3-D is not just hype It can help you diagnose binocular vision disorders and build your practice You can even help patients overcome their problem s with 3-D viewing By Dominick M Maino 00

you see stories about simulated the most important ques-

MEd

Why is there such Logie Baird while the an incredible 1950s ushered in the interest in 3-D first Golden Age of movies televishy commercially successshy

sion video games and the ful and popular 3-D use of 3-D technology in the movies (such as Bwana classroom Every time you Devil and House of pick up a newspaper read a Wax) magazine or a blog surf the Thirty years later Internet or listen to the news another smaller 3-D

boom appeued which 3-D Whats aU the hype about Is it rea lly hype or something more important to your patients and your practice

Can we improve the entertainshyment value of 3-D movies for the movie-going audience Can we make the extra cos t of buying 3-D televisions worthwhile even for those who now have headaches when they watch 3-D programshyming And what can we do for those children wbo cannot apprecishyate the sense of depth in 3-D video games or benefit from the 3-D classroom educational experience Can we ensure that they do not miss out on the fun and improved academic learning environment

When it comes to 3-D viewing and the patients we serve one of

54 REVIEW OF OPTOMETRY OTOSfH 15 2011

tions for the optometrist is Ca n we improve the actual user of 3-D conshytent so that the experience can be better appreciated no matter their age or the type of simulated 3-D content experienced

The answer is of course yes

3-~ Through the Years 3-D viewing and its relation

to binocular vision is not a new phenomenon Thanks to Charles Wheatstone and his stereoscope (in the 1830s) and the soon-to-follow stereopticon invented by Oliver Wendell Holmes (1862) many could enjoy this new form of 3-D entertainment

In more modern times the first stereoscopic 3-D television was created in the 1920s by Charles

was initiated by IivlAX Unfortunately there were many difficulties with this method of proshyducing 3-D viewing because of the large size and unusual dimensions of the theater screen needed l

As the history of 3-D technolshyogy moved into the present day Avatar (2009) could be noted as bringing the next golden age of 3-D to the masses In just the past few years weve witnessed a boom in movies telev ision videogames and other media depicted in 3-D

It should be no surprise then that the events that soon followed this current explosion of interest in 3-D should include the American O ptoshymetric Association and an industry group called the 3DHome Conshysortium signing a memorandum of

Make 3-0 Pop Up in Your Prce With the unending attention centered on 3-D movies 3-D televisions 3-D video games and 3-D in the cfassroom your office should take advantage of the educational and marshyketing possibilities Your existing and potential patients are aware of many of the issues surrounding simulated 3-D viewing but have you made them knowledgeable about the services you offer so that they can enjoy the digital dazzle associated with this new techshynology

Heres how bull Offer a seminar about 3-D in your office Use this article or other resources to

help tell your patients how simulated 3-D is produced and why some individuals have problems associated with 3-D Vision Syndrome Use prism to make individuals in the audishyence diplopic Use the Brock string to see how many in the audience have binocular vision dysfunctions-l did this at the 2011 Consumer Electronics Show and the response was astounding [Watch the video at httnllmamosmemosblogspolcoml2011J04dr-domiOlckshymaino-atmiddotconsumerhtmlj

bull Set up a Google Alert search on 3-D Find all the media topics and post links on your office webpage Also post these links with commentary on your blog Facebook page and Linkedln page

bull Let your patients know you can diagnose and treat or refer for treatment those with 3-D Vision Syndrome

bull Obtain copies of 3-D in the Classroom See Well Learn Well from the AOA and send it to the schools in your area with compliments from your office Put links on your office web page and social media sites to this document and send email toalltheteachersprincipals school adminshyistrators and parents you know (Go to 3deyeheallhorg for more information)

bull Display 3-D art movie posters and photographs in your office (See the astounding work of Almont Green at a1montgreencom He creates great 3-D photographic art There are also 3-D movie posters available from wwwallshyoosterscommiddotsV3-0-Movie-Posters c118624 hlm while vintage 3middotD movie posters can be found at www3dstereo comlviewmaster3dpostershtml)

bull Offer 3-D glasses with your patients prescripshytion in them Samsung displayed a number of active shutter prescription ready glasses at the 2011 Consumer Electronics Show Other manufacturers offer prescription-ready glasses as well (such as those by Marchon which now offers Marchon 3-D glasses and even 3-D clip-ons wwwmarchoncomIM3D and Gunnar Optiks wwwgunoars comshoolPremium30-EyeweaO Gunnar Opliks Anime 3-D glasses

