Fetal Alcohol Syndrome (FAS) is the most severe manifestation of Fetal Alcohol Spectrum Disorders (FASD), resulting from prenatal alcohol exposure. Alcohol consumed by the mother during pregnancy crosses the placenta, causing harmful effects on the developing fetus. FAS is characterized by growth deficiencies, central nervous system abnormalities, and a distinctive set of facial features. The eyes and surrounding structures are sensitive to this exposure, making specific ocular findings a strong indicator used in the diagnosis of FAS.
Defining the Key Ocular Features
The most defining eye feature of Fetal Alcohol Syndrome is the presence of short palpebral fissures, which refers to a reduced horizontal length of the eye opening. This measurement, taken from the inner corner to the outer corner of the eye, is considered characteristic when it falls two or more standard deviations below the mean for a child’s age and ethnicity. Specialized charts are used to establish these measurements, and the finding is considered a highly discriminant sign for diagnosis. The presence of these visibly smaller eye openings contributes significantly to the overall facial appearance associated with FAS.
Another common periocular finding is the presence of epicanthal folds, which are folds of skin extending from the upper eyelid and covering the inner corner of the eye. While these folds can occur naturally in some populations, their presence alongside other features supports a diagnosis of FAS. These skin folds can give the eyes a more oval or almond-shaped appearance.
Mild ptosis, or the slight drooping of the upper eyelid, is also frequently observed in individuals with Fetal Alcohol Syndrome. This drooping is generally a minor cosmetic finding but is part of the structural changes affecting the eyes and surrounding tissues. Together, the short palpebral fissures, epicanthal folds, and ptosis contribute to the distinct facial phenotype that clinicians use to identify FAS in children.
The Developmental Mechanism of Damage
The physical features observed in FAS arise from damage that occurs during a narrow and vulnerable window of embryonic development. The period between three and six weeks after fertilization, corresponding to the first trimester, is when the basic structures of the face and brain are rapidly forming. During this time, alcohol exposure significantly interferes with cranial neural crest cells (CNCCs).
These CNCCs are responsible for migrating to the midfacial region and differentiating into the bones, cartilage, and connective tissues of the face and skull. Alcohol acts as a potent teratogen, causing a massive increase in programmed cell death (apoptosis) among these migrating cells. This excessive cell death and impaired migration result in a deficiency of the cellular building blocks necessary for proper formation of the midface and orbital structures.
The resulting underdevelopment of the facial skeleton directly causes the characteristic features, such as the shortened distance between the eyelids. The concentration and timing of alcohol exposure directly correlate with the severity of these defects. Greater exposure during this period leads to more pronounced abnormalities, establishing the physical appearance of FAS long before birth.
Associated Functional Vision Problems
Beyond the structural changes, prenatal alcohol exposure frequently leads to functional vision and ocular health problems that can persist throughout life. One common finding is optic nerve hypoplasia, the underdevelopment or small size of the optic nerve. Since the optic nerve transmits visual information from the eye to the brain, its hypoplasia can result in permanently reduced visual acuity or even developmental blindness.
Another widely reported functional issue is strabismus, or the misalignment of the eyes, which occurs because the muscles controlling eye movement are often affected. Strabismus may present as an eye turning inward, outward, upward, or downward, and it requires intervention to prevent long-term vision loss. Many children with FAS also commonly require corrective lenses due to refractive errors, such as nearsightedness or farsightedness.
The effects of alcohol on the brain can also lead to cortical visual impairment, a vision problem where the eyes are healthy but the brain struggles to process the visual information correctly. These issues manifest as visual perception problems, including difficulties with depth perception, spatial orientation, and navigating new environments. Studies have found that over half of young adults with FASD report visual perception problems, leading to significant challenges with independence and quality of life.