Risk Factors of Sleep Disorder After Stroke:

Risk Factors of Sleep Disorder After Stroke: Risk factors of sleep disorder after stroke: A Meta analysis Running title: Risk factors of sleep disorder after stroke Highlights: Diabetes mellitus has a 41% increased risk of sleep disorder in stroke patients Alcohol use has a 59% increased risk of sleep disorder in stroke patients Habitual snoring has a 1377% increased risk of sleep disorder in stroke patients Body-mass index has a 17% decreased risk of sleep disorder in stroke patients Abstract Objectives: To explore the related risk factors of sleep disorder in stroke patients by conducting a meta-analysis Methods: PubMed, Medline, Springer, Elsevier Science Direct, Cochrane Library and Google scholar database were searched from inception up to May 2014. Studies investigating risk factors for sleep disorder after stroke were included. Characteristics including author’s name, year of publication, country, sample size, age of participants and gender were extracted independently by two reviewers. Results: A total of 8 studies, involving 1381 patients (578 experimental groups and 803 control groups) were eligible for the meta-analysis. The meta-analysis showed that there were significant association between risk of sleep disorder after stoke between diabetes mellitus (OR = 1.41, 95% CI = 1.09 to 1.84, P OR = 1.59, 95% CI = 1.19 to 2.12, P OR = 14.77, 95% CI = 5.52 to 39.53, P WMD = 0.83, 95% CI = 0.63 to 1.03, P OR = 1.23, 95% CI = 0.72 to 2.1, P > 0.05), hypertension (OR = 1.22, 95% CI = 0.83 to 1.80, P > 0.05), dyslipidemia (OR = 0.96, 95% CI = 0.70 to 1.33, P > 0.05), smoking (OR = 1.27, 95% CI = 0.73 to 2.20, P > 0.05), previous stroke (OR = 1.05, 95% CI = 0.74 to 1.49, P > 0.05), chronic obstructive pulmonary disease (OR = 0.79, 95% CI = 0.40 to 1.57, P > 0.05) when compared with control groups. Furthermore, the results of Egger test showed no statistical publication bias. Conclusions: Diabetes mellitus, alcohol use, habitual snoring and body-mass index are associated with risk of sleep disorder in patients with stroke. Key words: Sleep disorder; Risk factors; Meta-analysis; Stroke Introduction Stroke is a serious global health problem, and considered as the fourth leading cause of death and the primary cause of adult disability in all around the world [1-3]. Sleep-related breathing disorders (SDB) is a frequent clinical phenomena, and characterized by repetitive apneas and hypopneas during sleep [4, 5]. The relationship of SDB with stroke has been investigated in the recent years. Many researches have reported increased incidence of SDB in stroke patients, which could lead to progression of the stroke [6, 7]. Furthermore, SDB following stroke may result in high mortality and morbidity [4]. Although SDB and stroke have common established risk factors including age, gender, elevated body-mass index (BMI), hypercholesterolemia, hypertension and habitual snoring [8-10], risk factors leading to SDB in stroke patients remains unclear. Thus, it is important to identify contributing risk factors or associated conditions that can impact on outcome of SDB following stroke. Previously existing literature and primary analyses on risk factors of sleep disorder after stroke only involved in research of certain factor, and statistical power was deficient and insufficient in these studies [4, 11]. In this study, to investigate the risk factors for SDB after stroke and obtain a quantitative estimate of the risk, we systematically review the literature that have studied patients with stroke for SDB risk factors, (namely gender, Hypertension, Diabetes mellitus, Dyslipidemia, Smoking, alcohol use, Previous stroke history, Chronic obstructive pulmonary disease, Habitual snoring and Body-mass index)by conducting a meta-analysis. Methods Search strategy and study selection We retrieved the relevant studies up to May 2014 in several public databases, mainly including PubMed, Medline, Springer, Elsevier Science Direct, Cochrane Library and Google scholar. The main search words were â€Å"factor† or â€Å"influence†, â€Å"affect† or â€Å"element† or â€Å"determinant† or â€Å"cause† or â€Å"reason† and â€Å"sleep disorder†, â€Å"apnoea† or â€Å"obstacle† or â€Å"impediment† or â€Å"barrier† or â€Å"obstruction† or â€Å"balk† and â€Å"stroke† or â€Å"cerebral apoplexy† or â€Å"acute cerebral accident† and â€Å"research† or â€Å"survey† or â€Å"study† or â€Å"trial†. Meanwhile, references from retrieved papers were checked for more relevant studies not identified in database search. Eligibility of relevant studies For relevant abstracts, full publications were retrieved for evaluation on the basis of criteria that were established a priori. All selected research articles were considered except case reports. We sought to include studies of any design that reported risk factors in sleep disorders, and relationships between sleep-disordered breathing, sleep apnea or insomnia symptoms and stroke without the limitation of sample size and range of age. Studies were excluded from the systematic reviews and reports that only described sleep disorder after stroke. Studies with no control group were also excluded. Reviews, reduplicated studies and studies published in language other than English were excluded as well. Data extraction Information from each study was extracted independently by two reviewers using a data extraction form. Study general characteristics (e.g., author, year of publication, location of participants, design of studies, ethnicity and number of cases), and characteristics of participants (e.g., age, gender and sample size) were recorded (where available) and doubled-checked. Meanwhile, the effect size of risk factors of sleep disorder in stroke patients compared with stroke patients without sleep disorder with corresponding 95% confidence interval (CI) were extracted as reported by authors. The effect size of gender, hypertension, diabetes mellitus, dyslipidemia, smoking, alcohol use, previous stroke, chronic obstructive pulmonary disease (COPD) and habitual