Functions of the Eye

Question 0

Focal point

Answer 0

Point at which light rays converge after being refracted through a convex lens

Question 1

Degree of Refraction

Answer 1

Dependent upon:

1. Ratio of refractive indices
2. Angle between the interface and rays of light

Question 2

Focal length

Answer 2

distance behind a convex lens at which parallel light rays converge

Question 3

Four Refractive interfaces of the eye

Answer 3

1. Interface b/w air and anterior cornea

2 B/w posterior cornea and aqueous humor

3. B/w aqueous humor and anterior lens
4. B/w posterior lens and vitreous humor

Question 4

Refractive power of the eye

Answer 4

2/3- Cornea

1/3- lens

Question 5

Ciliary muscle fibers

Answer 5

Meridonal- extend to corneoscleral jnxn; pulls lens ligaments medially and forward

Circular- when contracted, they decrease the diameter of the circle to which the suspensory ligaments attach releasing tension on the lens

*Both funxn to give the lens a more spherical, refractive shape

Question 6

Parasympathetic function on ciliary muscles

Answer 6

Adapts lens for focusing on nearby objects

Question 7

Presbyopia

Answer 7

Gradual decline in the ability to accommodate the lens

-Corrected with bifocal lens

Question 8

Functions of iris

Answer 8

1. Control the amount of light entering the eye
2. Control the depth of field

• Depth of field is GREATEST when pupil diameter is smallest
• light rays are allowed little chance to diverge

Question 9

The Near Triad

Answer 9

1. Convergence of the eyes
2. Accommodation of the lenses
3. Miosis to maximize depth of field

Question 10

Emmetropia

Answer 10

Normal eye

Question 11

Hyperopia

Answer 11

Light rays are not bent to a sufficient degree due to decreased refractive power of the cornea of a short eyeball

• Ciliary muscles constantly contract to correct
• Corrected with a CONVEX lens

Question 12

Myopia

Answer 12

Light rays converge before the retina due to an eyeball that is too long or an overpowered lens system

• Ciliary muscle is constantly relaxed to decrease the refractive power of the lens
• Corrected with CONCAVE lens

Question 13

Astigmatism

Answer 13

Uneven curvature of the cornea resulting in unequal bending of light

• Lens is unable to accommodate
• Corrected with a cylindrical lens

Question 14

Keratoconus

Answer 14

Progressive thinning and bulging of the cornea causing chaotic refraction of light

-Corrected with a contact lens

Question 15

Cataract

Answer 15

An opaque lens that obscures the transmission of light

-Corrected by removing the lens and replacing with an artificial, plastic lens

Question 16

Normal intraocular pressure

Answer 16

15 +/- 2 mmHg

-Determined by the resistance to outflow of aqueous humor through the Canal of Schlemm

Question 17

Glaucoma

Answer 17

damage to the optic nerve that results in loss of vision

• Elevated intraocular pressure=risk factor
• Treated w/ carbonic anhydrase inhibitors(decreased formation of aqueous humor) and prostaglandin analogs (increased outflow thru the Canal of Schlemm)

Question 18

Tonometry

Answer 18

measurement of intraocular pressure

Question 19

Opthalmoscopy

Answer 19

Visual inspection of the optic nerve/disk

Question 20

Gonoiscopy

Answer 20

Measurement of the angle b/w the iris and cornea

*Closure of angle impedes outflow of intraocular fluid => increased pressure

Question 21

Vertical Pathway

Answer 21

Photoreceptors and bipolar cells generate graded potentials that release glutamate

Ganglion cells receive NT and generate an AP

*Glutamate can be either excitatory or inhibitory

Question 22

Lateral Pathway

Answer 22

Maintain inhibition b/w photoreceptors by releasing GABA (horizontal cells) or dopamine, Ach serotonin, GABA (amacrine cells)

Question 23

Dark current

Answer 23

Continuous inward current of Na and Ca due to the opening of CNG ion channels giving photoreceptors a slightly depolarized resting potential

-Held open by increased levels of cGMP

Question 24

PDE in photoreceptors

Answer 24

Activated by light stimulation; degrades cGMP closing CNG ion channels making the membrarne hyperpolarized

Question 25

Composition of photopigment

Answer 25

1. Retinal- light absorbing chromophore | 2. Opsin- retinal binding protein

Question 26

Transducin

Answer 26

stimulates PDE; activated by all-trans-retinal

Question 27

Bleaching

Answer 27

Absorbance of light causing retinal to change from purple to yellow

Question 28

Light adaptation

Answer 28

PDE becomes less effective in closing CNG channels due to a decrease in intracellular Ca causing 1. Increased guanylyl cyclase activity 2. Increased affinity of CNG for cGMP

Question 29

Cone sensitivity

Answer 29

Requires at least 100 photons of light to respond -Cannot provide specific info about wavelength of light due to overlapping sensitivities

Question 30

Red/Green deficiency

Answer 30

Loss of red and green cones X-linked; more commonly affects males

Question 31

Scotopic vision

Answer 31

Vision under low-light conditions; mostly uses rods

Question 32

Mesopic vision

Answer 32

Vision under moonlight that uses both rods and cones

Question 33

Photopic vision

Answer 33

Vision under lighting that uses only cones

Question 34

On-center bipolar cells

Answer 34

Stimulation of the center of these fields will hyperpolarize the photoreceptor causing decreased glutamate release - Contain glutamate receptor receptor that closes CNG channels when stimulated - Inhibited by off-center illumination

Question 35

Off-center bipolar cells

Answer 35

Contains conventional ionotropic glutamate receptors that are excited (depolarized) by the glutamate from photoreceptors in the dark -Hyperpolarize when center of field is in light

Question 36

Horizontal cell function

Answer 36

Releases GABA onto lateral photoreceptors when stimulated by glutamate release from its own receptor

Question 37

Synaptic connections of rods

Answer 37

Only to on-center bipolar cells Output gets relayed by A-II amacrine cells onto cones

Question 38

Ganglion cell output

Answer 38

Dependent upon the ratio of intensities of light (Ratio of background light-focused light determines neuron firing rate) -Poorly stimulated by diffuse illumination

Question 39

M-type ganglion cells

Answer 39

"Magnocellular" - 5% of gangilion - Large - Fast firing - Detects movement

Question 40

P-type ganglion cells

Answer 40

"Parvocellular" - 90% of ganglion - Small receptive field - Slow conductors - Sensitive to different wavelengths - Detect fine form and detail

Question 41

Red-green ganglion cells

Answer 41

Stimulated by red light in center; blue light on outside -R+G- Center excited by red; surround inhibited by green White light=ineffective stimulus

Question 42

The eye is what type of lens?

Answer 42

Convex cylindrical

Question 43

Ora Serata

Answer 43

Anterior border of the retina -Non-photosensitive portion continues over the ciliary body

Question 44

Function of Pigmented Epithelium

Answer 44

- Synthesize Brush's membrane * attaches retina to the choroid - Transport nutrients to the retina - Remove waste products - Phagocytosis and recycling of photoreceptors - Metabolism of retinol

Question 45

Muller Cells

Answer 45

Form the inner limiting membrane of the retina -Function as glial cells