DEFINITION: Measurement of capacity for discrimination of fine details at high contrast.

EVALUATION: Distance vision is evaluated using age-appropriate methods of measurement that may be converted to a standard Snellen acuity; normal milestones of visual development are shown in Table 21.1.

Infants and Toddlers (0-3 y): Assess ability to fix and later follow a light or toy. Optokinetic nystagmus can confirm cortical vision and can be obtained by ˜6 wk with large gratings across the entire visual field. Nystagmus may develop by 8 to 12 wk of age and may be the harbinger of visual impairment. Roving, non-purposeful eye movements may signal profound visual impairment. For quantification of acuity, Teller acuity cards that use gratings of alternating black and white stripes may be used.

Preschool-age children (3-5 y): For quantification, use symbol optotypes (Allen or Lea symbols) or letter optotypes when appropriate (HOTV letters, tumbling Es).

School-age children (>5 y): Usually able to use Snellen chart; otherwise use same methods as for preschool-age children.

Retinoscopy may be used to confirm that vision changes are not secondary to correctable refractive error.

Standard tests include pseudoisochromatic Ishihara color plates and Hardy-Rand-Rittler (HRR) plates. More detailed tests, including Farnsworth-Munsell 15- or 100-Hues tests, may be used to further characterize the type of color deficiency (i.e., trouble with distinguishing colors in the red-green spectrum: protanopia or deuteranopia, or trouble with distinguishing colors in the blue-yellow spectrum: tritanopia). Testing of color vision may be confounded by visual impairment (<20/200). Monocular dyschromatopsia is a characteristic of an ipsilateral optic neuropathy.

EVALUATION: Infants and Toddlers (9 mo-3 y): Evaluate presence of saccade toward a toy or light brought into view in each quadrant of the visual field tested binocularly and if able, monocularly. Preschool-age children (3-5 y): Can assess by having the child fixate at a point between the examiner’s eyes, ask child to point to fingers moving in the periphery. School-age children (>5 y): Use confrontation visual fields as described. Formal Goldmann visual field perimetry can be used reliably by age 8 to 9 y and automated Humphrey visual field perimetry in young teens and older.

Examine pupillary size, shape, and symmetry in light and dark conditions.

SHAPE: Irregular pupillary shape may be caused by a variety of congenital conditions (aniridia, iris coloboma, isolated corectopia); it can also be caused by local trauma or inflammation.

SYMMETRY: In physiologic anisocoria, pupillary response is normal, and the relative asymmetry in size between the pupils is the same in light and dark; most often, this disparity is <1 mm in light and dark. Anisocoria being greater in light implies parasympathetic abnormality in larger pupil and may implicate dysfunction of the third cranial nerve (see “Third Nerve Palsy” below). Anisocoria greater in dark suggests sympathetic abnormality in smaller pupil (see “Horner Syndrome” below).

LIGHT REACTION: Direct and consensual pupillary light reaction is best examined with a bright light in a dimly lit room, while patient fixates on a distant target. Use swinging flashlight test to evaluate for relative afferent pupillary defect, which is characteristic of asymmetric compromise of optic nerve function. Constriction of the pupils in darkness indicates a paradoxical pupillary response. Differential diagnosis includes retinal disease, such as congenital stationary night blindness and achromatopsia (see “Retinal Dystrophy/Degenerative Disease” below).

ALIGNMENT: Observe position of corneal light reflex in each eye at rest to detect misalignment (Hirschberg method). Observe head posture; large head turn toward the affected eye in a child with esotropia is suggestive of a 6th nerve palsy; a head tilt away from the affected eye may represent 4th nerve palsy.

MOTILITY: Test conjugate movement of both eyes together (versions) and then test movements of each eye separately with the other eye covered (ductions). In convergence spasm, there is a disparity between versions and ductions; versions show evidence of an abduction limitation but ductions will demonstrate full abduction in each eye helping to distinguish this process from a 6th nerve palsy.

EXTERNAL EXAM: Note abnormalities of the orbit (e.g., proptosis) and eyelids (e.g., ptosis or eyelid retraction).

ANTERIOR SEGMENT EXAM: Any anomalies of the anterior aspect of the eye are noted (i.e., anomalies of the conjunctiva, cornea, anterior chamber, iris, or lens) either with a handheld light or using slit-lamp biomicroscopy.

VITREOUS: Note the clarity and document whether abnormal cells are present.