snoring were measured by, and body-mass index (BMI) by weighted mean difference (WMD). In addition, we contacted authors of incorporated studies to obtain further information for data items that needed clarification. Discrepancies were resolved by discussing within our research team or contracting with the original investigators via e-mail. Statistical analysis The meta-analysis was focused on the risk factors of sleep disorder in stroke patients versus stroke patients without sleep disorder. The pooled estimates of effect size of risk factors were calculated by averaging OR or WMD based on a fixed or random effects model depending on the overall heterogeneity. Then, heterogeneity of effect size across studies was evaluated by applying Cochran’s Q-statistic and and the I2 statistic [12, 13]. P value I2 value > 50% was considered to heterogenous across the studies. When substantial heterogeneity was detected, we calculated the overall estimate of ORs or WMDs using Mantel–Haenszel method in the fixed effect model [14]. If not, the pooled estimates were presented based on the random effect model by using DerSimonian and Laid method [15]. In addition, the publication bias were evaluated using Egger’s linear regression test [16], which measures funnel plot asymmetry by the natural logarithm scale of the effect size. Meta-analysis was performed using the software of the STATA package v.11.0 (Stata Corporation, College Station, TX, USA). P value Results Literature research and study characteristics The details of the literature search were shown in a flow diagram (Figure 1). We obtained 972 citations (131 from Medline, 341 from Pubmed, 164 from Springer, 103 from Elsevier Science Direct, 16 from Cochrane Library and 217 from Google Scholar) with our electronic literature search. We obtain 84 citations after removing duplicates or irrelevant studies. In addition, 47 citations were excluded after screening based on the abstracts. Then 37 remained citations were full-text reviewed for detailed assessment. Finally, 8 citations satisfied the inclusion criteria and were eligible for the meta-analysis. The characteristics and information of the included studies were presented in Table 1. The 8 selected studies contained 1381 patients with average age (ranging from 43.0 to 75.2 years old), including 578 experimental groups (stroke patients with sleep disorder) and 803 control groups(stroke patients without sleep disorder) [17-24]. Overall analysis of gender As shown in Table 2, a total of 7 separate studies [17-20, 22-24], involving 1321 stroke patients (539 experimental groups and 782 control groups), were eligible for the meta-analysis. Meta-analysis showed no association between gender and sleep disorder after stroke was found (OR = 1.23, 95% CI = 0.72 to 2.1, P > 0.05), yet with significant heterogeneity between studies (Q2 = 22.73, I2 = 73.6%, P the result of Egger’s test showed no evidence of publication bias (P = 0.91) Overall analysis of hypertension As presented in table 2, a total of 8 studies [17-24], including 1381 stroke patients (578 experimental groups and 803 control groups ), were finally eligible for the meta-analysis. Meta-analysis showed no association between hypertension and sleep disorder after stroke compared with control groups (OR = 1.22, 95% CI = 0.83 to 1.80, P > 0.05), yet with significant between-study heterogeneity was found (Q2 = 14.13, I2 = 50.5%, P In addition, the result of Egger’s test showed no evidence of publication bias (P = 0.43). Overall analysis of diabetes mellitus As shown in Table 2, a total of 7 studies [17, 19-24], involving 1326 stroke patients (549 experimental groups and 777 control groups), were eligible for the meta-analysis. Meta-analysis showed diabetes mellitus had a 41% increased risk of sleep disorder in stroke patients compared with control groups (OR = 1.41, 95% CI = 1.09 to 1.84, P Q2 = 1.59, I2 = 0%, P > 0.1). In addition, the result of Egger’s test showed no evidence of publication bias (P = 0.72) Overall analysis of dyslipidemia As shown in Table 2, a total of 4 studies [17, 19, 22, 24], involving 832 stroke patients (373 experimental groups and 459 control groups), were eligible for the meta-analysis. Meta-analysis showed no association between dyslipidemia and sleep disorder after stroke compared with control groups (OR = 0.96, 95% CI = 0.70 to 1.33, P > 0.05), yet with significant between-study heterogeneity (Q2 = 4.78, I2 = 37.3%, P > 0.1). In addition, the result of Egger’s test showed no evidence of publication bias (P = 0.68) Overall analysis of smoking As presented in Table 2, a total of 5 studies [17, 19, 20, 22, 23], containing 1234 stroke patients (495 experimental groups and 739 control groups), were eligible for the meta-analysis. Meta-analysis showed no association between smoking and sleep disorder after stroke compared with control groups (OR = 1.22, 95% CI = 0.83 to 1.80, P > 0.05), yet with significant between-study heterogeneity (Q2 = 13.82, I2 = 71.0%, P the result of Egger’s test showed no evidence of publication bias (P = 0.43). Overall analysis of alcohol use As shown in Table 2, a total of 5 studies [17, 19, 20, 22, 23], involving consisting of 1234 stroke patients (495 experimental groups and 739 control groups), were eligible for the meta-analysis. Meta-analysis showed alcohol use had a 41% increased risk of sleep disorder in stroke patients compared with control groups (OR = 1.59, 95% CI = 1.19 to 2.12, P no significant between-study heterogeneity (Q2 = 4.49, I2 = 10.9%, P > 0.1). In addition, the result of Egger’s test showed no evidence of publication bias (P = 0.65). Overall analysis of previous stroke As shown in Table 2, a total of 5 studies [17, 19, 21, 22, 24], involving 892 stroke patients (412 experimental groups and 480 control groups), were eligible for the meta-analysis. Meta-analysis showed no association between previous stroke and sleep disorder after stroke compared with control groups (OR = 1.05, 95% CI = 0.74 to 1.49, P > 0.05), and with no significant between-study