Vision Flashcards
What is the path through which tears travel from the lacrimal gland to the nostril (lacrimal apparatus)?
- lacrimal gland
- ducts
- lacrimal punctum
- lacrimal canaliculus
- lacrimal sac
- nasolacrimal duct
- inferior meatus of nasal cavity
- nostril
What are the three functions of tears?
- Cleanse and lubricate the eye surface
- Deliver oxygen and nutrients to the conjunctiva.
- Protect from infection (contain lysozyme and antibodies).
What are the three layers or tunics of the eyeball, starting from the outermost to the inner layer?
Fibrous, vascular, and neural tunics
Name the two structures of the fibrous tunic.
The sclera (white of the eye) and cornea.
What are the three structures composing the vascular tunic?
Iris, ciliary body, and choroid.
What structure of the vascular tunic is a muscular ring that secretes aqueous humor?
Ciliary body.
What is the function of the choroid?
It contains high density of blood vessels, provides nutrients and waste removal to eye structures.
Where is the retina found?
In the neural tunic, lining the back of the eye.
(a) What is the cornea? (b) what function does it serve? (c) Is it capable of regeneration after sustaining damage?
(a) A transparent membrane that protects the eye (b) It allows light to enter the eye (c) Yes, it contains stem cells.
Which eye structures are responsible for light refraction?
The cornea and lends bend (refract) light and focus it on the retina.
Are images projected onto the retina in an inverted or non-inverted manner?
Images are projected as 2-D, in an inverted and reversed manner.
Describe the iris.
The iris is an adjustable diaphragm, found between the cornea and lens, that controls pupil diameter, thus the amount of light entering.
(a) What is the pupil (b) Which two muscles of the iris control pupil diameter? (c) Which one is closest to the pupil?
(a) ) Aperture through which light enters the eye. (b) Sphincter pupillae and dilator pupillae. (c) The dilator pupillae.
Which muscle of the iris receives sympathetic input, and which one receives parasympathetic innervation?
The dilator pupillae receives sympathetic input while the sphincter pupillae recieves parasympathetic innervation.
What response does the pupil have for close-up vision, and why?
Pupil constriction (through stimulation of the sphincter pupillae by the parasympathetic nervous system ) to increase the depth of focus and decrease spherical aberration.
What is spherical aberration?
It is an optical phenomenon that occurs when light rays passing through the periphery of a lens or optical system focus at a different point than those passing through the center. This can result in a blurring or distortion of the image.
What does the term “focal point” refer to?
The focal point refers to the specific point on the retina where light rays converge after being refracted by the cornea and lens.
Describe the lens.
A clear, biconvex, and flexible structure structure suspended in the eye by suspensory ligaments. Function include light refraction and adjustment of focal length.
What muscle controls the lens shape?
The ciliary muscles.
(a) Where is the aqueous humor produced and drained? (b) What function does it serve?
It is produced by the ciliary body and flows out through the trabecular meshwork in the drainage angle. (b) Supplies nutrients to the avascular structures of the eye, cornea, and lens, and maintains intraocular pressure (IOP).
How does the lens accommodate to close-up vision?
Parasympatheic stimulation causes contraction of ciliary muscles and relaxation of the zonular fibers resulting in the bulging of the lens.
What is emmetropia?
Emmetropia means normal eye. An emmetropic eye sees distant objects clearly, without using accommodation.
How is eye convergence produced?
By contraction of both medial rectus muscles which orients the visual axis of each eye toward the object for close-range vision
What are the 3 processes involved in the adjustment to close-range vision?
Pupillary constriction, lens thickening (accommodation), and inward rotation of the eyes (eye convergence)
What liquid fills the globe of the eyeball, and what is its function?
Vitreous humor. It maintains the round shape of the eye and help with vision clarity (it is clear so light can pass through)
What is the overall function of the retina?
It receives the image that the cornea focuses through the lens and transforms this image into electrical impulses that are carried by the optic nerve to the brain
What is macula (yellow spot) and the fovea?
In the macula there is a concentration of cone cells. These cells are responsible for color vision, sharp visual acuity and central vision. The highest concentration of cones is in the fovea, a tiny area in the center of the macula.
What are the six types of cells found in the neural layer of the retina involved in vision?
Photoreceptors (rods and cones), bipolar cells, ganglion cells, amacrine cells, and horizontal cells.
Which cells do photoreceptors contact and transmit the electrical signals?
Bipolar cells.
Sequence the light path from photoreceptor cells to the optic nerve (CN II).
- Photoreceptors
- Bipolar cells
- Ganglion cells
What is the definition of phototransduction?
The conversion of light energy to electrical signals by photoreceptors.
Define rhodopsin and identify ist primary components, along with its location.
Rhodopsin is a light-sensitive protein found in the disc membranes of the rod cells. Its main components include a protein called opsin and a light-absorbing molecule called retinal.
Are Na+ channels opened or closed at night, and why? Which molecule stimulates their opening, and is it available at night?
They are opened since there is cGMP available, the molecule that activate the sodium channels.
What are the three types of cones?
Short wavelength cones (blue), medium wavelength cones (green), long wavelength cones (red).
Which neurotransmitter is released by the inner segment of the rods, and to which neuron?
Glutamate, to bipolar cells,
What is the definition of “bleaching” in the context of vision?
It refers to the temporary loss of sensitivity to light in rods, where trans retinal needs to be regenerated to 11-cis retinal
Describe the visual projection pathway.
- optic nerve
- optic chiasm
- optict tract
- thalamus (lateral geniculate nucleus)
- occipital lobe
What is the optic chiasm?
It is the point where the optic nerves from both eyes partially cross in the brain, allowing each hemisphere to receive visual information from both the left and right visual fields.