OPTIC NERVE: Evaluate the size, color, and sharpness of the nerve border; note any peripapillary abnormalities.

FOVEA: Evaluate the contour of the foveal pit (in albinism, the pit may be absent or hypoplastic); note any pigmentary changes of the macular region.

VASCULATURE: Note the course and caliber of the retinal arterioles and venules.

PERIPHERAL RETINA: May be visualized with pupillary dilation; particular attention is paid to any peripheral retinal pigmentary changes.

Diseases of the retina suspected in children with bilateral visual loss, light sensitivity, color vision deficiency, visual loss confined to nighttime or day-time. Patients with retinal disease often are referred to a neuro-ophthalmic practice in the setting of unexplained visual impairment, nystagmus, or roving eye movements secondary to subnormal vision or true vision loss misdiagnosed as psychogenic or nonorganic.

LEBER CONGENITAL AMAUROSIS: Congenital retinal dystrophy involving both rods and cones.¹ Genetics: Usually autosomal recessive, occasionally autosomal dominant. Presentation: Onset of visual impairment variable but may be present at birth with signs of roving, non-purposeful eye movements, positive oculodigital sign (pushing on the eyes or rubbing them with a finger), high hyperopia; retinal examination may be normal initially. Evaluation: ERG useful to establish the diagnosis.

ACHROMATOPSIA: Congenital, nonprogressive defect of cone receptors more common in males; children present with nystagmus, decreased vision, dyschromatopsia, and paradoxical pupillary response (constriction of pupils with dim light).² Complete achromatopsia: autosomal recessive with absent cone function; vision ranges from 20/200 to 20/400. Incomplete achromatopsia: commonest form of color vision deficiency; X-linked, vision ranges from 20/40 to 20/400; may have residual sensitivity to one or a combination of red, green, or blue light stimuli.

CONGENITAL STATIONARY NIGHT BLINDNESS: Characterized by impaired dark adaptation and often high myopia; vision ranges from 20/20 to 20/200 and does not deteriorate with time. Genetics: Various subtypes and genetic causes recognized. X-linked form is most common, due to mutations in Nyx gene (encoding nyctalopin).³

STARGARDT MACULAR DYSTROPHY: Hereditary syndrome of macular degeneration beginning in childhood; over time, atrophic macular degeneration with foveal pigmentary changes that may have bull’s-eye configuration (bull’s-eye maculopathy); yellow flecks in retinal periphery; dyschromatopsia; may be mistaken for psychogenic visual loss, as retina may appear normal initially in spite of vision loss. Genetics: Autosomal recessive secondary to mutations in ABCA4 gene. Evaluation: ERG usually normal early in the disease; dark choroid on fluorescein angiography.

ALBINISM: Hereditary condition characterized by decreased pigmentation either specifically in ocular structures (ocular albinism) or ocular structures, skin, and hair (oculocutaneous albinism, OCA). Genetics: Most commonly OCA is autosomal recessive and ocular albinism is X-linked recessive; dominant forms of OCA have been reported but are rare. Presentation: Subnormal visual acuity, nystagmus, transillumination defects of the iris (seeing the red reflex through the pigmented iris), photophobia, foveal hypoplasia, blonde fundus, aberrant decussation of fibers of the anterior visual pathway at the optic chiasm. Systemic associations: Albinism and bleeding diathesis seen in Hermansky-Pudlak; more common in patients of Puerto Rican descent; albinism and increased susceptibility to infection in Chediak-Higashi. Evaluation: Genetic testing and workup for associated systemic disorders when indicated.

ACUTE IDIOPATHIC BLIND SPOT ENLARGEMENT: Unilateral enlarging paracentral scotoma, which may obscure central vision; believed to be a post-viral retinopathy; sometimes, but not always, improves spontaneously. Evaluation: multifocal ERG may reveal peripapillary areas of retinal dysfunction.⁴

Retinal degeneration is seen in a variety of syndromes and neurodegenerative disorders, including sphingolipidoses and neuronal ceroid lipofuscinoses.