heterogeneity was found (Q2 =2.31, I2 =0%, P > 0.1). In addition, the result of Egger’s test showed no evidence of publication bias (P = 0.24). Overall effects of chronic obstructive pulmonary disease (COPD) As shown in Table 2, a total of 2 studies[19, 22], containing 623 stroke patients (280 experimental groups and 343 control groups), were eligible for the meta-analysis. Meta-analysis showed no association between COPD and sleep disorder after stroke compared with control groups (OR = 0.79, 95% CI = 0.40 to 1.57, P > 0.05), yet with no significant between-study heterogeneity was found (Q2 = 0.24, I2 = 0%, P > 0.1). Overall effects of habitual snoring As shown in Table 2, a total of 2 studies [20, 21], involving 422 stroke patients (138 experimental groups and 284 control groups), were eligible for the meta-analysis. Meta-analysis showed habitual snoring had a 1377% increased risk of sleep disorder in stroke patients compared with control groups (OR = 0.79, 95% CI = 0.40 to 1.57, P > 0.05), yet with no significant between-study heterogeneity was found (Q2 = 1.29, I2 = 22.6%, P > 0.1). Overall effects of Body-mass index (BMI) As shown in Table 2, a total of 3 studies [20, 21, 23], involving 494 stroke patients (176 experimental groups and 318 control groups), were eligible for the meta-analysis. Meta-analysis showed BMI had a 17% decreased risk of sleep disorder in stroke patients compared with control groups (WMD = 0.83, 95% CI = 0.63 to 1.03, P Q2 = 0.95, I2 = 0%, P > 0.1). In addition, the result of Egger’s test showed no evidence of publication bias (P = 0.998). Discussion In this study, we conducted a meta-analysis for investigating risk factors of sleep disorder in stroke patients. Based on the data from 8 studies including 1381 patients, the factors (Diabetes mellitus, alcohol use, habitual snoring and BMI) were associated with risk of sleep disorder in stroke patients when compared with control groups, yet with no significant between-study heterogeneity. The magnitude of this association was greatest for habitual snoring with stroke patients experiencing a 1377% increase in risk of sleep disorder compared with stroke patients without sleep disorder. However, there were no association between risk of sleep disorder after stroke and other factors (gender, Hypertension, Dyslipidemia, Smoking, Previous stroke history and COPD). In addition, there was no indication of publication bias from the result of Egger’s test. Researchers have shown increased incidence of SDB in stroke patients, which may lead to a poor outcome and recurrence [25, 26]. SDB progresses from habitual snoring to the increased upper airway resistance syndrome to sleep apnea [27], and it is biologically plausible that habitual snoring could increase the risk of sleep disorder in stroke patients. Habitual snoring is significantly associated with daytime sleepiness, restless sleep, and hyperactivity, which could lead to sleep disorder [28, 29]. In our literature search we did not identify results of any randomized clinical trials evaluating the effect of risk factors on sleep disorder after stroke. However, it is reasonable to infer that habitual snoring may contribute to incidence and development of sleep disorder in stroke patients. The previous studies have shown significant gender-related differences in presenting symptoms of patients with SDB [30], and the risk for the development of sleep disorder was significantly lower in women [31]. However, in our study, we found no association between gender and risk of sleep disorder after stroke, yet with the most significant between-study heterogeneities. This might result from unavoidable difference in study sample sizes and distinct adjustments across studies. Thus, we suggest that the present analyses might have underestimated the true effects of gender on risk of sleep disorder after stroke, and further studies are needed to be demonstrated this. The present meta-analysis has a series of limitations, such as lack of uniformity (e.g. sleep disorder diagnostic criteria, the duration of patients with stroke) and exclusion of studies written in languages other than English. Furthermore, another limitation was the narrow coverage of information of the present analysis. After all, the results in this analysis were only obtained data from Asia, Europe, North America and Oceania, and the majority of the included studies did not state if there were any racial differences among participants. The differences in regions and races among studies might have an influence on pooled risk estimates of sleep disorder after stroke. In summary, the present meta-analysis suggest that the factors (Diabetes mellitus, alcohol use, habitual snoring and BMI) is associated with risk of metabolic syndrome. The conclusion has a great significance for public health, especially in countries of high incidence of stroke. In addition, further investigations, both epidemiological and mechanistic, are needed to investigate whether regulating these factors can prevent occurrence and development of metabolic syndrome. 3D Technology: Types and Uses 3D Technology: Types and Uses CHAPTER 1: INTRODUCTION This report will focus on how different 3D technologies work, it will include the entire work flow, from recording the action, encoding the footage, playing back the media via a cinema projector or television and finally how the audience views the 3D film or video, whether it be through specially designed glasses or an auto-stereoscopic television. At present the most popular way to view 3D media is with the use of specialised glasses, the most popular being, active shutter glasses, passive polarised glasses and colour separationbased glasses. Wearing glasses to watch a movie is often mentioned as a negative aspect of 3D. There is a technology available that allows you to watch 3D on screens without wearing any additional glasses, it is called autostereoscopy, this will also be looked at. The health impacts that result from watching 3D will also be examined, along with factors that will prevent a person from being able to correctly view 3D images. There will be impacts on the entire industry from studios and cinemas to smaller production companies and independent producers if 3D films become the norm and these will be examined. A good place to start this report is to examine how two of the highest profile media companies around at present are currently viewing 3D technology. Phil McNally stereoscopic supervisor at Disney-3D and Dreamworks was quoted as saying, consider that all technical progress in the cinema industry brought us closer to the ultimate entertainment experience: the dream. We dream in colour, with sound, in an incoherent world with no time reference. The cinema offers us a chance to dream awake for an hour. And because we dream in 3D, we ultimately want the cinema to be a 3D experience not a flat one.'