EASA ATPL HPL Chapter 6 "Visual Systems"

What is monocular vision?

- Both eyes are used separately. - The field of view is increased. - Depth perception is limited.

What is the function of cone cells?

- Central vision is provided by cones. - Sensitive to bright light - Distinguish form and colour - Concentrated in foveal area

List some factors that may degrade visual acuity.

- Lack of visual stimulus (relaxed focus) - (i) the sharpness of the retinal focus - (ii) the health and functioning of the retina, - (iii) the sensitivity of the interpretative faculty of the brain.

State some limitations with regard to night vision.

- No rod cells in Fovea. (central area of retina) - Therefore poor dim light adaption. - Creates night blind spot. - Can use peripheral vision for night vision.

What is the function of rod cells?

- Provide peripheral vision - Concentrated outside of foveal area - Achromatically sensitive to low light

What are risk factors for cataracts?

- Race - Family history - Age - Diabetes - Hypertension - UV exposure - Smoking - Drugs

What is the retinal image size?

- The nearer the object is to the observer, the larger the retinal size. - Very important for distance perception - Can also determine relative size of two objects

Explain why colour blindness occurs.

- Unable to distinguish between green and red - Males 20 times more like that females to have it.

What must sunglasses do on the flight deck?

1. Absorb UV and IR 2. Absorb all colours equally.

What are photosensitive cells affected by?

1. Accleration 2. O2 deficiency 3. Toxic influence

What are some monocular cues for depth perception?

1. Geometric perspective 2. Motion parallax 3. Retinal image size 4. Aerial perspective

What illusion can white out create?

1. Loss of depth and orientation.

What is motion parallax?

1. The apparent relative motion of stationary objects as viewed from a moving observer. 2. Most important to depth perception 3. Close objects move rapidly in opposite direction 4. Distant objects remain fixed or move with observer.

What are some measures that can be taken to protect yourself from flash blindness?

1. Turn up lights 2. Look inside 3. Wear sunglasses 4. Use blinds when installed

Explain how the adaption mechanism caters for low light.

7 mins dark = 20 x increase in cone cell sensitivity 45 min dark =10000 x increase in rod cell sensitivity Pupil dilation = 16 x increase in sensitivity

What is idopsin?

A chemical present in cone cells

What is an illusion?

A false impression of reality

What sort of sunglasses should you wear in a glass cockpit?

A natural grey lens with 15% luminance transmittance.

What is piercing vision?

Ability to read alphanumeric information. Limited to foveal area of retina.

What conditions lead to black hole effect?

Absence of ground features especially with no VASIS / PAPI and few surrounding lights.

What effect does varying saccade time have on the scan?

Allows better peripheral vision at night.

What is the time of saccade (dwelling time) whilst performing an outside scan?

Around 1/3 of a second.

Where are there no photosensitive cells?

Around the retinal nerve and vessels converging to the optic disc.

Why is it important to use this scanning technique?

Because visual acuity is not uniform across the retina and foveal region.

At short range , depth perception is enabled by...

Binocular vision

What is the basis for depth perception and why is it important for flying?

Binocular vision allows us to perceive... 1. Depth 2. Distance 3. Shape

State some methods to avoid illusions during takeoff and landing.

Blackhole - stay on 3 degree path. Don't go low.

What is the "scanning technique"?

Breaking the sky into 10 degree segments and pausing between moving onto the next segment.

What are some problems with vision with regard to blue light and ultra violet light?

Can cause damage to lens. Swelling, pain, extreme sensitivity to light "snow blindness"

What sort of lens would you use to correct for short sightedness?

Concave lens

What are the basic principles of colour vision?

Cone cells are able to distinguish form and colour. Photopigments absorb different wavelengths Iodopsin pigments - Blue - 419 nanometers - Green - 531 nanometers - Yellow - 559 nanometers

State the time necessary for the eye to adapt to the dark.

Cones - 7 minutes Rods - 45 minutes Light adaption - "a few minutes"

Describe the distribution of rod and cone cells and their relevance to perception.

Cones - Foveal area Rods - Not in foveal area Cones - Central vision Rods - Peripheral vision

What sort of lens would you use to correct for long sightedness?

Convex lens

State the basic functions of the components in the eye.

