cataracts are the greatest single cause of blindness in the world, and even in the United States more than 3 million people are visually handicapped by catar aas. Although most lens opadfication develops after the fifth decade of life, congenital and early developmental cataracts constitute the most important single cause of visual impairment in childhood.
The crystalline lens, cornea, and vitreous comprise three highly specialized ocular tissues sharing the unique characteristic of transparency. This ability of the lens to transmit incoming light accurately onto the retina is essential for the eye to function as an effective visual organ.
Of the several pathologic processes affecting the human lens, the most important and the most common is alteration of its transparency, or cataract formation. Although any change in lens structure resulting in translucence or opacification of this normally transparent tissue may technically be called a cataract, the term is generally reserved for those opacities of sufficient size or density that their presence will interfere with the development or maintenance of good vision.
The embryonal eye arises from primordial neural tissues, and its development parallels the earliest tissue specialization occurring in the central nervous system. This proximity of time and location accounts for the high incidence of related neural and ocular defects.
The lens is situated deep in the anterior segment of the eye, cushioned anteriorly by the iris diaphragm and posteriorly by the condensed face of the transparent vitreous body. It is supported securely in position by numerous zonular fibers that extend from the lens equator radially in a spokelike fashion, attaching peripherally to the ciliary body.
The lens structure is avascular, isolated, and protected by a double-layered capsule and is impervious to all but fluids and metabolites. It is bathed by aqueous fluid, which by osmotic transfer furnishes its nutrition and hydration.
New lens fibers are formed throughout our lifetime, but total lens size and volume change minimally after childhood. As new lens fibers arise from the equatorial germinal centers and extend centrally beneath the hyaline capsule, they compress the older fibers deeper towards the central nucleus. In later life these deeper lens fibers may become sclerosed and progressively less transparent and form the cataracts so commonly seen in older persons.
Athough abnormalities of transparency or cataract formation are the most serious and common pathologic changes in the lens, abnormalities of position or lens displacement may also cause severe visual disability.
Eccentric displacement of the lens in infants and children occurs primarily as a heritable disorder and differs from that in adults in that it is less frequently associated with intrinsic ocular abnormalities or as a sequela to trauma. The lens is structurally normal but becomes thickened because of a weakness or absence of the zonular support fibers at the lens equator.
Lens displacement or subluxation is usually bilateral in the hereditary disorders but unilateral when following trauma. Bilateral displacement, as in Marfan's syndrome, usually assumes a symmetric mirror-imaged position, usually upward and inward, although in the Weill-Marchesani syndrome the direction of displacement is more commonly inferior.
Marfan's syndrome is an autosomally dominant connective-tissue disorder. Familial arachnodactyly and loose joints in a patient with cardiovascular disease and dislocation of the lens are considered diagnostic. Ectopia Jentis is the most common ocular manifestation and occurs in up to 80 percent of patients with Marfan's syndrome, with more than half of these being detected before age five. The lens displacement is generally toward the upper and outer quadrant but can occur in other directions. Other commonly associated ocular findings are excessively high degrees of myopia and astigmatism, poor pupil dilation, iris heterochromia, and glaucoma. There is a significantly high incidence of retinal detachment in early life.
Homocystinuria also has a high incidence of lens dislocation. This condition is similar to Marian's in that there are frequently elongated extremities and cardiovascular abnormalities, and there is a high incidence of mental retardation and convulsions in these children. Thromboemboíic phenomena associated with coagulation defects are common, and general anesthesia must be undertaken with caution since thrombosis and occlusion are the leading causes of death.
Lens displacement tends more often to be inferior and nasal, and a diagnosis is usually made by demonstration of increased homocystine in the urine by cyanonitroprusside reaction, with further confirmation by enzyme analysis of cultured fibroblasts.