Remember that 3-D TV glasses only work with specified televisions Make sure you mention this to your patients so they know that a new pair of glasses may be necessary if they buy a different TV

bull Make your own 3-D art and photographs and display them in your office (www3d-lmagenetl

understanding vbjch ~tated their intent to hare da ta and joint ly p roshymote vision healrh urili7i n~ tereoshyscopic 3-D d isplays2 Borb [he AOA an d 3DHome have joined forces by collaborating on a new enrure 3deyehealrhoq

Creating 3-~ As every optometrist kn ws the

creation of simulated 3-D content requires the input of one image into the right eye and 3nother similar but laterally disp laced image into the other eye When rJ1e brain receives the two images fUSion occurs and a sense of depth is creshyated Whcn optomctric visiun thera py i ~ uscd to trcat those with binocula r vis ion dysfuncti n thi ~ i typically done by havi ng the patient wear anaglyph (redgreen or rcd blue) gbsses p( la roid glasses or by synchronIzing the t iming of thc image to be received by each eye in such a way sO that only one cye secs an image a t any me timc T his is also true for most of the 3-D conshytent our patients view commercially

There are several ty pes of glasses that consumers can I I e to expeshyrience simulated 3-~ T hey arc catego rized as pa s ivc polarized or activ sh uttcr ( 1 here is als() a yvay to create 3-D withou t tbe nt ed for glasse such as w ith the Nimendo 3-DS or the photographic art of Al mo nt Green but I ll limit the disshycussion to the passive polarized and active shu tter gla se 3-4)

Passive po larized glasse are either linearly or cir ularly po larshyized Linear p I rized -D tgtla e work with the older Stereo proj ecshytors StereoJet prints and modern projecto r systems wi th li near p olarshyizers If YOLl use li near polarized gLasses you ca nnot turn or til t your head withom 10 ing the 3-D effect Circular polarized glasses a llow you more leeway in terms o f head

56 REVIEW OF OPTOMETRY OCfOSEI1 152011

position and are the glasses most often used in movie theaters

Active shutter glasses work when voltage is applied to one of the lenses which makes it turn dark while the other lens remains clear and vice versa This quick alternation of the image is synched with the screen showing the 3-D content being viewed by each eye at a slight lateral disparity which creates the 3-D effects

Most 3-D movies use various polarizing techniques while 3-D TVs favor active shutter methodologies

The most frequently used technologies for 3-D entertainment in theaters are those produced by IMAX 3D RealD 3D Dolby 3D and XpanD 3-D When lMAX first started showing 3-D it used active shutter glasses but it now uses linear polarization RealD 3D uses circularly polarized glasses which reduces problems when viewers tilt their heads Dolby 3D however uses a special color wheel attached to the projector This color wheel splits the wavelengths used by the left and the right eyes The glasses used for Dolby 3D have very accurate color filters (dichroic or interference filters) that send the appropriate waveshylengths of light into the eyes of each movie patron Lastly XpanD 3-D uses active shutter glasses that are synchronized with the projector using infrared signals

Diagnosing 3-D Vision Syndrome (3DVS) Although the technology to produce 3-D viewing

is constantly being improved not everyone is able to experience and enjoy simulated 3-D because of vision problems tl1at cause headaches nausea diplopia and other symptoms This is not only true for children but also for adults6

According to the American Optometric Associashytions 2011 American Eye-Q survey parents are concerned about the possible detrimental effects of 3-D viewing Fifty-three percent of respondents with children 18 or younger believe that 3-D vievving is harmful to a childs vision7 However the AOA and several other organizations note that there is currently no research to support the belief that 3-D viewing is harmful to a childs vision

