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I am fairly short-sighted and wear glasses pretty much all the time. Naively, I would expect that when I take my glasses off, the image I see should look very much the same as as a photograph that's out of focus, or an image to which someone has applied a Gaussian blur filter. In bright conditions this is mostly true, but at night if I look at distant point sources of light, the blurry halos around them appear to have quite a complex structure, and a fairly well-defined edge. Why is this?
To make it clearer what I mean, and at the same time to make a hypothesis about the answer, here is a public domain image of some lights, taken with a camera out of focus:
(image source.) Notice that the image cast by each light is not simply a uniform circle. They are each slightly hexagonal; they are slightly brighter around the edge than in the middle; and there are distinct nonuniformities in the brightness in the interior of each shape.
What I see is actually fairly similar to this but much more extreme. The shape formed by a light is much further from a circle, being very irregular in shape and distinctly elongated in one direction. (This latter is perhaps not surprising given that I have a strong astigmatism.) The bright edge to the shape, and the non-uniformities in its brightness, are much more pronounced than in the camera image.
Now, in the photograph I know that the hexagonal shape is due to the hexagonal aperture in the camera. This can be ruled out in my eyes because my pupils are definitely circular. (Unless some light also passes through parts of the iris?) I would guess that the bright edges are caused by diffraction, and that the nonuniformities are caused by defects in the lens and/or dirt on its surface. I suppose that diffraction and lens aberrations must be the causes of what I see when looking at distant lights without my glasses.
So in the end, my question is mostly just, am I right about this? Are the shapes I see the result of defects in my eye's optics, and which specific anatomical features of the eye are likely to be their main causes?
This phenomenon is known as bokeh.
You are right in the hexagonal shape being produced by the iris (of the camera), and from this, it is clear why this happens: The iris blocks out some of the light travelling into it, and a shape approximating that of the camera's iris aperture is projected onto the CCD.
The same thing happens for the eye. The iris will block out a portion of the light, causing the bokeh to approximate the shape of the iris aperture (aka the pupil), which is roughly circular for humans. Animals with non-circular pupils will perceive differently shaped bokeh. If the lens suffers from astigmatism, it will also result in non-spherical bokeh being projected onto the retina.
This stackexchange link goes into greater detail on Gaussian blur vs bokeh.
Perfect Sight Without Glasses/Chapter 16
PERSONS with imperfect sight always have illusions of vision so do persons with normal sight. But while the illusions of normal sight are an evidence of relaxation, the illusions of imperfect sight are an evidence of strain. Some persons with errors of refraction have few illusions, others have many because the strain which causes the error of refraction is not the same strain that is responsible for the illusions.
The illusions of imperfect sight may relate to the color, size, location and form of the objects regarded. They may include appearances of things that have no existence at all, and various other curious and interesting manifestations.
When a patient regards a black letter and believes it to be grey, yellow, brown, blue, or green, he is suffering from an illusion of color. This phenomenon differs from colorblindness. The color-blind person is unable to differentiate between different colors, usually blue and green, and his inability to do so is constant. The person suffering from an illusion of color does not see the false colors constantly or uniformly. When he looks at the Snellen test card the black letters may appear to him at one time to be grey but at another moment they may appear to be a shade of yellow, blue, or brown. Some patients always see the black letters red to others they appear red only occasionally. Although the letters are all of the same color, some may see the large letters black and the small ones yellow or blue. Usually the large letters are seen darker than the small ones, whatever color they appear to be. Often different colors appear in the same letter, part of it seeming to be black, perhaps, and the rest grey or some other color. Spots of black, or of color, may appear on the white and spots of white, or of color, on the black.
Large letters may appear small, or small letters large. One letter may appear to be of normal size, while another of the same size and at the same distance may appear larger or smaller than normal. Or a letter may appear to be of normal size at the near-point and at the distance, and only half that size at the middle distance. When a person can judge the size of a letter correctly at all distances up to twenty feet his vision is normal. If the size appears different to him at different distances, he is suffering from an illusion of size. At great distances the judgment of size is always imperfect, because the sight at such distances is imperfect, even though perfect at ordinary distances. The stars appear to be dots, because the eye does not possess perfect vision for objects at such distances. A candle seen half a mile away appears smaller than at the near-point but seen through a telescope giving perfect vision at that distance it will be the same as at the near-point. With improved vision the ability to judge size improves.
The correction of an error of refraction by glasses seldom enables the patient to judge size as correctly as the normal eye does, and the ability to do this may differ very greatly in persons having the same error of refraction. A person with ten diopters of myopia corrected by glasses may (rarely) be able to judge the sizes of objects correctly. Another person, with the same degree of myopia and the same glasses, may see them only one-half or one-third their normal size. This indicates that errors of refraction have very little to do with incorrect perceptions of size.
Round letters may appear square or triangular straight letters may appear curved letters of regular form may appear very irregular a round letter may appear to have a checkerboard or a cross in the center. In short, an infinite variety of changing forms may be seen. Illumination, distance and environment are all factors in this form of imperfect sight. Many persons can see the form of a letter correctly when other letters are covered, but when the other letters are visible they cannot see it. The indication of the position of a letter by a pointer helps some people to see it. Others are so disturbed by the pointer that they cannot see the letter so well.