Weill-Marchesani syndrome is another syndrome with ectopia lentis. These children usually are reduced in stature, with short, broad hands and feet and relatively stiff, immobile joints. The supporting lens zonules may be completely absent, so the lens assumes a spheric or globular shape. Secondary glaucoma is a frequent sequela. The baste deficiency in this syndrome is unknown.
Other syndromes with ectopia lentis include several rare disorders with isolated lens dislocation and, more rarely, with Ehlers-Danlos syndrome, dwarfism, Sturge-Weber syndrome, Cruzon's syndrome, oxycephaly, sulfite oxidase deficiency, mandibulofacial dysostosis, and polydactyly.
IMPORTANT CHARACTERISTICS OF PEDIATRIC CATARACTS
Cataracts in infants and children have four characteristics that will help responsible physicians have a better understanding of the etiology, suggest the degree of visual impairment that might reasonably be expected, and determine the course of specific treatment and long-term management. They are: 1. The size, density, and position of the opacities.
3. Whether the cataracts are unilateral or bilateral.
4. The association of other defects, ocular or systemic.
Size, density, and position of lenticular opacities. The term cataract is used to describe this clinical entity only when there is significant distortion or obstruction of light rays as they pass through the lens towards the retinal receptors. Very small opacities, no matter what their position, will rarely decrease vision and are of importance only if they progress in size and density. Examples of these are small anterior and posterior polar cataracts and fine, scattered "snowflake" or dustlike opacities. Larger opacities that are peripheral may have little effect on vision, while densities of similar size located in the visual axis may be incompatible with the development of good vision.
Time of onset and progression. The gestational age at the time of insult will generally determine the zone of the lens affected. Before the end of the first month, when the lens vesicle and primary nucleus are being formed, they are susceptible to penetration of any organism that may cross the placental barrier from the maternal bloodstream. Insult during this period will alter the transparency of the embryonal nucleus.
After the fifth week the hyaline capsule is securely formed, and organisms will be effectively screened out. The lens, however, remains susceptible to the toxic effects of circulating drugs and metabolites, and many congenital cataracts develop secondary to hormonal and metabolic dysfunctions and drug toxicities of the maternal system.
Unilateral or bilateral cataracts. Monocular cataracts are usually nonhereditary and present as part of a dysgenetic or altered developmental course. Bilateral cataracts, in contrast, are generally related to hereditary transmission or such generalized embryopathies as maternal infection.
The presence of associated ocular or systemic defects. An important early diagnostic determination is whether cataracts are an isolated defect and limited exclusively to the lens structure, whether they involve other ocular structures in addition to the lens, or whether the cataract is merely one expression of a syndrome of abnormal development affecting other organ systems.
Children with congenital cataracts frequently have other anomalies as well. Several studies indicate that at least 30 percent will have some associated abnormality of other nonocular organ systems, and as many as 60 percent will have a related defect of ocular structure or function. Associated defects of the visual and ocular system often are not identified until later years or after successful cataract removal.
DESCRIPTIVE TERMINOLOGY USED FOR PEDIATRIC CATARACTS
Congenital cataracts traditionally have been described and classified on the basis of their appearance. The following terms are commonly used to describe their size, shape, appearance, etc. Generally a dilated pupil and slit-lamp biomicroscope will be required for adequate visualization.
Total or complete cataracts are dense opacifications affecting the entire lens substance or filling the pupil aperture; little or no light enters the eye and no effective retinal stimulation is possible.
Partial or incomplete cataracts are smaller or less dense opacities that significantly distort central vision but allow sufficient light entry to stimulate some degree of functional retinal development.
Nuclear cataracts may be embryonal or fetal. When the primary or embryonal nucleus is involved, this most central zone is affected early in the first month of gestation, prior to formation of the lens capsule. Fetal nucleus: secondary lens fibers that surround the primary nucleus are affected during mid- and late gestation.
Capsular and subcapsular cataracts are opacities in the hyaline capsule. They are clinically important when the central visual axis is affected. In childhood these areas are frequently the site of opacification in complicated cataracts, polar cataracts, and posterior lemiconus.
