NVG Flashcards
What are the 5 major structures of the eye?
- cornea
- iris
- pupil
- lens
- retina
What is the purpose of cones in the eye?
- identify colors
- utilized during daylight
- sharp visual acuity due to 1:1 ratio of cone cells to neuron cells
- uses photochemical iodopsin
What is the purpose of rods in the eye?
- operate in low illumination
- identify shades of black, grey and white
- 10:1-10,000:1 ratio of rod cells to neuron cells
- utilize photochemical rhodopsin (visual purple)
Describe the day blind spot
- exists because the optic disk contains no photoreceptors cells
- covers an area of 5.5-7.5 degrees
- compensated for by binocular vision
Describe the night blind spot
- occurs when the fovea is inactive in low light
- covers 5-10 degrees
- an object will fade if stared at for longer than 2 seconds
What are the three night vision techniques? (SOS)
- scanning
- Off center viewing
- shapes and silhouettes
What are the three types of vision?
- photopic (day)
- mesopic (dawn/dusk/full moonlight)
- scotopic (dimly lit nights/partial moonlight/starlight)
Monocular cues (GRAM)
- geometric perspective (LAV)
- linear perspective
- apparent foreshortening
- vertical position in the field - retinal image size (KITO)
- known size of objects
- increasing or decreasing size
- terrestrial association
- overlapping contours
- Aerial perspective (FLP)
- fading of colors and shades
- loss of texture and detail
- position of light source
- Motion Parallax
Describe dark adaptation
-The process by which the eyes become more sensitive to low levels of illumination

-optimal night vision acuity approaches its maximum level in about 30 to 45 minutes
- if the eyes are exposed to bright light after dark adaptation, their sensitivity is temporarily impaired
- illness adversely affects dark adaptation due to higher than normal oxygen consumption rate
Visual Illusions
FFAACCSSSSVH
- fascination/fixation
- false horizon
- aerial perspective
- autokinesis
- confusion with ground lights
- cratering
- structural
- size-distance
- size constancy
- shape constancy
- vection
- height-depth perception
How can you identify deteriorating weather conditions at night under NVGs?
(FLASH)
- fog
- loss of moon or stars
- ambient light levels
- shadows
- halo effect
What are the NVG considerations?
CALMWWADSOS
- color
- air/ground speed
- lights
- magnification vs. intensify
- weather
- weapons
- aircraft lighting
- depth perception/distance estimation
- spatial disorientation
- obstacle detection
- scanning techniques
Describe the image intensifier of the NVGs.
6 parts
- objective lens
- photocathode
- micro channel plate
- phosphor screen
- fiber optic inverter
- eyepiece lens
How does ABC work?
NVGs
Automatic Brightness Control
-adjusts MCP voltage to maintain brightness at preset levels by controlling number of electrons that exit the MCP (micro channel plate)
How does BSP work?
(NVGs)
Bright Source Protection
-reduces voltage to the photocathode when exposed to bright light sources
