Amblyopia occurs in approximately 2% of the general population, although some have found the incidence to be as high as 5% to 6%. This makes it one of the most common physical ailments in children. Early treatment is probably the most important factor in determining the outcome of this condition. In this article we will examine the definition of amblyopia, its relationship to suppression, and its causes, classification, diagnosis, treatment and prevention. Since many other serious eye problems are associated with amblyopia, its early diagnosis is one of the most common means of diagnosing all forms of eye problems. The determination of the presence or absence of amblyopia is the most important aspect ofthe routine eye examination of the pediatric patient.
Amblyopia is defined as poor vision in an eye despite correction with glasses for any refractive problem. A person may have poor visual acuity in one or both eyes as a result of farsightedness, nearsightedness, or astigmatism. If the vision corrects to a normal level in both eyes with proper glasses, that person does not have amblyopia. If, however, proper glasses improve the vision in one eye to a normal level but will not improve the vision in the other eye to an equally good level, that person does have amblyopia. Although it may on rare occasions occur in both eyes, it is usually present only on one side, with normal vision in the other eye. Amblyopia can occasionally alternate from one eye to the other eye during the course of therapy and can frequently recur when therapy is discontinued.
The normal visual acuity certainly varies with the age and cooperation ofthe patient as well as with other testing circumstances. Children six or less years of age should have 20/30 vision in each eye. After that age, they should be able to read the 20/25 line or better. If the acuity is worse than this and if no significant refractive error is present, the patient probably has amblyopia. Also, if there is a difference of more than one line in the acuity of the two eyes, amblyopia should be suspected. Thus, a fiveyear-old child with 20/ 15 vision in one eye and 20/30 in the other may have a mild case of amblyopia.
AMBLYOPIA VERSUS SUPPRESSION
Amblyopia and suppression are often confused. It is important to understand their differences and relationship, particularly in regard to the etiology of amblyopia. Amblyopia and suppression are distinct entities and are identified by different tests. Amblyopia refers to poor vision in an eye tested by itself (opposite eye covered). All the visual cells are operating at their maximum capacity. Suppression occurs only when both eyes are being used simultaneously (binocular vision). In this condition the cells ofthe macula of one eye are actively suppressed from registering any visual stimulation. In such cases, the peripheral retinal elements usually function together normally (peripheral fusion), but the retinal cells responsible for the central vision in one eye are completely suppressed.
Suppression can occur only in one eye at a time, although it may alternate from one eye to the other. If the patient with suppression fails to alternate that suppression from one eye to the other and if the patient is young, the constant suppression of one macula will cause a functional "disuse atrophy" ofthat macula. This is carried over to monocular seeing conditions. When such patients are tested with the better eye covered, suppression ceases and the macular cells begin to function to the utmost of their ability, which will not be normal. Thus, suppression can lead to amblyopia. Almost all patients with amblyopia can be shown to have a constant suppression of one macula under binocular seeing conditions.
CAUSES OF AMBLYOPIA
There are two basic causes for amblyopia: 1) organic and 2) functional
Organic causes refer to disease processes that are obviously disrupting the cellular structure of the retina or the visual pathways. Such conditions are usually visible with the ophthalmoscope. They are permanent and irreversible by any mode of therapy. Examples of such causes would be macular scarring from chorioretinitis associated with congenital toxoplasmosis, macular scarring due to trauma, retinoblastoma involving the macula and hypoplasia or atrophy of the optic nerve. Cortical blindness following meningoencephalitis would also be considered an organic cause of amblyopia.
Functional cause» of amblyopia are numerous. Inali these cases the cellular structure of the retina and visual pathways appear normal; it is the function of these structures that is impaired. The degree of impairment depends on: 1) age at onset, 2) severity of impaired retinal image, 3) duration of impaired vision, and 4) age of the patient at time of effective treatment.
