Diseases causing visual impairment in infancy and childhood may be arbitrarily classified as (IJ opacities of media (physical obstruction to the passage of light through the eye); (2) refractive errors (optical distortion of image formation); (3) neuroretinal defects (problems precluding retinal reception of images, transmission of images to central pathways, and interpretation and integration of information in higher centers); and (4) effects of trauma (which may combine elements of the previous three categories).
OPACITIES OF OCULAR MEDIA
The ocular media are structures that transmit (and focus) light from in front of the eye to the retina. They include the cornea, anterior chamber, lens, and vitreous body. Opacities of any of these may diminish vision.
Cornea. The cornea, or "clear window," of the eye may be opacified in a variety of disorders. Congenital opacities are treated elsewhere in this issue. Certain other corneal conditions will be discussed here.
Corneal ulcers. The cornea is at risk to infection (Figure 1 ) because of its avascular structure, thereby being sequestered from some of the bloodborne body defense mechanisms. The infection may be bacterial - for example, Neisseria infections in the newborn. It may be fungal - for example, following injury to the eye (in particular, with vegetable matter). Or it may be viral, the most common virus of which is the herpes-simplex virus, type 1. The infection may present as a primary blepharokeratoconjunctivitis, involving eyelids, cornea, and conjunctiva, in which caution should be taken about the use of steroids. Steroids, given topically, may facilitate virus replication and turn an essentially self-limited epithelial disease into an ulcerative stromal disease yielding permanent scar formation and ultimate visual deficit.
The initial epithelial lesion may be treated with reasonable success with topical antivirals or debridement. When the stroma becomes affected, vascularization and opacification often follow, resulting in an irregular, opacified cornea. Occasionally, corneal transplantation may be required. Because of the danger of microbial spread with the use of steroids, cortisone preparations are probably contraindicated in the nonophthalmic primary treatment of "red eyes."
Keratoconus. This is a disorder in which there is a thinning of the central cornea (Figure 2). Keratoconus is probably not one disease; it may be found, for example, in a number of diverse conditions, such as atopic dermatitis, mongolism, and aniridia or as a hereditary condition. The thinning is progressive and is generally first noted in adolescence, with corneal astigmatism and frequent changes of eyeglass prescriptions the first clue. As internal corneal layers stretch, there may ultimately be a rupture in deep corneal layers, leading to acute edema in the corneal stroma and decreased vision. Perforation is not a concern. The usual first treatment for keratoconus is hard contact lenses, with corneal transplantation required when contact lenses no longer suffice.
Chemical burns. Burns of the cornea may be acidic, basic, or thermal. Acid generally has an immediate, tissue-coagulative effect, and damage may be assessed early. Alkali burns tend to incite an ongoing, collagenolytic activity, in which corneal infection and perforation are the chief concerns. Initial therapy in either case consists of copious irrigation with water for at least 30 minutes. Thermal burns generally result from high temperature, probably having a tissue-coagulative effect as well. In any of the cases, the initial therapy is designed to maintain the integrity of the globe and to eliminate infection. The early subsequent considerations are the re-formation of the anterior surface (epithelium), and again, in the long range, corneal transplant is occasionally required.*
Anterior chamber. The anterior chamber of the eyes may be affected in a variety of inflammatory and traumatic conditions.
Anterior uveitis ("iritis"). Iritis is an inflammatory condition of the anterior segment. However, the term typically is used only to describe the nature and extent of the findings when one is unable to ascribe cause. Iritis may be associated with a diverse group of intraocular conditions (such as herpes simplex and zoster and toxoplasmosis) and systemic problems (for example, sarcoidosis, ankylosing spondylitis, syphilis and tuberculosis). The worrisome visual sequelae that may result are secondary glaucoma due to blockage or scarring of outflow channels); cataract (which may be secondary to inflammation or steroid therapy); synechiae (attachments of iris to lens or peripheral outflow channels, causing an additional secondary glaucoma mechanism); or corneal decompensation (causing edema).
Treatment is generally nonspecific and usually given in the form of topical steroids and mydriatics.
Hyphema. Hyphema is a hemorrhage into the anterior chamber, generally resulting from trauma. There are other, much rarer, reasons for hemorrhage in the anterior chamber, such as rubeosis iridis (new-vessel formation on the surface of the Ìris) and juvenile xanthogranuloma (a self-limited disease). The traumatic form of hyphema, by far the most common, is generally treated with bed rest and sedation. The attempt is to avoid secondary bleeding. The sequelae of hyphema may be serious, including glaucoma resulting from damage to outflow channels ("angle recession") and corneal blood staining. Blood staining of the cornea generally recedes with time, in infants and children, however, amblyopia may ensue in the months to years that this resolution can take. Children who have had hyphema need to be followed for the development of glaucoma.
