The anterior surface of the iris is divided into two zones:

Pupillary zone - the inner, relatively small and flat portion that surrounds the pupil and features folds; it extends from the pupillary margin to the collarette;
Ciliary zone - the large outer portion that extends from the collarette to the ciliary margin.

Both zones meet at the collarette, a slightly raised, circular, wavy ridge that represents the thickest part of the iris. It marks the former attachment site of the pupillary membrane (which typically regresses after birth). It is also the site where the sphincter and dilator pupillae muscles overlap. The collarette is located approximately 0.06 - 0.08 inches (1.5 - 2 millimeters) from the pupillary margin.

The ciliary zone contains radial streaks, which are structural lines formed by radial iris vessels and connective tissue. These streaks appear relatively straight when the pupil is constricted and become more wavy during its dilation.

Between the radial streaks are depressions known as crypts. These structures mark the sites where the superficial layer of the iris is absent. They are found in two locations - near the collarette (central crypts) and in the periphery near the root (peripheral crypts). Those present near the collarette are relatively large and known as Fuch's crypts.

The ciliary zone shows several faint concentric lines that run parallel to the colarette in the peripheral part of the ciliary zone, closer to the ciliary margin. These are contraction furrows. They are formed by the folding of the iris stroma during pupillary movements, and they become more prominent during the dilation of the pupil.

Additionally, the peripheral portion of the anterior iris may present with small, round, white or yellowish deposits called the Wölfflin nodules. They are benign, elevated collagen accumulations found in approximately 10-25% of the general population. These structures are considered a normal anatomical variant and are more commonly observed in lighter-colored eyes. They do not affect vision or ocular function.

And finally, the anterior surface of the iris may display small, flat, dark brown or black pigmented spots - the iris freckles. They are usually found in the ciliary zone and often appear in clusters. These structures are caused by a harmless accumulation of melanin, and they are usually benign. They are superficial and can be unilateral or bilateral. They do not affect vision or require treatment.

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Anterior surface of iris