Multiple images are frequently seen by persons with imperfect sight, either with both eyes together, with each eye separately, or with only one eye. The manner in which these multiple images make their appearance is sometimes very curious. For instance, a patient with presbyopia read the word HAS normally with both eyes. The word PHONES he read correctly with the left eye but when he read it with the right eye he saw the letter P double, the imaginary image being a little distance to the left of the real one. The left eye, while it had normal vision for the word PHONES, multiplied the-shaft of a pin when this object was in a vertical position (the head remaining single), and multiplied the head when the position was changed to the horizontal (the shaft then remaining single). When the point of the pin was placed below a very small letter, the point was sometimes doubled while the letter remained single. No error of refraction can account for these phenomena. They are tricks of the mind only. The ways in which multiple images are arranged are endless. They are sometimes placed vertically, sometimes horizontally or obliquely, and sometimes in circles, triangles and other geometrical forms. Their number, too, may vary from two to three, four, or more. They may be stationary, or may change their position more or less rapidly. They also show an infinite variety of color, including a white even whiter than that of the background.
A period following a letter on the same horizontal level as the bottom of the letter may appear to change its position in a great variety of curious ways. Its distance from the letter may vary. It may even appear on the other side of the letter. It may also appear above or below the line. Some persons see letters arranged in irregular order. In the case of the word AND, for instance, the D may occupy the place of the N. or the first letter may change places with the last. All these things are mental illusions. The letters sometimes appear to be farther off than they really are. The small letters, twenty feet distant, may appear to be a mile away. Patients troubled by illusions of distance sometimes ask if the position of the card has not been changed.
ILLUSIONS OF NON-EXISTENT OBJECTS
When the eye has imperfect sight the mind not only distorts what the eye sees, but it imagines that it sees things that do not exist. Among illusions of this sort are the floating specks which so often appear before the eyes when the sight is imperfect, and even when it is ordinarily very good. These specks are known scientifically as "muscae volitantes," or "flying flies," and although they are of no real importance, being symptoms of nothing except mental strain, they have attracted so much attention, and usually cause so much alarm to the patient, that they will be discussed at length in another chapter.
ILLUSIONS OF COMPLEMENTARY COLORS
When the sight is imperfect the subject, on looking away from a black, white, or brightly colored object, and closing the eyes, often imagines for a few seconds that he sees the object in a complementary, or approximately complementary, color. If the object is black upon a white background, a white object upon a black background will be seen. If the object is red, it may be seen as blue and if it is blue, it may appear to be red. These illusions, which are known as "after-images," may also be seen, though less commonly, with the eyes open, upon any background at which the subject happens to look, and are often so vivid that they appear to be real.
ILLUSIONS OP THE COLOR OF THE SUN
Persons with normal sight see the sun white, the whitest white there is but when the sight is imperfect it may appear to be any color in the spectrum - red, blue, green, purple, yellow, etc. In fact, it has even been described by persons with imperfect vision as totally black. The setting sun commonly appears to be red, because of atmospheric conditions but in many cases these conditions are not such as to change the color, and while this still appears to be red to persons with imperfect vision, to persons with normal vision it appears to be white. When the redness of a red sun is an illusion, and not due to atmospheric conditions, its image on the ground glass of a camera will be white, not red, and the rays focussed with a burning glass will also be white. The same is true of a red moon.
BLIND SPOTS AFTER LOOKING AT THE SUN
After looking at the sun most people see black or colored spots which may last from a few minutes to a year or longer, but are never permanent. These spots are also illusions, and are not due, as is commonly supposed, to any organic change in the eye. Even the total blindness which sometimes results, temporarily, from looking at the sun, is only an illusion.
ILLUSIONS OF TWINKLING STARS
The idea that the stars should twinkle has been embodied in song and story, and is generally accepted as part of the natural order of things but it can be demonstrated that this appearance is simply an illusion of the mind.
CAUSE OF THE ILLUSIONS OF IMPERFECT SIGHT
All the illusions of imperfect sight are the result of a strain of the mind, and when the mind is disturbed for any reason illusions of all kinds are very likely to occur. This strain is not only different from the strain that produces the error of refraction, but it can be demonstrated that for each and every one of these illusions there is a different kind of strain. Alterations of color do not necessarily affect the size or form of objects, or produce any other illusion, and it is possible to see the color of a letter, or of a part of a letter, perfectly, without recognizing the letter. To change black letters into blue, or yellow, or another color, requires a subconscious strain to remember or imagine the colors concerned, while to alter the form requires a subconscious strain to see the form in question. With a little practice anyone can learn to produce illusions of form and color by straining consciously in the same way that one strains unconsciously and whenever illusions are produced in this way it will be found that eccentric fixation and an error of refraction have also been produced.
The strain which produces polyopia is different again from the strain which produces illusions of color, size and form. After a few attempts most patients easily learn to produce polyopia at will. Staring or squinting, if the strain is great enough, will usually make one see double. By looking above a light, or a letter, and then trying to see it as well as when directly regarded, one can produce an illusion of several lights, or letters, arranged vertically. If the strain is great enough, there may be as many as a dozen of them. By looking to the side of the light or letter, or looking away obliquely at any angle, the images can be made to arrange themselves horizontally, or obliquely at any angle.
To see objects in the wrong location, as when the first letter of a word occupies the place of the last, requires an ingenuity of eccentric fixation and an education of the imagination which is unusual.
The black or colored spots seen after looking at the sun, and the strange colors which the sun sometimes seems to assume, are also the result of the mental strain. When one becomes able to look at the orb of day without strain, these phenomena immediately disappear.
