Vision Flashcards
Optical component of the eyes
Cornea, aqueous humor, vitreous humor, lens
Neural component of the eyes
Rods, cones, bipolar cells, ganglion cells
Function of the optical component of the eyes
Focus images on the photoreceptors
Function of the neural component of the eyes
Transforms images that reach the photoreceptors into neural discharges which are transmitted to the brain
Primary refractive media of the eye
Cornea
Color of the cornea
Transparent to allow the light pass through
Why is the cornea transparent
Uniform structure, avascularity, deturgescence (stroma of the cornea is kept dehydrated to maintain clarity and transparency)
Metabolism of the cornea
Glucose, aerobic (30% glycolysis, 65%PPP)
Two parts of the conjunctiva
Palpebral: behind the eyelid (check color; pale = anemia)
Bulbar: covers the sclera
Fibrous outer layer of the eye consisting of collagen
Sclera
Fine elastic tissue covering the outer anterior sclera
Episclera
Nourishment of sclera
From blood vessels of episclera
Parts of the uveal tract
Iris, ciliary body, choroid
Central opening of the iris
Pupil
Function of the pupil
Controls amount of light entering the eye
Pupillary response to bright light
CN III; sphincter pupillae; miosis (constricted)
Pupillary response to dark light
Sympathetic; dilator pupillae; mydriasis (dilated)
Two zones of the ciliary body
Pars plicata: corrugated anterior zone
Pars plana: flattened posterior zone
Function of the ciliary body
Controls conformation and focus of the lens through the suspensatory ligaments; produces aqueous humor
Posterior part of the uveal tract, located between the sclera and the retina
Choroid
Function of the choroid
Supplies blood to the outer portion of the retina
Blood supply of the inner part of the retina
Retinal arteries
Blood supply of the outer part of the retina
Choroid
Biconvex, avascular, clear structure of the eye
Lens
Components of the lens
65% water, 35% proteins and minerals
Parts of the lens
Capsule: semipermeable to water and e-
Lens nucleus
Cortex
Metabolism of the lens
Glucose, aerobic metab (85% glycolysis, 10% PPP, 5% TCA)
Structural integrity of the lenses are due to
Na-K ATPase, glutathione reductase, protein synthesis
Junction of the peripheral cornea and root of the iris
Anterior chamber angle
Function of the anterior chamber angle
Contains a trabecular meshwork that resorbs aqueous humor
Function of the intraocular fluid
Maintain pressure in eyeball to keep it distended
Parts of the intraocular fluid
Aqueous and vitreous humor
Isoosmotic fluid lies in front of the lens
Aqueous humor
Function of the aqueous humor
Nourishment to cornea and lens;
Removes end-products of metab
Aqueous humor pathway
Ciliary process > posterior chamber > pupil > anterior chamber > canal of schlemm
Posterior chamber vs posterior segment of the eye ball
Posterior chamber = behind the iris
Posterior segment = behind the lens
Posterior to the lens; occupies the posterior segment
Vitreous humor
Clear, avascular body with 2/3 volume is of the weight
Vitreous humor
Components of the vitreous humor
1% collagen and hyaluronic acid
What makes the vitreous humor gel-like
1% collagen and hyaluronic acid = gel like due to its ability to bind large amounts of water
Refractive interfaces of the lens system
Between air and anterior cornea;
Between posterior cornea and aqueous humor;
Between aqueous humor and anterior lens;
Between posterior ens and vitreous humor
Total optical power of the eye
60 diopters
- cornea = 40
- lens = 20
Convex vs concave lens
Convex = focuses light rays into a single focal point; Concave = diverges light rays
Refractive power is defined as
Ability to bend light so the image will be focused on the retina
Cloudy/opaque areas in the lens obscuring light transmission
Cataracts
Pathophysio of cataracts
Loss of osmolariy and change in solubility of lens proteins –> high light scatter
Treatment for cataract
Removal of lens nucleus and replacing it with artificial plastic lens
Senile vs Diabetic cataract
Senile: age related; changes in architechtural arrangement of lens crytalline due to breakdown of proteins
Diabetic: increased osmolarity of lens due to aldose reductase and polyol (aldose) dehydrogenase
Myopia
Nearsightedness;
Light rays coming from distant objects are focused in front of the retina due to (1) longer eyeballs (2) steeply curved cornea (3) higher refractive power;
Use biconcave lenses to diverge rays to lessen refractive power
Hyperopia
Farsightedness;
Light rays are not bent by lens to focus by the time they reach the retina due to (1) short eyeball (2) flatly-curved cornea (3) weak lens system;
Corrected by biconvex lens to bend light more;
Accommodation by ciliary muscles to strengthen lens
Astigmatism
Disparity in corneal curvature between the axes;
Cornea is more of an oblong;
Visual image in one plane to focus at different distance from that of the plane at right angles;
Trial and error spherical lens that corrects the focus of one of the planes
