The ciliary body
Describe the posterior pars plana
approximately 4mm wide - from the posterior pars plicata ending at the ora serrata. Ends at the ora serrata: the sharp junction where non-pigmented ciliary epithelium undergoes a transition to become the neural retina.
What is the blood supply of the ciliary body?
1- 2 long posterior ciliary arteries: arise from the opthalmic artery --> pierce through the sclera near the optic nerve head -> they travel forward in the choroid in a medial and lateral plane. Reaching the ciliary body they divide --> then anastomose with the anterior ciliary arteries = forming the major circle of the iris. 2- anterior ciliary arteries
What are the 3 functions of the ciliary body?
1- production of aqueous humour 2- accommodation 3- production of lens zonules, vitreal glycosaminoglycans, and vitreal collagen
Describe the anterior pars plicata
2 mm wide consists of 70 radially arranged folds known as the ciliary processes - where aqueous humor is produced. The tips are paler as a result of decreased pigmentation
Define the ciliary body
5-6mm ring of tissue that extends from the scleral spur anteriorly to the ora serrata posteriorly. Temporally it measures: 5.6-6.3mm nasally it measures: 4.6-5.2mm It is divided into 2 zones: Anterior pars plicata (corona ciliaris) Posterior pars plana
What is the parasympathetic nerve supply of the ciliary body?
Postganglionic fibers travel into the eye in the short ciliary nerve and they terminate as an extensive plexus in the ciliary muscle.
How does the ciliary muscle increase aqueous humor flow?
Since the ciliary muscles are attached to the scleral spur and with their tendons to the inner wall of canal of schlemm, contraction causes distention of the inter and intratrabecular spaces in the trabecular meshwork thus preventing collapse of schlems canal in periods of high pressure. this is the mode of action of miotic drugs such as pilocarpine - used to inc aqueous humor flow in patients with glaucoma.
Describe the role of the ciliary body in accommodation
The anterior 2/3 of the ciliary body are occupied with the ciliary muscle. The ciliary muscle, suspensory ligament, and the elastic nature of the lens functions to alter the refractive power of the lens. Histology: outer longitudinal ciliary muscle middle radial ciliary muscle inner circular ciliary muscle During accommodation: the ciliary body undergoes forward and inward shift, which lessens the tension of the suspensory ligaments = increase the refractive power of the lens
How does the ciliary body produce aqueous humor?
The ciliary body contains ciliary processes which are finger like projections of loose vascular connective tissue covered by bilaminar columnar epithelium. Na is actively secreted from the inner non-pigmented epithelium, followed by passive flow of: Cl, HCo3, and water.
What is the role of the pars plana?
The pars plana plays a role in secretion of zonular fibers, and extracellular vitreal components such as collagen and hyaluronic acid
What is the sympathetic nerve supply of the ciliary body?
The preganglionic nerve fibers are situated in the lateral grey horn of the 1st thoracic segment of the spinal cord. Postganglionic fibers leave as the internal carotid nerve and plexus. these fibers either enter directly into the orbit, or they join the opthalmic division of the trigeminal nerve and its main branch: the nasocilliary nerve. Nerves then pass either uninterrupted to the ciliary ganglion or to the retrobulbar plexus behind the eye. They leave as short ciliary nerves to the blood vessels of the eye and the ciliary body. Sympathethic action is mediated by NA on 2 subclasses of receptors: a1 and b1 adrenoceptors, which are inhibitory.