Special Senses: Vision Flashcards
What is another name for the eyeball?
Bulbus oculi
State 3 functions of the eyelids
- Protection
- Cutoff light for sleep
- Lubrication when blinking
State 4 contents of the palpabrae
- Maeibomian glands + other Sebaceous glands
- Cilia
- Lacrimal gland
- Conjuctiva
Give the 2 parts of the conjuctiva.
Bulbous portion covers the eye
Palberal portion lines palpabrae inner surfaces
What are the functions of tears?
- Protection from infection
2. Keep conjuctiva moist
Contents of tears include _______ which kill bacteria.
Lysozymes
Which nerve controls the secretion of tears?
CN VII (Facial nerve) parasympathetic fibers
The wall of the eye ball has
a) 4 layers
b) 3 layers
c) 5 layers
d) 2 layers
b) 3 layers; outer, middle, and inner
The middle layer of the eyeball wall is also called
a) Tunica Medialis
b) Tunica Vastalis
c) Tunica Media
d) Tunica Medius
c) Tunica media
What part of the eye acts like the diaphragm of a camera?
The iris
Name the 3 layers of tears. Give their functions and what structure secretes each layer
- Lipid layer - Sebaceous glands
- lubrication
- prevents overflow
- prevents evaporation
- prevents air from entering - Aqueous layer - Lacrimal gland
- hydration
- acts as buffer to changes in pH - Mucin layer - Conjuctival goblet cells
- lysozymes and antibodies for protection
Differentiate between intrinsic and extrinsic muscles of the eye.
- Intrinsic are smooth muscles. Extrinsic are skeletal muscles
- Intrinsic are innervated by autonomic fibers. Extrinsic innervated by somatic fibers.
List the extrinsic muscles of the eye as well as their innervations.
*SIMI Loves Slurping OATs.
Superior rectus Inferior rectus Medial rectus Inferior oblique (all innervated by cranial Nerve III - Oculomotor nerve)
Lateral rectus (innervated by cranial nerve VI - Abducens nerve) Superior oblique (innervated by cranial nerve IV - Trochlear nerve)
Give the 10 layers of the retina and their features.
FROM OUT GOING INWARDS
- Pigment epithelium (single layer of epithelial cells)
- Photoreceptive area (contains inner and outer segments of rods and cones)
- Outer limiting membrane (where inner segments connect to cell bodies of rods and cones)
- Outer nuclear layer (contains cell bodies of rods and cones)
- Outer plexiform layer (where axons of rods and cones synapse with dendrite of bipolar and amacrine cells)
- Inner nuclear layer (has cell bodies of bipolar cells, amacrine cells, and Muller cells)
- Inner plexiform layer (synapse between axons of bipolar and amacrine cells with dendrites of Ganglionic cells)
- Ganglionic layer (cell bodies of ganglionic cells)
- Nerve fiber layer (where axons of ganglionic cells form optic nerve
- Inner limiting membrane (made of only Muller fibers)
Major components of vitreous humor.
Albumin and Hyaluronic acid
Properties of aqueous humor
- 98.7% water
- 1.3% solids (organic and inorganic)
- alkaline pH (7.5)
- Refractory index - 1.34
Aqueous humor formation
Diffusion of plasma by ciliary processes’ capillary network
The interface where the greatest refraction occurs is?
Air to cornea transition because has largest refraction index change
Most of the refraction (80%) occurs in the …
Cornea
Enumerate drainage of aqueous humor.
- filtered through ciliary processes
- enters between suspensory ligaments to enter posterior chamber
- passes through pupil to enter anterior chamber
- Limbus
- Trabeculae
- Canal of Schlemm
- Anterior ciliary vein
Enumerate the layers of the cornea.
- Corneal epithelium
- 5-7 layers thick
- where cells are shed and completely replaced in 1 week
- surface for tears - Bowman’s layer
- dense C.T.
- protects eye from getting scratches *scratches past this layer cause irreparable damage to vision - Stroma
- the thickest layer (90%)
- made of collagen arranged parallel which allows cornea to be clear - Descemet membrane
- thickens with age - Endothelial layer
- maintains aqueous humor
* damage to this layer causes edema of eye
True or false: The anterior 5/6th of outer wall of eyeball is transparent and the posterior 1/6th is opaque.
