Iris Flashcards

Study the anatomy of the iris, including its layers, muscles, nerve supply, blood vessels, pupillary reflexes, and anatomical landmarks.

Card 1 of 30Question

What is the iris?

The colored, contractile, anterior portion of the vascular tunic (uvea) of the eyeball.

In This Section

1. What is the iris?

The colored, contractile, anterior portion of the vascular tunic (uvea) of the eyeball.

2. Where is the iris located within the eye?

Posterior to the cornea and anterior to the lens, separating the anterior and posterior chambers.

3. What is the central opening of the iris called?

The pupil.

4. What is the primary function of the iris?

To regulate the amount of light entering the eye by adjusting pupil diameter.

5. What are the two principal muscles of the iris?

The sphincter pupillae and dilator pupillae muscles.

6. Where is the sphincter pupillae muscle located?

In the iris stroma near the pupillary margin, forming a circular band of smooth muscle.

7. What action does the sphincter pupillae muscle perform?

It constricts the pupil, producing miosis.

8. What type of autonomic innervation controls the sphincter pupillae?

Parasympathetic innervation.

9. Which cranial nerve carries preganglionic parasympathetic fibers for pupillary constriction?

The oculomotor nerve (cranial nerve III).

10. Where do parasympathetic fibers supplying the sphincter pupillae synapse?

In the ciliary ganglion.

11. Which nerves carry postganglionic parasympathetic fibers to the sphincter pupillae?

The short ciliary nerves.

12. Where is the dilator pupillae muscle located?

In the anterior part of the iris pigment epithelium, with radially oriented contractile processes.

13. What action does the dilator pupillae muscle perform?

It enlarges the pupil, producing mydriasis.

14. What type of autonomic innervation controls the dilator pupillae?

Sympathetic innervation.

15. Which sympathetic ganglion supplies postganglionic fibers to the dilator pupillae?

The superior cervical ganglion.

16. Which nerves carry most postganglionic sympathetic fibers to the dilator pupillae?

The long ciliary nerves, with some fibers traveling through the short ciliary nerves.

17. What are the principal histological components of the iris?

The anterior border layer, vascular stroma, and posterior double-layered epithelium.

18. What structures are found within the iris stroma?

Melanocytes, fibroblasts, collagen fibers, blood vessels, nerves, and the sphincter pupillae.

19. What is the function of the heavily pigmented posterior iris epithelium?

To absorb stray light and prevent its transmission through the iris.

20. What primarily determines the visible color of the iris?

The amount and distribution of melanin in the anterior border layer and stroma.

21. What is the iris collarette?

An irregular circular ridge marking the boundary between the pupillary and ciliary zones of the iris.

22. What are the two anatomical zones of the iris?

The inner pupillary zone and outer ciliary zone.

23. Where does the peripheral root of the iris attach?

To the anterior region of the ciliary body.

24. What is the major arterial source of the iris?

The major arterial circle of the iris, formed mainly by the long posterior ciliary and anterior ciliary arteries.

25. Through which vessels does venous blood from the iris ultimately drain?

Primarily through the ciliary body venous plexuses into the vortex veins.

26. Which nerve forms the afferent limb of the pupillary light reflex?

The optic nerve (cranial nerve II).

27. What is the consensual pupillary light reflex?

Constriction of the opposite pupil when light is directed into one eye.

28. What happens to the pupil during the near response?

It constricts as part of the near response, together with accommodation and ocular convergence.

29. What pupillary abnormality is associated with interruption of the ocular sympathetic pathway?

Miosis, commonly occurring as part of Horner syndrome.

30. What is an iris coloboma?

A congenital defect of the iris, typically inferonasal, caused by incomplete closure of the embryonic optic fissure.