1. Aviation Human Factor : AHF 2103
Lecture 8: vision
Aviation Human Factor : AHF 2103

2. 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.

3. 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.
Terrain: a stretch of land, kawasan
mechanism for receiving light and transforming it into electrical energy
light reflects from objects
images are focused upside-down on retina
retina contains rods for low light vision and cones for colour vision
ganglion cells (brain!) detect pattern and movement

4. Eyes anatomy

5. Cross Section of the Human Eye
Light from the object is refracted by cornea
Image is focused onto the retina by lens
The image is detected by Nerve cells (rod and cones) on the retina
Signals of the image are transmitted along optic nerve to the brain.
The brain interprets the signals and ‘sees’ an upright image of the object.

6. eyeball
eye muscles
eye muscles: allows eyeball to move in various directions
Cones
The cornea is a transparent, colorless protective tissue, consisting of collagen fibers, located over the front of the eye. The strength of the cornea as a protective covering lies in the fact that it is kept well hydrated by an endothelial pump action. Since the cornea contains no blood vessels, it receives its primary oxygen supply through a tear film action. As light travels, it initially enters the eyes through the cornea and then continues toward the iris.
The iris is the round, pigmented (colored) membrane that surrounds the pupil. For example, if an individual has green, brown, or hazel eyes, this colored portion is the iris. The iris contains ciliary muscle, which is controlled by the parasympathetic nervous system to automatically adjust the size of the pupil and regulate the amount of light entering the eye. Bright light can reduce the pupil diameter to as little as 1.5mm. At the other end of the spectrum, when it is dark, the iris can open the pupil up to 8mm wide, almost six times it’s minimum size. This leads us to the next component -- the pupil.
The lens is a transparent, bi-convex membrane held in place by zonular fibers in the lens capsule and is positioned directly behind the pupil. The lens capsule flexes the lens so the light entering the eye is properly focused on the retinal wall. When individuals are in their twenties, the lens is fairly elastic and flexible with a 15-diopter range of refractive power. But as individuals reach their late forties, the lens begins to harden and the diopter range can be reduced to as low as 4- diopters. This condition is commonly referred to as Presbyopia. Virtually all of the components of the eye are designed to package the light for delivery to the retinal wall.
Fovea:
Area of retina that mediates the most acute vision. Contains only color-sensitive cones.
Optic Disk:
Location on retina where fibers of ganglion cells exit the eye. Responsible for the blind spot.
Rods

7. 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).
refract
1 make (a ray of light) change direction when it enters at an angle.
Accommodation
Changes in the thickness of the lens, accomplished by the ciliary muscles, that focus images of near or distant objects on the retina

8. Anatomy of the Eye Lens – Refracts and focuses light onto the 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.
RETINA
Rods
Night vision
work well in dim light
contain visual purple (視紫)
distribute throughout the retina
none at yellow spot and blind spot
Cones
3 types: sensitive to long, medium and short wavelength
Often red, green, blue but actual peak sensitivity is yellow, yellowish-green, and blue
work in brighter light
concentrated at yellow spot
objects are seen most sharply in focus
Bipolar Cells
Ganglion Cells
Light passes through cell layers and then back to the ganglion cells.

9. 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.

10. 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

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

12. Impairment of Vision (Eyes Disorder)
Eye Defects
Farsighted
(Hyperopia)
Color
Blindness
Nearsighted
(Myopia)
Short sight
Myopia (nearsightedness)
see nearby objects clearly but not distant objects
Due to abnormally long eyeball and too strong refractory power
Long sight
Hyperopia (farsightedness)
Can see distant objects normally but problem in near objects
Due to short eyeball and inadequate refractory power of the lens
Colour blindness
cannot see some or all colours

13. Impairment of Vision (Eyes Disorder)
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
The image of distant object is formed in front of the retina because of 2 reasons:
Lens too convex
Eyeball too long
can be corrected by concave lens
The image of near object is formed behind the retina because of 2 reasons:
1) Lens not convex enough
2) Eyeball too short
can be corrected by convex lens
Colour blindness
due to reduced number of / some defects in one or more of the 3 types of cone cells
inherited

15. Corrective Lenses Nearsightedness (Myopia) –
Correction: Use Concave lenses
to expand focal lengths.
Farsightedness (Hyperopia)–
Correction: Use Convex lenses to
shortens the focal length.
Vision – Eye is a convex lens.
Concave Lenses

16. Color blindness Let’s have a test! What numbers do you see?
Due to reduced number of / some defects in one or more of the cone cells
Inherited
Let’s have a test!
What numbers do you see?

19. 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.
Astigmatism
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 rather than dish shaped lenses.
Presbyopia - decrease in vision with age
Cataract - Increase in protein in lens
Glaucoma - Increased intraocular pressure
Infections - Inflammation of the eye
Retinitis Pigmentosa - familial disorder causing loss of rod cells. Includes peripheral visual loss and night blindness

20. Others Visual Impairment
Astigmatism
Normal Vision

21. 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.

22. Factors affecting visual acuity
Fatigue (continue..)
The most common symptom in visual fatigue:
Blurred Vision
Excessive Tearing
“Heavy” Eyelid Sensation
Headaches

23. 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.

24. 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)

25. 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.

26. Focus on the Specific Object
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).

27. Dark Adaptation
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

28. Dark Adaptation
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)

29. Performing Series of Shot
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.

30. 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. 1
2 4 5 3

31. 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
OBJECT
10°

32. Performing off center viewing
OBJECT
10°
By switching eyes every 2-3 seconds, we can continue to detect the object.