L&T: RxPertise

Mar
2012

The EYEvolution of 3D


Photograph by Ned Matura


3D viewing is more popular now than at any other time in history. With its promise of an enhanced and more immersive viewing experience, 3D is trying to capture our imagination and our dollars.

But why should 3D succeed now, as it repeatedly has not in the past 100 years? Although historically driven by business and entertainment interests, our scientific understanding of stereoscopic viewing technology, how it interacts with our visual system, and its new importance for the diagnosis and treatment of eye-teaming or tracking deficiencies will catapult 3D to take its place alongside the Internet and social media as dominant paradigm shifts in the 21st century.

Today, 3D is finally ready to deliver a virtual reality experience not far from the Holodeck in the science fiction series “Star Trek,” wherein the viewer unconsciously submits to an intimate and total immersive experience within an alternate reality. The question before us is centered on betting where this immersive experience will first gain serious transaction with consumers. Marchon, Oakley, Polaroid, Gunnar/Zeiss, Live Eyewear and other companies are initially placing their bets in the traditional theatrical environs, where passive circular polarizing eyewear has an established presence. Their message to moviegoers is:

“Why put up with uncomfortable and inferior throw-away 3D glasses when, for less than the cost of a cell phone bill, you can permanently enjoy a brighter, sharper and more satisfying 3D experience?”

Although 3D for home viewing is currently dominated by active-shutter technology, passive circular polarizing glasses are expected to become the standard for in-home use in the near future.

At the same time, 3D is now poised to take an important place within microsurgery as a unique and essential tool that enhances a doctor’s technical precision and skill. To understand how 3D has arrived at this important crossroad, we’ll take a look at the reasons for our long attraction to 3D and trace its development within the scope of human vision and visual aesthetic.

THE IMPORTANCE OF DEPTH AND DISTANCE
For our ancestors, their survival depended upon making the best choice in the daily challenge of deciding whether to eat, flee or fight a predator. Making determinations here meant evaluating a complex recipe containing threat, risk and reward, all of which placed high importance in being able to analyze distance and depth. As always, experience proved to be the best teacher. Even when mistakes were made and meals were missed, something was learned. As a library of visual experience was amassed, new visual challenges were constantly evaluated against what was known. The result was a set of reliable clues used to optimally determine distance and depth. Early one-eyed creatures evolved the following monocular spatial clues to determine depth:
  1. Size—Determined by both an object’s angular subtense and focal accommodation.
  2. Brightness—Brighter objects are assumed to be closer.
  3. Color Saturation—More intense colors are assumed to be closer.
  4. Texture—The rougher the texture, the closer the distance, and vice versa.
  5. Shadow direction—Intense and obvious shadow lines indicate closer proximity.
  6. Object Occlusion—Partial blocking helped determine which objects were in the foreground, and which were further behind.
  7. Relative Movement and Speed—Faster movement is considered closer because of increased parallax.
  8. Line of Perspective—A “vanishing” point is inferred from converging lines, suggesting distance.
Considering all these terrific monocular clues, what could two eyes bring to the table in determining the distance to food or a predator?

THE ADVANTAGES OF TWO EYES
The first reason can be summed up in one word: backup—you’ve got a spare. However, evolution also used the availability of a companion eye to help create some significant enhancements:
  1. Expanded scope of vision—With two eyes placed apart, the field of view seen is increased.
  2. Improved contrast discrimination—Increased sensitivity in detection of faint objects from improved signal-to-noise ratios.
  3. Increased areas of precise depth perception—Through the integration of disparate views coming from two eyes, depth perception is enhanced.
The fusing of disparate images from each eye into a single, “solid” image is called stereopsis or binocular vision. While receiving images from two eyes simultaneously, our visual cortex can produce a single “cyclopean” image, with a visual perspective originating from a virtual point midway between our eyes. The advantages accrued upon improved depth perception and distance discrimination helped our ancestors overcome the daily challenge of obtaining food or escaping a predator.

THE DEVELOPMENT OF EYE MOVEMENT
Our eyes and other sensory organs evolved ways to ensure efficient use of the neural processing required to maintain optimal attention and discrimination thresholds. One of those was to keep our retinal image from fading when we fixate on a single point. This helps ensure optimal vision when we find ourselves in a low-contrast or low stimulus environment immediately after being in a high-contrast environment. As the eye’s conical receptors’ response declines under a static stimulus, evolution helped develop eye muscles, which keep our eyes moving and stimulus thresholds changing, all of which reduces retinal image fading. These tiny but constant movements our eyes undergo, even when apparently fixated on a single image, are called micro-saccades.