False: the anterior 1/6th is transparent and the posterior 5/6th is opaque
Innervation to ciliary muscles is by…?
Oculomotor nerve parasympathetic fibers
The iris is a part of which layer of the eyeball?
Tunica Media
Fibrous tunic refers to which layer of the eyeball?
Outer layer consisting of cornea and sclera
True or false: axons of ganglionic cells are myelinated.
false; they are unmyelinated
Which layers of the retina contain retinal blood vessels?
Ganglionic cell layer
Nerve fiber layer
Which area of the eye has the most acute vision and why?
Fovea centralis on the macula centralis because it has only rods and cones
Define EXTRAFOVIAL VISION
When image falls on other part of retina other than the fovea centralis
Enumerate blood supply to the retina.
Outer 1/3rd gets the Choroid artery
Central 2/3rds gets the central artery
Describe clinical basis of cataracts.
Opaqueness of the lens caused by accumulation of cells in the capsule, and fluid causing denaturation of lens fibers. Can be caused by diabetes, long-term drug usage, excess alcohol, prolonged unprotected exposure to sun
Cataract can be removed by Phacoemulsification
Define intraocular pressure
the pressure exerted by aqueous humor
Normal intraocular pressure
12-20 mmHg
True or false: the lens is biconvex
TRUE
True or false: the image on the retina is upside down, but not reversed from side to side
FALSE: the image on the retina is upside down, and reversed from side to side
True or false: the eye has more rods than cones
TRUE; 12 million rods and 6 million cones
Describe distribution of rods and cones as you move from the fovea to edges of retina
Fovea has only cones —> number of rods increases while cones decreases —> Edge of retina has only rods
Compare the outer segments of rods and cones
For rods
- have membranous disks
- disks synthesized from inner segment and push older ones outwards
- disks contain rhodopsin pigment
- disks renewed every 3-4 hrs
Cones
- have saccules instead
- saccules made from more than one point
- saccules take longer time to be renewed
- saccules contain Porphyropsin, Iodopsin, and cyanopsin
Define; Scotopic vision
dim light vision
Components of rhodopsin.
- Opsin called scotopsin
2. Chromophore called retinal present as 11cis retinal also called retinine 1
True or false: resynthesis of rhodopsin from 11-cis retinal is faster than from 11 cis retinol
True
Explain the greater than usual resting membrane potential of photoreceptors (-40 mV)
Sodium ions pumped out through outer segment, but leak back in to inner segment carrying that positive charge with them and preventing the cell potential from sinking to -70mV
What protein causes sodium to leak back into inner segment?
cGMP keeps sodium channels open
Enumerate the mechanism of phototransduction.
Rodhopsin absorbs photon and decomposes to Metarodhopsin 2 –> which activates transducin G protein –> which goes to activate cGMP phosphodiesterase –> which converts cGMP to 5’-AMP = decrease in cGMP = closure of sodium channels = hyperpolarization because sodium no longer leaking back in = production of action potential = activation of bipolar cells
State which light porphyropsin, iodopsin, and cyanopsin are sensitive to.
Porphyropsin –> Red
Iodopsin –> Green
Scotopsin –> Blue
Mechanism for dark adaptation.
Resynthesis of rhodopsin for rods to function
Dilatation of pupil to allow more light to enter eye
Nyctalopia
loss of vision when environment gets dark because rodhopsin not being resynthesized
caused by Vit A deficiency
1. diet low in vit A
2. poor absorption of vit A from intestines
if not treated, causes distortion and irreparable damage to layers of cornea
Define VISUAL FIELD
part of the external world visible to the eye
Differentiate binocular from monocular vision
Binocular vision - visual fields overlap
Monocular vision - there is very little overlap
Where is the visual field NOT restricted?
Temporal part
Define FAR-POINT OF VISION
the distance beyond which lens doesn’t need to change shape to focus (the farthest distance an object is and still remains clear)
The most stressed muscles in the body are…?