(Mendiburu, 2009) In the BBC Research White Paper: The Challenges of Three-Dimensional Television, 3D technology is referred to as a continuing long-term evolution of television standards towards a means of recording, transmitting and displaying images that are indistinguishable from reality'(Armstrong, Salmon, Jolly, 2009) It is clear from both of these high profile sources that the industry is taking the evolution of 3D very seriously, as a result this is a topic that is not only very interesting but will be at the cutting edge of technological advances for the next couple of years. This report will be covering the following things: What does the term 3D mean with reference to film and video A look at the history of 3D in film How does 3D technology work The implications of 3D on the film business and on cinemas The methods used to create the media and also the ways in which the 3D image is recreated for the viewer The reasons I have chosen to do my project on this topic is that I am very interested in the new media field. 3D video when accompanied with high definition film and video is a field that is growing rapidly. Earlier this year, on 02 April 2009, Sky broadcast the UKs first live event in the 3D TV format, it featured a live music concert by the pop group Keane, it was sent via the companys satellite network using polarisation technology. Traditionally we view films and television in two dimensions, this in essence means we view the media as a flat image. In real life we view everything in three dimensions, this is because we get a slightly different image received in each eye, the brain then combines these and we can work out depth of vision and create a 3D image. (this will be explained further in Chapter 3) There is a high level of industrial relevance with this topic, as 3D technology coupled with high definition digital signal is at the cutting edge of mainstream digital media consumption. Further evidence of this is that the sports company ESPN will be launching their new TV channel, ESPN-3D in North America in time for this years Summer Football World Cup. In January 2009 the BBC produced a Research White Paper entitled The Challenges of Three-Dimensional Television on this subject and over the next couple of years they predict that it will start to be introduced in the same way that HD (High Definition) digital television signal is currently being phased in, with pay-per-view movies and sports being the first take advantage of it. Sky have announced that their existing Sky+HD boxes will be able to broadcast the 3D signals so customers will not even need to update their equipment to be able to receive the 3D Channel that they are starting to broadcast later this year. On Sunday January 31st 2010, Sky broadcast a live Premier League football match between Arsenal and Manchester United for the first time in 3D to selected pubs across the country, Sky equipped the selected pubs with LGs new 47-inch LD920 3D TVs. These televisions use the passive glasses, similar to the ones uses in cinemas as opposed to the more expensive Active glasses which are also an option. (The differences between Active and Passive technologies will be explained in Chapter 8) It is also worth noting that at the 2010 Golden Globe awards, on acceptance of his award for Best Picture for the 3D Box Office Hit Avatar, the Canadian director James Cameron pronounced 3D as the future. At the time of writing this report (27/01/2010) the 3D film Avatar has just taken over from Titanic (also a James Cameron film) to become the highest grossing movie of all time, with worldwide takings of $1.859 billion. This is being accredited to the films outstanding takings in the 3D version of its release, in America 80% of the films box office revenue has been received from the 3D version of its release. In an industry where money talks, these figures will surely lead to an dramatic increase in production of 3D films and as a result Avatar could potentially be one of the most influential films of all time. After completing this dissertation I hope to be able to have a wide knowledge base on the subject and hopefully this will appeal to companies that I approach about employment once I have graduated. In the summer of 2010 when I will be looking for jobs, I believe that a lot of production companies will have some knowledge of 3D technology and be aware of how in the near future it may be something that they will have to consider adopting in the way that many production companies are already or soon will be adopting HD into their workflow. In order to ensure that I complete this project to a high standard it is important that I gain a complete understanding of the topic and study a variety of different sources when compiling my research. 