The age of onset of visual impairment is probably the most important factor in determining the ultimate outcome of treatment of functional amblyopia. There is a group of clinical conditions (congenital cataract, unilateral severe ptosis, corneal scarring) that prevents a normal clear image from being focused on the structurally normal retina from the earliest stages of infancy. The functional impairment that results is extremely difficult to correct. There are other groups of patients (with acquired strabismus or traumatic cataracts) whose visual systems develop normally in early life but are then lost at a later age. The later these problems develop, the easier they are to correct. A brilliant experimental model for this concept has been developed by 1981 Nobel Prize recipients Hubel and Weisel, working with kittens.1 By temporarily blocking the vision of one eye at various stages, they found that more permanent and irreversible functional disturbances occurred when the vision was blocked at an early age. Studies with monkeys have confirmed that higher primates respond in a similar manner.
The severity of the problem that is interrupting the vision of one eye also affects trie depth and seventy of the amblyopia. Loss of formed vision on one side- such as from a traumatic cataract, a severe traumatic corneal scar, or excessive patching by parents that neglects proper follow-up care- can cause rather severe amblyopia of the eye. The active suppression of the macular area in patients with strabismus can also cause amblyopia if that suppression is constant in one eye. A milder amblyopia may occur if the severity of the problem is less, as in a case in which there is astigmatism slightly blurring the vision in one eye.
The duration of the amblyopia is of obvious importance in determining how reversible the functional disturbance will be. This would represent the delay from the onset of the condition to its effective treatment. It can be due to a delay in diagnosis or a delay in getting effective treatment. The longer the problem is present, the more significant will be its effect on the function of the eye. Thus, a person with a severe amount of astigmatism that is diagnosed and treated with glasses at age four or five will rapidly recover normal acuity. However, if the disorder is not diagnosed and treated until years later, it will take much longer to respond and a corrected acuity of 20/20 may never be attained.
The age of the patient undergoing treatment is a corollary to the first factor and almost as important. Thus, deprivation amblyopia from a unilateral cataract may be treated effectively at two months of age but is quite resistant to treatment after four months of age. Strabismic amblyopia can be treated effectively before the age of four years but becomes much more difficult after the age of six. Refractive amblyopia can often be corrected at a later age (early teenage) but is more effectively treated at a younger age.
Amblyopia can be classified broadly under four headings: I) organic amblyopia, 2) deprivation amblyopia, 3) strabismic amblyopia, and 4) refractive amblyopia.
This classification can be quite convenient and helpful to the pediatrician in understanding the significance of the different forms of amblyopia. It also helps in understanding the problems associated with diagnosis and treatment ofthe various types. It should be noted that these categories are arbitrary and that patients occasionally have a combination of two or more types of amblyopia.
Organic amblyopia is due to organic causes, as discussed above. It is usually congenital in onset but may be acquired. Although most lesions are grossly visible with the ophthalmoscope, there are some types of organic amblyopia in which the changes may be subophthalmoscopic. This would include nystagmus, achromatopia (total color blindness), partial albinism and the early stages of hereditary macular dystrophy.
Organic amblyopia is characterized by poor vision in one or both eyes, uncorrectable with glasses and unresponsive to patching therapy. When it occurs in one eye. there may be a decrease in color perception in the amblyopic eye. It can sometimes be identified better with the "swinging flashlight test." In this test the pupil ofthe good eye will contract with the stimulation of the light, but on stimulation of the amblyopic eye its pupil will dilate or contract only briefly. The asymmetry of the response on swinging a flashlight from one eye to the other will be significant.
A great deal of psychologic trauma can be avoided if one can make the diagnosis of organic amblyopia and avoid extensive efforts at rehabilitating such an eye. Frequently, patching the good eye of such patients will cause them to withdraw and fall asleep persistently. Treatment should be discontinued in these patients, particularly if there is other evidence of organic amblyopia. The organic nature of many vision problems can be ascertained from a family history of hereditary problems or the circumstances surrounding the onset of the problem.
Deprivation amblyopia has also been called amblyopia ex anopsis or amblyopia of disuse. It is the most serious type of functional amblyopia and the most difficult to treat. In this type there is a lack of formation of a retinal image, usually in one eye. This can be due to a congenital cataract, total ptosis, corneal opacity or other problems that lead to total disuse of the amblyopic eye. The precipitating problem usually occurs from birth but can occur later, as in the two- or three-year-old with a traumatic cataract. These patients have a very severe loss of vision. The amblyopic eye will frequently have vision no better than light perception or seeing hand motions. This is the case even when the cataract has been removed or the ptosis corrected. Delay of more than two or three months in effectively treating this condition in infants leads to irreversible changes along the visual pathway. Although data on histologic changes in human beings are not available, the changes are probably similar to those found by Hubel and Weisel in kittens deprived of visual stimulation during the first six weeks of life.1 In the course of the visual pathways, they could demonstrate atrophy in the area of the lateral geniculate body on the side of the amblyopia. Thus the end state of deprivation amblyopia may actually be an amblyopia that cannot respond to treatment.
