Module D-05 Flashcards
The sclera is continuous with________
Dura that covers the optic nerve
_________ is the outer layer and ________ is the inner layer of the eye
Sclera; Retina
what 2 fluids are found in the eye
1) Aqueous humour ( anterior and posterior chambers)
2) Vitreous Humor ( rest of the eye, more viscous)
Light enters the eye through the _______
pupil
__________ and _________ take part in accomodation
The ciliary muscle and the zonule fibers (suspensory ligaments)
What is the optic disk(papilla) ?
- is the part of the retina overlying the lamina cribrosa. It
has a diameter of about 2 mm, is devoid of photoreceptors and represents the blind spot. - contains axons of retinal ganglion cells, the output elements of the retina
- blood vessels converge here and exit and enter the eye
What is the blind spot?
- a region inside the boundaries of the visual field, where we don’t receive visual information
- caused by optic disk
What is the Fovea?
- the location of the highest visual acuity,
- highest density of cones.
- It has a diameter of about 1.5 mm.
- Its center (diameter about 0.4 mm), which is the point of fixation, contains no rods, but only cones
- no blood vessels found here
The back of the eyeball is called the_____________
Ocular Fundus
What is the Macula?
region of high visual acuity. It has a diameter of
about 5 mm)
around the fovea, no blood vessels here
What is the unit of measurement for refractive power?
Diopters
What part of the human eye makes the greatest contribution to the refractive power of the eye?
Cornea - interface btw air and tissue
42 Diopters
What is the function of the lens?
modulation of refractive power (refractive plasticity) during accommodation
How does the lens accommodate during far vision?
the ciliary muscle, which is a circularmuscle around the lens, is relaxed => tightening of the suspensory ligaments
(zonule fibers) => pull on the lenses’ equator => flattening lens => minimizing its refractive power to 13D
How does the lens accommodate during near vision?
constriction of the circular ciliary muscle => reduces its’ diameter => relaxes the suspensory ligaments => The lens follows its own elasticity and gets a more rounded (more convex) shape => increases its refractive power to
about 26 D
What fibers activate Ciliary muscle?
Parasympathetic fibers of ANS
Where are the cell bodies of the parasympathetic fibers for primary (preganglionic)Efferents for ciliary muscle located?
Edinger Westphal nucleus
in which CN do the parasympathetic EFFERENT fibers of the eye run?
CN III
Where do the preganglionic parasympathetic fibers synapse in which ganglion?
Ciliary ganglion
postganglionic (second order) fibers form the ciliary ganglion emerge as
short ciliary nerves which then innervate the ciliary muscle
what is refractive plasticity?
The variability of the refractive power of the lens between far vision (13 D) and near vision (26 D)
What is presbyopia
the lens loses its elasticity during aging, thereby reducing the ability to focus on near objects
What is visual acuity?
it is visual two point discrimination
When is visual acuity high?
When 2 point discrimination threshold is low ,ie there is high spatial resolution
What is visual acuity dependant on?
1) density of photoreceptors
2) If optical apparatus of eye is properly functioning to accomodate
Which part of ANS is responsible for pupillary dilation?
Sympathetic nervous system
Which part of ANS is responsible for pupillary constriction?
Parasympathetic nervous system
Which muscle is responsible for pupillary dilation(miosis)?
dilator pupilae muscle
Describe the path the sympathetic fibers take to the pupillary dilator muscle.
Preganglionic sympathetic fibers originate in the intermediolateral cell column in the upper thoracic region of the spinal cord. They exit the spinal cord through the anterior (ventral)
roots and enter the sympathetic chain, where they ascend to the superior cervical
ganglion, where they form synapses on second order neurons. The postganglionic fibers follow the path of the internal carotid artery, the ophthalmic artery and its terminal branches until they reach the iris, where they innervate the radial smooth muscle fibers of the dilator pupilae muscle
Describe the path the sympathetic fibers take to the pupillary constrictor muscle.
Preganglionic parasympathetic fibers originate again in the Edinger-Westphal
nucleus of CN III. They synapse in the ciliary ganglion from where the short
ciliary nerves originate.
Which muscle is responsible for pupillary constriction(mydriasis)?
constrictor pupilae muscle
Define emmetropia
the normal refractive condition of the eye, in which the rays of light are accurately focused on the retina
Define myopia
the focus of parallel light rays, as in far vision, is anterior to the photosensitive elements of
the retinal photoreceptors
What defect in myopia?
The refractive power of the optical apparatus of the eye is too strong or the eye ball is too long
Define hyperopia
the focus of parallel light rays would be beyond the retina, in case the ciliary muscle is relaxed and the lens has its lowest
refractive power
What defect in hyperopia?
The refractive power of the optical apparatus of the eye is too weak or the eye ball is too short
What is Papilledema?
Optic Disk Edema
What causes Papilledema?
increased intracranial pressure compromises the venous drainage of the eye, leading to a dilation of the retinal veins. As a consequence, the optic disc is pushed forward and the disk appears white
What is a detached retina?
retina separates from the retinal pigment epithelium and the areas detached loose their function
symptms of age related macular degeneration
- poor central vision
- loss of vision in individuals 60 years of age
What causes diabetic retinopathy?
blood supply dysfunction including reduction of permeability of basal membranes of capillary endothelial cells and blood vessel damage (aneurysms)