Cortical cataracts involve the lamellar cortex fibers between the central nucleus and the external capsule. They may be present as scattered opacities of varying sizes and shapes or may be concentrated in single or multiple layers, with a three-dimensional lamellar distribution.
Lamellar or zonular cataracts are one of the most common types of congenital cataracts and affect an entire layer or zone of lens fibers. They occur at a specific and limited time during gestation and are thought to result from a brief period of fetal insult. Among causes are inheritance of an autosomaldominant trait, avitaminosis D, or a hypocalcémie episode related to decreased parathyroid function - the so-called tetany cataract.
Polar cataracts constitute a large group of localized opacities of the anterior or posterior central axis of the lens, which may variably affect vision.
Sutural or Y-shaped cataracts involve the anterior or posterior Y sutures, the terminal junctions of the secondary fibers in the visual axis.
Tumescent or morgagnian cataracts may occur when a lens undergoing degenerative-liquefaction necrosis becomes swollen, displaces the iris anteriorly, blocks the aqueous outflow channels, and causes a secondary acute glaucoma.
Complicated cataracts are progressive translucence and opacification of the lens secondary to other ocular disorders, particularly chronic inflammation and glaucoma. Some other causes are chronic uveitis associated with juvenile rheumatoid arthritis, ankylosing spondylitis, and toxicity from steroids or other drugs.
Rubella cataracts are characteristic opacifications of nuclear sclerosis, with cortical liquefaction following early viral invasion.
Miscellaneous cataracts may be given many other morphologic terms. Among adjectives used to describe the appearance of cataracts are spokelike or radial, floriform, stellate, sutural, snowflake, pulverulental (dustlike), discoid, and pacoid.
Genetic transmission constitutes a major causative factor of cataracts that occur in children. They may present as isolated defects in children who are otherwise completely normal or may be associated with other ocular defects or generalized systemic abnormalities. Isolated cataracts may be of autosomal-dominant transmission, X-linked, or present as an autosomal recessive.
Metabolic disorders accompany a great many of the cataracts found in children. In fact, of the cataracts associated with systemic abnormalities, those accompanying metabolic disorders constitute a very large segment. These may be disorders of carbohydrate, amino-acid, lipid, or heavy-metal metabolism.
Of the carbohydrate metabolic disorders, galactosemia, galactokinase deficiency, and mannosidosis are the most important. Glucose-6-phosphate-dehydrogenase deficiency has also been reported. Of the amino-acid disturbances, homocystinuria has previously been mentioned as having a high incidence of dislocation of the lens. Fabry's disease and Refsum's syndrome and familial cerebrotendinous xanthomatosis are examples of abnormal lipid metabolism having associated pediatrie cataracts. Wilson's disease, or hepatolenticular degeneration, may uncommonly be associated with copper deposition in the lens.
Renal disease syndromes associated with cataracts include Lowe's syndrome (which has a relatively high incidence of cataracts) and Alport's syndrome (found primarily in males, which has a lesser frequency of cataracts).
Musculoskeletal diseases may have congenital or developmental cataracts occurring in several syndromes - specifically, chondrodysplasia punctata, myotonic dystrophy, Albright's hereditary osteodystrophy, Stickler's syndrome, and the Roben syndrome.
The connective-tissue disorders are primarily those previously mentioned with dislocation of the lens, many of which will also have cataract formation.
Central-nervous-system disorders with associated cataracts would primarily include the Marinesco- S jögren syndrome, with progressive cerebellar ataxia.
Dermatologie disorders include Cockayne's syndrome, incontinentia pigmenti, and ichthyosis.
Several craniofacial malformations may also have congenital or infantile cataracts associated, and these would inlude Hallermann-Streiff, Rubinstein-Taybi, Smith-Lemli-Opitz, Marshall, and cerebro-oculof acial- skeletal syndromes.
