Ophthalmology – Fetal Alcohol Syndrome

Fetal alcohol syndrome (FAS) represents the most severe end of the fetal alcohol spectrum disorders (FASD), a group of developmental abnormalities caused by prenatal alcohol exposure. FAS is characterized by abnormalities in three major domains: growth restriction, characteristic facial features, and central nervous system dysfunction or structural abnormalities.

Typical facial features include short palpebral fissures, a thin upper vermilion border, and a smooth philtrum. Growth restriction is generally defined as height or weight at or below the 10th percentile. Central nervous system abnormalities may include structural brain anomalies, reduced head circumference, developmental impairment, or neurobehavioral dysfunction.

FAS may be diagnosed either with or without confirmed maternal alcohol exposure, although a documented history strengthens the diagnosis. Partial FAS is used when characteristic facial abnormalities are present but only one of the other major diagnostic domains is fulfilled.

Epidemiology and Risk Factors

The estimated prevalence of FAS is approximately 0.5–2 cases per 1,000 live births, although true rates vary between populations and are difficult to determine because prenatal alcohol exposure is frequently underreported.

The major risk factor is maternal alcohol consumption during pregnancy. Heavy daily intake and binge drinking carry particularly high risk, but a completely safe threshold has not been established.

Genetic factors may modify susceptibility. Variants in genes involved in alcohol metabolism, including ADH1B and CYP2E1, have been investigated as possible modifiers of fetal risk. However, prenatal alcohol exposure remains the essential causal factor.

Prevention

FAS is considered preventable by avoiding alcohol during pregnancy. Because alcohol exposure can occur before pregnancy is recognized, avoidance is also important when pregnancy is planned or possible.

Screening for unhealthy alcohol use and appropriate behavioral counseling before and during pregnancy can reduce fetal exposure.

Pathophysiology

Alcohol is a proven teratogen. The precise mechanisms by which it damages the developing fetus are complex and incompletely understood.

Ethanol and its metabolites, including acetaldehyde, can interfere with embryonic development during critical periods of gastrulation and neurulation. Proposed mechanisms include oxidative stress, free-radical formation, interference with cellular signaling, altered gene transcription, impaired neural crest development, and disruption of neuronal proliferation and migration.

Because the eyes and central nervous system develop closely together, prenatal alcohol exposure can affect the eyelids, globe, retina, optic nerve, and visual pathways.

Associated Systemic Features

Children with FAS may have growth restriction, developmental delay, learning disabilities, reduced IQ, behavioral disorders, poor adaptive functioning, impaired social judgment, and communication difficulties.

Attention-deficit/hyperactivity disorder and other psychiatric or behavioral disorders are common. Some affected individuals later develop problems with substance use and mental health.

Congenital heart defects and other systemic malformations may also occur.

Ophthalmic Manifestations

Ocular abnormalities are common in FAS. External features may include short palpebral fissures, ptosis, epicanthal folds, and telecanthus.

The globe may be smaller than normal, producing microphthalmos.

Strabismus, particularly esotropia, is common and can lead to amblyopia if untreated.

Visual acuity may be reduced in one or both eyes. Refractive errors are also common, with myopia frequently reported.

Anterior segment abnormalities and media opacities can occur. Posterior segment findings may include retinal dysplasia and tortuous retinal vessels.

One of the most important abnormalities is optic nerve hypoplasia, which may cause substantial and permanent visual impairment.

Severely affected children may also have cortical visual impairment, reflecting damage to central visual pathways rather than the eyes themselves.

Diagnosis

A careful prenatal history should assess possible maternal alcohol exposure, although clinicians should recognize that alcohol consumption may be underestimated or underreported.

The physical examination should evaluate growth, head circumference, characteristic facial features, neurologic development, and associated congenital abnormalities.

A complete ophthalmic evaluation should assess visual acuity or age-appropriate visual behavior, ocular alignment, eyelid anatomy, cycloplegic refraction, anterior segment structures, retina, and optic nerves.

Because visual problems can interfere further with development and learning, ophthalmologic abnormalities should be identified as early as possible.

Diagnostic Testing

There is currently no single reliable laboratory test that confirms fetal alcohol syndrome.

Several biochemical markers of maternal alcohol exposure have been investigated, including fatty acid ethyl esters in meconium or hair, gamma-glutamyl transferase, carbohydrate-deficient transferrin, and acetaldehyde-associated markers. None is sufficiently sensitive and specific to replace clinical diagnosis.

CT or MRI of the brain may be useful when structural central nervous system abnormalities are suspected.

Electroretinography has shown variable findings and is not a standard diagnostic test for FAS.

Differential Diagnosis

Several genetic and congenital syndromes can resemble the facial or ophthalmic findings of FAS. Important differential diagnoses include velocardiofacial syndrome, Williams syndrome, blepharophimosis syndrome, and Dubowitz syndrome.

Because prenatal alcohol exposure may coexist with an unrelated genetic disorder, atypical features should prompt consideration of clinical genetics or dysmorphology consultation.

Treatment

There is no medication that reverses the congenital ocular abnormalities of FAS. Management is therefore directed toward maximizing visual development and treating specific ocular problems.

Refractive errors should be corrected promptly with appropriate spectacles or other optical correction.

If amblyopia is present, treatment may include patching of the better-seeing eye or other standard amblyopia therapy.

Strabismus surgery may be indicated when significant ocular misalignment persists despite optical and amblyopia treatment.

Ptosis surgery may be considered when eyelid drooping interferes with the visual axis or causes significant functional impairment.

Children with optic nerve hypoplasia, cortical visual impairment, or other permanent visual deficits may benefit from low-vision and developmental services.

Associated systemic and neurodevelopmental disorders require multidisciplinary care.

Follow-up

Children with FAS should have ongoing ophthalmologic follow-up, particularly during the amblyogenic years.

Monitoring should include visual acuity, refractive error, ocular alignment, amblyopia, ptosis, and optic nerve function.

The frequency of follow-up depends on the severity of ocular involvement. Children with significant strabismus, amblyopia, or refractive error require more frequent examinations.

Patient Education

Families should understand that many behavioral, developmental, and learning problems are manifestations of the underlying neurodevelopmental disorder and may require long-term educational, behavioral, and medical support.

Parents should also understand the importance of early treatment of refractive error and strabismus, because preventable amblyopia can compound visual impairment caused by FAS.

When ongoing maternal alcohol misuse is identified, referral for appropriate substance-use treatment and support services is important.

Prognosis

Visual prognosis depends on the specific ocular abnormalities. Children whose reduced vision is primarily caused by refractive error or amblyopia can improve substantially when diagnosed and treated early.

Visual loss from optic nerve hypoplasia, retinal abnormalities, or cortical visual impairment may be permanent.

Early ophthalmologic evaluation in infancy or the preschool years provides the best opportunity to preserve useful vision and prevent avoidable visual disability.

Complications

The major ophthalmic complication is permanent reduction in visual acuity from untreated amblyopia, particularly when associated with strabismus, anisometropia, or significant refractive error.

More severe congenital abnormalities, including optic nerve hypoplasia and cortical visual impairment, can cause substantial lifelong visual disability.