After-images have been attributed to fatigue of the retina, which is supposed to have been so overstimulated by a certain color that it can no longer perceive it, and therefore seeks relief in the hue which is complementary to this color. If it gets tired looking at the black C on the Snellen test card, for instance, it is supposed to seek relief by seeing the C white. This explanation of the phenomenon is very ingenious but scarcely plausible. The eyes cannot see when they are closed and if they appear to see under these conditions, it is obvious that the subject is suffering from a mental illusion with which the retina has nothing to da. Neither can they see what does not exist and if they appear to see a white C on a green wall where there is no such object, it is obvious again that the subject is suffering from a mental illusion. The after-image indicates, in fact, simply a loss of mental control, and occurs when there is an error of refraction, because this condition also is due to a loss of mental control. Anyone can produce an afterimage at will by trying to see the big C all alike - that is, under a strain but one can look at it indefinitely by central fixation without any such result.
While persons with imperfect sight usually see the stars twinkle, they do not necessarily do so. Therefore it is evident that the strain which causes the twinkling is different from that which causes the error of refraction. If one can look at a star without trying to see it, it does not twinkle and when the illusion of twinkling has been produced, one can usually stop it by "swinging" the star. On the other hand, one can start the planets, or even the moon, to twinkling, if one strains sufficiently to see them.
ILLUSIONS OF NORMAL SIGHT
The illusions of normal sight include all the phenomena of central fixation. When the eye with normal sight looks at a letter on the Snellen test card, it sees the point fixed best,- and everything else in the field of vision appears less distinct. As a matter of fact, the whole letter and all the letters may be perfectly black and distinct, and the impression that one letter is blacker than the others, or that one part of a letter is blacker than the rest, is an illusion. The normal eye, however, may shift so rapidly that it appears to see a whole line of small letters all alike simultaneously. As a matter of fact there is, of course, no such picture on the retina. Each letter has not only been seen separately, but it has been demonstrated in the chapter on "Shifting and Swinging" that if the letters are seen at a distance of fifteen or twenty feet, they could not be recognized unless about four shifts were made on each letter. To produce the impression of a simultaneous picture of fourteen letters, therefore, some sixty or seventy pictures, each with some one point more distinct than the rest, must have been produced upon the retina. The idea that the letters are seen all alike simultaneously is, therefore, an illusion. Here we have two different kinds of illusions. In the first case the impression made upon the brain is in accordance with the picture on the retina, but not in accordance with the fact. In the second the mental impression is in accordance with the fact, but not with the pictures upon the retina.
The normal eye usually sees the background of a letter whiter than it really is. In looking at the letters on the Snellen test card it sees white streaks at the margins of the letters, and in reading fine print it sees between the lines and the letters, and in the openings of the letters, a white more intense than the reality. Persons who cannot read fine print may see this illusion, but less clearly. The more clearly it is seen, the better the vision and if it can be imagined consciously - it is imagined unconsciously when the sight is normal - the vision improves. If the lines of fine type are covered, the streaks between them disappear. When the letters are regarded through a magnifying glass by the eye with normal sight, the illusion is not destroyed, but the intensity of the white and black are lessened. With imperfect sight it may be increased to some extent by this means, but will remain less intense than the white and black seen by the normal eye. The facts demonstrate that perfect sight cannot be obtained with glasses.
The illusions of movement produced by the shifting of the eye and described in detail in the chapter on "Shifting and Swinging" must also be numbered among the illusions of normal sight, and so must the perception of objects in an upright position. This last is the most curious illusion of all. No matter what the position of the head, and regardless of the fact that the image on the retina is inverted, we always see things right side up.
Many organizations have developed autostereoscopic 3D displays, ranging from experimental displays in university departments to commercial products, and using a range of different technologies.  The method of creating autostereoscopic flat panel video displays using lenses was mainly developed in 1985 by Reinhard Boerner at the Heinrich Hertz Institute (HHI) in Berlin.  Prototypes of single-viewer displays were already being presented in the 1990s, by Sega AM3 (Floating Image System)  and the HHI. Nowadays, this technology has been developed further mainly by European and Japanese companies. One of the best-known 3D displays developed by HHI was the Free2C, a display with very high resolution and very good comfort achieved by an eye tracking system and a seamless mechanical adjustment of the lenses. Eye tracking has been used in a variety of systems in order to limit the number of displayed views to just two, or to enlarge the stereoscopic sweet spot. However, as this limits the display to a single viewer, it is not favored for consumer products.
Currently, most flat-panel displays employ lenticular lenses or parallax barriers that redirect imagery to several viewing regions however, this manipulation requires reduced image resolutions. When the viewer's head is in a certain position, a different image is seen with each eye, giving a convincing illusion of 3D. Such displays can have multiple viewing zones, thereby allowing multiple users to view the image at the same time, though they may also exhibit dead zones where only a non-stereoscopic or pseudoscopic image can be seen, if at all.
Parallax barrier Edit
A parallax barrier is a device placed in front of an image source, such as a liquid crystal display, to allow it to show a stereoscopic image or multiscopic image without the need for the viewer to wear 3D glasses. The principle of the parallax barrier was independently invented by Auguste Berthier, who published first but produced no practical results,  and by Frederic E. Ives, who made and exhibited the first known functional autostereoscopic image in 1901.  About two years later, Ives began selling specimen images as novelties, the first known commercial use.
