illumination, but the anisometropic amblyopia has a lower CSF under low illumination than the normal eye, and is the same as the organic lesion. These results suggest that neutral density filter can only identify strabismus and organic amblyopia and can not identify anisometropia and organic amblyopia.

2. Contrast sensitivity

Contrast sensitivity (CSF) examination is one of the methods to check the shape function. The visual function is evaluated by measuring the black and white contrast required by the viewer to identify sinusoidal grids of different spatial frequencies. It not only reflects the resolving power of the visual target on small targets, but also reflects the resolving power of the coarse target, so it can reflect the visual function more comprehensively, far more sensitive than the visual acuity check. Rogers examined the CSF of children with amblyopia and found a linear relationship between visual acuity and CSF. When vision is reduced, the CSF is also low, and the high peak of the curve shifts to the left (to the low spatial frequency end). When the visual acuity of the amblyopia has reached 20/20, there is still a significant difference in the CSF between the primary eye and the amblyopic eye. The CSF of the original amblyopic eye is still lower than that of the primary eye. Both strabismus and anisometropic amblyopia have this phenomenon. Hess found that the CSF of form deprivation amblyopia was significantly different from those of strabismus and anisometropia. The sensitivity of the former to fixed and moving optotypes was extremely low. In some cases, only the movement of objects in the field of view was observed, but the specifics could not be distinguished. Barrier.

3. Crowding

One of the signs of amblyopia is that the ability to recognize a single font is much higher than that of a font of the same size but arranged in a row. This phenomenon is called crowding. Hilton found that children with amblyopia may have normal or near-normal vision for a single word. Amblyopia can only be found by examining the lines in a line. Therefore, the results of the examination with a single font cannot reflect the real situation of amblyopia.

About one-third of developmental amblyopia is not crowded at the beginning, but suddenly appears during treatment. Each amblyopic eye has a large difference in line font and single font recognition. The lower the line of sight, the lower the difference between the two, and some are amazing. For example, in some cases, the line font can only recognize 6/30 and the single font has a recognition power of 6/6. The single E-word chart is 0.6, which is only about 0.25 of the line font E-word list. This is because the contours between adjacent optotypes affect each other.

It was initially thought that crowding was only seen in amblyopia and was characteristic of patients with amblyopia. Tommila disagreed and thought that the crowding phenomenon was related to the level of vision. The worse the vision, the more serious the crowding. This phenomenon can also be caused by a decrease in vision due to other eye diseases. At the same time, artificial phenomena (blurring vision with lenses) can also cause this phenomenon.

Using the Snellen eye chart as a basis for examining the degree of amblyopia and the therapeutic effect is not entirely appropriate, especially for deep amblyopia, because the Snellen eye chart has only 1 to 3 words at 0.1 to 0.3 lines, which is easy to remember due to the small number of words. Not easy to cause crowding. To overcome these shortcomings, Tommila designed a new type of eye chart with equal numbers of words per line. Using Snellen eye chart and new watch to test and compare 84 children with amblyopia, it was found that only in children with visual acuity of 0.05-0.1, the results of these two different E-words were significantly different. The biggest difference was 5.8 times, a single E word table of 0.6 is only about 0.25 of the rank E word list.

Developmental amblyopia patients should have two types of visual acuity check in single font and rank font. The purpose of amblyopia treatment is to make the line font vision normal. Line fonts with abnormal eyesight cannot be counted as amblyopia cure. After a period of treatment, if the recognition power of a single font becomes normal and the visual acuity of the line font is still abnormal, the prognosis is poor, and the acquired visual acuity cannot be maintained. The greater the difference between the two, the worse the prognosis, and the difference between the two is gradually reduced, the prognosis is good.

At the end of treatment, the patient's presence or absence of congestion is of considerable value in determining prognosis. Checking for crowding is clinically relevant and should be routinely performed.

4. Attention to nature

There are two different gaze properties in amblyopia patients, namely central gaze and paracentral gaze. Can be checked with a projectionoscope. Covering the healthy eye, the patient directly looks at the black star in the projection mirror with the amblyopic eye, and the examiner watches whether the black star in the projection mirror is located directly on the fovea of the affected eye. The center of the macula is called the center of the gaze, and the center of the fove is called the center of the center.

