Flashcards in Orbits II Deck (49):
The three functional layers of the eye
Sclera, Choroid, Retina
The section of the eye with the steepest curvature
The anterior 1/6th where the cornea is
The primary refractor of light in the eye? The secondary refractor?
Secondary: Lens- for up close vision
Which part of the eye handles refracting light for everything 10-12 feet away and beyond?
Which part of the eye handles refracting light for things up close?
What fills the choroid layer?
Blood vessels and nerve fibers
Space between the iris and the lens
Aka the vitreous body. This is where the vitreous humor is located. It helps absorb stray photons so has a little bit of pigment associated with it.
Area filled with blood vessels, visible if the Sclera is peeled off. Busy area between Corneal Limbus and the Ora Serrata.
Where are the ciliary muscles located? What shape do these muscles have and how does that affect their function?
In the Uveal layer. Most of them are circumferential so when they contract, they shrink thereby releasing tension on the zonular fibers, allowing the lens to "get fat". When they are relaxed, they expand, stretching the lens out flat.
Ciliary processes vs Ciliary Body
Process: Double epithelial layer which creates aqueous humor.
Body: Everything, including the muscle
Thin watery substance which carries oxygen and proteins to keep the Cornea healthy. Stored in the anterior chamber.
Pressure from what, helps to hold the shape of the cornea?
From the aqueous humor
Why and how is aqueous humor drained?
There is more aqueous humor being produced then is needed at a given time. Overproduction without drainage will cause an increase in pressure, damaging the Cornea.
It is drained via the Canal of Schlemm, in the limbus area where the cornea meets the sclera. It is also known as the scleral-venous sinus.
What sits on top of the Canal of Schlemm?
The trabecular network. This means that aqueous humor must be actively pumped into the Canal of Schlemm.
What causes Glaucoma?
Caused by a blockage of the drain or disabling of the pumps, needed to drain aqueous humor. Leads to the pressure bulging backwards onto the vitreous humor and compressing the neural retina in the back of the eye, leading to blindness.
Two types of Glaucoma
Angle closure (iris is pushed over the trabeculi, blocking the Canal of Schlemm).
Open Angle (Aqueous does not drain through opening due to pump not working or some other blockage)
Bright light causes what type of nervous system stimulation?
Parasympathetic (causing pupil constriction)
Difference between the sympathetic and parasympathetic muscle shape in the eye.
Parasympathetic muscles are circular, allowing them to constrict the pupil size.
Sympathetic muscles are radially oriented allowing them to dilate the pupil size.
Meridonal fibers of the Ciliary Muscle
Ensure that when the circular ciliary fibers contract they only affect the lens and don't pinch in and change the shape of the cornea.
Connect the ciliary muscle to the lens. Insert into glycoprotein capsule which surrounds the lens (we don't want to insert directly into the lens).
Nuclei for the lens are located where?
In the periphery of the lens cells, so as not to interfere with the light refraction. The older one gets, the fewer of these nuclei remain.
Ciliary muscle is innervated only by...
Parasympathetic nervous system
Why do older folks need to where reading glasses?
As you get older, the lenses lose elasticity, so there is more trouble focusing on objects that are close to you-- called presbyopia.
3 Distinct Layers of the Retina
Ganglian Cell Layer, Internuclear Layer (cell bodies of all of the interneurons), Photoreceptor Layer
Blood vessels which run through the neuro retina
There are none. All the needed vessels sit on the top and feed the inner limiting membrane which then feeds Muller cells. The Muller cells then transport the nutrients to the neuronal cells.
The supporting cells of the neurons in the retina. Help to create and maintain a favorable microenvironment , fill in empty spaces and provide metabolic support. The span the full length of the retina, to the outer limiting membrane (but not past the photoreceptor layer).
Are there more rods or cones in the photoreceptor layer?
Lots of rods, very few cones
What part of the eye has all cones and no rods?
Most likely location to detach a retina.
Between the pigmented epithelium and the photoreceptor, because they have a very weak attachment.
Losing that blood supply from the epithelium will kill the photoreceptors, so there is a 24 hour window or so to fix it.
3 main differences between a rod and a cone
(1) Rods have small invaginations which form intramembranous discs (increases surfaces area for the protein which converts light into action potentials)
(2) Shape: Rods are long, Cones are stubby and actually coned shaped
(3) Cone has a very wide foot at the end of its synaptic zone (synaptic bouton). The Rod synaptic bouton is smaller.
Main differences in Rod and Cone function
Rods: Made for poor light so very sensitive (night vision); no differences in color; good at detecting motion; usually in periphery of retina
Cones: Made for bright light; color transduction so many types of photopigment
Where are the action potentials in Rods and Cones?
There are NO action potentials in the photoreceptors (rods or cones) or any of the interneurons. The first action potentials will be in the ganglion cell.
Fewest number of neurons to get out of the retina
THREE (photoreceptor cell, interneuron, ganglion cell)
Function of the Interneurons
To adjust the information coming in from rods/cones, so that the ganglion cells have a fairly even, constant output. (That is the delay in sight which occurs when you enter a very bright or very dark room).
Area directly in line with pupil in which everything except for photoreceptors, has been pushed out to the sides. This allows light to go directly to photoreceptors. There are only cones here. IT IS ALSO AVASCULAR, TO PREVENT THE BLOOD VESSELS FROM GETTING IN THE WAY. This avascular area is known as the macula.
Exist to compensate for the fact that light must travel through all of the layers of the eye in order to reach the photoreceptors. This could potential disrupt the incoming information.
Where does information go from the ganglion cells?
The optic disc (which is devoid of photo receptors) , and then the optic nerve
What is the name of the part of the sclera where the optic nerve exits?
The Lamina Cribrosa
The blind spot of the eye
The Optic Disc (retina overlying the lamina cribrosa) because there are no photoreceptors here.
It is the medial portion (or nasal portion) of the retina.
Why does the optic nerve triple is size after leaving the eye?
Myelin sheath, so that the messages are passed very swiftly.
How does the blood supply enter the eye
Central artery and vein of the retina (branches of ophthalmic), pierce the optic nerve and follow it into/ out of the back of the eye.
Effect that increasing intracranial pressure can have on blood supply in eye?
Will squish the central vein of the retina and causes flood vessels in the eye to dilate (because blood can't flow out of the eye). This bulging is called papilledema.
The ciliary processes are primarily responsible for which function in the eye?
Production of aqueous humor
Where is aqueous humor found?
Anterior and Posterior chambers of the eye
Clouding of the lens results in...
Name the layers which ensheath the Optic Nerve, in order.
Meningeal Dura, Arachnoid membrane, and Pia Mater
What structures and vessels are associated with the cavernous sinus?
There are one of these sinuses on either side of the pituitary gland.
The following run along the lateral wall of the sinus:
Abducens nerve runs through the middle of the nerve along with the internal carotid artery
Optic nerve lies just above and outside the sinus
The duct of the lacrimal gland open into the...
Superior fornix of the conjunctiva