Numerous chromosomal disorders have now been demonstrated to have associated cataracts, the best known of which is trisomy-21 , or Down's syndrome, in which 60 to 85 percent of patients may develop cataracts, the majority of which occur after puberty.
Nonhereditary cataracts occur for many reasons and in a variety of circumstances. They can be placed in four categories:
1. Dysgenetic: random spontaneous developmental variations.
2. Environmental: disturbances of the maternal/ fetal biologic systems.
3. Ocular: associated with or secondary to other primarily ocular conditions.
4. Systemic: associated with or secondary to generalized systemic abnormalities.
Dysgenetic cataracts are random spontaneous variations of lens development resulting from disturbances of tissue formation of an individual eye. They usually cause monocular or unilateral cataracts. Since any disturbance of lens hydration may alter its transparency, abnormalities in the formation of the lens capsule that allow fluid to enter the lens substance frequently result in progressive opacification. the majority of these developmental variations affect the central lens axis, particularly the anterior or posterior polar areas.
Anterior polar cataracts are a relatively common type of opacity that often have minimal effect on vision. They may be tiny pinhead lesions or sufficiently large to fill the pupillary axis. They are generally stationary, flat, and sharply circumscribed, although they may sometimes assume a pyramidal shape, with the apex pointed anteriorly.
Developmental variations of the posterior lens capsule can vary to a greater extent in severity and degree. There may be a discrete focal opacity within the vitreous body immediately posterior to the central lens capsule. These represent a persistence of the embryonal fibrovascular hyaloid tissue and may include a filamentary strand extending posteriorly as a vestigial remnant of the embryonic stalk. These are termed Mittendorf Dot.
Posterior polar cataracts are discrete circumscribed opacities of the posterior central lens capsule often involving some of the underlying lenticular fibers. Vestigial hyaloid remnants may or may not be present.
Posterior lenticonus and lentiglobus are central ectatic posterior deformities of the lens and its capsule, usually with some degree of opacification of the associated lens fibers.
Dense posterior capsular and cortical cataracts associated with persistent hyperplastic primary vitreous are characterized by marked opacification of the combined posterior central lens fibers and the defective posterior capsule. This may occur with persistence of the fibrovascular plaques of unabsorbed primary vitreous. The condition is usually unilateral and occurs in an eye that is microphthalmic. The visual prognosis is very poor.
Environmental causes include toxins, maternal infections, and diseases, radiation, diet, or other factors affecting the mother during pregnancy.
Several drugs have been demonstrated as cataractogenic in the offspring of laboratory animals, although similar mechanisms remain questionable in human beings. Substances implicated have been MER-29, trichlorbutanol, 2,4-dinitrophenol, and trypan blue.
The prolonged use of both systemic and topical steroids has been demonstrated to cause a characteristic posterior subcapsular cataract in animals and humans of all ages. Several studies suggest that between 42 and 80 percent of patients will develop cataracts following the systemic administration of 1 5 mg. / day of prednisone for a year or more. Several topical cortisone derivatives used over long periods in ocular therapy have also been demonstrated to cause similar posterior subcapsular cataracts. These opacities are usually bilateral and in the early stages have minimal effect on vision. They may remain stationary or regress slightly following cessation of exposure to the drug. Oxygen therapy related to prematurity may be a factor. Although cataracts are not a direct sequela of the retinopathy of prematurity, in advanced cases they may be part of the panophthalmopathy of the syndrome. They are usually bilateral.
Maternal infections. In man, cataracts have been documented to occur following the transplacental transmission of several organisms from the maternal system to the developing fetus; these include rubella, herpes simplex, herpes zoster, cytomegalovirus, and varicella. The most extensively investigated and documented syndrome of this group has been congenital rubella.
