Eyes and Vision

The eyes develop very early in pregnancy; the first sign of eye development comes even before the neural tube closes.

The eyes begin to develop around 5 to 6 weeks of pregnancy, when optic indentations (pits or grooves) appear in the neural folds. These indentations lead to hollow vesicles as the neural tube closes, which then leads to optic cups. The optic cups becomes the retina of each eye.

The lens develops rapidly around 7 to 9 weeks of pregnancy, which is followed by rapid growth of the entire eye from 10 to 16 weeks. The eyes are initially located on the sides of the head but move forward by 8 weeks as the rest of the face grows to bring them together.

Around 10 weeks, the optic retina is formed. Both retinas combine to form an “X” (optic chiasm) before connecting to the brain by more than one million nerve fibers.

The retina has one of the highest requirements for oxygen than any other tissue in the body, when accounting for the amount of oxygen relative to weight. Due to this, defects in the retina are common, as the eye is very sensitive to any disturbances in the formation of its blood vessels.

Around 14 weeks of pregnancy, the optic cup thins out to form a thin ring that will become the iris of the eye.

By week 14, several eyelashes are visible, while eyebrows appear at 22 weeks.

The first sign of eyelid development occurs around the beginning of week 8 when small depressions develop immediately above and below the already developing eye. These depressions rapidly deepen to form the eyelid folds. Distinct upper and lower eyelid folds are well defined by 9 weeks. Eyelids can be seen on ultrasound examination after the first trimester.

Eyelid development has four steps: formation, fusion, development, and separation. After formation (described above), they immediately fuse at the beginning of week 10, and are completely fused within 7 days.

Eyelid fusion has an important purpose; it is crucial this fusion occurs before the start of kidney function, which would result in the fetus urinating into the amniotic fluid, which could negatively impact the eye.

There is debate regarding the timing of eyelid separation, but it is generally accepted that eyelids separate around 20 to 24 weeks. Separation at this point is now safe for the eyes, as the cornea has developed almost five full layers of epithelium and no longer needs protection from urine or other factors in amniotic fluid, such as in bacteria.

Fetal blinking may begin as early as 31 weeks, with a rate of about 6 blinks an hour (adults blink around 19 to 20 times per minute). It is possible that blinking starts even earlier, but these movements are likely undetectable by ultrasound that early.

Eye color results from the pigmentation of the iris, which is genetically determined regarding the quality and quantity of melanin that gets produced.

Research indicates the iris color is usually light-blue or gray in most newborns; the iris acquires its definitive color later in life as pigmentation continues to accrue during the first 6 to 10 months.

Further, brown eyes are not always dominant to blue eyes, and parents who both have blue eyes can have a baby with brown eyes (or another color). This is because the genes that determine eye color are complex and multiple genes are involved.

Fetal eye movements can be detected at approximately 14 weeks and movement increases after 29 weeks. The relationship between eye movement and vision develops after birth, but fetal eye response to light has been reported to begin between 28 to 32 weeks.

Eye inactivity becomes more common after 36 weeks and is likely associated with a longer “quiet sleep” state.

There is great debate among researchers and HCPs about the vision status of newborns and infants, especially because it is very difficult to study and test. There does appear to be general agreement that normal newborns can see, but not very well and are far-sighted. However, they respond well to light and can fixate on points of contrast such as black and white, which improves significantly during the first year of life.

Pregnant women who have questions regarding their babies' eye development during pregnancy should talk to their HCP, or their infant's pediatrician after delivery.

Women should inquire about their MMR (measles, mumps, and rubella) vaccination status – ideally – prior to pregnancy. Rubella infection during early pregnancy is a major cause of abnormal development of the eyes/vision of infants.

Although this type of infection is very uncommon in the United States (due to vaccinations), it is recommended that women obtain a booster vaccination prior to pregnancy (not during) if needed. HCPs can check a woman's antibody status with a blood test. Women may also be vaccinated in the postpartum period if it is determined during pregnancy their antibodies are considered low (read more).

Vision Development (UNSW Australia (Embryology); Dr. Mark Hill) *Note that embryology begins Day 1 as the day of conception; therefore week 5 in embryology is week 7 of pregnancy.

Infant Vision (American Optometric Association)