JOUBERT SYNDROME: Episodic neonatal tachypnea and apnea, rhythmic protrusion of the tongue, ataxia, hypotonia, and gross motor delay; 50% have retinal dystrophy with visual acuity 20/60 to 20/200; genetically heterogeneous; MRI demonstrates characteristic dysgenesis or hypoplasia of the cerebellar vermis with associated brainstem cleft and altered morphology of superior cerebellar peduncles (molar tooth sign).⁵

Congenital anomalies of the optic disc account for ˜15% of severe visual impairment in children; thought to result from injury or maldevelopment early in gestation.⁶ Unilateral anomalies typically present in the preschool period with strabismus (most commonly esotropia); bilateral anomalies present in infancy with poor vision and nystagmus. There is a high prevalence of associated CNS malformations and systemic disorders, often necessitating further workup.

EMBRYOGENESIS: After closure of the embryonic neural tube (˜4 wk gestation), evaginations from the anterior part of the neural tube extend laterally, forming the optic stalk (proximally) and the optic cup (distally). Retinal ganglion cell axons project directly to the optic cup and enter the optic stalk, forming the optic nerve; all RGC axons enter the optic nerve by ˜20 wk gestation. During development, ˜2 million RGCs send projections into the optic nerve; programmed cell death eliminates about ½ of these, so that the adult optic nerve contains ˜1.2 million axons. Myelination of the anterior visual pathways begins at the lateral geniculate body at ˜20 wk
gestation, reaches the lamina cribrosa at term, and continues over the first 2 y of life; geniculostriate pathway begins around term and is fully mature about 4 mo postnatally.

OPTIC NERVE HYPOPLASIA: Most common congenital anomaly of the optic disc;⁷ appears as an abnormally small, discolored (gray or pale) optic nerve head, reflecting loss of optic nerve axons often with peripapillary halo (double ring sign). Epidemiology: Risk increased by a variety of prenatal factors, including young maternal age, primiparity,⁸ and exposure to teratogens (alcohol, cocaine, LSD, PCP, phenytoin, quinine);⁹ segmental hypoplasia occurs in infants of diabetic mothers.¹⁰ Genetics: Currently no strong genetic associations for isolated optic nerve hypoplasia. Presentation: Localized visual field defects and constriction of the visual fields; acuity ranges from normal (if macular fibers are spared) to no light perception; more commonly bilateral than unilateral; may be associated with other CNS malformations, ocular anomalies, and multisystem genetic disorders. Evaluation: (1) Neuroimaging with MRI. (2) Endocrine evaluation: Hormonal dysfunction may be present in spite of normal anatomic appearance of pituitary on MRI. Growth hormone deficiency resulting in pituitary dwarfism is most common; there may also be deficiencies in thyroid, adrenal, and gonadal axes, panhypopituitarism, or diabetes insipidus due to ADH deficiency; hyperprolactinemia is common. Associated conditions: Septo-optic dysplasia (de Morsier syndrome): optic nerve hypoplasia, absent septum pellucidum, and thinning or agenesis of the corpus callosum; associated with mutations in HesX1 gene.¹¹

OPTIC NERVE APLASIA: Complete absence of the optic nerve and disc, retinal ganglion and nerve fiber layers, and optic nerve vessels, sometimes with a whitish area or cavity in the site normally corresponding to the optic disc;¹² typically unilateral and frequently associated with other malformations in the same eye (microphthalmia, iris hypoplasia, cataracts, colobomas, retinal dysplasia); when bilateral, usually associated with CNS malformations.¹²

OPTIC NERVE COLOBOMA: Well-defined, bowl-shaped excavation centered in the inferotemporal part of the optic disc, often involving adjacent choroid and retina, due to faulty closure of embryonic fetal fissure of optic stalk and cup.^13,14 Genetics: Sporadic or inherited, with multiple modes of transmission (AR, AD, X-linked)¹⁵; associated with multisystem disorders, including CHARGE association (60% with CHD7 mutation), Walker-Warburg syndrome, linear sebaceous nevus syndrome (see below). Presentation: May present with microphthalmos, microcornea, iris defects, or strabismus; acuity mildly to severely decreased; prone to serous retinal detachment. Evaluation: Consider genetics evaluation to exclude associated syndromes.