3D media itself is not a new concept so there are a wide range of books and articles on the theory of 3D and stereoscopy along with anaglyphs. However in recent years there has been a resurgence in 3D with relation to film and TV. This is due mainly to digital video and film production making it easier and cheaper to create and manage the two channels needed for three-dimensional video production. It has proved more difficult to study books and papers on this most recent resurgence of 3D because it is still happening and evolving all the time. I have read various research white papers on the subject, which have been cited in the Bibliography, I have also used websites and blogs along with some recently published books, one of the problems with such a fast moving technological field such as 3D though, is that these books quickly become outdated. CHAPTER 2: HUMAN VISION In the real world we see in three dimensions as opposed to the two dimensions that we have become accustomed to when watching TV or at the cinema. Human vision appears in three dimensions because it is normal for people to have two eyes that both focus on the object, in the brain these two images are then fused into one, from this we can work out depth of vision, this process is called stereopsis. All of these calculations happen in the brain without the person ever even noticing, as a result we see the world in three dimensions very naturally. The reason that we see in 3D is because of stereoscopic depth perception. There are various complex calculations going on in our brains, this coupled with real experience allows our brain to work out the depth of vision. If it wasnt for this it would be impossible to tell if something was very small or just very far away. As humans, we have learnt to judge depth even with only one view point. This is why, if a person has one eye they can still manage to do most things that a person with two eyes can do. This is also why when watching a 2-D film you can still get a good judge of depth. The term for depth cues based on only one viewpoint is monoscopic depth cues. One of the most important of these is our own experience, it relates to perspective and relative size of objects. In simple terms, we have become accustomed to object being certain sizes. An example of this is that we expect buildings to be very big, humans are smaller and insects are smaller still. So this means that if we can see all three of these objects next to each other and they appear to be the same size then the insect must be much closer than the person, and both the insect and the person must be much closer that the building (see figure 1). The perspective depth cue (shown in figure1) was backed up when an experiment was carried out by Ittelson in 1951. He got volunteers to look through a peep hole at some playing cards, the only thing they could see were the cards and so there were no other types of depth cue available. There were actually three different-sized playing cards (normal size, half-size, and double size), and they were presented one at a time at a distance of 2.3metres away. The half-sized playing card was judged to be 4.6 metres away from the observer, whereas the double-sized card was thought to be 1.3 metres away. Thus, familiar size had a large effect on distance judgement'(Eysenck, 2002). Another monoscopic depth cue that is very effective is referred to as occlusion or interposition. This is where an object overlaps another object. If a person is standing behind a tree then you will be able to see all of the tree but only part of the person. This tells us that the tree is nearer to us that the person. One of the most important single view depth cues in called motion parallax, it works on the basis that if a person moves their head, and therefore eyes, then objects nearer to them, whilst not physically moving, will appear to move more than the objects in the distance. This is the method that astronomers use to measure distances of stars and planets. It is in extremely important method of judging depth and is used extensively in 3D filmmaking. In filmmaking, lighting is often talked about as being one of the key elements to giving the picture depth, and this is because it is a monoscopic depth cue. In real life the main light source for millennia has been the sun. Humans have worked out how to judge depth based on the shadows that are portrayed from an object. In 2D films shadows are often used to display depth by casting them across actors faces it allows the viewers to see the recesses and expressions trying to be portrayed. So far all of the methods that have been described for determining depth have been monoscopic, these work independently within each eye. If these were the only methods for determining depth there would be no need for 3D films as it would not add anything because all of these methods could be recreated using a single camera lens. This is not the case however, a lot of the more advanced methods used in human vision for judging depth need the use of both eyes, these are called stereoscopic depth cues. A great deal of stereoscopic depth cues are based around the feedback that your brain gets when the muscles in the eye are manipulated to concentrate your vision on a particular point. One of the main stereoscopic depth cues is called convergence, this referrers to the way that the eyes rotate in order to focus on an object (see figure 2). If the focus is on a near object, the eyes rotate around the Y axis and converge on a tighter angle , similarly if the focus is on a distant object the rotation means the eyes have a wider angle of convergence. It is a lot less stressful on the muscles in the eye to have a wide angle of convergence and look at objects far away, in comparison looking at very close object for any amount of time causes the muscles in the eye to ache. This is a very important factor that should be considered when creating 3D films, as it doesnt matter how good the film is, if it is going to hurt the audience it will not go down well. A second stereoscopic depth cue that we use is called accommodation, this is the way that our eyes changes focus when we look at an object at different distances, it is very closely linked with convergence. Usually when we look at an object very close up, our eyes will change rotation and point towards the object (convergence) allowing us to look at the item, our eyes will at the same time change focus (accommodation). Using the ciliarybody muscles in the