In the early 2000s, Sharp developed the electronic flat-panel application of this old technology to commercialization, briefly selling two laptops with the world's only 3D LCD screens.  These displays are no longer available from Sharp but are still being manufactured and further developed from other companies. Similarly, Hitachi has released the first 3D mobile phone for the Japanese market under distribution by KDDI.   In 2009, Fujifilm released the FinePix Real 3D W1 digital camera, which features a built-in autostereoscopic LCD measuring 2.8 in (71 mm) diagonal. The Nintendo 3DS video game console family uses a parallax barrier for 3D imagery on a newer revision, the New Nintendo 3DS, this is combined with an eye tracking system.
Integral photography and lenticular arrays Edit
The principle of integral photography, which uses a two-dimensional (X-Y) array of many small lenses to capture a 3-D scene, was introduced by Gabriel Lippmann in 1908.   Integral photography is capable of creating window-like autostereoscopic displays that reproduce objects and scenes life-size, with full parallax and perspective shift and even the depth cue of accommodation, but the full realization of this potential requires a very large number of very small high-quality optical systems and very high bandwidth. Only relatively crude photographic and video implementations have yet been produced.
One-dimensional arrays of cylindrical lenses were patented by Walter Hess in 1912.  By replacing the line and space pairs in a simple parallax barrier with tiny cylindrical lenses, Hess avoided the light loss that dimmed images viewed by transmitted light and that made prints on paper unacceptably dark.  An additional benefit is that the position of the observer is less restricted, as the substitution of lenses is geometrically equivalent to narrowing the spaces in a line-and-space barrier.
Philips solved a significant problem with electronic displays in the mid-1990s by slanting the cylindrical lenses with respect to the underlying pixel grid.  Based on this idea, Philips produced its WOWvx line until 2009, running up to 2160p (a resolution of 3840×2160 pixels) with 46 viewing angles.  Lenny Lipton's company, StereoGraphics, produced displays based on the same idea, citing a much earlier patent for the slanted lenticulars. Magnetic3d and Zero Creative have also been involved. 
Compressive light field displays Edit
With rapid advances in optical fabrication, digital processing power, and computational models for human perception, a new generation of display technology is emerging: compressive light field displays. These architectures explore the co-design of optical elements and compressive computation while taking particular characteristics of the human visual system into account. Compressive display designs include dual  and multilayer    devices that are driven by algorithms such as computed tomography and Non-negative matrix factorization and non-negative tensor factorization.
Autostereoscopic content creation and conversion Edit
Tools for the instant conversion of existing 3D movies to autostereoscopic were demonstrated by Dolby, Stereolabs and Viva3D.   
Dimension Technologies released a range of commercially available 2D/3D switchable LCDs in 2002 using a combination of parallax barriers and lenticular lenses.   SeeReal Technologies has developed a holographic display based on eye tracking.  CubicVue exhibited a color filter pattern autostereoscopic display at the Consumer Electronics Association's i-Stage competition in 2009.  
There are a variety of other autostereo systems as well, such as volumetric display, in which the reconstructed light field occupies a true volume of space, and integral imaging, which uses a fly's-eye lens array.
The term automultiscopic display has recently been introduced as a shorter synonym for the lengthy "multi-view autostereoscopic 3D display",  as well as for the earlier, more specific "parallax panoramagram". The latter term originally indicated a continuous sampling along a horizontal line of viewpoints, e.g., image capture using a very large lens or a moving camera and a shifting barrier screen, but it later came to include synthesis from a relatively large number of discrete views.
Sunny Ocean Studios, located in Singapore, has been credited with developing an automultiscopic screen that can display autostereo 3D images from 64 different reference points. 
A fundamentally new approach to autostereoscopy called HR3D has been developed by researchers from MIT's Media Lab. It would consume half as much power, doubling the battery life if used with devices like the Nintendo 3DS, without compromising screen brightness or resolution other advantages include a larger viewing angle and maintaining the 3D effect when the screen is rotated. 
Movement parallax refers to the fact that the view of a scene changes with movement of the head. Thus, different images of the scene are seen as the head is moved from left to right, and from up to down.
Many autostereoscopic displays are single-view displays and are thus not capable of reproducing the sense of movement parallax, except for a single viewer in systems capable of eye tracking.
Some autostereoscopic displays, however, are multi-view displays, and are thus capable of providing the perception of left-right movement parallax.  Eight and sixteen views are typical for such displays. While it is theoretically possible to simulate the perception of up-down movement parallax, no current display systems are known to do so, and the up-down effect is widely seen as less important than left-right movement parallax. One consequence of not including parallax about both axes becomes more evident as objects increasingly distant from the plane of the display are presented: as the viewer moves closer to or farther away from the display, such objects will more obviously exhibit the effects of perspective shift about one axis but not the other, appearing variously stretched or squashed to a viewer not positioned at the optimum distance from the display.
Causes of Impaired Depth Perception
A lack of depth perception can be caused by numerous conditions. These include:
- Amblyopia: Also called "lazy eye," this is a condition in which one eye is weaker than the other. This typically happens because of abnormal vision development in childhood and features decreased vision in one or both eyes.
- Optic nerve hypoplasia: This occurs when the optic nerve, which sends visual signals from your eyes to your brain, has incomplete development before birth. It can result in partial or total vision loss in children.
- Strabismus: This occurs when the eyes point in different directions, such as one pointing straight ahead and the other pointing inward or down.
- Blurry vision: Numerous conditions can cause the vision in one or both eyes to be blurry, as can trauma to an eye.
- Injury to one eye: Trauma can alter your vision, either temporarily or permanently.
A lack of depth perception can impact your life in several ways:
- It can affect a child's ability to learn.