What the primary care optometrist needs to do is improve the patients binocular vision skiLls This will create a better 3-D viewing audience that can particishypate in an enhanced and symptom free 3-D experishyence The first step to making this happen is to use all the resources available to you to get the word out about how optometry can help make the 3-D viewing experience more enjoyable This will enable you to reach those patients most in need

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In order to assist you in getting ing binocular vision simply wont the word out abou t what optomshy see 3-D While this doesn t pose etry can do to improve the 3-D any problem viewing the screen viewing experience the AOA it certainly significantly detracts 3DHome Co nsortium and 3deyeshy from the enj oyment most experishyhealthorg havE come together to let ence while viewing 3-D content and the public know about The 3Ds of makes spending the extra money 3-D Yiewing for the 3-D experience worthless

bull Discomfort Beca use 3-D viewshy This can however serve as a pubshying is based on the eyes converging lic hea lth vision screening that in front of or beyond the screen something is abnormal with the viewing 3-D images can potentiall y viewers vision create eyestrain and headaches Although not sta ted directly the

Diagnosing 3~D Vision Syndrome During the following elements of the examination consider these factors if you suspect 3-D vision syndrome

bull Case history Always ask if your patient has seen a 3-D movie and experienced asthenopia headaches blurred vision eyestrain diplopia dizzinessnausea andor visionshyinduced motion sickness If they have never seen a 3-D movie ask why not The answer may also suggest vision problems are present

bull Visual acuity If accommodation is affected visual acuity may varyAny amblyopia will disrupt 3-D viewing

bull Entrance tests Stereopsis is usually reduced and suppression can occur bull Oculomotor assessment Cover test near point of convergence Hirschberg Angle

Kappa and Bruckner tests all can indicate a binocular vision problem bull Refractive error The objective (retinoscopy) and subjective assessment of refractive

error can give variable results The patient may not be able to give aclear unambiguous end point during the manifest subjective assessment procedure

bull PhoriaNergence Both distance and near heterophoria findings as well as positive and the negative fusional vergence tests can indicate the presence of afusional vergence anomaly

bull Accommodation Negative and relative accommodation accommodative facility findshyings and the monocular estimation method (MEM dynamic retinoscopy) will give high or low inconsistent or variable results

bull Ocular health Eye health will usually be unremarkable

For iolonnatWn on how10 perform ttlestl l~ts see bull 3chlmge D Maino D Clm ical beHavl lal objectives dSsessmenttechniques for special popufalions In Maino D(ed) Diagnosis and Mantlg ment 01 SpeclJI PopulatiOnS SI Louis MO Mosby-Yearbook Inc 199515Hl8 bull ~Illiman MWick B Cl inical Managenenl of Binocular ViSion HeterophoricAccommodaliV1) and Eye Movement Discrdw POIIdelphi Lippincott 2008 bull Pang Y Gabriel H Frantz KA Saeed F Aprospective study of dilferentlesllargels for the rear painl of convergence OphllJ] lmiC Physiol Op 2010 May30(3)298-303

bull Dizziness 3-D technology can fourth D of 3-D viewing should be exaggerate visual motion hypersenshy If you do not appreciate 3-D or you sitivity (YMH) or vision-induced experience asthenopia while watchshymotion sickness which can cause ing 3-D content you should immeshyindividuals to feel dizzy o r naushy diately make an appointment with seous during or after viewing 3-D your D octor of Optometry H

content Tbe way to crea te a better 3-D bull Lack of Depth A viewer lack- viewing audience is first to di agnose

60 REVIEW OF OPTOMETRY ~)CI)~~ll 11011

any binocular vision problems presshyent to determine if your patient has 3-D vision syndrome (see Diagshynosing 3-D Vision Syndrorne beloW)9-1 r 3-D vision syndrome (3DYS) is comprised of a group of symptoms that collectively indicate the presence of a functiona l vision disorder which adversely affects the enjoyment level of watching 3-D content 3DVS symptoms include but a re not limited to as thenopia headaches blurred vision eyeshystrain diplopia dizzinessnausea and vision-induced motion sickness after watching a 3-D movie viewshying 3-D television programming participating in a 3-D classroom educational activity or after pla ying a 3-D video game12