In order to reconcile maintaining stereoptic fusion while preventing retinal image fade, our eyes have evolved as partners: They team up to jointly follow objects as they move in space to maintain a single, cyclopean image, but never linger long enough on a single object point to allow fading. These twin aspects of our binocular vision are part of eye-teaming, which has recently found new importance in today’s toolbox of optometric diagnostics.

SEEKING RELIEF

Beginning in the 19th century, individuals began to experiment with ways to help recreate a three-dimensional experience. Charles Wheatstone was able to recreate a feeling of image depth and relief using mirrors to combine two images taken from slightly different vantage points. The disparity in the images mimics the parallax difference seen by our individual eyes in real life. He called his device an anaglyph, which comes from the Greek: “ana” (meaning “up”) and “glyphein” (meaning “to carve out”). Later this century, Brewster, Holmes and Bates further developed devices to view stereograms in the home.

The ABCs of 3D Technology

In the search to create a new and truly immersive screen experience, William Shaw, Graeme Ferguson and others designed a large format/large screen movie experience called Imax in the 1970s. Although impressive, the need for dedicated cameras, film, and projection equipment and facilities kept Imax from enjoying widespread availability. With the development of digital projection and software-based post-editing tools, Imax-style films can be experienced at almost any neighborhood multiplex. As Imax evolved, so did Imax 3D, which initially used active-shutter glasses with 45 degree linear polarizers to deliver the 3D image. As with anaglyph colored glasses, audiences found the bulky glasses uncomfortable and fatiguing.



In an effort to rid the 3D experience of the need for either colored filters or heavy eyewear, a passive—meaning non-powered—manner of 3D projection and viewing was developed using circular polarizers. A circular polarizer is nothing more than a linear polarizer that has a phase-slowing/altering filter placed in its path. The effect of this quarter-wave retarding plate is to impart a rotational spin in the phase of the linear wave, as shown in the diagram below: Think of a stretched-out Slinky toy and you’ll get the idea. There are both right-handed and left-handed circular polarizers, and these separate the images for each eye, respectively.

An important distinction between active and passive 3D methods is based on resolution. Active 3D, using powered glasses to separate the R & L images at the viewer deliver the highest resolution, similar to a Blu Ray disc’s, at 1080p. Passive 3D systems interlace the R & L images at the projector, and so deliver half the resolution, about 1080i. Today, 3D systems such as RealD, employ circular polarizers for both theatrical and home viewing. Compared to old style anaglyph colored filter glasses, passive circular polarizers deliver truer and more saturated colors as well as a brighter 3D image. These are popular not only because the glasses are lighter in weight and lower cost, but also because consumers have found passive 3D more pleasing, less fatiguing and enjoyable over much wider viewing angles. 3D passive circular polarizers are expected to become the de facto standard in 3D home and theater viewing in the near future.

3D WITHOUT GLASSES
Remember those old baseball or trading cards that had a raised, semi-transparent surface that morphed into two different images when you altered the angle to your eyes? This lenticular display technology actually forms the conceptual basis for glassless 3D viewing. Using micro lenticels, or lenses, right and left eye image separation is achieved based on the differing viewing angles of our eyes.

Lenticular technology is well-suited to hand viewing, where optimizing the triangular relationship between the display’s R & L images and a viewer’s PD simply requires adjusting the viewing distance for the best 3D effect. Variations in this technology, in the form of electronic masks, allow flat screen TVs to deliver a glassless 3D experience, albeit for a limited range of “sweet spot” viewing positions. —BS


ENHANCING THE VISUAL EXPERIENCE
Beginning in the early 20th century, eyeglasses featuring different colored filters such as red and blue or green, were used to separate similarly encoded images in print and film to deliver a colored, virtual-3D effect. None of these succeeded in holding the attention of the public beyond their novelty factor. With the significant technical constraints required in both photography and projection, 3D soon fell out of favor, and interest did not rekindle again until the arrival of television.

In the early 1950s, Hollywood executives saw TV as a real threat to their livelihood from movie production, distribution and theater presentation. They first turned to developing wide-screen presentations, such as Cinemascope and Cinerama, in an effort to enhance and differentiate the thrill of the movie house from the small screen experience of TV. The reintroduction of 3D technology followed for these same reasons. But the colored eyeglasses required proved to be distorted, uncomfortable and unwanted, and along with story emphasis centered on in-your-face visual effects, 3D again fell out of favor  with the moviegoing public.

