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S&F 2: Exam 1 > Functions of the Eye > Flashcards

Functions of the Eye Flashcards

0
Q

Focal point

A

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

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1
Q

Degree of Refraction

A

Dependent upon:

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

Focal length

A

distance behind a convex lens at which parallel light rays converge

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3
Q

Four Refractive interfaces of the eye

A
  1. Interface b/w air and anterior cornea

2 B/w posterior cornea and aqueous humor

  1. B/w aqueous humor and anterior lens
  2. B/w posterior lens and vitreous humor
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4
Q

Refractive power of the eye

A

2/3- Cornea

1/3- lens

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5
Q

Ciliary muscle fibers

A

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

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6
Q

Parasympathetic function on ciliary muscles

A

Adapts lens for focusing on nearby objects

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7
Q

Presbyopia

A

Gradual decline in the ability to accommodate the lens

-Corrected with bifocal lens

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8
Q

Functions of iris

A
  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
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9
Q

The Near Triad

A
  1. Convergence of the eyes
  2. Accommodation of the lenses
  3. Miosis to maximize depth of field
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10
Q

Emmetropia

A

Normal eye

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11
Q

Hyperopia

A

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
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12
Q

Myopia

A

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
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13
Q

Astigmatism

A

Uneven curvature of the cornea resulting in unequal bending of light

  • Lens is unable to accommodate
  • Corrected with a cylindrical lens
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14
Q

Keratoconus

A

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

-Corrected with a contact lens

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15
Q

Cataract

A

An opaque lens that obscures the transmission of light

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

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16
Q

Normal intraocular pressure

A

15 +/- 2 mmHg

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

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17
Q

Glaucoma

A

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)
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18
Q

Tonometry

A

measurement of intraocular pressure

19
Q

Opthalmoscopy

A

Visual inspection of the optic nerve/disk

20
Q

Gonoiscopy

A

Measurement of the angle b/w the iris and cornea

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

21
Q

Vertical Pathway

A

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

22
Q

Lateral Pathway

A

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

23
Q

Dark current

A

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

24
Q

PDE in photoreceptors

A

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

25
Q

Composition of photopigment

A
  1. Retinal- light absorbing chromophore

2. Opsin- retinal binding protein

26
Q

Transducin

A

stimulates PDE; activated by all-trans-retinal

27
Q

Bleaching

A

Absorbance of light causing retinal to change from purple to yellow

28
Q

Light adaptation

A

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
29
Q

Cone sensitivity

A

Requires at least 100 photons of light to respond

-Cannot provide specific info about wavelength of light due to overlapping sensitivities

30
Q

Red/Green deficiency

A

Loss of red and green cones

X-linked; more commonly affects males

31
Q

Scotopic vision

A

Vision under low-light conditions; mostly uses rods

32
Q

Mesopic vision

A

Vision under moonlight that uses both rods and cones

33
Q

Photopic vision

A

Vision under lighting that uses only cones

34
Q

On-center bipolar cells

A

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
35
Q

Off-center bipolar cells

A

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

36
Q

Horizontal cell function

A

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

37
Q

Synaptic connections of rods

A

Only to on-center bipolar cells

Output gets relayed by A-II amacrine cells onto cones

38
Q

Ganglion cell output

A

Dependent upon the ratio of intensities of light

(Ratio of background light-focused light determines neuron firing rate)

-Poorly stimulated by diffuse illumination

39
Q

M-type ganglion cells

A

“Magnocellular”

  • 5% of gangilion
  • Large
  • Fast firing
  • Detects movement
40
Q

P-type ganglion cells

A

“Parvocellular”

  • 90% of ganglion
  • Small receptive field
  • Slow conductors
  • Sensitive to different wavelengths
  • Detect fine form and detail
41
Q

Red-green ganglion cells

A

Stimulated by red light in center; blue light on outside

-R+G-
Center excited by red; surround inhibited by green

White light=ineffective stimulus

42
Q

The eye is what type of lens?

A

Convex cylindrical

43
Q

Ora Serata

A

Anterior border of the retina

-Non-photosensitive portion continues over the ciliary body

44
Q

Function of Pigmented Epithelium

A
  • 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
45
Q

Muller Cells

A

Form the inner limiting membrane of the retina

-Function as glial cells

S&F 2: Exam 1 (14 decks)

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