eye, the lens will change shape to let more or less light in the same way a camera does, thus changing focus. In everyday life convergence and accommodation usually happen in parallel. The fact that we can, if we wish choose to converge our eyes without changing the focus means that 3D films are possible. When you are sat in the cinema all of the action is projected onto the screen in front of you, so this is where your eyes need to focus. With 2D films the screen is also where your eyes need to converge, but with 3D films this is not the case. When watching a 3D film the focus never changes from the screen, else the whole picture would go out of focus, but objects appear to be in front and behind the screen, so your eyes need to change their convergence to look at these objects without altering their focus from the screen. It has been suggested that this independence of accommodation and convergence is the reason for eye strain when watching a 3D picture as your eyes are doing something that they are not in the habit of doing (see chapter 12: Is 3D bad for you). It is also worth noting that our monoscopic depth cues work at almost any range, this is not the case with stereoscopic depth cues. As objects become further away they no longer appear differently in each eye, so there is no way the brain can calculate a difference and work out depth. The limit occurs in the 100 to 200-yard range, as our discernment asymptomatically tends to zero. In a theatre, we will hit the same limitation, and this will define the depth resolution and the depth range of the screen.(Mendiburu, 2009) This means that when producing a 3D film you have to be aware that the range of 3D that you have to use is not infinite and is limited to 100-200 yards. CHAPTER 3: Early Stereoscopic History (1838 1920) Three dimensional films are not a new phenomenon, Charles Wheatstone discovered, in 1838, that the mechanism responsible for human depth perception is the distance separating the retinas of our eyes . (Autodesk, 2008) In a 12,000 word research paper that Wheatstone presented to the Royal Society of Great Britain he described the stereoscope and claimed as a new fact in his theory if vision the observation that two different pictures are projected on the retinas of the eyes when a single object is seen.(Zone, 2007) Included in the paper were a range of line drawings presented as stereoscopic pairs, these were designed to be viewed in 3D using Wheatstones invention, the stereoscope. Wheatstone was not the first person to look at the possibility of receiving separate views in each eye, In the third century B.C, Euclid in his treatise on Optics observed that the left and right eyes see slightly different views of a sphere'(Zone, 2007). However, Wheatstone was the first person to create a device to be able to re-create 3D images. Between 1835 and 1839 photography was starting to be developed thanks to work from William Fox Talbot, Nicephore Niepce and Louise Daguerre. Once Wheatstone became aware of the photographic pictures that were available he requested some stereoscopic photographs to be made for him. Wheatstone observed that it has been found advantageous to employ, simultaneously, two cameras fixed at the proper angular positions'(Zone, 2007). This was the start of stereoscopic photography. Between 1850 and 1860 work was starting to be done by various people to try and combine stereoscopic photography with machines that would display a series of images very quickly and therefore using persistence of vision to create a moving 3D image. These were the first glimpses of 3D motion. In 1891 a French scientist, Louis Ducos du Hauron patented the anaglyph, a method for separating an image into two separate colour channels and then by wearing glassing with the same colours but on opposite eyes thereby cancelling out the image, thus reproducing one image, but in 3D. Another method used at this time to create 3D was proposed by John Anderton, also in 1891. Andertons system was to use polarisation techniques to split the image into two separate light paths and then employ a similar polarisation technique to divert a separate image to each eye on viewing. One of the main advantages of polarisation over anaglyphs is that they do not lose any colour information, this is due to the fact that both images retain the original colour spectrums. They do however loose luminance. It is common for a silver screen to be necessary, it serves two purposes, firstly the specially designed screen maintains the separate polarisation required for each image. It also reflects more light than conventional screens, this compensates for the loss of luminance. During 1896 and 1897 2D motion pictures started to take off, and by 1910 after a lot of initial experimenting the creative formats of film that we recognise today such as cuts and framing had started to become evident. In 1920 Jenkins, an inventor that worked hard to try and create a method for recreating stereoscopic motion picture was quoted as saying Stereoscopic motion pictures have been the subject of considerable thought and have been attained in several waysbut never yet have they been accomplished in a practical way. By practical, I mean, for example without some device to wear over the eyes of the observer.'(Zone, 2007) It is worth noting that this problem of finding a practical method of viewing 3D has still to a large extent not been solved. Chapter 4: Early 3D Feature Films (1922 1950) 4.1 The first 3D feature film The first 3D feature film, The Power of Love was released in 1922, it was exhibited at the Ambassador Hotel Theatre in Los Angeles. Popular Mechanics magazine described how the characters in the film did not appear flat on the screen, but seemed to be moving about in locations which had depth exactly like the real spots where the pictures were taken(Zone, 2007). The Power of Love was exhibited using red/green glasses using a dual strip anaglyph method of 3D projection. (Anaglyphs are explained in chapter 8.3) The film was shot on a custom made camera invented by Harry K.Fairall, he was also the director on the film. The camera incorporated two films in one camera body.