Congenital nystagmus

Introduction to congenital nystagmus Congenital nystagmus (CN) is a congenital eye disease with unknown causes, complex performance, and more harmful and difficult to treat. basic knowledge The proportion of illness: 0.002% Susceptible people: children Mode of infection: non-infectious Complications: amblyopia strabismus

Causes of congenital nystagmus

(1) Causes of the disease

Although most people think that congenital nystagmus is caused by poor development of fixation or fixation, the true cause is still unclear.

(two) pathogenesis

The determination of trace elements in the hair of patients with congenital nystagmus showed that the manganese content of the patients was significantly higher than that of the control group, and the copper content was lower than that of the control group. After statistical treatment, the former P<0.001, the latter P<0.05, and The Mn and copper content of the parents of the patients also showed abnormalities, but no nystagmus, which revealed that the etiology or pathogenesis of congenital nystagmus may be related to this, which may indicate that the incidence of the disease is related to environmental factors, according to Statistics (statistical analysis of 648 cases of congenital nystagmus), only 2.9% of family history, indicating that genetic factors are not dominant in the pathogenesis of this disease, 97.1% of cases are distributed, which also supports the environment Factor perspective.

Ultrastructural examination of the extraocular muscles of patients with congenital nystagmus was observed by transmission electron microscopy. Different types of congenital nystagmus were found, and the ultrastructure of extraocular muscles was different. The beating congenital ocular muscle cells had long axis with cells. A vertical myofiber with a sarcomere structure, which is arranged on the fast phase side between the myofibrils and the myofibrils parallel to the long axis of the muscle cells, and the slow phase is perpendicular to the myofibrils of the long axis of the muscle cells. Located in the vicinity of the nucleus or in the peripheral part of the cell, scattered and non-aligned, and the myofibrils are significantly less than the fast-phase muscle, which may cause the muscle strength on the fast phase side to be less than the muscle strength on the slow phase side. The performance is consistent, the contraction and relaxation of different directions and unequal muscle fibrils, resulting in strong muscle contraction imbalance and muscle tension changes, thus causing abnormal movement of the eyeball, which constitutes the fast phase and slow phase of the nystagmus, pendulum type In the congenital nystagmus, no abnormalities of myofibrils were observed in the muscle cells of the lateral rectus muscle. However, the myofibrils arranged in parallel with the long axis of the myocytes were disordered, the length of the sarcomere was not equal, and the Z line was not neat, M It is not clear that the bright and dark bands are not at the same level, and there is no typical fast-shrinking muscle fiber structure. Because the length of the sarcomere is different, the thin muscles slide to the thick muscles, which makes the changes of the length of the muscles inconsistent, which may result in Muscle fiber contraction disorder, resulting in abnormal eye movements. In addition, the degeneration of mitochondria in different types of congenital ocular muscle cells can reduce the excitability of myelinated nerve fibers that innervate the muscles, decrease the muscle tone of the muscles, and lose balance by strong contraction. These findings may be associated with the pathogenesis of congenital nystagmus.

Transmission electron microscopy was used to observe the ultrastructure of the proprioceptor (muscle spindle) of the extraocular muscle of patients with congenital nystagmus. The abnormal changes were mainly caused by the appearance of a large number of myeloid bodies and lipofuscin, and the mitochondria decreased and swollen. Degeneration such as rupture, degeneration, disorder and necrosis of intrafusal muscle fibers, proliferation of a large number of collagen fibers, myelin deformation and demyelination in sensory nerve endings, mitochondrial swelling in the nerve endings, tendon rupture, severe axons The composition disappears, it is vacuolized, some of the receptor structure is completely disordered, the nerve components are absent, the myofibrils are degenerated, dissolved, the sarcomere structure disappears, homogenization and vacuolization, these changes and abnormalities and their etiology and pathogenesis The association is for further study.