- It can cause problems driving and navigating roads properly.
- It can prevent an athlete from reaching their full potential.
- It can stop you from getting a job that requires good depth perception.
You can be getting a headache from your new glasses no matter if they are prescribed “correctly” or not. Some eye doctors will insist that this means there must be an mistake with the prescription, especially if it was some other eye doctor who prescribed it, or there must be some other vision problem that wasn’t addressed. The rationale is that glasses make things better and that certainly glasses would never be causingthese headaches.
Most headaches like these are tension headaches. The pain is caused by muscle contractions in the head and neck regions. A feeling of tightness around the eyes, or within the eyes, is evidence of this, not to mention a stiff neck or a need to massage your temples. Why would glasses be causing this? It has to do with the way you use your eyes. There are bad habits that cause chronic tension as you struggle to do something that your body or brain was not designed to do. This is part of what this website is all about.
4.1. Significant Findings
Presbyopes with high myopia had poorer overall QOL compared to those with low myopia. Similarly, high myopes had worse functionality scores compared to low myopes. Compared to SVD users, PAL users, on average, had better overall QOL scores for both myopic groups. PAL users also had better perception scores for high myopes. The difference in gender distribution did not have a significant effect on the QOL score.
The highly myopic group had significantly poorer visual acuity, with a difference of 0.05 logMAR, which equates to 2𠄳 letters from the visual acuity chart. This slight decrease in visual acuity may not be considered clinically significant by clinicians. However, it may have a tangible effect, contributing to poorer QOL and functionality outcomes with glasses. Therefore, this study’s outcome from the QOL reflected the tangible effects of reduced vision felt by the participants, which were often dismissed as insignificant by clinicians.
Reduced best-corrected visual acuity with spectacle lenses in high myopia has been found in previous studies [9,18,19,20,21,22,23,24,25]. In addition, there was a higher proportion of high myopes who experienced severe trouble with driving at night and in the rain . Besides visual acuity affecting the corrected vision of high myopes, the night vision threshold , higher-order aberration [20,21], and larger pupil size may also contribute to poorer vision under dim lighting, as experienced when driving at night and in the rain. Further physiological stretching from axial elongation due to myopia also reduces the function and resolution of photoreceptors [22,26]. Some studies also found reduced contrast sensitivity at high spatial frequencies in fully corrected high myopes, which may contribute to reduced functionality with glasses . However, we did not find any differences in contrast sensitivity between low and high myopic groups, as found by Collins et al. . Further investigation is required to measure contrast sensitivity at different spatial frequencies in order to elucidate the underlying cause of reduced functionality with glasses.
It was expected that the difference in the refractive error between high- and low- myopic groups (𢄥.52 ± 2.4 D compared to 𢄣.1 ± 1.7 D p < 0.001) would have a significant impact on the unaided visual acuity of high-myopic groups, even though it was not measured. With significantly poorer vision without glasses, a higher proportion of high-myopic presbyopes would have issues seeing both far and near, as they are severely under-corrected for both distances. This would result in a poorer outcome in functionality without glasses for the high-myopic group. The poorer outcome in QOL regarding uncorrected vision was also reflected in other studies [18,28,29]. Our study shows that a larger proportion of high myopes had difficulty reading and doing near work, as well as waking up with clear vision and looking at an alarm clock without glasses. All the affected activities, as mentioned above, were near-distance activities, as also reported in other studies [18,29]. The lack of distance activities reported without glasses was due to the inability to carry them out without glasses. No high myopes drove without glasses.
This study found that highly myopic PAL wearers had a better score for perception subscales compared to SVD lens wearers. In the perception subscale, highly myopic SVD lens wearers were more raid to do things due to their vision” and were also more 𠇏rustrated with their glasses.” SVD lenses only correct distance vision and not near vision hence, highly myopic SVD lens wearers will have poor near and intermediate vision, with or without glasses. To overcome blurred vision due to working distance, they may need to remove and put on SVD glasses more frequently, adding to the frustration. Compared with SVD wearers, low-myopic PAL wearers also had a significantly better overall QOL, with no other difference in the other subscales. Despite the lack of a significant difference in each subscale, the significant differences in the overall QOL may be due to the additive effect of multiple components. Other studies have found that near vision is affected while using SVD lenses for presbyopes, while having better outcomes using PAL [30,31,32,33]. Poorer near and intermediate vision with SVD lenses may significantly affect QOL outcomes in low myopes they may also significantly affect the perception subscale for high myopes. Moreover, Pesudovs et al., 2006 found that PAL wearers have reduced sensitivity to light, eye pain, and redness compared to SVD lens wearers, while doing near work, for early presbyopes . As such, the visual comfort from PAL could be another factor in this outcome.
4.2. Strengths and Limitations of the Study
This is the first study that explores the correction habits of presbyopes and the impact of the severity of myopia on QOL. This study was able to measure the subjective differences between the severity of myopia and the types of visual correction, which was otherwise not significantly different from clinical measures. However, the recruitment rate of patients with high myopia (27.5%) was much lower compared with those having low myopia (72.5%). This, however, is a reflection of myopia’s prevalence in the population . Refraction and axial length measurements were not conducted to directly link the causal effect of refractive error and elongation of the eye to the QOL outcome. Unaided visual acuity and contrast sensitivity with spatial frequencies need to be measured to directly understand the contribution of these factors to some of the subscales, such as functionality with and without glasses. More details such as the lens design of PAL should be included in order to further understand whether it has an impact on QOL. Though the RSVP questionnaire has been shown to be deficient in several psychometric properties with underutilised response scales, it was chosen not only because it was validated but also because it includes measures for quality of vision and life [11,12,13,14,15,34,35,36].
