An iris coloboma is caused by incomplete closure of the embryonic fissure and is usually located in which quadrant?

An iris coloboma is caused by incomplete closure of the embryonic fissure and is usually located in which quadrant?

• A. Inferior nasal
• B. Superior nasal
• C. Inferior temporal
• D. Superior temporal

Answer: (A)

The defect arises because the embryonic fissure, which runs along the inferonasal edge of the developing optic cup, fails to close. As a result, iris tissue in that region remains absent, producing a coloboma. Since the fissure is located inferonasally, the iris defect most commonly appears in the inferior nasal quadrant, often seen as a notch or keyhole-shaped pupil at the lower, nasal side. The other quadrants are less typical because closure occurs predominantly in that inferonasal area during development.

The defect arises because the embryonic fissure, which runs along the inferonasal edge of the developing optic cup, fails to close. As a result, iris tissue in that region remains absent, producing a coloboma. Since the fissure is located inferonasally, the iris defect most commonly appears in the inferior nasal quadrant, often seen as a notch or keyhole-shaped pupil at the lower, nasal side. The other quadrants are less typical because closure occurs predominantly in that inferonasal area during development.