OPTIC NERVE PIT: Round or oval depression in the optic disc formed by herniation of dysplastic retina into a pocket formed by a defect in the lamina cribrosa. Presentation: Variable visual acuity and visual field defects if any; associated with serous retinal detachments.¹⁶

MORNING GLORY ANOMALY: Funnel-shaped excavation of the posterior fundus, involving the optic disc; the optic nerve appears enlarged with a central glial tuft (resembling the morning glory flower) and may be surrounded by a halo of chorioretinal pigmentary disruption; radial orientation of retinal vasculature as it emerges from the disc. Presentation: Decreased acuity (usually 20/200 to finger counting, although cases with 20/20 vision and no light perception have been reported), or discovered in workup for midline defects (see below). Associations: (1) Transsphenoidal basal encephalocele: Occult midline congenital malformation in which meningeal pouch protrudes into nasopharynx through round defect in sphenoid
bone; affected children may have other midline defects (hypertelorism, midline cleft lip, cleft palate, callosal agenesis, absence of the optic chiasm, panhypopituitarism) and may present with rhinorrhea or symptoms of airway obstruction. (2) Vascular anomalies: ˜45% of patients with morning glory anomaly, including carotid hypoplasia and moyamoya syndrome.¹⁷ Evaluation: MRI and MRA indicated to evaluate for associated anomalies.

TILTED DISC ANOMALY: Discs appear tilted bilaterally, with superonasal elevation; anomalous origin of retinal vessels; secondary to posterior ectasia of the inferonasal fundus and optic disc; may have bitemporal visual field defects that do not respect the vertical meridian.

MYELINATED RETINAL NERVE FIBERS: White, striated patches at the upper and lower poles of the optic disc (less often, discrete patches are seen separate from the disc), which may elevate the disc and obscure the disc margin; recognizable by irregular, fan-shaped appearance of distal border; can be associated with high myopia, amblyopia, and visual field loss; pathogenesis unclear, may be familial (autosomal dominant).

PAPILLORENAL SYNDROME: Centrally excavated discs, normal in size, with radial orientation of retinal vessels that emanate from the edge of the optic disc; associated with renal dysfunction. Genetics: Often caused by mutations in PAX2 gene.¹⁸ Presentation: Visual acuity typically normal, but may be diminished due to choroidal or retina hypoplasia, or serous retinal detachment; peripheral field defects due to areas of retinal hypoplasia. Evaluation: Renal workup, including renal ultrasound.

AICARDI SYNDROME: Constellation of infantile spasms, agenesis of the corpus callosum, and pathognomonic peripapillary chorioretinal lacunae or “punched out lesions” (defects in retinal pigment epithelium) surrounding an optic disc which is often anomalous. Considered to be X-linked lethal in males.

End result of any of various insults to the anterior visual pathway leading to loss of retinal ganglion cell axons; appearance is of a pale optic disc of normal size, often with fewer-than-normal fine vessels; degree of optic atrophy on examination is not well-correlated with visual acuity.

COMPRESSIVE OPTIC NEUROPATHY: Optic atrophy may result from lesions resulting in chronically increased pressure on the optic pathways.

Optic nerve glioma: Tumor arising from astrocytes surrounding optic nerve axons, most often low grade and pathologically identical to juvenile pilocytic astrocytoma; may initially present with disc edema, but eventually result in optic atrophy. Epidemiology: 75% within the 1st decade of life, 90% within the 1st 2 decades. Presentation: Vision loss may occur although some optic nerve gliomas do not affect visual acuity; strabismus, painless proptosis, and monocular nystagmus may all be signs of an optic nerve glioma. Associations: 25% are associated with NF-1; frequency of optic gliomas in NF-1 patients varies from 10% to 70%; in NF-1 patients gliomas may be multifocal, affecting both optic nerves independently. Evaluation: MRI often shows homogeneous thickening and kinking of orbital optic nerve(s), enlargement of chiasm, infiltration of hypothalamus. Prognosis: Varies; may remain stable, enlarge, or regress spontaneously. Treatment: Controversial and dependent upon impact of tumor on visual function; observation, chemotherapy, surgical debulking may be pursued; radiation less commonly pursued given risk of secondary tumors in NF1 and secondary effects on vascular integrity (radiation induced moyamoya disease) and neurodevelopment.

Craniopharyngioma: Most common supratentorial tumor of childhood; location frequently causes anterior visual pathway compression and endocrine dysfunction; may present as seesaw nystagmus.

Congenital Hydrocephalus: Common cause of optic atrophy in children; optic atrophy is often coincident with cortical visual loss; major mechanism appears to be long-term increase in intracranial pressure.

TOXIC AND NUTRITIONAL OPTIC NEUROPATHY: Several nutritional deficiencies and drugs have been associated with symmetrical, usually insidious bilateral optic neuropathy with loss of acuity and centrocecal scotomas (Table 21.2).