4.3. Suggestions for Future Work
From this study, the QOL assessment recorded outcomes that could not be measured through typical clinical tests or may be deemed clinically insignificant. Hence, such questionnaires should be administered during dispensing to achieve higher success rates. Work should be done to understand which are the important and contributing subscales for each eye condition and interventions, in order to apply the right questionnaire for each condition. A systematic review could be done on all types of vision correction used for presbyopia, such as PAL, SVD, contact lenses, and intraocular lenses, in order to understand their impact on QOL.
Previous research has demonstrated the ability of people to perceive and update haptic stimuli within arm’s reach. This is true for both single targets (Barber & Lederman, 1988 Hollins & Kelley, 1988) and configurations of a small number of targets (Giudice et al., 2009 Giudice et al., 2011 Pasqualotto, Finucane, & Newell, 2005). Rotational updating of locations perceived beyond arm’s reach, i.e. by touching them with a cane, has also been demonstrated (May & Vogeley, 2006). The present experiments used the blind walking/gesturing method of Ooi and her colleagues (Ooi et al., 2001, 2006 Wu et al., 2004) to investigate the ability of people to perceive targets sensed with a long probe, which extended the reach of the arm by 1 or 2 m. The 2-m pole condition was of greatest interest, for it involved purely haptic exploration involving the hand and arm.
Because we were primarily interested in the perception of targets varying in height and distance using extended touch, we focused our analysis more on the targets that were initially straight ahead. In Experiment 1 both accuracy and precision were best for those trials ( Figures 3 and and4) 4 ) in Experiment 2, which showed that auditory localization cues were not a factor in extended touch, only straight-ahead targets were used. Figures 5 and and6 6 give these results for Experiment 1 and 2, respectively. As expected from prior work (Ooi & He, 2006 Ooi et al., 2001, 2006 Wu et al., 2004), vision led to responses with the greatest accuracy ( Figure 5 ). Precision was also slightly better. The most notable result is the remarkably good accuracy and precision with which people perceive targets using a 2 m pole ( Figures 5 and and7). 7 ). This result extends the research of Chan and Turvey (1991), which showed that people wielding a probe were able to perceive the vertical distance to a horizontal surface up to 80 cm away. It is also noteworthy that the short pole and hand touch conditions resulted in comparably good performance. Both of these conditions involve haptic input from hand and arm and proprioceptive input associated with walking forward to reach the target and then walking backward to the origin. Previous work investigating haptic learning during ambulation and hand exploration, where blindfolded participants were guided through a room-sized layout of six sequentially exposed objects, has shown accurate learning (Yamamoto & Shelton, 2005, 2007).
Although the manipulation of target azimuth in Experiment 1 resulted in significant azimuthal errors ( Figures 2 and and3), 3 ), participants nevertheless showed the ability to update the locations of targets initially lying in all directions about the starting orientation. Although we did not report the results for height, accuracy and precision of the responses to height and distance for targets straight ahead were only slightly better than those for the other directions. It is noteworthy that in all four of the perception conditions, participants were able to update the locations of targets directly behind them while sidestepping. Indeed, in a study that controlled for differences in body turning during the perception and response phases, Horn and Loomis (2004) showed that updating performance is about as good in back as in front.
As discussed in the introduction, phenomenological reports indicate that the most salient aspect of the experience of contacting a surface or point target with a wielded probe is not the vibrations and forces in the probe but the perception of the point of contact. We maintain that the participant does indeed perceive the point of contact in external space, not unlike perceiving the location of a target with the bare hand. Moreover, as other research has shown with visual and auditory targets (for a summary, see Loomis et al., in press), accompanying the perceived location is a more abstract spatial representation of the same location (spatial image) that continues even after the stimulus and its corresponding percept have ceased. The experiments here provide evidence of a 3-D spatial image corresponding to the perceived contact point between target and probe. In particular, requiring the participants to sidestep precluded them from simply making an estimate of the contact point and performing the blind walking/gesturing response in a ballistic fashion. Instead they needed to form a representation of the contact point (a spatial image) and update this location in order to perform the subsequent response.
Our notion of the spatial image, as built up from extended touch, is a representation of the object at the end of the probe through a linkage of what is being perceived from the external world and an internal model of the extension (Loomis, 1992). This idea is somewhat different from other views positing that use of a tool actually leads to a change in the body schema, such that the representation of the limb expands to encompass the tool (Maravita & Iriki, 2004). In other words, the perceptual-motor expansion of peripersonal space afforded by tool use leads to expansion of the neural representation of the arm in our body schema, as evidenced by monkeys (Iriki, Tanaka, & Iwamura, 1996) and humans (Cardinali et al., 2009). While these alterations of body schema are known to occur after extended training, the current results were demonstrated almost immediately after initial perception with the probe. We interpret these findings as supporting the development of a spatial image of surrounding space based on accurate perception of the tool and an internal model of its extent, rather than inducing a more enduring modification of the body schema. As the spatial image is postulated as representing the perceived contact point of the probe, it can readily support spatial behaviors after the percept has ceased, such as the spatial updating performance shown in this paper. This notion is congruent with the phenomenological claim that people experience the point of contact at the end of the probe, rather than the probe itself (Gibson, 1966 Katz, 1925/1989) and is in agreement with the suggestion that the tip of the tool is what is being represented, rather than considering it as an extension of the arm’s representation in the body schema (Holmes & Spence, 2004). This interpretation is also consistent with the view that we may have separate representations of the hand and tool which are co-registered during context-appropriate actions (Povinelli et al., 2011).