Regarding the classification of the side-centered gaze, the opinions of different families are different. Malik uses a projection mirror to combine the classifications of each family into a very detailed and comprehensive taxonomy. However, this classification is too cumbersome and complicated, and is not suitable for clinical applications. We agree to use the projection mirror to classify the nature of the gaze into 4 types: 1 central gaze - the fovea of the macula is just in the center of the black star, and if the fovea moves slightly on the black star but does not range from the black star, it is gazing at the unstable center; 2 side concave gaze - the fovea is outside the black star but within the 3° ring; 3 the macula gaze - the fovea between the 3° ring and the 5° ring; 4 peripheral gaze - the fovea at the edge of the macula Between the optic discs, occasionally in the nasal side of the optic disc. This classification is simple and easy to remember, and is also consistent with clinical and scientific applications.

The paracentral gaze can be horizontal or vertical, and can be either stable or migratory. The farther away from the fovea, the greater the migration. The prognosis of migratory paracentral gaze is superior to that of a stable paracentral gaze. The general trend is that the farther the gaze point is from the fovea, the worse the vision of the amblyopic eye.

Those without a projection mirror can use a flashlight to compare the Kappa angles of both eyes, and estimate whether the amblyopic eye is a central fixation or a side center fixation. If the center is gazing, the corneal light reflection must be at the same position of both eyes, indicating that the size of the Kappa angle of the two eyes is exactly the same as "positive" and "negative". If you look at the side center, there is a significant difference in the Kappa angle between the two eyes. The flashlight is used to estimate the nature of the gaze. The method is simple and easy, and no special equipment is needed, but the result is not absolutely accurate, and the extremely mild side-center gaze is not easy to detect.

The incidence of paracentral gaze reported by foreign countries is extremely inconsistent (23% to 82%).

Checking the nature of gaze has important clinical implications for estimating prognosis and guiding treatment. If the affected eye cannot be turned into a central gaze, the chances of visual progress are small. This does not mean that vision will return to normal and lasting after the gaze point is turned to the center, but it cannot be denied that central fixation is the basis for obtaining standard vision.

Refractive examination

Retinoscopy was performed under ciliary muscle paralysis.

2. Fundus examination

Extremely important. First of all, it is necessary to exclude fundus diseases that cause low vision. If the fundus is normal and the patient has a history or clinical findings (such as strabismus), then it is likely that the diagnosis of developmental amblyopia is correct.

Differential diagnosis

Refractive amblyopia: Both eyes have obvious hyperopia, myopia, astigmatism, and can not be blurred by the single eye, even if the visual acuity declines quickly.

Simple myopic astigmatism: When a parallel ray on a major meridian is imaged on the retina, and parallel rays on another meridian perpendicular to it are imaged in front of the retina, we call this refraction state a simple myopic astigmatism.

Refractive myopic astigmatism: If two parallel main rays are imaged in front of the retina, but their refractive power is not equal, we call this myopic astigmatism refractory myopic astigmatism.

Myopia arc: The most common fundus change in myopia. The smallest is not easy to see, the large can reach the size of the disc. Some surround the optic disc, and even reach the macular area. Myopia arc does not affect the macular area, and has little effect on vision; visual acuity (including near vision) is significantly reduced in those who invade the macula. In general, it is difficult to determine whether myopia is still in progress based solely on the shape of the arc. However, according to fundus observation, if the edge is clear, it can be speculated that myopia has stopped; otherwise, if the edge is irregular, the expansion of the eyeball may still be in progress. When the range of myopic arc is large, especially when a scleral cone or a scleral staphyloma has been formed, the optic disc is not a perfect circle but a longitudinal ellipse due to the inclination of the optic canal. Since the temporal portion of the optic papilla is farther from the cornea than the nasal side, it is also a cause of tilting of the surface of the optic disc.

The material in this site is intended to be of general informational use and is not intended to constitute medical advice, probable diagnosis, or recommended treatments.