Advanced Iris Quiz

Q1. Why does shining light in one eye normally constrict both pupils?

• Each optic nerve directly innervates both sphincter pupillae muscles
• Pretectal pathways project bilaterally to parasympathetic oculomotor nuclei
• Sympathetic fibers cross within the iris
• Aqueous humor transmits the light stimulus to the opposite eye

Q2. Why can an oculomotor nerve lesion produce a dilated pupil when parasympathetic fibers are affected?

• CN III normally activates the dilator pupillae
• The iris root detaches from the ciliary body
• Loss of parasympathetic sphincter pupillae input leaves dilation relatively unopposed
• The optic nerve becomes overactive

Q3. Why can interruption of the cervical sympathetic pathway cause miosis?

• The optic nerve stops detecting light
• Loss of sympathetic supply paralyzes the sphincter pupillae
• Loss of sympathetic supply reduces dilator pupillae activity
• The ciliary ganglion becomes hyperactive because of direct injury

Q4. Why is the iris root clinically vulnerable to traumatic separation?

• It contains the thickest part of the iris stroma
• It is fused firmly to the central cornea
• It is a thin peripheral attachment to the ciliary body
• It is attached directly to the optic nerve

Q5. How can forward bowing of the peripheral iris contribute to angle-closure glaucoma?

• It blocks the central retinal artery at the optic disc
• It prevents vitreous production
• It can obstruct aqueous access to the trabecular outflow pathway
• It closes the lacrimal puncta

Q6. Why can posterior synechiae interfere with normal aqueous humor flow?

• Adhesion of sclera to lens closes the optic canal
• Adhesion of iris to lens can obstruct flow through the pupil
• Adhesion of iris to cornea increases tear drainage
• Adhesion of retina to choroid blocks vitreous flow

Q7. Which embryologic origin is characteristic of the sphincter and dilator pupillae?

• Neuroectoderm of the optic cup
• Surface ectoderm of the lens placode
• Paraxial mesoderm only
• Endoderm of the foregut

Q8. Which optic cup layer contributes to the posterior pigmented epithelium of the iris?

• Pharyngeal endoderm
• Surface ectoderm
• Neuroectoderm of the optic cup
• Intermediate mesoderm

Q9. Why can inflammation of the iris produce photophobia and pain during pupillary movement?

• The cornea contracts whenever the pupil constricts
• Light causes movement of inflamed iris tissue during pupillary constriction
• The optic nerve contains the sphincter pupillae
• Light directly stimulates pain fibers in the retina

Q10. Which statement best integrates the anatomy and function of the iris?

• It is a vascular, pigmented, autonomically controlled diaphragm that regulates pupil size
• It is a neural layer containing rods and cones
• It is a transparent fibrous layer that provides most ocular refraction
• It is a posterior gel-filled chamber that supports the retina