In his book "Children's Ophthalmology", David Taylor wrote about the cause of congenital nystagmus: "The cause of congenital nystagmus is unknown. Cogan's claim and argument in 1967, that is, pendulum nystagmus, is due to sensory defects. The beating nystagmus is due to the theory of motor defects, which is untenable in clinical or neurophysiological. Congenital nystagmus is a complex neurological defect that maintains stable gaze. In a sports environment, Optokinetic responses act to maintain the eye in a stable position, while optokinetic reflex of the congenital nystagmus is defective, and its optokinetic nystagmus (OKN) is abnormal. Some are reversed (ie, reversed OKN), some abnormal gains (ie, the movement of the eyeball is larger or smaller than the movement of the OKN striped drum), the nystagmus waveform is superimposed; or the OKN is obviously disordered, especially the slow phase is obviously abnormal, these tips In the very early stages of development, the slow phase defect of OKN can be a persistent defect, even if the initial defect is transient, transient, congenital nystagmus is often hereditary, but heredity is not A factor, because a large number of cases are non-familial, even in familial cases, the type of nystagmus is not the same, it along with nystagmus twins who are different, "

Simon JW et al believe that congenital nystagmus occurs in X-linked recessive inheritance, but autosomal dominant inheritance is also common. Currently known genetic traits are sexually linked dominant, sexually linked recessive, autosomal dominant and often There are 4 kinds of cryptic recessive genes. Among the families reported abroad, sex-linked dominant inheritance is the most, which is characterized by continuous passage; male patients are only passed to daughters, sons are normal; female patients have about half of their children; penetrance Not high; especially female heterozygotes do not necessarily occur, sexual chain recessive inheritance is second only to the former, basically only found in males (female carrying, male onset), autosomal dominant inheritance, relatively rare, characterized by generations; The incidence of both sexes is equal; when one of the parents is sick, about 50% of the offspring are affected; for more than 3 generations, autosomal recessive inheritance is also rare, characterized by the onset of the patient's siblings, other members are normal, and some parents ( In the previous generation, there was a history of close relatives, and Kerrison JB reported that the autosomal dominant congenital nystagmus gene was located at 6p12.

Congenital nystagmus prevention

There is no effective preventive measure for this disease. Early detection and early diagnosis are the key to the prevention and treatment of this disease.

Congenital nystagmus complication Complications amblyopia

The most common complications of congenital nystagmus are: amblyopia, side view and strabismus. As for side view, the actual performance is the reverse performance of the compensated head position. For example, when the contemporary head position is turned to the left, the eyes must be right. Turning to sideways, on strabismus, according to statistics, the complications accounted for 21.1%, common external exotropia, accounting for 60.6% of the combined strabismus, common internal oblique accounted for 30.0%, and upper oblique accounted for 1.4%.

Congenital nystagmus symptoms common symptoms nystagmus visual impairment diplopia vertigo eye movement deflection

In addition to a few individual congenital eye shocks, almost all eyes are sick, and most of the eye movements are conjugating. The prominent features of clinical manifestations are: early onset or onset time cannot be clearly determined, and the eyeball is involuntarily Continue to beat or swing.

1. Involuntary continuous regular eyeball beating or swinging (eyeball tremor) The nystagmus of this disease is generally not self-controllable, that is, the so-called involuntary, but there are also some cases, when attention is concentrated, nystagmus It can be alleviated or even disappeared; in some cases, when the adjustment and convergence are used, the nystagmus is reduced or disappeared, indicating that the regulation and convergence or near reflex have an inhibitory effect on nystagmus, which can be seen clinically. Many patients are looking at the near earthquake without seeing the earthquake. The mechanism is here. However, some patients have the opposite. Even some patients show more nervousness, more concentration, more severe or more obvious nystagmus, and more Those who look far away from the earthquake can see the near-shock; or the far-sighted nystagmus is lighter, and the near-eye stun is heavier.

One feature seems to be the unique feature of congenital nystagmus, namely "inverted OKN", in which the nystagmus phase is in the same direction as the striped drum. In normal cases, the slow phase of nystagmus coincides with the direction in which the stripe drum rotates. The mechanism of this situation is not clear, but this is not the case with other anomalies.

The nystagmus of this disease is generally continuous, unless the nystagmus stops completely when sleeping, but there are some cases, when the attention is relaxed, or when looking far, or when closing the eyes, the nystagmus is obvious. Relieve or disappear, eyelid closure inhibits nystagmus, probably not due to blockage of gaze, may be due to the eyelid closure activity itself, and nystagmus disappears during sleep.