Presbyopia
Lens stiffens which decreases the ability to change shape;
Power of accommodation decreases with age
Diseases which the intraocular pressure become too high due to accumulation of aqueous humor
Glaucoma
Pathophysio of glaucoma
Accumulation of aqueous humor, IOP rises, posterior pressure increases, axons of optic nerve are compressed
Most common cause of irreversible blindness
Glaucoma
Most common cause of reversible blindness
Cataract
Treatment for glaucoma
Surgery
Wide/open angle glaucoma
Aqueous humor has complete physical access to the trabecular meshwork;
Increased IOP is due to an increased resistance to aqueous outflow
Narrow/closed angle glaucoma
Peripheral zone of iris adheres to trabecular meshwork; physical impediment to egress of aqueous humor (drainage obstruction); fluid cannot reach the trabecular meshwork
Parts of the retina seen on fundoscopy
Optic nerve: physiologic blind spot
Macula lutea: 3mm yellowish pigmentation due to xanthophylls
Fovea: center of macula
Foveola: most central and thinnest part of retina (cones only)
Metab of retina
Anaerobic glycolysis;
NADH reduces pyruvate to lactate, increasing lactate dehydrogenase
Fuel for lactate dehydrogenase of retina
NADH or NADPH
Function of rods vs cones
Rods: function at low light; monochromic night vision
Cones: function at higher light levels; high acuity color daylight vision
Photoreceptors mostly found in the fovea centralis
Cones
Photoreceptors mostly found in the eyes except the fovea centralis
Rods (20:1)
Function of rhodopsin
Absorption at 500nm;
With 7 transmembrane helices with 11-cis-retinal
Pathway of light
Rods and cones > bipolar cells > ganglion cells > optic nerve
Provide inhibitory feedback to photoreceptors
Horizontal cells
3 types of ganglion cells
Magnocellular 5%: movement, location, depth; largest; respond to rapid changes in visual images
Parvocellular 55%: color, form, texture; small visual fields; accurate localization and fine details; receive from >=1 cone
W cells 40%: directional movement; small with large diffused receptive fields; receive from crude rod
Types of fibers of the optic nerve
Visual 80%: synapse in LGB on neurons whose axons terminate in the visual cortex
Pupillary 20%: bypass geniculate body en route to pretectal area
T/F: optic sheath is continuous with the meninges
T
Neurotransmitter for phototransduction
glutamate
Phototransduction in the dark
Photorec not activated by light > all-cis retinal maintained > no activation of transducin > no activation of phosphodiesterase > no conversion of cGMP > Na channels are open > Na influx > depolarization > release neurotransmitter > synapse is inhibitory to the next bipolar cell
Visual field for temporal side
Lateral;
Projected to the nasal side of retina
Visual field for nasal side
Medial;
Projected to the temporal side of the retina
Crosses the optic chiasm
Nasal side
L optic tract
L temporal + R nasal
R optic tract
R temporal + L nasal
What is affected in loss of peripheral vision?
Both nasal sides
Affected in tunnel vision
Lesion/s in the optic chiasm
Pathway of visual signal
retinas > optic nerves > optic chiasm > opposite optic trac >t lateral geniculate body > optic radiation > visual cortex/calcarine fissure of the occipital lobe
Accommodation
Ability of the lens to refocus divergent rays of light on the retina
Contraction of the muscles of ciliary body
Diameter of ciliary body is decreased; zonules relax > less pull on the lens > lens assumes spherical shape (more convex) > light is bent > see near objects
No contraction of the muscles of ciliary body
Diameter of ciliary body is increased; zonules taut > lenses taut > lenses flattened (less convex) > focus more on far objects
Types of ciliary muscles
Meridional fibers
Circular fibers
Innervation of ciliary muscles
CN III
Wviewing near objects, eyes [converge/diverge] at the center
converge
Light entering constricted pupil
More focused, more depth
Light entering dilated pupil
More scattered, less depth of focus
Responsible for pupillary constriction
Pupillary sphincter muscle
Depth of focus is [directly/inversely] proportional to pupillary diameter
Inversely
Moving parallax
Images of close-by objects move rapidly across the retinas, while the images of distant objects remain almost completely stationary
Stereopsis
Images on the two retinas are different rom each other;
For the perception of depth
Types of cones
Blue: 420nm
Green: 535nm
Red: 565nm
Young-Helmholtz Trichromatic (3-color) Theory
Variations in color are accounted for by differential stimulation of the blue, green, or red cones
Color blindness
Inability to distinguish colors;
Photore are present but aa are changed = change in absorption spectra = abnormal color vision
Protanopia
Red-Green color blindness;
Lack either red or green cone
Cannot distinguish green, yellow, orange, red;
X linked recessive
Macula and fovea arise from
Temporal side
Origin of blood vessels entering the eye
Optic disc = physiological blindspot
