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.

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

Eyes anatomy

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.

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

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

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.

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.

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

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

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

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

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

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?

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

Others Visual Impairment Astigmatism Normal Vision

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.

Factors affecting visual acuity 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.

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)

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.

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).

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

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)

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.

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

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°

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