In view of the characteristics of congenital nystagmus, Dell'Osso uses precise eye movement recording technology. According to different waveforms, more than 40 different types of congenital nystagmus have been identified, using eye movement records and high-speed camera technology. It shows the back and forth swing of the patient's eyeball pointing and leaving the optotype. In such a period of swinging, the eyeball is relatively stable, the vision is best, the head shakes or the abnormal head position, and the eye shock is weakened, and the nystagmus is flattened. The crests and troughs or other parts of the waveform, roughly representing the time when the fovea is facing the optotype, unfortunately, many waveforms do not indicate the cause of the tremor, but waveform analysis can show that the tremor is pendulum or beating or both Mixed, with significant spatial and temporal differences, as well as variations in various waveforms and foveal foves.

The nystagmus of the disease is generally more regular, conjugated, rather than erratic, but in some cases of mixed nystagmus, although the tremor is conjugated, the regularity is often poor, often It is a mixture of beating and pendulum; or a mixture of tremor directions. The more common tremor direction is mixed with the mixture of oblique tremor and rotational tremor; or the mixture of vertical tremor and rotational tremor, which may be related to the direction of vertical and oblique muscles. It is related to the rotation.

Regarding the direction of nystagmus, the number of horizontal tremors is more, according to the statistical data accounted for 97.5%, the proportion of vertical tremor and mixed tremor is very small.

Regarding the earthquake type of nystagmus, the jerky type is mostly, and the so-called pulsation type, that is, tremor is composed of two phases of fast phase and slow phase. It is generally considered that the muscle strength of the fast phase side is weak, and the slow phase muscle is weak. Strong force, such as combined compensation head position, the face is generally turned to the fast phase side, while the two eyes turn to the slow phase side, forming a typical side view phenomenon, the beating type horizontal eye vibration, fast phase on the left side, slow phase in There are more right side, so the left side turns more and the right side of the two eyes is more. The side view phenomenon of congenital nystagmus is different from the TV side view. The former usually has side view performance when walking or playing, pay attention to things. There is aggravation, while the latter, when walking or playing, there is no head abnormality or side view phenomenon. Only when watching TV or focusing attention, such as reading a book or writing, there is a side view phenomenon, also known as TV torticollis. (TV torticollis).

Compared with the beating type, pendular nystagmus is significantly less, the ratio of the two is 3:1 to 4:1, but according to statistics, the beating type is 68.2%, and the pendulum type is 30.3%. It may be due to the relatively large number of patients with pendulum type nystagmus. The so-called pendulum type nystagmus, as the name implies, has no tremor and slow phase performance. The two phases have basically the same oscillating speed, which is quite like the pendulum swing.

Mixed nystagmus (mixed nystagmus), according to the statistics of the proportion of about 1.5%, the so-called mixed nystagmus, as mentioned above, some are mixed with the pendulum type of pendulum type, and some are the mixing of the tremor direction Due to the poor seismicity and seismicity of mixed nystagmus, the naked eye is often difficult to check clearly, and it is generally necessary to check through the EK survey. In addition, the visual acuity of mixed nystagmus , generally lower.

Regarding the neutral zone of nystagmus, many authors have mentioned this problem. The so-called intermediate zone refers to the position where the nystagmus is the lightest, but there is no specific number, which is not suitable for clinical application, for example. In a case of congenital nystagmus, the amplitude of each gaze is 200 times per minute, and the amplitude of the earthquake is only 198 times per minute. According to the above regulations, this orientation should be the middle zone. "It doesn't have much clinical significance. Therefore, we use the "resting eye position" or "zero zone" or "null point" rule, which is considered appropriate. The so-called resting eye position or zero belt or zero point , refers to the position where the nystagmus basically stops. In the statistics, only those who have resting eyes are only 6.3%, all of which are pulsating horizontal nystagmus. The resting eye position is significantly more on the right side than on the left side. "right handed" is related.

2. Amblyopia congenital ocular amblyopia is almost binocular (except for monocular or asymmetrical congenital nystagmus). If there are no complications such as strabismus or refractive error, the degree of amblyopia in both eyes is mostly similar, according to statistics. Amblyopia cases accounted for 86.7%, of which visual acuity 0.1 or single eye vision is less than 0.1, that is, severe amblyopia, accounting for 20.2% (one eye less than 0.1% accounted for 1.3%); visual acuity 0.2 to 0.5, that is, moderately low vision, accounting for 52.3% Vision 0.6 to 0.8, that is, mild amblyopia, accounting for 14.2%, visual acuity 0.9 or 0.9 or 13.3%, it can be seen that the impact of congenital nystagmus on vision is common.