While weve known for some time that 3-D viewing can cause vision problems to manifest research is only now beginning to determine which functional or group of functional vision disorders are involved in causing the 3DYSshyassociated symptoms IJ-15 One or more papers suggest that the sympshytoms produced are caused by1 6 1S

bull Excessive demands placed upon the linkage of accommodation-conshyvergence by viewing fast-moving 3-D images

bull Spatial and temporal inconshysistencies created by 3-D artifacts from insufficient depth information

bull Blur A more recent study notes that

conflicts in motor responses drive visual discomfort and fatigue because if the visual system does not a ttempt to make a motor response when a vergence-accomshymodation conpoundlict is present no discomfort occurs 19 This is an interesting finding because at least one other paper suggested the primary ca use of symptoms in a t least one binocular vision disorder (convergence insufficiency) is the

In order to assist you in getting ing binocular vision simply wont the word out abou t what optomshy see 3-D While this doesn t pose etry can do to improve the 3-D any problem viewing the screen viewing experience the AOA it certainly significantly detracts 3DHome Co nsortium and 3deyeshy from the enj oyment most experishyhealthorg havE come together to let ence while viewing 3-D content and the public know about The 3Ds of makes spending the extra money 3-D Yiewing for the 3-D experience worthless

bull Discomfort Beca use 3-D viewshy This can however serve as a pubshying is based on the eyes converging lic hea lth vision screening that in front of or beyond the screen something is abnormal with the viewing 3-D images can potentiall y viewers vision create eyestrain and headaches Although not sta ted directly the

Diagnosing 3~D Vision Syndrome During the following elements of the examination consider these factors if you suspect 3-D vision syndrome

bull Case history Always ask if your patient has seen a 3-D movie and experienced asthenopia headaches blurred vision eyestrain diplopia dizzinessnausea andor visionshyinduced motion sickness If they have never seen a 3-D movie ask why not The answer may also suggest vision problems are present

bull Visual acuity If accommodation is affected visual acuity may varyAny amblyopia will disrupt 3-D viewing

bull Entrance tests Stereopsis is usually reduced and suppression can occur bull Oculomotor assessment Cover test near point of convergence Hirschberg Angle

Kappa and Bruckner tests all can indicate a binocular vision problem bull Refractive error The objective (retinoscopy) and subjective assessment of refractive

error can give variable results The patient may not be able to give aclear unambiguous end point during the manifest subjective assessment procedure

bull PhoriaNergence Both distance and near heterophoria findings as well as positive and the negative fusional vergence tests can indicate the presence of afusional vergence anomaly

bull Accommodation Negative and relative accommodation accommodative facility findshyings and the monocular estimation method (MEM dynamic retinoscopy) will give high or low inconsistent or variable results

bull Ocular health Eye health will usually be unremarkable

For iolonnatWn on how10 perform ttlestl l~ts see bull 3chlmge D Maino D Clm ical beHavl lal objectives dSsessmenttechniques for special popufalions In Maino D(ed) Diagnosis and Mantlg ment 01 SpeclJI PopulatiOnS SI Louis MO Mosby-Yearbook Inc 199515Hl8 bull ~Illiman MWick B Cl inical Managenenl of Binocular ViSion HeterophoricAccommodaliV1) and Eye Movement Discrdw POIIdelphi Lippincott 2008 bull Pang Y Gabriel H Frantz KA Saeed F Aprospective study of dilferentlesllargels for the rear painl of convergence OphllJ] lmiC Physiol Op 2010 May30(3)298-303

bull Dizziness 3-D technology can fourth D of 3-D viewing should be exaggerate visual motion hypersenshy If you do not appreciate 3-D or you sitivity (YMH) or vision-induced experience asthenopia while watchshymotion sickness which can cause ing 3-D content you should immeshyindividuals to feel dizzy o r naushy diately make an appointment with seous during or after viewing 3-D your D octor of Optometry H

content Tbe way to crea te a better 3-D bull Lack of Depth A viewer lack- viewing audience is first to di agnose

