AHF 2203 AVIATION HUMAN FACTORS Lecture 8: Vision 1

Presentation Outline Introduction The importance of VISION Anatomy of EYE How Eyes work Factor affecting vision Visual Impairment Types of Vision Causes of Impaired Vision How to have better scan of object in the flight? 2

Learning Outcomes At the end of this session, student should be able to: – identify the parts of the eye and most importantly the main functions of each part. – understand the limitations of human visions through given types of vision, dark adaptation, blind spot and etc. – factors that lead to vision impairments and the steps to overcome it. 3

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. 4

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. You need good depth perception for determining height and distance 5

Eyes anatomy 6

Cross Section of the Human Eye 7

8 eyeball eye 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). Lens: refracts and focuses light onto the retina 9

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. Rod: – Nerve cells in the retina. Very sensitive to light & dark (black & white vision) – times more sensitive to light than fovea (cones) – Used for low light condition/night vision. – Involve in peripheral vision to detect position references. – Cannot be used to detect detail or to perceive colour. Cone: – Nerve cells help to see light/color (color vision) – Area of sharpest vision. 10

Internal structures of the eyeball 11 Retina transverse section through the eyeball special regions: yellow spot(fovea), blind spot, retina peripheral a) yellow spot (fovea)— sharpest vision; most concentrated with cones b) Optic tip (blind spot)— no cones or rods; place where optic nerve leaves the eye c) Retina peripheral – contains rods yellow spot Optic tip optic nerve retina

How eyes work? Light from the object enters the eye through cornea The light continues to the pupil and control the amount of light entered. The light was focused by the lens to the retina. Retina record the image and send it to the brain via optic nerve. 12

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 13

Formation of an image in the human eye object To brain retina Optic Nerves 14

Factors Affecting Vision The better visibility of the object when: – Greater the object size – Greater ambient illumination – Greater Contrast – Greater Viewing Time – Greater Atmospheric Clarity During day – object can be identified easier at great distance with good details resolution. 15

Cont. During night – The identification range of deem object is limited and the details resolution is poor. Excess ambient illumination – Especially from light reflected off surface inside aircraft, cloud, water, snow, and desert terrain can produce GLARE. 16

GLARE may cause – Uncomfortable Squinting *Squinting: Half Eye is half close in order to see better. – Eye tearing – Temporary Blindness 17 Cont.

Eye Defects Nearsighted (Myopia) Farsighted (Hyperopia) Color Blindness Impairment of Vision (Eyes Disorder) 18

Near Sighted – – Eyeball is too long – Image focuses in front of the retina. – Eye Lens too convex Far Sighted – – Eyeball is too short – Image is focused behind the retina. – Eye Lens not convex enough © 2000 Microsoft Clip Gallery 19

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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. 21

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 22

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. 23

Astigmatism Normal Vision 24

Types of vision Photopic vision (DAY) Scotopic vision (NIGHT) Mesopic vision (Dawn/Dusk) 25

Photopic vision Occurs during day light or bright light Central vision Color sense and sharpness Best visual acuity 26

Occurs on dimly nights Decreases visual acuity Causes loss of color perception Causes night blind spot Involves the rods only Scotopic Vision 27

Mesopic vision n Occurs at dawn, dusk and in full moonlight n Reduces color vision and decreases visual acuity n Involves both rods and cones n Greater emphasis should be placed on off-center vision as cones become less effective 28

Causes of Impaired Vision Self-imposed stresses such as self-medication, alcohol consumption, tobacco use, hypoglycemia (low blood sugar), and sleep deprivation (not enough sleep)/ fatigue can seriously impair your vision. Inflight exposure to low barometric pressure without the use of supplemental oxygen (above 10,000 ft during the day and above 5,000 ft at night) can result in hypoxia, which impairs visual performance. 29

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. – We call this as visual fatigue. 30 Cont.

The most common symptom in visual fatigue: – Blurred Vision – Excessive Tearing – “Heavy” Eyelid Sensation – Headaches – Burning, scratchy, or dusty eye sensation. 31 Cont.

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, and sustained visual workload during flight. Cont. 32

Reduction night vision in varying altitude (8- 10% carbon monoxide blood content) Altitude Smokers (% reduction) Non-smokers (% reduction)

How to have better scan of object in the flight? Focus on the Specific Object Dark Adaptation Performing Series of Shot (space eye movement) Performing off center viewing (during low and ambient illumination) 34

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 seconds. If there are no specific object to focus, our eyes revert to a relax intermediate focal distance of ft. 35

Cont. Thats 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). 36

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 Adaptation 37

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) Cont. 38

Performing Series of Shot (space eye movement) A study of 50 m aircrafts collision reveal that only 8% were head on (opposite direction) collision. However 42 % aircrafts collide when heading in the same direction. Therefore, scanning the sky for other aircraft is very important factor to avoid MID-AIR COLLISION. 39

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. 40 Cont.

Each movement should not exceed 10° for each area and should not be observed at least 1 sec to enable detection. 41 Cont

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 42 OBJECT 10°

By switching eyes every 2-3 seconds, we can continue to detect the object. 43 OBJECT 10° Cont.

Do you know? The natural ability to focus your eye is critical to flight safety. It is important to know your eyes may required several second to refocus when switching view between near, intermediate, and distance object. For example likes witching view of reading chart/manual, monitoring instrument and looking for traffic or external visual references. 44

Conclusion Of all the sense used for flying by the human body and mind, vision is far most important. In aviation, vision supplies data for monitoring instruments, traffic, written materials, determines visual references for taxiing, takeoffs and approaches to landiong. The disruption of vision or impairment increase the unsafe flight level. 45

Key Points Eyes Anatomy and function. How your eyes work? Internal Structure of the eye. Factors affecting vision. Vision Impairment Correction of Vision Impairment Types of Vision How to have better scan of object? 46

End of Presentation #7 5 Minutes for Q/A session 47