Amblyopia is common in patients with congenital nystagmus, and it is mostly binocular, even more serious, but its binocular monocular function generally exists, unless the stereoscopic vision of the strabismus or severe visual impairment is significantly impaired. Generally, the three-level binocular vision function exists. The stereoscopic sharpness of the congenital nystagmus is related to poor visual acuity. It is not related to the nystagmus parameter. This problem is studied. The X2 test shows: far, close distance There was no correlation between SA (stereoscopic sharp) and far, close distance F, A, I (eye vibration parameters) (P>0.05).

The color vision of patients with congenital nystagmus, especially typical congenital nystagmus (normal CN), is normal. This is an important point in the identification of congenital nystagmus and cone dysfunction syndrome (CDS). one.

In the case of young children, their parents' vision is normal, because their play is unobstructed, and only when they need better vision because of reading, their visual defects are revealed. In vision, most children's vision is in the range of 0.2 to 0.5. However, their vision can be improved with age, and some can even reach normal. Typical children with congenital nystagmus or patients have little vision. Below 0.1, if the visual acuity is less than 0.1, special care must be taken to eliminate pathological reasons. Patients with low amplitude nystagmus usually have better vision, especially when they have adaptive mechanisms such as head shaking or abnormal head position. Typical congenital nystagmus patients have good near vision and poor distance vision. This is not due to the near-reflection reducing the intensity of the earthquake, but another mechanism, such as the change of the tremor waveform or the better use of the macula due to the intraocular rotation. Caused by central fovea, congenital nystagmus, general amblyopia, both manifested as good near vision and poor distance vision, which may be related to the development of vision, because near vision is the earliest development Under normal circumstances, the baby first or first to see the mother's teat, and later gradually see the mother's face, etc., the development of far vision is relatively late, is gradually developed with the growth of age, it is not as good as near vision, Therefore, the damage of far vision is often more obvious than near vision.

The visual function of patients with congenital nystagmus, in addition to reduced visual acuity, is also less sensitive to graphics and motion, but color vision is generally normal.

3. Compensating for the head position of congenital nystagmus, mainly for the left and right deflection of the face, only a few cases show the uplift or adduction of the lower jaw, and there are a few cases where the head can tilt left and right, according to According to statistics, congenital nystagmus accounted for 66.2% of the heads, especially those with horizontal pulsating nystagmus, accounting for 88.1% of the compensatory head, and almost the compensatory head of the nystagmus. The performance is that the face is turned to the fast phase side, except for some individuals. Because of the beating type of nystagmus, the fast phase is more on the left side. Therefore, the compensation head position is more to the left side of the face; a few fast phases are on the right side. The face is turned to the right side, there are individual horizontal tremors or individual pulsating horizontal tremors, the position of the resting eye position or the tremor is not on the side, but below or above, such patients, their compensation The head position is characterized by mandibular uplift or adduction, similar to beating vertical nystagmus, in the case of beating vertical nystagmus, or other nystagmus cases in which the resting eye position is below or above, the compensatory head position is expressed as the lower jaw. Lifting or advancing, in the case of rotating eye tremor, can be expressed as the left and right tilt of the head, For example, left-handed nystagmus (left-handed is fast phase) head tilted to the left, right-handed nystagmus (right-handed is fast phase) head tilted to the right, in pendulum-type nystagmus, some may also have compensatory head position, generally expressed as a facial Turn to the side where the tremor is heavier, and the two eyes turn to the side where the tremor is lighter (middle belt). In addition, there are some cases where the head swings or shakes abnormally.

4. Compensatory frequent blinking a small number of congenital nystagmus patients, can show frequent blinking, the more attention to watch the target, the more frequent the eyes, the faster and more frequent, and the mental stress is obviously related, some patients are after the nystagmus surgery In the first dressing change, the frequent blinking phenomenon disappeared completely, indicating that this abnormal action is related to the tremor of the eyeball. It is likely to be a compensatory mechanism. This phenomenon is mainly seen in patients with high frequency beating nystagmus, especially In the high-frequency medium amplitude, the earthquake intensity is large, there is no obvious compensatory head position, and the patient with poor eyesight is directly proportional to the frequency of the eye-shock. When the mental tension disappears or does not look at it, this frequent blinking action It also disappeared, but the nystagmus still exists, which is the point of differentiation from the eyelid nystagmus.

