Amblyopia

Amblyopia is a decrease in visual acuity, unilateral or bilateral, that occurs in visually immature children as a result of a lack of a clear image projecting onto the retina. The unformed retinal image can occur secondary to a deviated eye (strabismic amblyopia), an unequal need for vision correction between the eyes (anisometropic amblyopia), a high refractive error in both eyes (ametropic amblyopia), or a media opacity within the visual axis (deprivation amblyopia).

The development of visual acuity normally proceeds rapidly in infancy and early childhood. Anything that interferes with the formation of a clear retinal image during this early developmental period can produce amblyopia. Amblyopia may occur only during the critical period of development, before the cortex has become visually mature, within the first decade of life. The younger the child, the more susceptible he or she is to the development of amblyopia.

The diagnosis of amblyopia is confirmed when a complete ophthalmologic examination reveals reduced acuity that is unexplained by an organic abnormality. If the history and ophthalmologic examination do not support the diagnosis of amblyopia in a child with poor vision, other causes (neurologic, psychologic) must be considered. Amblyopia is usually asymptomatic and detected only by screening programs. Screening is easier in older children. Just as amblyopia is less likely to occur in an older child, it is also more resistant to treatment at an older age. Amblyopia is reversed more rapidly in younger children whose visual system is less mature. The key to the successful treatment of amblyopia is early detection and prompt intervention.

Treatment generally first consists of removing any media opacity or prescribing appropriate glasses, if needed, so that a well-focused retinal image can be produced in each eye. The sound eye is then covered (occlusion therapy) or blurred with glasses or drops (penalization therapy) to stimulate proper visual development of the more severely affected eye. Occlusion therapy can provide a speedier improvement in vision, but some children better tolerate atropine penalization. The best treatment for any one patient should be selected on an individual basis. The goals of treatment should be thoroughly understood, and the treatment must be carefully supervised. Close monitoring of amblyopia therapy by an ophthalmologist is essential, especially in the very young, to avoid deprivation amblyopia in the good eye. Many families need reassurance and support throughout the trying course of treatment. Although full-time occlusion has historically been considered the best way to treat children with amblyopia, a series of prospective studies have shown that some children can achieve similar results with less patching or through the use of atropine drops. In the past it was generally thought that older children would not respond to amblyopia therapy, but this has been shown to be untrue. Studies now suggest that treatment should be offered to children who previously were deemed visually mature and thus thought to have no hope of improving their vision.

Diplopia

Diplopia, or double vision, is generally a result of a misalignment of the visual axes. Occluding either eye relieves the diplopia if it is binocular in origin; affected children commonly squint, cover one eye with a hand, or assume an abnormal head posture (a face turn or head tilt) to alleviate the bothersome sensation. These mannerisms, especially in preverbal children, are important clues to diplopia. The onset of diplopia in any child warrants prompt evaluation; it may signal the onset of a serious problem such as increased intracranial pressure, a brain tumor, or an orbital mass.

Monocular diplopia results from dislocation of the lens, cataract, or some defect in the media or macula. With this type of diplopia, occluding the nondiplopic eye will not relieve the symptoms.

Suppression

In the presence of strabismus, diplopia occurs secondary to the same image falling on different regions of the retina in each eye. In a visually immature child, a process can occur in the cortex that eliminates the disability of seeing double. This is an active process and is termed suppression. It develops only in children. Although suppression eliminates the annoying symptom of diplopia, it is the potential awareness of a second image that tends to keep our eyes properly aligned. Once suppression develops, it can allow an intermittent strabismus to become constant or strabismus to redevelop later in life, even after successful treatment during childhood.

Amaurosis

Amaurosis is partial or total loss of vision; the term is usually reserved for profound impairment, blindness, or near blindness. When amaurosis exists from birth, primary consideration in the differential diagnosis must be given to developmental malformations, damage consequent to gestational or perinatal infection, anoxia or hypoxia, perinatal trauma, and the genetically determined diseases that can affect the eye itself or the visual pathways. Often, the reason for amaurosis can be readily determined by objective ophthalmic examination; examples are severe microphthalmia, corneal opacification, dense cataracts, chorioretinal scars, macular defects, retinal dysplasia, and severe optic nerve hypoplasia. In other cases, an intrinsic retinal disease might not be apparent on initial ophthalmoscopic examination or the defect might involve the brain and not the eye. Neuroradiologic (CT or MRI) and electrophysiologic (electroretinography) evaluation may be especially helpful in these cases.