Glaucoma. Glaucoma is a disease that results from high intraocular pressure (causing progressive strangulation and ultimate loss of optic-nerve function), which occurs in many circumstances, some of which have already been discussed. One additional form is a primary infantile ("congenital") glaucoma. The condition apparently results from an imperfect development of the corneoscleral angle, or outflow channels. The signs of congenital glaucoma in the newborn are light sensitivity, tearing, and enlarged, possibly cloudy corneae. The condition is generally bilateral but may be either unilateral or asymmetric in its presentation. The treatment is primarily surgical, usually goniotomy.
Figure 1. Corneal ulcer, caused by a pseudomonas infection.
Figure 2. Keratoconus. Note displacement of apex of cornea downward and laterally.
Figure 3. Stargardt's disease (hereditary degeneration of the macula, occurring during childhood or adolescence).
The lens. The lens may cause visual deficiency through loss of clarity and aberrations resulting from abnormal position. Cataract, or cloudy lens of the eye, may arise from metabolic disease (e.g., galactosemia, Lowe's syndrome, or hypoparathyroidism) and developmental (e.g., familial and/or congenital) or traumatic (e.g. , physical or electrical agent) conditions. Cataracts may in addition be present in a large number of congenital and infantile syndromes, the scope of which is beyond this presentation. Cataracts, if sufficiently large and dense, may require surgical removal, but the lens's focusing power must be replaced with spectacles or contact lenses.
Lenses in abnormal positions (ectopia lentis) may also result in diminished vision and may be present in Marfan's syndrome, Marchesani's syndrome, trauma, and syphilis, among other disorders. The vitreous gel. The vitreous may be opacified, through structural change or deposition of material not normally found within it. Three examples of such conditions are diabetes mellitus, inflammation, and trauma. While the vitreous gel is normally quite clear in infancy and childhood, perhaps the most common condition yielding opacification of the vitreous occurs in diabetes mellitus. Following the primary intraretinal neovascularization, there is invasion of the vitreous gel, with fibrovascular proliferation of incompetent new vessels. These vessels often leak, causing vitreous hemorrhage. Therefore, in addition to the primary fibrovascular proliferation, products of hemorrhage may be deposited" in the vitreous cavity, ultimately decreasing visual acuity.
Inflammatory conditions - for example, Toxocara canis and the retmochoroiditis of TOJCOplastna gondii infestation - may cause a secondary vitreous involvement, with inflammatory products deposited into the vitreous gel.
Trauma may cause a secondary fibrosis of the vitreous gel if the vitreous cavity has been penetrated through injury. A second risk of this type of trauma is the introduction of fungi or bacteria that may lead to an endophthalmitis (infection in the vitreous cavity). Such infections are usually catastrophic in their result and difficult to treat.
Refractive anomalies may be classified as myopia (nearsightedness), hyperopia (farsightedness), and astigmatism. Astigmatism may be associated with either myopia or hyperopia. Astigmatism refers to an irregularity of the focusing elements. Most astigmatism is corneal in nature but may also be present in the lens. The word astigmatism derives from the Greek a ("without") and stigma ("a point**). The front surface of the eye may, for example, be shaped somewhat like the front surface of an American football, more curved in one meridian and less curved in another. Since light rays enter the eye in all meridians, light will be focused at different points depending on its angle of incidence to the eye. When this is of sufficient degree, vision is compromised
When each eye has a different refractive character, the term applied is anisometropia ("without the same measurement"). The threat to the person having eyes of different focusing capacity is that his brain may be presented in developmental months and years with a relatively clear image from the better eye and a relatively blurry image from the poorer-seeing eye, yielding a condition known as amblyopia, or lazy eye.
Generally, significant refractive errors are best treated with eyeglass correction. When anisometropic amblyopia is present, occlusion of the sound eye may be indicated in young children to facilitate vision in the amblyopic eye. Occasionally, contact lenses are used (as well) for the treatment of refractive errors.
A wide variety of neuroretinal disorders may compromise vision in infants and children, including tumors, primary degeneran ve chorioretinal disease, retinal detachment, optic atrophy, amblyopia, central-nervous-system diseases interrupting visual pathways, and cognitive disorders. (Central-nervous-system diseases interrupting visual pathways and cognitive disorders are beyond the scope of this presentation and will not be discussed further). Tumors. The most common retinal tumor of childhood is reti no blastoma. Retinobla stoma may be familial or sporadic. The diagnosis may be made early, because of the presence of an abnormal light reflex from the pupil ("cat's-eye" reflex), strabismus, or ocular inflammation.
Recent treatment modalities, primarily radiation, have dramaticallly altered the life expectancy for children affected by this tumor, and more than 80 percent of children may be expected to live five years past their diagnosis without evidence of active disease.
Primary degenerative chorioretinal diseases. Included in this diverse group of disorders are diseases that affect the area of central vision - maculae - thus diminishing vision. Many are hereditary or congenital - for example, Best's disease congenital macular degeneration), Stargardt's disease (hereditary macular degeneration; Figure 3), and vitelliform macular degeneration. Primary degenerative chorioretinal diseases may be present in Tay-Sachs disease, Batten-Mayou disease, and Refsum's disease and may also be accompanied by cerebral degeneration. Treatment is generally not available for these conditions.