Cornea - glassy front of eye. Light enters here. Pupil - black area. Iris - Colourful part of eye. Controls size of pupil. Lens - Behind pupil. Focus light to retina. Cilliary muscle - changes shape of lens / refraction Sclera - white of eye. Fovea - large accumulation of cone cells

What effects can low relative humidity have on the eye?

Discomfort and increased risk of infection

Central vision is used to...

Distinguish colour and detail

Explain how rod cells work.

Each cell has three pigments. Absorbs light between wavelengths 419-559 nano meters. This allows colours such as blue green and yellow to be identified.

What is Glaucoma?

Elevated intraocular pressure due to a sudden closure of the angle between the cornea and the iris and the aqueous humour usually drains. - narrowing of visual field - insidious onset. - Blurred vision - halo around bright lights - pain - vomiting - total blindness.

What is necessary for colour vision?

Enough ambient light

Whats presbyopia?

Hardening of the lens as age increases.

When does hypoxia effect rods?

Hypoxia effects rods at 5000'

What is cataracts?

Lens opaqueness leading to blurred vision. Affects distance judgement.

How long does adaption take?

Light adaption = 10 secs Full adaption = 30 mins

What is actually occurring during "Dark adaption"

Light adaption within first few minutes Regeneration of rhodopsin (pigment) is main element

State the effect of speed on the function of photosensitive cells.

NO effect

What are some limitations with binocular vision?

Only useful when an object is close enough that there is perceived difference in viewing angle from each eye. This is rare when flying.

What is the visual cortex?

Part of the brain where information from the eye is interpreted.

What sort of sunglasses could cause perceptional problems in flight?

Phototrope sunglasses (variable filtration)

Define Central Vision

Provided by cones which are sensitive to bright light and can distinguish form and colour.

Define Peripheral Vision

Provided by rod cells with are achromatically sensitive to low light intensity and movement.

What is the effect of smoking or hypoxia on night vision?

Reduce night vision

Give some examples of an illusion.

Runway width illusion Runway slope illusion Featureless terrain illusion White out Atmospheric illusions Ground lighting illusions False horizon Autokinesis

Give some examples of takeoff and landing illusions.

Runway width illusion Runway slope illusion Rain on windscreen Fog penetration Bright approach lighting Dim approaching lighting

What are the differences between scanning by day and night?

Scan more slowly at night to enable better peripheral detection. Look 15-20 degrees off the object at night.

What is binocular vision or stereopsis?

The ability to focus both eyes simultaneously on one object. This allows a 3D image to be interpreted by the brain.

Define visual acuity

The ability to resolve the shapes and fine details of objects.

What conditions lead to empty field myopia?

The absence of visual stimulus. i.e flying over a featureless sky means your eye muscles relax forming blurry vision and making traffic pick up harder.

What is aerial perspective?

The clarity of an object and the shadow cast by it can be used by the brain to determine distance.

What is Myopia?

The eyeball is too long. Light from distant objects being focused in front of retinal plane causing blurring of distant objects.

What is hypermetropia? (long sightedness)

The eyeball is too short. Light from nearby objects being focused behind the retinal plane causing blurring of nearby objects.

What is the fovea?

The fovea centralis is a small, central pit composed of closely packed cones in the eye. It is located in the center of the macula lutea of the retina.

What causes night blind spot?

The fovea has no rods and becomes inactive in dim light

Define visual field.

The locus of all points on a surface in front of and concentric with the stationary eye from which a visual signal can be stimulated. Basically what the eye can see.

Whats astigmatism?

Unequal curvature of the cornea or lens. This leads to improper refraction of light. For instance, to focus on towers caring electricity lines, the towers would be in focus but the electricity lines would be out of focus

What is the interaction between vision, equilibrium, proprioception and hearing with regard to spatial orientation?

Vision most important.

How can poor diet influence vision?

Vitamin A is essential for build up of rhodopsin, without which, night flight would be degraded.

Define "Accommodation"

When the ciliary muscles adjust the shape of the lens to achieve specific refraction of light entering the eye.

What is the visible spectrum wavelenghth range?

about 350-750 nanometers.

What is geometric perspective?

ie. Train lines converging in the distance