60 REVIEW OF OPTOMETRY ~)CI)~~ll 11011

any binocular vision problems presshyent to determine if your patient has 3-D vision syndrome (see Diagshynosing 3-D Vision Syndrorne beloW)9-1 r 3-D vision syndrome (3DYS) is comprised of a group of symptoms that collectively indicate the presence of a functiona l vision disorder which adversely affects the enjoyment level of watching 3-D content 3DVS symptoms include but a re not limited to as thenopia headaches blurred vision eyeshystrain diplopia dizzinessnausea and vision-induced motion sickness after watching a 3-D movie viewshying 3-D television programming participating in a 3-D classroom educational activity or after pla ying a 3-D video game12

While weve known for some time that 3-D viewing can cause vision problems to manifest research is only now beginning to determine which functional or group of functional vision disorders are involved in causing the 3DYSshyassociated symptoms IJ-15 One or more papers suggest that the sympshytoms produced are caused by1 6 1S

bull Excessive demands placed upon the linkage of accommodation-conshyvergence by viewing fast-moving 3-D images

bull Spatial and temporal inconshysistencies created by 3-D artifacts from insufficient depth information

bull Blur A more recent study notes that

conflicts in motor responses drive visual discomfort and fatigue because if the visual system does not a ttempt to make a motor response when a vergence-accomshymodation conpoundlict is present no discomfort occurs 19 This is an interesting finding because at least one other paper suggested the primary ca use of symptoms in a t least one binocular vision disorder (convergence insufficiency) is the

Pha e of Optometric Vision Th rapy Phase 1 Monocular The monocular phase of therapy often includes the following oculomotor handshyeye and accommodative therapy procedures bull Hart chart saccades bull Hart chart accommodative rock (WWWyoulubecomwatchJ- tX8matodzgs) bull Rotating pegboard bull Computer paddle ball (wwwyoutubecomlwatchv-EenLQ3mKow J bull Bunt ball (wwwyoytubecomfwatcllv=BTy3080wONB) bull Plus and minus lens flippers bull Wayne saccadic fixator (wwwyoutubecomwalchv-S21z6hBpFOy) bull Vision coach lwwwyoulubecomwalchv==kbcXr5IxXAM)

Phase 2

BiocularThe biocular therapy phase is often used to break down any suppression present and includes oculomotor hand-eye accommodative and anti-suppression therapies bull Barrel card (WWWvoutubecomlwatchv- HtzEHSle-90) bull Split vectogram (wwwvoutubecomwalChv=Tzieb5g0vJA)

Phase 3 BinocularThis binocular phase of therapy often includes the following oculomotor handshyeye (if still needed) accommodative and vergence therapy procedures bull lifeSaver cards BI (wwwyaulubecomlwalchv=Ul3KTZOdzbo) bull lifeSaver cards BO (wwwYOutubecomwatchv=wGYX684r3xQ) bull Brock string (WWWyoulubecomwBchy=EGICVTdNafw) bull Vectograms (wwwYOutubecomwatchvlt=0IuzE6hc7NI)

Fun with vectograms

Phase 4 IntegrationStabilization This phase includes combined oculomotorhand-eyeaccommodashytivevergence therapy (This is where you might use plus or minus lens andor prism flipshypers with Vectograms aperture rule and other vergence andor oculomotor activities) bull Brock string with flippers (wwwyoutubecomwatcllv==5S fYs-EAlO)

Also note that although randomized clinical trials have shown that in-office optometric therapy is most effective for binocular vision disorders home computer therapy is helpful for treating these disorders as well These home therapeutic digital programs include but are not limited to Home Therapy Systems (wwwhomevlsiontherapycom) PVT Perceptual Visual Tracking and Amblyopia iNet (wwwvisiontherapysolutionsnet) and Computer Aided Vision Therapy Track and Read and Computer Vergences (wwwcavlnet)

associated dysfunction noted in accommodation lo

Treating 3DVS No stanJard successful treatshy

ment has yet been esta blished for 3DVS However at last years American Academy of Optometry meeting we presented a single subshyject design study that clearl y demshyonstrated how a patient with 3DVS can be treated successfully with optometric vision therapy (OVT)Y (See Phases of Optometric Vision Therapy left)