Cataracts are only one of several important ocular manifestations of the congenital-rubella syndrome. Early fetal exposure to rubella virus causes not only viral infestation of the lens but numerous focal areas of inflammation throughout the iris and ciliary body and possibly also the retina. Such eyes are characteristically microphthalmic and may less frequently develop an unusual type of glaucoma, suggesting an arrest or failure of development of the anterior-chamber angle.
Cataracts in the rubella syndrome may be unilateral or bilateral, and it is presumed that the virus enters the lens structure before the development of its impermeable capsule at the 13-mm. stage (fifth week of gestation). Rubella cataracts are almost always present at birth. Live rubella virus has been recovered from several ocular tissues and from the lens itself as late as 36 months of age. The frequent presence of associated ocular abnormalities and postoperative ocular inflammation contributes to the high incidence of surgical complications. Since these infants also have a high incidence of defects in hearing and in intellectual and motor functions, accurate assessment of visual rehabilitation measures is often difficult.
Endocrine-metabolic dysfunctions in the mother may include diabetes mellitus, thyroid, parathyroid or abnormal vitamin metabolism disorders.
Diabetes mellitus. Children of mothers with diabetes mellitus are reported to have a higher incidence of all types of congenital defects than the average population, ranging from 3.2 to 15 percent. Among these abnormalities are congenita] cataracts. Even more important is the increased incidence of cataracts of the developmental type associated with juvenile diabetes mellitus. Although cataracts rarely appear until 10 to 15 years following the onset of diabetes, their incidence in this group seems to be increasing.
The development of diabetic cataracts appears to be directly related to elevated blood sugar levels and the associated accumulation of sorbitol in the crystalline lens. Sorbitol, the sugar alcohol of glucose, penetrates cell membranes poorly and becomes trapped within the cells of the lens, increasing its osmolarity and thus drawing water into its intracellular spaces. The associated electrolyte disturbance results in further swelling, cellular disruption, and cataract formation.
Thyroid. There is much evidence that either an excess or a diminution of thyroid activity can induce considerable effects on the fetus. In regions where goiter is endemic, congenital defects, including cataracts, have a higher incidence.
Parathyroid. A deficiency of parathyroid hormone during gestation may cause the well-documented fetal syndrome of zonular cataracts, imperfect calcification of the bones and permanent teeth, and infantile tetany. These cataracts are characterized by a normally transparent and unaffected centrallens nucleus with a surrounding area of zonular opacification and subsequent normal development of the outer layers of the lens.
Abnormal vitamin metabolism. Although a deficiency of many vitamins (at least nine of the B-complex vitamins) has been found to be teratogenic in laboratory animals, only two vitamins have been found to be teratogenic in excess, vitamin A and nicotinic acid. Hypervitaminosis A, in particular, can be cataractogenic, with the critical period being the third week of gestation.
Radiation. Although ionizing radiation has long been known to incite cataract development in the animal and human lens, the cataractogenic effect of radiation on the maternal and developing fetal system is highly speculative. There is, however, a positive cause-effect relationship in the cataract changes observed following radiation therapy to the eye or immediately surrounding orbital structures in the treatment of retinoblastoma and other area-related malignancies.
Nonionizing radiation of the hertzian type includes microwave, radiowave, and diathermy and may cause a thermal type of burn. These are probably of more importance and concern to the adult population than to children. Posterior subcapsuJar cataracts have been reponed as an occupational hazard in such areas as airports, because of exposure to radar and other radiowaves over a long term. The possible effect of hertzian radiation from microwave ovens is poorly defined at this time.
Ocular cataracts are those associated primarily with other ocular conditions. Cataracts may occur on a primary basis as part of many ocular conditions or with delayed onset as a secondary process. Such developmental abnormalities as aniridia, congenital glaucoma, persistent hyperplastic primary vitreous, and other disturbances of hyaloid dissolution may present with cataracts from the time of birth.