TRAUMATIC OPTIC NEUROPATHY: Damage to one or both optic nerves may result from direct or indirect trauma, including contusion, avulsion, or laceration of the optic nerve, or hemorrhage into the optic nerve sheath; optic disc typically appears normal at first, with atrophy ensuing quickly after the inciting event¹⁹; high-dose steroids have been used but are not clearly beneficial and may be harmful.²⁰

RADIATION OPTIC NEUROPATHY: Cumulative doses of 50 to 60 Gy or single doses of >10 Gy to the anterior pathway increase risk of radiation optic neuropathy²¹ can occur within several weeks of radiation (early form) or years after treatment with a peak at 18 mo (late form).

HEREDITARY OPTIC NEUROPATHY: Heterogeneous group of disorders, many with evidence of mitochondrial dysfunction; systemic mitochondrial disorders may also produce optic atrophy.²²

Dominant optic atrophy (Kjer): Most common form of hereditary optic atrophy; onset insidious, typically between ages 4 to 8 y. Genetics: Autosomal dominant with incomplete penetrance and variable phenotype; genetically heterogeneous, most mutations described in OPA1, with additional loci at OPA3 (dominant optic atrophy with cataract), OPA4, and OPA5.²³ Presentation: Often discovered during routine visual screening; visual acuity typically 20/70 to 20/100 (range 20/20 to count fingers), but may vary even between eyes in the same individual; mild photophobia and dyschromatopsia are also common. Prognosis: Visual function usually stabilizes after teenage years; 80% of patients over 45 y have acuity better than 20/200.

Leber Hereditary Optic Neuropathy (LHON): Mitochondrial disorder causing rapid loss of vision, more commonly affecting males; usually presents between ages 18 to 35 y (range: 1-80 y). Risk of females carrying this mutation is <10%. Genetics: Maternally inherited, associated with mitochondrial
DNA mutations²³; 3 most common mutations include m.11778 G>A (most common), m.3460 G>A, and m.14484 T>C of which spontaneous visual recovery is more likely in the m.14484 T>C mutation. In addition to primary causative mutations, many mitochondrial mutations/polymorphisms have been identified that are weakly associated but not sufficient for the onset of disease. Presentation: Rapidly progressive, painless unilateral vision loss, with involvement of the other eye usually within days to months; acutely may detect peripapillary telangiectasia of the vessels and swelling of the retinal nerve fiber layer without true optic nerve edema. Prognosis: Visual acuity usually stabilizes at ˜20/200, with dyschromatopsia; central or centrocecal scotoma; most often permanent but some patients show visual recovery. Evaluation: Fluorescein angiography may be useful in distinguishing the pseudoswelling in LHON from true optic nerve edema. In LHON there is no evidence of leakage around the optic nerve, whereas in true optic nerve edema, there is leakage of fluorescein around the optic nerve.

Wolfram syndrome (DIDMOAD): Constellation of Diabetes Insipidus, Diabetes Mellitus, Optic Atrophy, and sensorineural Deafness.²⁴ Epidemiology: Most patients under 25 y, with different manifestations presenting at different ages; mean age at diagnosis of diabetes mellitus at 9 y, optic atrophy at 12 y, diabetes insipidus at 15 to 20 y, clinical deafness >20 y. Genetics: Several mutations described in WFS1 gene on 4p16.3 (also associated with dominant optic atrophy with hearing loss); deletions at this locus may predispose to multiple mitochondrial deletions. Presentation: Vision loss with optic atrophy; final vision usually worse than 20/200. Evaluation: MRI with widespread atrophy of brainstem, middle cerebellar peduncle, and cerebellum, with decreased signal intensity in posterior pituitary.

Recessive optic atrophy: Monosymptomatic, isolated, rare form of hereditary optic atrophy; present at birth or develops at an early age; severe visual defects are characteristic (acuity worse than 20/200 with achromatopsia).²⁵

Behr syndrome: Form of recessive optic atrophy with other associated neurologic abnormalities including ataxia, spasticity, and mental retardation; onset usually between 1 and 8 y; may overlap with several other genetic disorders.²⁶

Costeff syndrome (methylglutaconic aciduria type 3): Autosomal recessive disorder with early bilateral optic atrophy, extrapyramidal dysfunction, late-onset spasticity, and sometimes cognitive deficits; caused by homozygous mutations with complete absence of OPA3 gene²³; elevated urine 3-methylglutaconic and 3-methylglutaric acid.

Associated with neurodegenerative disorders:

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