Examination of congenital nystagmus

The determination of manganese and copper in the blood can be increased in some patients.

It mainly includes seismic frequency, amplitude and seismic intensity check, frequency (F), amplitude (amplitude, A) and intensity (I). These three indicators are used to judge the degree of nystagmus and evaluate the therapeutic effect. The most important objective indicators, the best means of obtaining these three indicators, at present, in addition to direct video, is the electro-nystagmus graphy (ENG).

The EOG program of AC-NEUROPACK IV Mini electrophysiological instrument produced by Nippon Optoelectronics Co., Ltd. was used to perform nystagmus electrograms, and a classification standard of 4 levels of amplitude, amplitude and intensity (I=F×A) was proposed. ?

F1100 times/min

F2=101200 times/min

F3=201300 times/min

F4>300 times/min

A1100V

A2=101200V

A3=201300V

A4>300V

I1 100 × 100 (ie 1 × 104) V times / min

I2=1.0001×1044×104Vtime/min

I3=4.0001×1049×104Vtimes/min

I49.0001×104Vtimes/min

In addition to the above-mentioned objective indicators, ENG can also display the nystagmus parameter, and clearly show the position of the endless eye position and the resting eye position. It can also display the direction and type of nystagmus, horizontal or vertical. It is a beating type or a pendulum type. The ENG is a sawtooth wave (Fig. 1A, B), and the ENG of the pendulum type nys is a sine wave. Therefore, the ENG check can obtain 6 important data and objective indicators, that is, F, A, I, resting eye position and shock type and earthquake direction, and whether eye movement disappears when closing eyes or blinking in the dark, etc. Therefore, ENG is an important inspection item for congenital nystagmus, basically a must In the investigation project, without this examination, it is impossible to accurately determine the severity of nystagmus, and it is not easy to objectively evaluate the patient's treatment effect.

Diagnosis and diagnosis of congenital nystagmus

diagnosis

To distinguish between congenital nystagmus or non-congenital nystagmus, there must be clear diagnostic criteria. According to existing diagnostic techniques, the following standards are generally prescribed.

1. The onset of the disease is early from childhood, that is, nystagmus, or the onset time is not clear.

2. There is no sloshing (oscillopsia), that is, there is no swaying feeling, even if the nystagmus is quite serious, there is no swaying of the visual object, which is the main criterion for diagnosing congenital nystagmus.

3. The involuntary continuous swinging or beating of the eyeball is regular, not an irregular eyeball disorder, and is different from visually impaired nystagmus.

4. There is no restriction on the movement of the eyeball, no eye deformity or other congenital anomalies.

5. General daily activities without obvious obstacles Both binocular vision and corrected visual acuity are generally above 0.1, and the color vision is normal. If there is no strabismus, there are generally three levels of binocular vision.

6. No symptoms of central nervous system disorders and vestibular dysfunction such as balance disorders and dizziness.

7. Closed eyes or blinking in the darkness is a congenital nystagmus, but congenital nystagmus is not the case.

Differential diagnosis

The diagnosis of congenital nystagmus is generally not difficult. Most patients can confirm the diagnosis with reference to clinical manifestations and examinations. However, some situations require or must be identified to reduce or avoid the occurrence of false diagnosis.