Cataracts occurring as a delayed sequela to other ocular processes would include all of the above conditions plus many forms of chronic ocular inflammation. Prominent in this group are chronic iritis, iridocyclitis, and posterior uveitis. Retrolental fibroplasia, another form of panophthalmopathy, may include cataract formation in its later stages, as may ocular neoplasms and some forms of degeneration.
Cataracts associated primarily with systemic conditions are often hereditary. Other pediatrie cataracts in this category that are acquired at a later age are associated with such disorders as juvenile rheumatoid arthritis, ankylosing spondylitis, the mucopolysaccharoidoses and other storage diseases, disorders of carbohydrate and amino-acid metabolism, and hormonal imbalance.
Although congenital cataracts still constitute a major cause of blindness, advances in pediatrie ophthalmology can provide safe and effective treatment measures that offer the best opportunities for visual rehabilitation that have ever been possible.
Essential to this process of successful management are early identification and the institution of early treatment. The definitive treatment of cataracts that obstruct vision and prevent visual development in infants and children necessitates a carefully directed therapeutic program, with good communication and cooperation between parents and physicians.
The surgical removal of the cataractous lens is the only effective and definitive method of treatment available in all but a very small number of infants and children. In a few selected cases, methods may be helpful to aid visual development or to temporize before proceeding with cataract extraction. These would include the use of medications to enlarge the pupil, permitting additional light to bypass central-lens opacities, or, occasionally, a surgical iridectomy - removing a segment of the iris - will accomplish the same effect.
Usually, surgical removal of the cataractous lens is required. The treatment regimen must include early institution of appropriate optical correction (either spectacle lenses or contact lenses) and usually a course of occlusion or patching of the betterseeing eye to stimulate visual development. Each of these measures bears further elaboration.
Surgical treatment of infantile cataracts has improved dramatically in the past two decades. Current techniques rely on the high-quality magnification and illumination provided by modern operating microscopes and by surgeons experienced in microsurgical procedures on small-infant eyes.
The use of mechanical suction-cutting instrumentation is now standard technique and allows the advantage of 2-3-mm. incisions to perform the extracapsular aspiration procedure. Extremely fine absorbable sutures with delicate micropoint needles also greatly aid these refined surgical procedures.
Optical treatment requires replacement of the abnormal cataractous lens by an external spectacle or contact lens. When cataracts occur in both eyes, a spectacle lens will often be more satisfactory; whereas in the case of unilateral cataract, because of disproportionate magnification with a replacement spectacle lens, a contact lens is more effective and satisfactory. Either hard or soft contact lenses can be used and usually require a hyperopic lens correction in the range of +10-20.00 diopters. Intraocular lenses, although widely used in the elderly and providing a great theoretic advantage in children with monocular cataract, have had very limited clinical use and are not generally advocated.
Occlusion therapy is required to stimulate visual development in an eye that has been disadvantaged by the presence of a cataractous lens. It has been well documented that early retinal stimulus is essential to the development of refined vision, and if the opportunity for early and appropriate retinal imagery is not present, a "stimulus deprivation" type of amblyopia will result. Both amblyopia and nystagmus may result from early visual deprivation. Each of these may, in turn, be irreversible and further contribute to the resulting poor vision if not identified and treated in time.
Currently accepted practice holds that when the size and density of infantile cataracts prevent effective retinal stimulation, cataract surgery may be considered as early as the first week of life and definitely should be accomplished within the first several months. In the presence of incomplete cataracts, where some light entry and retinal stimulus is present, surgery may be slightly less urgent but still is indicated before six months of age. The best visual results are obtained with early surgical intervention in infants with bilateral incomplete cataracts and the least good results with infants with monocular cataracts treated on a delayed basis.
Although the management of cataracts in infants and children is a process requiring great demands on the parents and physicians, there is unlimited satisfaction in the knowledge that a great number of these children in previous years would have been severely impaired or blind, and now many will have the opportunity for an essentially normal-sighted life.