Deprivation from a traumatic cataract in an older child (up to age six) behaves in much the same way. If visual rehabilitation is delayed for more than a few months, visual acuity does not seem to come back to a good level. Since cataracts are the most common cause of deprivation amblyopia and since early infancy is the most common age at onset of this problem, it is important in the routine examination ofthe newborn and the six-weekold to rule out the presence of a cataract. This can be done simply by observing the red reflex with the ophthalmoscope. If one is having difficulty, a single drop of 2.5% phenylephrine (Neo-Synephrine) and 0.5% atropine should provide an adequate, rapid, and safe method of dilating the pupils.
Strabismic amblyopia is poor vision in one eye associated with the deviation of that eye. Although about half of the amblyopia population will have some type of strabismus problem, the other half will have eyes that are essentially straight. Thus, the absence of strabismus does not rule out amblyopia. Most exotropic patients and most patients with esotropia from infancy will not have amblyopia.
The most common association of strabismus and amblyopia occurs in the acquired form of strabismus. This has its onset at an average age of about two and a half years, usually ranging from 18 months to four years of age. About 30% of these patients will have amblyopia. The angle of the strabismus has no bearing on the presence or extent of the amblyopia. Amblyopia rarely occurs when the strabismus develops after four years of age.
The mechanism of developing amblyopia in a strabismic child is as follows: The esotropia causes a diplopia that is quite bothersome to the child. To avoid this problem, the young visual system has the ability to suppress actively the macular image in the deviating eye. If the deviation persists, the suppression in that eye also persists. This solves the patient's problem of double vision quite nicely but prevents him from using the macula ofthe deviating eye until the eye is straightened or he is forced to use the deviating eye by patching the good eye. Within a month, this full-time macular suppression can lead to amblyopia.
Sometimes the eye that deviates will alternate from one side to the other and the suppression ofthe macula will thus alternate from one side to the other. In these cases prolonged suppression of one side does not occur, and amblyopia does not develop. If this does not alternate spontaneously from one side to the other, one can stimulate it to alternate by patching the straight eye. Despite extensive patching, one may never reach the point where the strabismus and suppression alternate from one side to the other.
Amblyopic patients can develop recurrent amblyopia at any time up to nine years of age. After that, constant suppression will not cause amblyopia. As long as the suppressed macula is stimulated periodically by patching until nine years of age, recurrent amblyopia can be avoided and the small zone of macular suppression should not cause the patient any symptoms in later life.
Thus we can see that although strabismus and amblyopia are related, they are distinct entities. Glasses and surgery are indicated for strabismus but cannot substitute for the patching treatment for amblyopia. Conversely, patching is not a substitute for strabismus therapy.
Before we leave the topic of strabismic amblyopia, it should be mentioned that, just as strabismus problems can lead to amblyopia, so can amblyopia problems lead to strabismus. It is common for blind eyes to deviate. In infancy and childhood they will usually cross in or turn upward. Later in childhood and in adulthood, a blind amblyopic eye will often drift outward. The position of the amblyopic eye is often quite variable in different directions of gaze and is sometimes associated with unilateral nystagmus on the amblyopic side.
Refractive amblyopia is poor vision that results when excessive nearsightedness, farsightedness or astigmatism blurs the retinal image in one or both eyes, preventing the development of optimal retinal function. In these cases there is often no suppression scotoma in the macula of one eye.
Severe astigmatism is probably the most common cause of bilateral refractive amblyopia. In such cases, corrective glasses at an early age will clarify the retinal image. The vision of such a patient may immediately improve from 20/ 100 to 20/50. After the glasses have been worn constantly for six to 24 months, the acuity is quite likely to improve gradually to 20/20 in each eye.
