LECTURE 8: VISION Aviation Human Factor : AHF 2103

LECTURE 8: VISION

Aviation Human Factor : AHF 2103

Introduction

Vision: the most important sense to obtain reference info during flight.

The eye send image to the brain about aircraft position, velocity and altitude relative to the ground.

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The importance of VISION

Read manuals data & monitoring cockpit instruments.

Determines visual references for taxiing, take-offs and approach.

It is the sense that makes you aware of the position of your aircraft.

Important for identifying terrain features and obstacles.

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Eyes anatomy

Cross Section of the Human Eye

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eyeballeye muscles

• eye muscles: allows eyeball to move in various directions

Rods

Cones

Anatomy of the Eye

Cornea: Transparent outer covering of the eye that

admits light Iris:

Round, pigmented (colored) membrane surrounding the pupil.(colored part of the eye).

Function: control the dilation of the pupil.

Pupil: Adjustable opening in the center of the iris Function: control the amount of light entered

the eye (same with aperture function of the camera).

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Lens – Refracts and focuses light onto the retina

Retina: Thin multi-layered membrane which

covers most of the posterior (backside) compartment of the eye.

Function: to record the image (similar to film function in the camera)

Retina contains TWO types of light-sensitive cells (photosensitive cells) which are rods and cones.

Anatomy of the Eye

How eyes work?9

Formation of an image in the human eye

Light from the object is refracted(by cornea and lens) and focused onto the retina.The image formed is real, inverted and smaller than the object.The image is detected by rods and cones which cause nerve impulses.Nerve impulses are transmitted along optic nerve to the brain.The brain interprets the nerve impulses and ‘sees’ an upright image of the object.

Nerve impulse: The electrical discharge that travels along a nerve fibre

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Formation of an image in the human eye

object

To brain

retina

Optic Nerves

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Eye Defects

Nearsighted(Myopia)

Farsighted(Hyperopia)

Color Blindness

Impairment of Vision (Eyes Disorder)

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Impairment of Vision (Eyes Disorder)

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Nearsighted: Unable to see things clearly unless they are

relatively close to the eyes, owing to the focusing of rays of light by the eye at a point in front of the retina.

Farsighted: Unable to see things clearly, especially if

they are relatively close to the eyes, owing to the focusing of rays of light by the eye at a point behind the retina

Seeing or able to see for a great distance

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Corrective Lenses

Nearsightedness (Myopia) – Correction: Use Concave lenses to expand focal lengths.

Farsightedness (Hyperopia)– Correction: Use Convex lenses to shortens the focal length.

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Let’s have a test!What numbers do you see?

Color blindness

Due to reduced number of / some defects in one or more of the cone cells

Inherited

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Others Visual Impairment

Astigmatism Impaired focus on object

of different meridians (height level).

Focus disorder of vertical and horizontal rays

Caused by irregular shape or the cornea, lens, or both

Can typically be corrected with glasses with relatively cylindrical lenses.

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AstigmatismNormal Vision

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Others Visual Impairment

Factors affecting visual acuity Self-imposed stress Hypoxia Fatigue

Cause the eye to overshoot or undershoot the target.

Effect pilot ability to quickly change focus between near (e.g. chart), intermediate (e.g. instrument), and distant (e.g. outside) vision.

Fatigue (continue..) The most common symptom in visual

fatigue: Blurred Vision Excessive Tearing “Heavy” Eyelid Sensation Headaches

Factors affecting visual acuity

Other factors that may have an adverse effect on visual performance include: windscreen haze Improper illumination of the cockpit and/or

instruments, scratched and/or dirty instrumentation inadequate cockpit environmental control

(temperature and humidity) inappropriate sunglasses and/or

prescription glasses/ contact lenses. sustained visual workload during flight.

Factors affecting visual acuity

Better Scan Techniques

Focus on the Specific Object Dark Adaptation Performing Series of Shot (space eye

movement) Performing off center viewing (during low

and ambient illumination)

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Focus on the Specific Object

Distant focus without specific object to look at tends to diminish rather quickly.

If we fly over water, hazy condition, or between cloud layer at night, our distant focus relax after 60-80 seconds.

If there are no specific object to focus, our eyes revert to a relax intermediate focal distance of 10-30 ft.

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That’s mean we are looking without actually seeing anything which are DANGEROUS!!

The solution of this phenomenon is to FOCUS on more distant object that we can see (even it is just a wing tip).

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Focus on the Specific Object

Dark adaptation is the process by which the eyes adapt for optimal night visual acuity under conditions of low ambient illumination.

The lower the starting level of illumination, the more rapidly complete dark adaptation is achieved.

Visual Purple (Rhodopsin) Light absorbing protein in membrane of rods Allows rods to detect images in the dark

Night flight 30 minutes required for full adaptation to

dark

Dark Adaptation27

To minimize the time necessary to achieve complete dark adaptation and to maintain it, you should:

avoid inhaling carbon monoxide from smoking or exhaust fumes

get enough Vitamin A in your diet adjust instrument and cockpit lighting to the

lowest level possible avoid prolonged exposure to bright lights use supplemental oxygen when flying at

night above 5,000 ft (MSL)

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Dark Adaptation

It should cover all area of the sky visible from the cockpit and monitoring cockpit instrumental as well.

This can be accomplish by performing the series of shot, regularly space eye movement that bring success area of the sky into fovea field.

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Performing Series of Shot

Each movement should not exceed 10° for each area and should not be observed at least 1 sec to enable detection.

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Performing Series of Shot

Performing off center viewing

To see or identify the object under condition of low and ambient illumination Avoid looking DIRECTLY to the object for

more 2 and 3 seconds because it will disappear.

Instead, use the off center viewing and that consist 10° ABOVE, BELOW and EITHER SIDE to look at the object

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OBJECT10°

10°

10°

10°

By switching eyes every 2-3 seconds, we can continue to detect the object.

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OBJECT10°

10°

10°

10°

Performing off center viewing