Ciliary muscles
Mechanism of focusing on close objects.
- Accomodation
ciliary muscles contract, lens ligaments loosen, lens curves to increase its refractory power. - Convergence
eyes move medially - Constriction
pupil constricted to prevent divergent light rays from entering
True or false: the ciliary muscles become less contractile with age, but the lens is not affected
False: the ciliary muscles do lose their contractility with age, but the lens is also affected because it also loses its contractility as it becomes more dense with age
What nerve innervates ciliary muscles?
Oculomotor nerve parasympathetic fibers
define EMMETROPIA
normal refractive power of the eye
define ANISOMETROPIA
both eyes have different refractive powers
Mechanism of astigmatism
light rays never meet because a meridian of the lens has an altered curvature OR meridian has different alterations
Functions of private pathway and diffuse pathway in the visual pathway.
Private pathway is for acuity and discrimination of intensity
Diffuse pathway is for other vision
Enumerate the visual pathway.
Receptor: Rods and Cones
1st Order neuron: Bipolar + Amacrine cells
2nd Order neuron: Ganglionic cell
3rd Order neuron: Lateral geniculate body nuclei
Center: Primary visual cortex occipital lobe (Brodmann 17)
What are the 6 components of the visual pathway?
Optic nerve Optic chiasma Optic tract Lateral geniculate body Optic radiation Visual cortex
The optic nerve leaves the eye through the…
Optic disk
True or false: the optic tract is formed by fibers from opposite sides of the optic nerve
False: its lateral fibers are from the ipsilateral optic nerve while its medial fibers are from the contralateral optic nerve
Fibers that go to superior collicus initiate…
visual reflexes
Optic tract fibers that don’t end in the lateral geniculate body end up in the _____ or the ______.
superior colliculus
pretectal nuclei
The anterior part of the visual cortex represents which kind of vision? And the posterior part?
Anterior part gets retinal representation (for peripheral vision)
Posterior part gets macular representation (for central vision)
State the functions of the following parts of the visual cortex: Brodmann 17, 18, and 19.
Area 17 –> perception of visual impulses
Area 18 –> Interpretation of visual impulses
Area 19 –> movement of eyes
Anopia refers to
loss of vision in on visual field
Enumerate causes of lesion to optic pathway structures
Aneurysms of carotid artery causes compression
Increased intracranial pressure due to thrombosis, tumors, stroke, high blood pressure
Dilation of 3rd ventricle compresses carotid artery against other structures
Type of anopia developed from damage to visual cortex.
If it’s the inferior visual cortex, patient gets inferior homonymous hemianopia
If it’s the superior visual cortex, patient gets superior homonymous hemianopia
Why does macular sparing occur?
- Supra-geniculate fibers project to both visual cortices
- The fibers have their own blood supply
- Fibers project to both anterior and posterior parts of each visual cortex
Define macular sparing
A phenomenon in which central vision is spared in supra-geniculate lesions
Quadrantanopia is a result of lesion to
optic radiation
The type of anopia resulting from lesions to optic radiation to temporal lobe is
superior quadrantanopia
Differentiate Presbyopia, Anisometropia, and Astigmatism
Presbyopia is caused by old age and causes lens to become less flexible.
Anisometropia is differences in refractive power of the eyes.
Astigmatism is when light rays do not meet at all due to difference in meridians of the lens.
Lesion to which area of the brain results in right superior quadrantanopia?
Lesion to the left temporal lobe
Lens used to correct presbyopia
convex lens
Describe glaucoma including causes, types, symptoms, and treatments.
Glaucoma refers to increase in intraocular pressure above 60 mmHg
The types of symptoms depend on the type of glaucoma involved.
1. Primary open-angle glaucoma caused by unknown obstruction. is the most common type. symptoms appear later and include headaches, rapid reduction of visual field, and heaviness around eyeball
- Primary angle-closure glaucoma caused by visible obstruction. results in severe headaches, nausea, blurry vision, and appearance of hallow rainbow around a light source
Treatment includes eye drops, laser eye surgery, or surgery