If you try shooting a basket or throwing a ball at a target, you'll probably come pretty close, even on your first try. But when you put on this special set of goggles and try to make the same shots, things get very interesting.
Tools and Materials
- Plastic safety goggles with a flat face plate (available at hardware and home improvement stores or from scientific supply companies)
- Scissors or craft knife
- Two fresnel prisms for correcting vision problems (such as 3M TM Press-On TM Prisms, 30 diopter)
- Masking tape
- Beanbag or ball that can be thrown indoors without breaking things
- Partner (optional)
- Look at the edge of each fresnel prism and note which direction the ridges point. For the next step, you will need to orient both prisms so that the ridges point in the same direction.
- Lay each prism over one lens of the goggles. Use scissors or a craft knife to cut away any excess so the prism fits precisely over the lens.
- Make sure the lenses of the goggles are clean and dry. Peel away the adhesive backing from one prism and press it to one of the lenses, making sure there are no bubbles of air between the prism and the lens. Do the same with the second prism and lens. No tape or glue is necessary the prisms should self-adhere.
- Using masking tape, mark a squarish target on a floor or wall, 12–16 inches (30-40 centimeters) on each side.
To Do and Notice
Stand about 9 or 10 feet (3 m) from the target. (The farther you are from the target, the more obvious the effect will be.) Throw the beanbag or ball at the target, underhand. Notice how close you get. Repeat your throw a few times.
Put the goggles on, and make sure that you can see the hoop or target through the goggles. Make sure that your throwing hand is positioned so that you cannot see it or the ball through the goggles.
Try to hit the target with the ball, again throwing underhand. Notice how close you get. What do you notice about the accuracy of your throw? Have your partner retrieve the ball for you if possible—it’s hard to do with the goggles on. Keep trying until you hit the target three times in a row. How many tries does it take you?
Take the goggles off and try again. Notice how close you get to the target. Keep trying until you score three times in a row. How many tries does it take you? What do you notice about the accuracy of your throws?
What’s Going On?
When you throw a ball at a target, many different parts of your brain are working together. Your eyes and visual systems give your brain information about where things are, while your proprioceptive systems give your brain information about where your body is in space. Your motor systems use all this information to produce movement, so you can throw the ball in the right direction.
When you first put on the goggles, the ball doesn’t go where your eye says it should. Because of the way it refracts, or bends, light, the prism makes objects in front of you appear to be to one side. Light travels from the target to your eye along the path shown by the arrows in the diagram below (click to enlarge).
As light passes through the prism, it is bent twice—once when it enters the prism and again when it leaves. Your eye-brain system tries to follow this light back to its origin in order to locate the target, but it doesn’t have the ability to recognize that the light was bent. It follows the light back along a straight line defined by the ray of light that enters your eye, and so the target appears to be somewhere on this line.
At first, your throws probably miss the target by a lot. Your brain, however, soon adapts to the distortion produced by the goggles, and your visual and motor systems make adjustments. You begin to aim farther to the side and get closer to hitting the target.
When you remove the goggles, your brain remembers the prism distortion, and it functions as if the goggles were still in place. It may take a few trials for your brain to “unlearn” the adjustments it made and return to normal. Your experience with the goggles shows that your brain and and its different systems are dynamic: They continually respond and adapt to your experiences, whether or not you’re thinking about them.
You forced your eyes and brain to adapt when you put on the goggles. But your brain is challenged on a daily basis to relearn skills and change the way it processes information—all it takes is driving someone else’s car, taking a new route to the grocery store, or putting your toothbrush in a new location. If we did not have the ability to adapt to changes in the world (or to changes in our perception of the world), life would be much harder.
How Fast Do People Adapt?
Try collecting quantitative data from different people using the prism goggles to find the range of learning and unlearning times.
Where Is Adaptation Happening?
Can you think of experiments that would help you to figure out whether your sensory systems, your motor systems, or both, adapt to the goggles? Try switching your throwing hand after taking the goggles off, throw overhand rather than underhand, or cover one eye during adaptation, then switch eyes after removing the goggles. What would the results of these experiments tell you?
Playing with Prisms
Experiment with your goggles. Try different orientations of the prisms, or use different prisms.
Old Habits Die Hard
Is there something in your house that you use a lot and that has been in the same location for a long time? Change its location and notice how long you reflexively keep trying the old location first. How long does it take for you to completely change?
Understanding age-related vision changes
Just like your body, your eyes and vision change over time. While not everyone will experience the same symptoms, the following are common age-related vision changes:
- Need for more light. As you age, you need more light to see as well as you used to. Brighter lights in your work area or next to your reading chair will help make reading and other close-up tasks easier.
- Difficulty reading and doing close work. Printed materials can become less clear, in part because the lens in your eye becomes less flexible over time. This makes it harder for your eyes to focus on near objects than when you were younger.
- Problems with a glare. When driving, you may notice additional glare from headlights at night or sun reflecting off windshields or pavement during the day. Changes in your lenses in your eyes cause light entering the eye to be scattered rather than focused precisely on the retina. This creates more glare.
- Changes in color perception. The normally clear lens located inside your eye may start to discolor. This makes it harder to see and distinguish between certain color shades.
