Orbit II Flashcards
What are the three layers of the eye?
SCR
S: sclera
C: Choroid
R: Retina
Describe glaucoma. When does it occur? What can cause it? What can result
most common cause of blindness.
- increased intraocular pressure which compresses retina, optic nerve & blood vessels.
- occurs when the production of aqueous humor exceeds the ability of the eye to drain this fluid.
- It can be caused by a decreased outflow of aqueous humor through the canal of Schlemm or an increase in aqueous humor production.
Damage to the retina (especially the optic disc), sometimes causing severe pain, can result. If increased intraocular pressure is severe and/or chronic this may result in eventual blindness. Symptoms include blurred vision, or halos around bright objects.
Describe the iris.
What innervates the constrictor pupillae?
What innervates the dilator pupillae muscles?
most anterior part of the uveal layer of the eye. It arises from the ciliary body and forms an adjustable diaphragm in front of the lens, thus dividing the anterior compartment of the eye into posterior and anterior chambers which communicate via the pupil.
constrictor- parasympathetic nervous system
dilator - sympathetic nervous system
What innervates the ciliary muscle. What results?
parasympathetic system ONLY.
Causes lens to thicken
For near vision, the ciliary muscle contracts, decreasing its overall diameter and tension on the zonule fibers, and the lens assumes a more globular (round) shape. This mechanism permits fine focusing of images onto the retina
What are the 3 types of cells in the retina?
1st layer ganglion
2nd layer interneurons
3rd layer photoreceptors (rods and cones are photoreceptors)
Describe rods and cones.
The photoreceptors are modified dendrites of two types of cells, rods and cones.
The rods are located primarily in the periphery and sensitive to movement and scattered light (low light levels).
The cones are located near the center of the eye (fovea) and are sensitive to colors (chiefly red, green and blue) and bright light. The cones offer the highest visual acuity during daylight hours.
The rod and cone receptors synapse onto a complex system of primary integrating neurons (interneurons, bipolar cells and ganglion cells).
Are cones or rods at the fovea?
CONES ONLY. no rods
What is the optic nerve invested by?
the optic nerve is invested by the meninges. The dura mater becomes continuous with its developmental equivalent, the sclera, while the pia-arachnoid continues into the eye as the uveal layer.
Describe the optic nerve.
Afferent nerve fibers from the retina converge to form the optic nerve which leaves the eye via numerous perforations through a part of the sclera known as the lamina cribrosa. The retina overlying the lamina cribrosa, the optic papilla (optic disc) is devoid of photoreceptors and is thus referred to as the blind spot of the eye.
Describe the arteries of the retina.
They will block or absorb light.
Central retinal artery
Where is aqueous humor made and reabsorbed?
What is it?
Why is it important?
ciliary processes are responsible for the continuous production of aqueous humor, which circulates into the anterior chamber via the pupil.
Aqueous humor is continuously reabsorbed into the canal of Schlemm at the angle of the anterior chamber.
Aqueous humor is a clear, watery fluid somewhat similar in composition to CSF and hypotonic with respect to plasma.
Balanced rates of secretion and reabsorption of aqueous humor result in the maintenance of a constant intra-ocular pressure of about 15mm of mercury which stabilizes the lens and cornea. The flow of aqueous humor also provides for a continuous exchange of metabolites to the cells of the avascular cornea and lens.
What would happen if there was increased CSF pressure? What structure would collapse? What would result
Increased CSF pressure is transmitted through the optic nerve. The dural sheath contains the increased pressure, and compresses the optic nerve and blood vessels within. The central vein of the retina is the first to collapse, due to its low pressure (~14 mmHg), resulting in the papilledema observed.
Describe the blood supply of the eye.
The blood supply of the eye is derived from the ophthalmic artery via two separate systems, the retinal and uveal systems. The retina is supplied by a central artery (of the retina) passing in the substance of the optic nerve. This central artery of the retina branches from the center of the optic papilla to give rise to end arteries which radiate over the surface of the retina.
the uvea is supplied by branches of the ophthalmic artery which perforate the sclera as the ciliary arteries (long & short).
Describe photoreception of the eye.
The eye is a highly specialized organ of photoreception, a process which involves the conversion of different quanta of light energy into action potentials by the ganglion cells, whose axons for the optic nerve. All of the neural cells are located in the inner layer of the eye, called the retina. The remaining structures of the eye serve to support the retina or to focus images of the visual world upon the retina.
Describe the anatomical differences between the sclera and cornea.
The outer sclera consists of dense, fibro-elastic connective tissue. The sclera is the posterior 5/6ths of the eye, and is opaque. It provides insertion for the extra-ocular muscles. The sclera varies in thickness, being thickest posteriorly and thinnest at the coronal equator of the globe.
The anterior one-sixth, the cornea, is transparent and has a smaller radius of curvature than the sclera. The cornea is the principal refracting medium of the eye and roughly focuses an image on to the retina; the focusing power of the cornea depends mainly on the radius of curvature of its external surface. The corneo-scleral junction is known as the limbus and is marked internally and externally by a shallow depression.
