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Aeromed BM > Vision > Flashcards

Vision Flashcards

1
Q

Anatomy of eye

A

*KNOW WHERE THEY ARE

Cornea - very front protective layer

Iris - colored portion of eye, opens and closes

Pupil - black part of eye

Ciliary muscles/fibers - close and open iris

Crystalline lens - lets light into eye, refracts it onto retina

Retina - back inner of eye, light is refracted on, Rods and Cons interpret

Optic nerve - sends data

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2
Q

Photoreceptor cells

A

On the retina

(Fovea - packed with cone cells, bump on rear of eye)

Cone cells - used in bright light, IDENTIFIES COLOR, sharp visual acuity and color sense, 7 million in fovea and parafoveal regions, 1:1 RATIO OF CONE CELLS TO NERVE CELLS

Rod cells - used in low light, can identify outlines/silhouettes, poor color sense and visual acuity, 120 million rod cells, 10:1 to 10000:1 ratio of rod cells to neuron cells. Produces Rhodopsin (visual purple)

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3
Q

Fovea centralis

A

Central vision , has no rod cells (produces night blind spot), the little bump on the retina near the optic nerve

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4
Q

Day blind spot

A

One of the retinal blind spots (1 of 2)

Related to the position of the optic (nerve) disk on the retina

Located 15 degrees from fovea

No photoreceptor cells (rods or cons)

*Encompasses 5.5 to 7.5 degrees of visual field

Compensate with binocular vision

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5
Q

Night blind spot

A

One of the retinal blind spots (1 of 2)

Located in central viewing axis (fovea)

*Absence of rod cells in fovea

Inability of cone cell function

*Encompasses an area of 5-10 degrees of central, visual field

Viewer must SCAN to compensate

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6
Q

Visual deficiencies

A

*Astigmatism - due to unequal curve of cornea, can ot focus on horizontal and vertical objects simultaneously

Glare disability - inability to detect objects against varying shades or backgrounds-related to contrast

  • Myopia - nearsightedness
  • Hyperopia - farsightedness
  • Presbyopia - (aging) hardening of lenses, cataracts
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7
Q

Allowable refractive surgeries

A

PRK - Photorefractive Keratectomy (slowest return, but least susceptible to flap issues

LASIK - Laser in Situ Keratectomy (most common)

LASEK - Laser Subepithelial Keratectomy (carving of corneas to big for LASIK)

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8
Q

Types of vison

A

*PMS

Photopic - daylight/bright light, central vision, visual acuity 20/20

Mesopic - dawn/dusk, full moonlight; parafoveal region (rods and cons), decrease acuity and color sense (increase scanning)

Scotopic Vision - night vision (partial moon/stars), peripheral vision only (rods), silhouette recognition, loss of color perception

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9
Q

Binocular cues

A

Valuable only when the object is close

Each eye has a slightly different view

Operates subconsciously

Little value in flight enviornment

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10
Q

Visual cues

A

Monocular cues - *GRAM

G) geometric perspective (LAV)
R) retinal image size (KITO)
A) aerial perspective (FLP)
M) motion parallax (*most common cue to depth perception)

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11
Q

Geometric Perspective (LAV)

A

Objects have different shapes when viewed at varying distances and altitudes (linear objects like rail lines seem to converge)

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12
Q

Retinal image size (KITO)

A

K) known size of objects
I) increasing or decreasing size of objects
T) terrestrial association
O) overlapping contours (position of convoy)

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13
Q

Aerial perspective (FLP)

A

An objects clarity and its shadow are perceived by the brain as cues for estimating distance

F) fading of colors and shades
L) loss of detail or texture
P) position of light and direction of shadow

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14
Q

Motion parallax

A

*Most important cue to depth perception (stationary objects, observer moving)

Rate depends on the relative distance of the object from the observer

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15
Q

Limitations of night vision

A

Depth perception (safe landings)

Visual acuity (obstacle identification)

Night blind spot

Dark adaptation (time factor)

Color perception

Night myopia (decreased color, visual acuity)

Visual cues

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16
Q

Depth perception

A

Mental projection of perceived object in space

Correlation of “real object” to projected visual space

Decreased light affects ability of depth perception

*Two most important monocular factors - motion parallax and retinal image size

17
Q

Visual acuity

A

How well you can see in daytime (20/20), is not how you see at night (legally blind status at night)

18
Q

Night blind spot

A

At 3ft can miss a wrench, at 3,000ft can miss commercial aircraft (need to visually scan - use peripheral vision)

19
Q

Dark adaptation

A

*average time required is 30-45 minutes

Red lens van help start dark adaptation

Exposure to intense sunlight, glare for 2-5 hours will increase time for dark adaptation for up to 5 hours

After full dark adaptation, 3-5 min of re-adaptation needed after exposure to brief bright light.

Vitamin A required for production of Rhodopsin

20
Q

Color perception

A

Scotopic vision degrades primary color perception

Shades of black, gray, and white

Other colors perceived if light intensity increases

21
Q

Night myopia

A

Blue wavelength light causes night myopia

  • image sharpness decreases as pupil diameter increases
  • mild refractive error factors combined, creates unacceptable blurred vision
  • focusing mechanism of the eye may move toward a resting position (increases myopic state)
22
Q

Visual illusions

A

ICCHAFFSS

I) induced motion
C) confusion with ground lights
C) crater illusion
H) height-depth illusion (loss of visual cues)
A) autokinesis**
F) false horizon
F) fascination/fixation
S) structural illusion
S) size distance illusion
23
Q

Flight hazards

A

Solar glare

Bird strikes

L.A.S.E.E.Rs (light amplification by a stimulated emission of radiation) intense <1in diameter up to 2m at 2km

Nerve agents

24
Q

Laser injuries

A

Lens - focuses and concentrates light rays entering eye

Concentration of energy inside eye is up to 100,000 times greater than light entering eye

Damage depends on laser type, exposure time, and distance (lesions on back of eye, flash blindness, impaired night vision, burns)

25
Q

Laser protective measures

A

Passive - take cover, NVDs, squinting, protective goggles

Active - evasive action, scanning with one eye or monocular optics

26
Q

Nerve agents

A

Threat in both day and night at low level flight

Consult FS immediately

Severity of miosis depends on agent concentration (direct or minute exposure will cause miosis - pupil constriction… severe miosis may last 48hrs, complete recovery could take 20 days)

27
Q

Self-imposed stresses

A

DEATH

Drugs
Exhaustion
Alcohol
Tobacco
Hypoglycemia

Aeromed BM (13 decks)

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