Amaurosis that develops in a child who once had useful vision has different implications. In the absence of obvious ocular disease (cataract, chorioretinitis, retinoblastoma, retinitis pigmentosa), consideration must be given to many neurologic and systemic disorders that can affect the visual pathways. Amaurosis of rather rapid onset can indicate an encephalopathy (hypertension), infectious or parainfectious processes, vasculitis, migraine, leukemia, toxins, or trauma. It may be caused by acute demyelinating disease affecting the optic nerves, chiasm, or cerebrum. In some cases, precipitous loss of vision is a result of increased intracranial pressure, rapidly progressive hydrocephalus, or dysfunction of a shunt. More slowly progressive visual loss suggests tumor or neurodegenerative disease. Gliomas of the optic nerve and chiasm and craniopharyngiomas are primary diagnostic considerations in children who show progressive loss of vision.

Clinical manifestations of impairment of vision vary with the age and abilities of a child, the mode of onset, and the laterality and severity of the deficit. The first clue to amaurosis in an infant may be nystagmus or strabismus, with the vision deficit itself passing undetected for some time. Timidity, clumsiness, or behavioral change may be the initial clues in the very young. Deterioration in school progress and indifference to school activities are common signs in an older child. School-aged children often try to hide their disability and, in the case of very slowly progressive disorders, might not themselves realize the severity of the problem; some detect and promptly report small changes in their vision.

Any evidence of loss of vision requires prompt and thorough ophthalmic evaluation. Complete delineation of childhood amaurosis and its cause can require extensive investigation involving neurologic evaluation, electrophysiologic tests, neuroradiologic procedures, and sometimes metabolic and genetic studies. Furthermore, attendant special educational, social, and emotional needs must be met.

Nyctalopia

Nyctalopia, or night blindness, is vision that is defective in reduced illumination. It generally implies impairment in function of the rods, particularly in dark adaptation time and perceptual threshold. Stationary congenital night blindness can occur as an autosomal dominant, autosomal recessive, or X-linked recessive condition. It may be associated with myopia and nystagmus. Children can have excessive problems going to sleep in a dark room, which may be mistaken for a behavioral problem. Progressive night blindness usually indicates primary or secondary retinal, choroidal, or vitreoretinal degeneration (Chapter 622); it occurs also in vitamin A deficiency or as a result of retinotoxic drugs such as quinine.

Psychogenic Disturbances

Vision problems of psychogenic origin are common in school-aged children. Both conversion reactions and willful feigning are encountered. The usual manifestation is a report of reduced visual acuity in one or both eyes. Another common manifestation is constriction of the visual field. In some cases, the symptom is diplopia or polyopia (Chapters 20 and 23).

Important clues to the diagnosis are inappropriate affect, excessive grimacing, inconsistency in performance, and suggestibility. A thorough ophthalmologic examination is essential to differentiate organic from functional visual disorders.

Affected children usually fare well with reassurance and positive suggestions. In some cases, psychiatric care is indicated. In all cases, the approach must be supportive and nonpunitive.

Dyslexia

Dyslexia is the inability to develop the capability to read at an expected level despite an otherwise normal intellect. The terms reading disability and dyslexia are often used interchangeably. Most dyslexic persons also display poor writing ability. Dyslexia is a primary reading disorder and should be differentiated from secondary reading difficulties due to mental retardation, environmental or educational deprivation, and physical or organic diseases. Because there is no one standard test for dyslexia, the diagnosis is usually made by comparing reading ability with intelligence and standard reading expectations. Dyslexia is a language-based disorder and is not caused by any defect in the eye or visual acuity per se, nor is it attributable to a defect in ocular motility or binocular alignment. Although ophthalmologic evaluation of children with a reading problem is recommended to diagnose and correct any concurrent ocular problems such as a refractive error, amblyopia, or strabismus, treatment directed to the eyes themselves cannot be expected to correct developmental dyslexia (Chapter 31).