Retinal detachment. Retinal detachment is generally classified as being rhegmatogenous (from the Greek word for rupture), nonrhegmatogenous, or due to traction. When the detachment is rhegmatogenous, there is a hole in the retina, usually following an injury; fluid seeps underneath and lifts the retina off the vitreous body. When it is nonrhegmatogenous (i.e., without a hole), the cause may be hemangioma of the choroid, with abnormal vessels exuding fluid into the subretinal space. The most common cause of traction detachments (after trauma) is probably diabetes mellitus. In this form of diabetes, the first observable histopathologic sign is the loss of endothelial pericyte. Following this there is a balloonlike aneurysmal dilatation of the vascular channel (microaneurysm). The microaneurysm may burst, causing intraretinal hemorrhages. When blood products persist beyond the breakdown of hemoglobin, fatty deposits are often left in deep retinal layers (deep, hard exudates). Ultimately, ischemia is assumed to occur in the portion of the retina peripheral to that served by diseased blood vessels, and the stimulus to new-blood-vessel formation occurs. First, there is intraretinal neovascularization, with subsequent proliferation into the vitreous cavity. Hemorrhage, previously discussed, may occur, with subsequent fibrous change in the vitreous gel. This fibrous change ultimately undergoes contraction, with elevation of underlying retina.
Treatment is designed first to decrease the metabolic needs of peripheral retina through argonlaser panretinal photocoagulation. When vitreous traction is present, surgical removal of the vitreous bands (vitrectomy) may be required, usually accompanied by scierai buckling and cryotherapy to anatomically reattach the retina to its supporting structures.
Optic atrophy. The optic nerve transmits retinal impulses to the lateral geniculate body via the chiasm and may be affected in a wide variety of pathologic conditions. For example, trauma, demyelinating disease, secondary inflammatory processes, metabolic diseases, poisons, and primary hereditary optic atrophies (e.g., Leber's optic atrophy) may affect the nerve. Treatment is often difficult but, when possible, is directed to the primary disease process.
Amblyopia. Amblyopia may present in a variety of clinical circumstances. First, and probably most commonly, it occurs in the framework of strabismus, or wandering eye; as a result of poor ocular alignment, one of the eyes is functionally deprived. Amblyopia may also occur in any conditions in which light is occluded from entering the eye - as, for example, in cataracts. Indeed, any obstruction that prevents light from being focused adequately to the retina may result in a functional deprivation amblyopia syndrome.
The third category of "lazy eye" was discussed above, in the treatment of anisometropia and other refractive anomalies.
In all three categories of amblyopia, the findings are similar. Visual acuity is diminished. Acuity is better for single letters than for whole lines. Fixation of the eye may be unsteady. And neutral density filters diminish vision in the amblyopic eye. Anatomically , certain changes have been observed in experimentally deprived primates in the lateral geniculate body. Alternating bands of trophic and atrophie tissue were observed in animals deprived of vision in one eye.
Treatment of amblyopia is required at a young age (generally before 7 years)* and typically consists of full optical correction and occlusion of the sound eye to facilitate development of vision in the lazy eye. Such occlusion is generally done either in conjunction with or before treatment of the antecedent or associated condition.
Trauma of the eye, like trauma in any other part of the body, can be protean in its manifestations. It may be classified according to whether surgical or nonsurgical treatment is indicated. It may further be classified according to the level of involvement - whether there is only superficial abrasion or penetration and perforation.
Corneal abrasion, probably the most common traumatic ocular condition, may be induced by unintended foreign objects (e.g. , fingernails, flying objects) or contact lenses. Treatment consists primarily of tight patching, with topical antibiotics and occasionally cycloplegics.
Penetrating injuries often require no treatment, while perforating injuries may require repair. The effects of trauma should be assumed to be more extensive than first observed. A small puncture wound on the eyelid, for example, may cover a penetrating ocular injury. Any injury to the full thickness of the lid should be assumed to have an ocular component until disproved. Lacerations of the lid margin nasally should be examined for lacrimal-system involvement. If a question of ocular perforation persists following initial observation, examination under anesthesia and even surgical exploration of the eye are indicated. No clinical circumstance tests the clinician's diagnostic and therapeutic skills more severely than trauma - particularly in children, in whom fear and lack of understanding may limit cooperation.
A wide variety of conditions, spanning the spectrum of human disease, may impair vision in infancy and childhood. Light may be blocked from entering the eye, it may not be properly focused to the back of the eye, or it may be improperly or inadequately transmitted to the central-nervous-system centers for proper association and discrimination. Trauma, the most preventable cause of all childhood eye diseases, may combine pathologic mechanisms of all of the above.
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