During which weeks does optic fissure closure normally occur?

• A. Weeks 5–7
• B. Weeks 3–5
• C. Weeks 7–9
• D. Weeks 1–3

Answer: (A)

The timing of optic fissure closure is during weeks 5–7 of gestation. In early eye development, the optic fissure remains open to allow the hyaloid vessels to reach the inside of the eye, and then the margins fuse to close the fissure, typically completing around week 7. This closure is essential to form a continuous ocular structure; if it occurs too early, too late, or incompletely, a coloboma can result in defects of the iris, retina, choroid, or optic nerve. That makes weeks 5–7 the normal window for optic fissure closure. Weeks 3–5 would be too early for complete closure, weeks 7–9 would be after closure is normally finished, and weeks 1–3 are far too early.