Unilateral refractive amblyopia is more common, particularly in patients who have more farsightedness in one eye than in the other. If there is no superimposed strabismus problem, one can frequently prescribe glasses to compensate for the difference in the refractive error and the acuity will improve spontaneously. This is also the case in patients with a significant difference in their astigmatism. In these cases full correction of the astigmatism at an early age is indicated.
The more difficult problem arises when the difference in the refractive error is of such a magnitude as to produce a difference in the image size of the two eyes. This is known as aniseikonia. These patients will find it necessary to suppress the vision in one eye to avoid diplopia. Their amblyopia can be more difficult to correct because of its association with the suppression scotoma on one side. Likewise, when refractive amblyopia is associated with strabismic amblyopia, treatment is more difficult. In many cases of pure refractive amblyopia, however, treatment has been effective much later, even into the teenage years.
This may be the most difficult type of amblyopia to diagnose. There are no associated defects, such as the macular scars in organic amblyopia, the cataracts in deprivation amblyopia, or a crossed eye as in strabismic amblyopia. These patients look perfectly normal to all outward appearances. The only accurate way to identify them is to do routine vision screening tests on all patients at about four years of age.
Some of these patients will require patching along with the corrective glasses. When the amblyopia clears, some patients can cut back to using the glasses part-time. A contact lens on one eye will frequently reduce or eliminate the image size difference in patients with marked nearsightedness in one eye or in patients who are markedly farsighted in one eye following the removal of a cataract.
The marked farsightedness that occurs after the removal of a cataract in a child has posed serious problems. Glasses often fit poorly on infants and are often lost or broken. Contact lenses have been a great improvement, particularly for infants under one year of age. The mother is taught to insert and remove the lens. If we can obtain the cooperation of mothers, 90% of infants can wear contact lenses successfully. Infants are very adaptable and do not have the fears of older children. By age two or three years, it becomes almost impossible to initiate contact lens therapy because of the poor cooperation of the child. If the contact lens has been worn since infancy, the child will often pass this age without much difficulty.
Figure 1. Positive family history of amblyopia.
Figure 2. Symmetrically centered corneal light reflex.
Figure 3. Attention-getting devices to aid fundus examination.
Figure 4. Patient accepts cover over his amblyopic eye (A) but will not accept cover over his only good eye (B).
Figure 5. Stycar Test- the examiner points out progressively smaller letters (A) as patient identifies them (B).
The mentally retarded child presents a particularly challenging case in which to correct refractive amblyopia. Intraocular lens implants may eventually prove to be beneficial in these cases. However, they are not yet generally accepted for use in children. There is concern over the adverse inflammatory effects that may develop over long periods.
Amblyopia can be suspected when there is a positive family history (Figure I) either in older siblings or in parents. A history of eye disease or previous amblyopia treatment should also alert the pediatrician to the possibility of amblyopia. It frequently recurs, and this aspect of the problem is sometimes not recognized. Also, because of the migratory nature of our society, follow-up observation for recurrence of amblyopia is often neglected. Because eye disorders are among the problems of the multihandicapped child, one should always be aware of the possibility of amblyopia in dealing with any child with congenital defects.
Vision tests can be done for any child regardless of age. For the child under three and a half to four years, there are two methods of testing for amblyopia. One is to observe the patient for associated eye defects. The second is to observe the patient's ability to fixate a penlight with each eye independently. Together, these are rapid, simple and probably 80% accurate. Let us discuss them separately.
The first test for amblyopia is to determine if there are any eye defects that are frequently associated with amblyopia. The penlight can again be used. If the corneal light reflex is symmetrically centered in both eyes, we can assume that the eyes are fairly straight and that no strabismus problem is present (Figure 2). If the reflex is centered in one eye but eccentrically situated in the other eye, the second eye can be presumed to have a strabismus problem and possibly strabismic amblyopia as well. The ophthalmoscope can determine if there are any disruptions to the red reflex, such as from a cataract. If the ophthalmoscope is put on a +1 and each eye is observed from about 12 to 18 inches, the red reflex can be readily seen. In some cooperative children, one can then check the fundus to get a glimpse of the disc and macula. This maneuver is sometimes aided by putting a drop of 2.5% phenylephrine and 0.5% atropine in each eye. This will usually dilate the eyes adequately in 10 to 15 minutes. Also, having an attention-getting device on one side of the room sometimes helps (Figure 3). Before inserting the eyedrops one should check the pupillary light reflex to see that the responses are equal on both sides. Patients with organic amblyopia often have a poor pupillary light reflex on one side, particularly when one swings the penlight from one pupil to the other (swinging flashlight test).