- Reduced tear production. With age, the tear glands in your eyes will produce fewer tears. This is particularly true for women experiencing hormone changes. As a result, your eyes may feel dry and irritated. Having an adequate amount of tears is essential for keeping your eyes healthy and for maintaining clear sight.
Encountering problems with near vision after 40
If you have never needed eyeglasses or contact lenses to correct distance vision, then experiencing near vision problems after age 40 can be concerning and frustrating. You may feel like you've abruptly lost the ability to read the newspaper or see the cell phone numbers.
These changes in your focusing power have been occurring gradually since childhood. Now your eyes don't have enough focusing power to see clearly for reading and other close vision tasks.
Losing this focusing ability for near vision, called presbyopia, occurs because the lens inside the eye becomes less flexible. This flexibility allows the eye to change focus from objects that are far away to objects that are close. People with presbyopia have several options to regain clear near vision. They include:
- Eyeglasses, including reading glasses, bifocals, and progressive lenses.
- Contact lenses, including monovision and multifocal lenses.
- Laser surgery and other refractive surgery procedures.
As you continue to age, presbyopia becomes more advanced. You may notice that you need to change your eyeglass or contact lens prescriptions more frequently than you used to. Around age 60, these changes in near vision should stop, and prescription changes should occur less frequently.
Presbyopia can't be prevented or cured, but most people should be able to regain clear, comfortable near vision for all of their lifestyle needs.
Dimenco demonstrates Simulated Reality solution in Los Angeles
A virtual reality-like experience without glasses, hand-held devices or other wearable gear can be experienced with the proof-of-concept demonstration at Display Week 2018, in Los Angeles.
Introduced by KDX/Dimenco, at the Los Angeles Convention Center, this May, Simulated Reality (SR) joins the other realities we’re now familiar with: virtual, augmented and mixed.
Simulated reality has been a key element in science fiction, and has been explored by game designers in computer and console games, and also by the video industry, in everything from films to TV series. Although some may confuse the term with virtual reality – which, again, some suggest can become very real – the truth is that simulated reality is something completely different and is, in fact, a goal which, if attainable, is still part of a very distant future, because it relates to a simulation that can be indistinguishable from “true” reality.
Having said this, the “simulated reality” presented by KDX/Dimenco should be taken with a grain if salt. It’s a marketing definition that attracts attention, but does not reach the level suggested by the original concept, being more a system which promises to offer immersive simulations that can be experienced without wearables, head-mounted displays or glasses. Dimenco, which is an international pioneer in display technologies and fully owned subsidiary of KDX, demonstrates at the Society for Information Display’s Display Week, until May 25, 2018, at the Los Angeles Convention Center, its concept for a first-of-its kind Simulated Reality (SR) display system.
The demonstration showcases emerging technologies to deliver a virtual reality-like experience without glasses, hand-held devices or other wearable gear. It also feature mid-air haptics technology, from strategic partner Ultrahaptics, that will allow users to interact with simulated objects just as they do with their real-world counterparts.
KDX/Dimenco will offer sample SR demonstrations at booth 1519 on the show floor and full demonstrations at its offsite showroom. The offsite demos will include simulations that will allow users to explore a jungle environment, take a breathtaking ride on a hang glider and engage in other thrilling, immersive experiences.
Additionally, Dimenco will serve as sponsor for Display Week’s annual Media Lunch on at noon on May 22nd in Press Room 507. Dimenco CEO Maarten Tobias will make a short presentation on the future of Simulated Reality at the event and present the company’s plans for introducing its first development kit and product launch in 2019.
“We believe in a future without limits, where our senses and physical location aren’t the boundary, but the starting point,” says Tobias. “Together with the brightest minds in our industry, we are developing technology to create a new experience, one that brings people together no matter where they are. We call it Simulated Reality.”
KDX/Dimenco is at the forefront of making multi-sensory immersive experiences, like those pictured in such films as Blade Runner, a reality. Simulated Reality is the next logical step beyond virtual reality and augmented reality. It will allow people to see, hear and interact with computer-simulated objects, environments and characters, without glasses or wearables.
Since its foundation in 2010, Dimenco, whose mantra is “We bring reality”, has striven to offer the best and most convenient 3D experience – no glasses required. The company explains on its website, how they make the magic happen. The information available reveals that “depth perception is created by bonding a specially developed lenticular overlay to an LCD screen, in such a way that projected light is transmitted in different directions. Introducing interference into what each eye perceives results in the perception of depth on a flat surface.”
For this you need special displays which are the technological key to the “magic”. According to Dimenco, “the observer’s left and right eye see different images on the display, which the brain fuses into single image, without requiring cumbersome, inconvenient 3D glasses. Dimenco’s 3D technology allows viewers to sit anywhere in a room and see a customizable 3D image. This is easy on the eyes and can be watched from different angles.”
In addition to the design of the lenticular overlay and optical bonding to an LCD, the technology developed by Dimenco also encompasses 3D image processing. Dimenco also offers vast experience in industrial 3D display and component manufacturing. The company has shown its technology at different events, since at least 2012, but we’re yet to see this solution become popular and mainstream.
“The technology promises to redefine the very concept of ‘experience,’” notes Tobias. “Time, location, capabilities and even budget will no longer limit what you can experience.”
One final note, which is important to remember if you’re interested in the subject and are in the Los Angeles area. Simulated Reality demonstrations at Dimenco’s offsite suite are by reservation only. For bookings, contact Greg Agostinelli at [email protected]