As television matured and developed into a true rival for the public’s leisure time, Hollywood made different attempts to introduce excitement in the movie experience. Distracting additions such as Sensurround (which employed vibrating seats) and Smell-o-Vision failed as well.

3D AND VISION PROBLEMS
Comfortable 3D viewing requires our eyes to be able to perform in-tandem binocular actions. All of the following items fall under the term eye-synching or eye synchronization:
  1. Eye Alignment
  2. Eye Tracking
  3. Eye Movement
  4. Eye Focus, Accommodation and Convergence
Research by experts has shown that problems, deficiencies or abnormalities in these binocular vision issues can inhibit successful perception of 3D images and are often linked to reading and comprehension issues in children. With recognition of this connection, the American Optometric Association is helping to better educate parents in understanding the need for a professional eye exam and diagnosis during the early stages of a child’s visual development. Here are some of AOA’s recommendations:
  1. Because of their underdeveloped vision systems, children under 6 years old should not be encouraged to view 3D movies at home or in theaters.
  2. Although experiencing some degree of fatigue may be considered normal in extended 3D viewing, children or adults who experience any symptoms of dizziness, discomfort, nausea, headache or lack of perceived depth should seek out a comprehensive eye exam and mention these problems to their doctor.
  3. Problems in eye-synching are often asymptomatic outside of the 3D environment, and parents are advised to not discount symptoms seen in their children because they also experience the same symptoms.
Of course not all problems in viewing 3D conclusively point to underlying vision issues. Over the years, filmmakers empirically discovered which factors make up comfortable 3D viewing. Vision researchers, such as James Sheedy, OD, at the Vision Performance Institute, have uncovered much of the science behind why virtual depth and disparity clues must be contained within certain value ranges to both avoid diminishing the 3D experience and to ensure no unwanted eye-synching or fatigue problems.

It is estimated that 25 percent of children are affected by eye-tracking and fusion-related learning issues. Luckily, today we have the awareness, diagnostic tools and the knowledge of how remedial vision therapy can help these kids overcome these hidden vision deficiencies. 3D enhanced instruction has also been proven to increase both comprehension and retention.

3D ENHANCED MEDICINE
Microsurgical skills have been shown to be improved or enhanced through the employment of 3D imaging. Through improvements in stereo acuity—which is defined as the smallest detectable depth difference in binocular vision—microsurgeons, particularly those in ophthalmology, have realized significant benefits in the operating room that directly influence their ultimate surgical skill. But a new problem has also arisen: As we now start to screen surgical residents for problems in 3D vision, we may be discouraging potentially successful individuals exactly at the point in their medical career where their nascent surgical skills are just beginning to be developed. Further complicating this is the fact that stereo acuity thresholds almost always improve manifold with perceptual training. Just as athletes have seen benefits that improved their athletic performance from vision training, perhaps we should prioritize integrating vision training and therapy in our medical schools, to the ultimate benefit of both surgeon and patient.

3D’S TIME HAS ARRIVED
With a history of failure in capturing the fancy of the public, why should 3D succeed now? Part of the answer is that improvements in the understanding of 3D technology and its effect on our eyes and vision processing, along with 3D’s arrival as an essential diagnostic, learning and surgical-enhancement tool, make a persuasive case to see 3D as more than an interesting novelty. The rest of the answer is that the entire business community of Hollywood is  recognizing that 3D technology has matured beyond the need to rely upon the shock of in-your-face visual effects. We’ve arrived at the juncture where 3D can finally deliver the type of intimate and immersive experience that the TV, movie, video game and mobile device-viewing public has always desired. With director James Cameron’s new reworking of the full 300,000 frames of his blockbuster movie “Titanic” into 3D for the 100th anniversary of its sinking in April 2012, there’s no better time than now for every eyecare professional to begin to learn about and embrace the benefits of 3D enhanced viewing and diagnostics.

For eyecare professionals, the availability of 3D eyewear presents a dispensing opportunity. Although 3D eyewear is presently available in nonprescription form only, at least one supplier, Samsung, is reportedly developing prescription 3D eyewear and is testing it in Korea.

Whether or not you dispense 3D eyewear, it’s important that you understand not only how it works and interacts with our visual system, but recognize that 3D viewing can serve as a diagnostic tool to determine if patients can adequately see 3D images, as the American Optometric Association has emphasized.

As more of your patients encounter 3D viewing in both recreational and vocational settings, knowing the ABCs of 3D will reinforce your position as the “go-to” source for eyecare advice.


Barry Santini is a New York State licensed optician based in Seaford, N.Y.

 

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