The second test for amblyopia is to assess fixing ability. The normal patient with good vision in both eyes can see and fixate on a penlight with either eye. Dropping a thumb or some other object down over the vision pathway of one eye should not prevent the child from maintaining a clear view of the penlight with the uncovered eye. When normal patients object to this test, the objection will usually be quite similar, whether it is the right or the left eye that is being covered. Patients with amblyopia have a marked asymmetry in their response to the test. They usually accept quite well a thumb covering the visual pathway of the amblyopic eye, but object strenuously to having the pathway of the good eye covered (Figure 4). Again, it is the asymmetry of the response that will determine whether or not they should be suspected of having amblyopia. This test need not be protracted; two to three seconds of fixation with either eye is enough to indicate that the vision is normal.
The presence of any associated defect should identify most of the cases of organic, deprivation, and strabismic amblyopia. Unequal fixating ability in the two eyes should identify most refractive amblyopic patients as well. Thus, with very simple tests, most amblyopia problems can be discovered before four years of age.
Once a child can respond reliably with verbal or sign language, there are many tests that can be employed to identify his acuity level accurately.
The four best charts for measuring visual acuity in older children are the Stycar chart (H, O ,V, T), the Allen chart (pictures), the E chart and the Snellen chart. Children often begin to respond manually before they respond verbally. The manual responses of a mentally retarded child may be more reliable than verbal responses. The Stycar and E charts rely primarily on nonverbal responses.
The Stycar chart (Figure 5) is a test that was developed in England and popularized in this country by Otto Lippmann, M. D. With this test the child holds in his lap a large card with an H, an O, a V and a T in large block letters in the corners. He is asked to point to the letter on his chart that matches the large test letter on the card the examiner shows him. Once he has matched the test letters accurately, he is asked to look at the test chart ten feet away. While the patient's mother covers one eye, he is asked to identify progressively smaller letters on the chart.
In utilizing the E chart, the child is taught to point his fingers in the same direction as the arms of the test block E held by the examiner. Once the child develops the knack of pointing his fingers in the appropriate direction, his attention is directed to the test chart, which is held at a distance of ten to twenty feet.
For children who are verbally responsive but not yet literate, the Allen chart, utilizing familiar pictures, is often useful in determining the acuity. With this test, the examiner has the patient identify the various pictures on a card held in his lap. Once the examiner learns what term the child uses to identify each symbol, he directs the child's attention to the testing card at the end ofthe room. The child then identifies progressively smaller symbols with each eye.
The Snellen chart for literate children offers a great advantage in that no specific instructions need be given. With the advent of education-oriented children's TV programs, we are finding more five-, four- and even threeyear-olds who are able to be tested with the Snellen chart.
There are several important factors to be considered in obtaining reliable visual acuity determinations with these four tests. Most children with amblyopia try their very best to peek around whatever is occluding the good eye. This is most frequently done by turning the head so that the child can find a "peephole" between the occluder and the bridge of the nose. For this reason, one cannot rely on the child to hold the occluder by himself while the examiner is at the opposite end ofthe room. The parent is usually needed to help occlude the eye and hold the patient's head straight. Failure to occlude properly the preferred eye probably accounts for the great majority of undetected amblyopia problems.
A second important factor in testing is the determination of the smallest full line the child can identify with at least 80% accuracy, rather than determining the smallest isolated letter he can see. Patients can have very significant amblyopia and still be able to identify very small symbols that are isolated. The "crowding effect" that occurs when the patient is presented with a line of symbols will reduce the acuity reading to its true amblyopic level.
In developing testing techniques, one must also adjust to the child's brief attention span. It is certainly a waste of valuable time to have a child identify every symbol on every line. It is better to go down the chart having him identify one symbol per line until he misses. One can then work on that line and the previous line to see which he can identify with at least 80% accuracy. Since so many young children have a very brief attention span, speed in testing becomes an important factor in diagnosing amblyopia at an early age.
