Congenital coloboma (absence of tissue) of iris (Fig.
7.6), ciliary body and choroid (Fig. 7.7) may be seen
in association or independently. Coloboma may be
typical or atypical.
Typical coloboma is seen in the inferonasal
quadrant and occurs due to defective closure of
the embryonic fissure.
Atypical coloboma is occasionally found in other
positions.
Complete coloboma extends from pupil to the optic
nerve, with a sector-shaped gap occupying about
one-eighth of the circumference of the retina, choroid,
ciliary body, iris, and causing a corresponding
indentation of the lens where the zonular fibres are
missing.
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