(Symmes, 2006) Power of Love was the first film to be viewed using anaglyph glasses, also the first to use dual-strip projection. Also in 1922, William Van Doren Kelley designed his own camera rig, based on the Prizma colour system which he had invented in 1913. The Prizma 3D colour method worked by capturing two different colour channels by placing filters over the lenses. This way he made his own version of the red/blue anaglyphic print. Kelleys Movies of the Future was shown at Rivoli Theatre in New York City. 4.2 The first active-shutter 3D film A year later in 1923 the first alternate-frame 3D projection system was unveiled. It used a technology called Teleview. Which blocked the left and right eyes periodically in sync with the projector, thereby allowing you to see too separate images. Teleview was not an original idea, but up to this point no one had been able to get the theory to actually work in a practical way that would allow for films to be viewed in a cinema. This is where Laurens Hammond comes in. Hammons designed a system where two standard projectors would be hooked up to their own AC generators, running at 60Hz this meant that adjusting the AC frequency would increase or decrease the speed of the projectors. The left film was in the left projector and right film in the right. The projectors were in frame sync, but the shutters were out of phase sync.'(Symmes, 2006) This meant that the left image was shown, then the right image. The viewing device was attached to the seats in the theatre. It was mounted on a flexible neck, similar to some adjustable gooseneck desk lamps. You twisted it around and centred it in front of your face, kind of like a mask floating just in front of your face. (Symmes, 2006) The viewing device consisted of a circular mask with a view piece for each eye plus a small motor that moved a shutter across in front of either the left or right eye piece depending on the cycle of current running through it. All of the viewing devices were powered by the same AC generator as the projectors meaning that they were all exactly in sync. One of the major problems Hammond had to overcome was the fact that at the time film was displayed at 16 frames per second. With this method of viewing you are effectively halving the frame rate. 8 frames per second resulted in a very noticeable flicker. To overcome this Hammond cut each frame up in to three flashes so the new sequence was: 1L-1R-1L-1R-1L-1-R 2L-2R-2L-2R-2L-2R and so on. Three alternate flashes per eye on the screen. (Symmes, 2006) This method of separating and duplicating certain frames effectively resulted in increasing the overall frame rate thereby eradicating the flicker. There was only one film produced using this method, it was called M.A.R.S and displayed at the Selwyn Theatre in New York City in December 1922. The reason the technology didnt catch on was not due to the image, as the actual theory for producing the image has changed very little from the Teleview method to the current active-shutter methods which will be explained later. As with a lot of 3D methods the reason this one did not become mainstream was due the viewing apparatus that was needed. Although existing projectors could be modified by linking them up to separate AC generator, meaning no extra equipment was needed, the headsets that were required did need a lot of investment and time to install. All of the seats in the theatre needed to be fitted with headsets, these were adjusted in front of the audience members. These also had to be linked up to the AC generator so as they were perfectly in sync, this meant that they had to be wired in to the seats. These problems have since been overcome with wireless technologies such as Bluetooth as will be explained later. 4.3 The first polarised 3D film The next and arguably one of the most important advancements in 3D technology came in 1929 when Edwin H. Land worked out a way of using polarised lenses (Polaroid) together with images to create stereo vision. (Find more on polarisation in chapter 8.6) Lands polarizing material was first used for projection of still stereoscopic images at the behest of Clarence Kennedy, an art history instructor at Smith College who wanted to project photo images of sculptures in stereo to his students. (Zone, 2007) In 1936 Beggars Wedding was released in Italy, it was the first stereoscopic feature to include sound, it was exhibited using Polaroid filters. This was filmed using polarised technology. The first American film to use polarising filters was shot in 1939 and entitled In Tune With Tomorrow, it was a 15 minute short film which shows through stop motion, a car being built piece-by-piece in 3D with the added enhancement of music and sound effects. (Internet Movie Database, 2005) Between 1939 and 1952 3D films continued to me made but with the Great Depression and the onset of the Second World War, the cinema industry was restricted with its output because of finances and as 3D films were more expensive to make their output started to be reduced. Chapter 5: Golden Age of 3D (1952 1955) With cinema ticket sales plummeting from 90 million in 1948 to 40 million in 1951 (Sung, 2009) largely being put down to the television becoming coming in peoples front rooms the cinema industry needed to find a way to encourage the viewers back the big screen, 3D was seen as a way to offer something extra to make viewers return. In 1952 the first colour 3D film was released called Bwana Devil,it was the first of many stereoscopic films to follow in the next few years. The process of combining 3D and colour attracted a new audience to 3D films. Between 1950 and 1955 there were far more 3D films produced that at any other time before or since, apart from possibly in the next couple of years from 2009 onwards, as the cinema industry tries to fight back again against falling figures, this time though because of home entertainment