An additional problem that can be quite confusing to the vision screener is inconsistency or hesitation in the patient's responses. The youngster of four to seven years of age may be uncertain about the names of the various letters. Other children may confuse letters of similar appearance. With experience the examiner will develop a "feel" for these factors and be able to determine the smallest line the patient can see accurately.
Because of the pitfalls associated with testing, determination of acuity should be made at four, five and six years of age and then every one or two years in school age children. Myopia often develops between eight and 1 4 years of age. Once it has been determined that the patient does have a vision problem, he should be referred to an ophthalmologist for further testing and diagnosis. It is important that a thorough medical history and examination of the eyes be obtained before therapy is instituted. Non-medical groups are currently seeking legislative mandates to become primary eyecare "physicians." For the sake of good patient care, we hope that referral lines never become legislated.
The ophthalmologist's evaluation will include a review of the history, redetermination of acuity, a careful check for any evidence of strabismus, testing for binocularity, a cycloplegic refraction and fundus examination. Cycloplegic refraction is desirable for youngsters because it is the most accurate means we have of determining the total refractive error in each eye. Although many of the eyedrops used to dilate the eyes can be quite strong, and dangerous if abused, they are relatively safe when used judiciously by those who are thoroughly educated in their pharmacology. The pediatrician should be aware that several state legislatures have now approved the use of drugs by optometrists.
Treatment of patients with organic amblyopia is directed at protecting the good eye. This might include glasses for protective purposes and warnings about hazardous areas where lawn mowing or hammering could cause chips to fly. When the organic amblyopia involves both eyes and is fairly severe, treatment must be directed at helping the parents and the child adjust to the handicap. Many communities have set up service organizations, such as Dallas Services for Visually Impaired Children. Such organizations offer a place where parents can turn when physicians have no curative treatment for the problem. It is amazing how few patients and their parents are aware of the available social services. It is important that the ophthalmologist and the pediatrician be aware of community services for visually impaired children.
Figure 6. Examples of eyecovers: clip-on shield (A), cartoon patch (B), homemade patch (C), and Elastoplast (D).
Amblyopia is treated by patching. This is the most universally effective way of improving vision to a normal or near-normal level. In most cases, no other means of treatment will be effective. If the parents are unable to accept this mode of therapy, they should be prepared to accept the amblyopic condition as permanent.
If patching is the most important aspect of amblyopia treatment, early treatment is perhaps the second most important factor. This is particularly true in deprivation amblyopia. Patients with a unilateral congenital cataract must receive effective amblyopia therapy within the first two or three months of life, or there will be little hope of salvaging vision. Patients under four years of age with traumatic cataracts must be visually rehabilitated within a month or two in order to recover good acuity.
Strabismic amblyopia, which occurs most commonly when a cross-eyed patient does not "alternate," should be treated within a few months of the onset of symptoms.
Effective treatment may then take only a matter of weeks.
If treatment is delayed until four to six years of age, it may take many months. Anisometropie amblyopia usually cannot be diagnosed until the child reaches an age at which one can measure the visual acuity accurately (ie, about age four). Fortunately this form of amblyopia often responds to treatment at a later age.
Figure 7. Semiopaque left lens.
Patching for amblyopia has been in use since the 1 8th century. It is most effective when it is complete and constant. Because it requires the cooperation of patient, parent and physician, patching therapy can be difficult to implement.
One must be aware of the problems that the child faces. To him, the patch will be uncomfortable, hot and irritating to the skin. It will leave him with marked visual impairment, depending on the severity of the amblyopia. It will make it difficult for him to watch television or do his schoolwork. It may make him uncertain of his surroundings and thus insecure. Older children may find the very obvious cosmetic blemish of the patch an extremely difficult problem with which to live.
Parents also face problems with patching therapy. Working parents frequently have a limited amount of time, particularly if there are several siblings. Some parents are not psychologically equipped to impose harsh treatment on theirchildren. Sometimes parents simply do no understand the amblyopia problem and the need for early treatment.