1. Cone deficiency syndmme (CDS)

This syndrome is caused by congenital hypoplasia of the cone function. The main clinical manifestations are: binocular tremor from childhood; severe photophobia; full color blindness; severe visual impairment (0.1 or less); secondly, combined strabismus, etc. Cell dysfunction syndrome is most likely to be confused with congenital nystagmus. A slight inattention can cause misdiagnosis, because ocular tremor of cone cell dysfunction syndrome is also started from childhood, and it is binocular tremor, and its eye examination is generally no other obvious. Abnormal findings, but its obvious photophobia and severe color vision disorder, are the main distinguishing points from congenital nystagmus. Congenital nystagmus patients have no obvious photophobia, while CDS patients cannot develop strong because of cone dysfunction. Light can only be weak light, so CDS patients show obvious photophobia in daylight or normal brightness (such as indoors during the day), can not open their eyes or can only slightly open a slit, but in the dark If you go to the dark room or at night, your eyes will be as big as usual. This performance is obviously different from congenital nystagmus. Another point is that the color vision of patients with congenital nystagmus is basically normal, and the color vision of patients with CDS is normal. Severe disorder or full color blindness, because of its cone dysfunction and hypoplasia, it can not feel the color light stimulation (cone-like glare and color light, rod cells can only feel the weak light stimulation without the function of color light), this It is also an important point of identification. Only these two points are enough to identify. As for other aspects, such as fundus examination, because the nystagmus of CDS patients is mostly high-frequency small tremor, photophobia is more serious, so it is difficult to check satisfaction, most Only the optic disc and blood vessels can be seen going back and forth through the illuminated area of the ophthalmoscope. Some can see that the macular area is dark and has no foveal reflection, but there is no discriminative meaning; regarding the examination of electrophysiology (ERG and VEP), although Abnormalities can be found, but because there is no specificity, there is no differential diagnostic value. The purpose of distinguishing between CN and CDS is to treat the two problems. For patients with CN, surgery can be considered, while CDS is not suitable for surgery and there is no good treatment. Methods, some can only consider wearing color-changing glasses to reduce the light stimulus, reduce excessive photophobia and improve symptoms.

2. acquired nystagmus (AN)

Any eye tremor with a late onset can be called acquired nystagmus. This is a general diagnostic name or a comprehensive diagnostic term. In fact, it includes a variety of nystagmus, especially late onset. Pathological nystagmus, such as central nystagmus, vestibular nystagmus, etc., the common features of acquired nystagmus are: late onset; clear onset time; obvious symptoms and pain, such as visual swaying (squint) , vertigo, etc.; after neurological examination or other special examinations (CT, MRI, etc.), the primary disease or cause can be found, nystagmus is only one of its clinical manifestations or symptoms, and congenital nystagmus is the opposite. The onset of CN is early, the onset time is not clear; CN patients have no obvious symptoms except visual acuity, no squint or dizziness; CN-based idiopathic diseases, in terms of current clinical examination techniques, can not be found The cause, the purpose of distinguishing CN and AN, is still about the treatment of the two. The examination and treatment of CN patients are basically in the field of ophthalmology, while for patients with AN, the primary disease and cause should be examined and found. Then the treatment of the cause and the primary disease, whether it is examination or treatment, is basically not in the field of ophthalmology, but mostly in the Department of Neurology or Otology, more specifically, CN is an eye disease, AN is basically a neurology Or otologic diseases, so the CN and AN must be identified to avoid treatment errors, especially if the AN cannot be treated as a CN.

3. Visual nystagmus (VN)

Such nystagmus is mainly seen in the congenital cataract with heavier eyes, congenital corneal leukoplakia, congenital vitreous opacity, and congenital fundus abnormalities of severe visual impairment in both eyes. The common feature of these eye diseases is congenital severe visual impairment in both eyes. The combined nystagmus is also very early after birth, so it is very confusing with congenital nystagmus. Fortunately, in patients with congenital cataract and corneal leukoplakia, it is easy to find congenital anomalies in the eye, but not difficult to distinguish from congenital Idiopathic nystagmus is congenital nystagmus, but in patients with congenital vitreous opacity and congenital fundus abnormalities, if the stenosis lamp and fundus examination are not performed, it is difficult to find the abnormalities in the posterior part of the inner eye, but VN Misdiagnosed as CN, especially in patients with nystagmus who cannot cooperate with the examination, the fundus and the inner eye should be examined as much as possible, although this has certain difficulties, especially for young children whose visual acuity is below 0.1 and the eye chart is not checked. Should try to check the inner eye and the fundus, young children who are not cooperative can use chloral hydrate or other sleeping pills to relax and check the fundus. More satisfactory results can be obtained, because the nystagmus stops during sleep, and it is easy to see the fundus. The visually impaired nystagmus is basically pendulum type or mixed type or very poor nystagmus, so when encountering these situations, Should pay attention to identification, to avoid misdiagnosis, the purpose of identifying CN and VN is also about their treatment. For the treatment of VN, the key is to find the primary disease and treat the primary disease, nystagmus is its complication, need to explain It is extremely difficult to eliminate this kind of nystagmus. Even after successful surgery for congenital cataract, nystagmus still exists. It is generally believed that congenital cataract can be operated early (before 2 years old).

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