WEEK 5: Iris, Pupil, Ciliary Body

Question 1

List the layers of the iris and be able to describe the function of the structures in each layer

Answer 1

Posterior Iris Epithelium, - more pigmented, cells are joined by gap junctions and desmosomes, from pupillary ruff Anterior Iris Epithelium - cells extended radially into the stroma to from the dillator muscle Spinchter Muscle - MIOSIS (constriction of the pupil) Iris Stroma - highly vascular connective tissue, loose structure with openings into the anterior surface allow fluid to move in and out of the stroma during dilation and contraction Anterior border layer - The surface layer of the iris, the anterior border layer, is a thin condensation of the stroma. It is composed of fibroblasts and pigmented melanocytes.

Question 2

Spinchter pupillae Muscle function and innervation?

Answer 2

Action is MIOSIS (pupil constriction) in response to light, during convergence and during sleep Innervated by the parasympathetic neurones with cell bodies in the edinger - westphal nucleas of CN3 axons synapse with postganglionic cell bodies in the ciliary ganglia located at the back on the orbit

Question 3

posterior synechia

Answer 3

the posterior iris surface is adherent to the anterior lens surface. If a posterior synechia involves a large portion of the pupillary margin, aqueous will accumulate in the posterior chamber. Continual production of aqueous causes the pressure in the posterior chamber to increase, which in turn causes the iris to bow forward in a configuration called iris bombé. This can push the peripheral iris against the trabecular meshwork, setting the stage for a dramatic increase of intraocular pressure (IOP). A drug-induced dilation usually will break a posterior synechia. The break usually occurs between the epithelial layers, leaving remnants of the posterior epithelium on the anterior surface of the len

Question 4

Anterior synechia

Answer 4

the anterior iris surface is adherent to the corneal endothelium or the trabecular meshwork. An anterior synechia usually occurs at the iris periphery and involves the meshwork. It is called a peripheral anterior synechia (PAS). Aqueous outflow is impeded by a PAS, causing an increase in IOP if the adhesion occupies a considerable amount of the trabecular meshwork.

Question 5

Anterior Epithelial Layer

Answer 5

Cells of this layer are joined by tight and gap junctions, extend basal processes 50 microns radially into the stroma forming the dilator pupillae muscle

Question 6

dilator pupillae muscle

Answer 6

Composed of myoepithelial cells joined by gap junctions arranged radially causes pupil to dilate (enlarge, when its dark, excitement or fear) innervated by the sympathetic neurons, cell bodies located in the superior cervical ganglia (just outside the spinal cord)

Question 7

posterior surface of the iris

Answer 7

The posterior surface of the iris is fairly smooth, but when viewed with magnification, small circular furrows are evident near the pupil. Radial contraction furrows (of Schwalbe) are located in the pupillary zone, and the deeper structural furrows (of Schwalbe) run throughout the ciliary zone and continue into the ciliary body as the valleys between the ciliary processes.1–3 Also found on the posterior surface are circular contraction folds similar to those seen on the anterior surface.

Question 8

What cause closed angle glaucoma - Pigment Dispersion Syndrome

Answer 8

pigment granules are shed from the posterior iris surface and are dispersed into the anterior chamber. They can be deposited on the iris, lens, or corneal endothelium or in the trabecular meshwork, where they might compromise aqueous outflow.4 Significant pigment loss will be evident on transillumination of the iris when the red fundus reflex shows through in the depigmented areas (Figure 3-10).

Question 9

Label each letter

Answer 9

A - Pupillary portion

B - Ciliary portion

C - Fuchs’ crypts

D - pupillary ruff

E - The iris vessels are shown beginning at the major arterial circle in the ciliary body

F - Radial branches of the arteries and veins extend toward the pupillary region. The arteries form the incomplete minor arterial circle

G - sphincter muscle

H - the radial processes of the dilator muscle

I - radial contraction furrows

J - the structural folds of Schwalbe

K - The pars plicata of the ciliary body

Question 10

Functions of the ciliary body

Answer 10

• production of the aqueous humor
• maintenance of intraocular pressure
• involved in accommodation
• component of the blood - aqueous barrier
• production of crystalline lens zonules