Many forms of eye patches are available (Figure 6). Elastoplast comes in a junior and an adult size. Opticlude is a hypoallergenic adhesive eye patch. Both of these are generally available at pharmacies in boxes of 20. They can be irritating to the skin, but this problem can be avoided by using a cotton swab to paint the skin with tincture of benzoin compound several times each morning before the patch is applied. This not only helps to protect the skin, but also will help the patch adhere more tenaciously.
Figure 8. A black contact lens occludes the right eye.
Various types of occlusive devices have been used with glasses, including a shield on the front or back surface, fingernail polish, tape or transparent contact paper applied directly to the lens, ora semiopaque lens (Figure 7). These have all met with some success in different situations. A hard black contact lens (Figure 8) or a soft contact lens incorporating a large refractive error have also been effective in occluding the vision ofthe good eye.
All these methods employ some type of mechanical device to obstruct the vision and are susceptible to the patient's ability to remove the obstruction. Many types of arm restraints have been used. Unfortunately, some youngsters can circumvent the best efforts of parents and physician (Figures 9 and 10). In such difficult cases, success has been obtained by keeping the good eye dilated with l% atropine ointment given three times a day for several weeks or months. This treatment is effective in some patients whose refractive error is enough to cause the vision in the dilated eye to be reduced below the level of the vision in the amblyopic eye. One must be available to renew the parents'enthusiasm when the progress seems rather slow. Other methods have been used to more actively stimulate the vision in the amblyopia eye. This kind of treatment is referred to as pleoptics. This may include a period of inverse occlusion, in which the amblyopic eye is patched for a time. A red filter is sometimes placed over the amblyopic eye to suppress peripheral rod vision and stimulate the macular cone vision. Light stimulation and stressing the macula with detailed visual tasks have also been used.
Of course, corrective glasses are always prescribed when a significant refractive error is responsible for the amblyopia. In some of these cases, the amblyopia will clear without the addition of patching to the treatment regimen.
Figure 9. An engineer father designed this elaborate homemade shield.
Figure 10. Despite the father's engineering skills the child finds an opening for his preferred left eye, circumventing treatment efforts.
In the case of strabismic amblyopia, one should try to eliminate the amblyopia before considering corrective surgery for the strabismus. The few cases that do not respond to amblyopia treatment may have to undergo the straightening procedure, although the strabismus correction may be less predictable.
Amblyopia frequently recurs, so periodic follow-up of these patients may be needed up to the age of nine. To prevent the recurrence of amblyopia, patients should be placed on a one- to two-hour per day patching routine until age nine. After that age the acuity usually does not drop significantly.
Two complications can occur with patching therapy. One is the development of occlusion amblyopia or poor vision in the good eye from being patched. One must recheck the amblyopic patient frequently enough to guard against the development of amblyopia in the eye that is being patched. This may be at weekly intervals in the infant or in one- or three-month checkups for older children. The problem can be avoided by reversing the patch from the good eye to the bad eye for one hour per day during the course of the patching therapy.
A second and less common complication is the development of strabismus. It can be distressing for a parent to follow the physician's patching routine very conscientiously, only to find that the child's eyes begin to cross with therapy. Sometimes this can be avoided by making sure the child wears the proper glasses. At other times it seems to be an unavoidable complication.
Amblyopia is one of the most common eye ailments in children. Early treatment can frequently eliminate this problem. The responsibility for early recognition falls primarily on the pediatrician. The following summarizes what ought to be done for each age group to rule out amblyopia and its associated conditions.
Newborn to age four months - Make sure the eyes appear normal externally and have a clear red reflex (no cataracts).
Infants after age four months - Check fixation of each eye with a penlight. Check for symmetrical corneal light reflexes. Also check red reflex and fundus. Be aware of a positive family history.
Age four - Visual acuity in each eye should be measured. Ideally all children should be referred for a complete eye examination and refraction if this is economically feasible.
School age - Check vision yearly.
If a person is going to have one complete routine eye examination by an ophthalmologist in the first half of his lifetime, checking him at age four years would be ideal. It should include a cycloplegic refraction to rule out excessive farsightedess, nearsightedness, astigmatism or unequal refraction in the two eyes. This should be done by a person thoroughly schooled in recognizing eye diseases rather than by a nonmedical practitioner. Annual eye examinations by an ophthalmologist are probably unnecessary if the visual acuity is good and the child is asymptomatic.
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