systems, video-on-demand, and legal and illegal movie downloads. Towards the end of the Golden Age, around 1955, the fascination with 3D was starting to be lost. There were a number of reasons for this, one of the main factors was that in order for the film to be seen in 3D it had to be shown on two reels at the same time, which meant that the two reels had to be exactly in time else the effect would be lost and it would cause the audience headaches. Chapter 6: Occasional 3D films (1960 2000) Between 1960 and 2000 there were sporadic resurgences in 3D. These were down to new technologies becoming available. In the late 1960s the invention of a single strip 3D format initiated a revival as it meant that the dual projectors would no longer go out of sync and cause eye-strain. The first version of this single strip 3D format to be used was called Space-Vision 3D, it worked on an over and under basis. This meant that the frame was horizontally split into two, during playback it was then separate in two using a prism and polarised glasses. However, there were major drawbacks with Space-Vision 3D. Due to the design of the cameras required to film in this format, the only major lens that was compatible was the Bernier lens. The focal length of the Bernier optic is fixed at 35mm and the interaxial at 65mm. Neither may be varied, but convergence may be altered'(Lipton, 1982).This obviously restricted the creative filmmaking options and as a result was soon superseded by a new format called Stereovision. Stereovision was similar to Space-Vision 3D in that is split the frame in two, unlike Space-Vision though, the frame was split vertically, and they were placed side-by-side. During projection these frames were then put through an anamorphic lens, thereby stretching them back to their original size. These also made use of the polarising method introduced by Land in 1929. A film made using this process was called The Stewardess, released in 1969, it cost only $100,000 to make but at the cinema it grossed $26,000,000 (Lipton, 1982). Understandably the studios were very interested in the profit margin that arose from this film. As a result 3D once again became an interesting prospect for studios. Up until fairly recently films were still shot and edited using old film techniques (i.e. not digitally). This made manipulating 3D films quite difficult, this lack of control over the full process made 3D less appealing to film makers. The digitisation of post-processing and visual effects gave us another surge in the 1990s. But only full digitisation, from glass to glass from the cameras to projector lenses gives 3D the technological biotope it needs to thrive (Mendiburu, 2009). Chapter 7: The Second Golden Age of 3D (2004 present) In 2003 James Cameron released Ghost of the Abyss, it was the first full length 3D feature film that used the Reality Camera System, which was specially designed to use new high definition digital cameras. These digital cameras meant that the old techniques used with 3D film no longer restricted the work-flow, and the whole process can be done digitally, from start to finish. The next groundbreaking film was Robert Semeckis 2004 animated film Polar Express which was also shown in IMAX theatres. It was released at the same time in 2D and 3D, the 3D cinemas took on average 14 times more money that the 2D cinemas. The cinemas once again took note, and since Polar Express was released in 2004, 3D digital films have become more and more prominent. IMAX are no longer the only cinemas capable of displaying digital 3D films. A large proportion of conventional cinemas have made the switch to digital, this switch has enabled 3D films to be exhibited in a large range of cinemas. CHAPTER 8: 3D TECHNOLOGIES 8.1 3D capture and display methods Each different type of stereoscopic display projects the combined left and right images together onto a flat surface, usually a television or cinema screen. The viewer then must have a method of decoding this image and separating the combined image into left and right images and relaying these to the correct eye. The method that is used to split this image is, in the majority of cases, a pair of glasses. There are two brackets of encoding method, passive and active. Passive means that the images are combined into one and then the glasses split this image in to two separate images for left and right eye. In this method the glasses are cheaper to produce and the expense usually comes in the equipment used to project the image. The second method is active display. This method works by sending the alternative images in a very quick succession (L-R-L-R-L-R), the glasses then periodically block the appropriate eye piece, this is done at such a fast rate that it appears to be continuous in both eyes. There are various different types of encoding encapsulated within each of the two methods mentioned above. The encoding can use either colour separation (anaglyph, Dolby 3D), time separation (active glasses) or polarisation (RealD). A separate method, which does not require the use of glasses is done by using a virtual space in front of the screen and is called autosterescopic. In cinemas across the world at the moment there are several formats that are used to display 3D films. Three of the main distributors are Real-D, iMAX and Dolby-3D. Once a 3D film has been finished by the studios, it then needs to be prepared for exhibition in various different formats, this can include amongst other things colour grading and anti ghosting processes. At present there is not a universally agreed format for capturing or playing back 3D films, as a result there are several different versions, these are explained below. A large majority of the latest wave of 3D technology options send the image using one projector, so removing the old problem of out sync left and right images. The methods that do use dual projectors are much more sophisticated that the older versions used in anaglyphic films so have eradicated the old problems of out of sync projectors. 8.2 Gho