The poster described a 27-yearshyold white female who began to experience severe symptoms after viewing a 3-D movie for 15 to 20 minutes These symptoms includeJ blurred visiun diplopia eyestrain visual tracking problems headshyache nausea and vision-induced motion sickness A comprehensive examination noted reduced random dot stereopsis no positivenegative fusional ranges (immediate diploshypia) and high exophoria at near Also she reported diplopia while accessing accommodative facility The initial findings included a varishyable Monocular Estimation Method (MEM dynamic retinoscopy) pain upon near point of convergence testing and reduced positive relashytive accOlllmodation and accommoshydative amplitudes

We diagnosed this pltuient with convergence insufficiency accomshymodative infacilitylinsta biLiry insufficiency and diplopia She was prescribed in-office OVT and home VT After the first six therapy sessions all symptoms were either improved o[ eliminated Upon comshypleting a program of out-of-officc (eight sessions) and home-based optometric vision therapy all findshyings normalized and all symptoms relieved

The patient was so pleased with

62 REVIEW OF OPTOMETRY OCTOBER 15 201 1

therapy outcomes that several weeks post therapy while she was in the middle of watching a 3-D movie she used her cell phone to text me about how much she enjoyed watching it without experishyencing any pain or discomfort bull

Dr Maino is a Fellow of the College of Optometrists in Vision Dellelopment and American Acadshyemy o Optometry as well as a Proessor o PediatricsBinocular Vision at the Illinois Eye Institute Illinois College of 01Jtometry and is in prillate practice in Harwood Heights Jl

1 Schubin M Eyes wide open 3-D lipping poinls loom PriceWaterhouseCoopers Available at WI pwccQmlen GXlgxentertaj OIeJI-medjalodflEye Wjde Ooen 3D noshyplno polors adl Accessed July 2011 2 TheAmerican Oplometric Association and 3-DHome Consor tium Sign Memorandum ot Understanding Available at m 3deyebeallhQrQIAOA-3-QaIHIHDe-MOU-aO1QunceshyOOlJlI Accessed July 2011 3 Nintendo 3-DS producl iniolmation Avai lable al t njoleodo cornl3d$hardWae Accessed July 2011

4 Almont Green hnplalrnQfilgreen com Accessed July 2011 5 Younkin AC Anderson GJ Doherty RA Corriveau PJ Toward acomprehensive assessment olliser experience wilh 3~ Proceedings ollhe Fifth International Workshop on Video Processing and Qualily Metr ics lor Consumer Eleclronics VPQM-2010Available at hllllleowb lulluo asueduresplvoomivoomlOPrOCeedlOOS YPOM2QlOi yoarn Il35 W Accessed July20 11 6 Maino O Chase C Aslhenopia Technology Induced Visual Impairment Rev Oplom201 1JuneSuppl Part 2 28-35 Available at Wo(N revoQtom comcmsdocyshymeOlst20 tl6ll611 b+1 13hedilionodt Accessed July 201 1 7 AmericanOptomelr ic Associat ion websile New Survey Data Reveals Parents Concerns Aboul Eye and Vis ion Health as More Classrooms Go High-TechAugust 2 2011 Availshyable at m aooOgIx18810 Wi Accessed Augus120 11 83-0 Vision and Eye Heallh websile Avail able al www Jdeieheallhom Accessed July 201 1 9 Maino O Identify Binocular ViSion Disorders Optome1ric Management 2009 Oec(12) Ava ilable a WI optometnr comladlcle ijQxartlcle-1 Q3756 Accessed July 2011 10 Maino D Thebrnocular vISion dyslunction pandemic Optom Vis Dev201041 (1 )6-13 11 Scheiman M Wick B Ctinicat Management 01 Binocular Vision Heterophoric Accommodative and EyeMovement Disorders 3rd ed Philadelphia Upprncoi 2008 12 Maine o Mainoss MemosWhat is 3-D Vision Syndrome Avai lableat f1aJnosmemOS bloosooL cnml20tpll3dlslao-syndlcme 12 him Accessed July 2011 13 Tsukuda S Murai Y A case report 01 manilest eSOlropia alier viewinganaglyph stereoscopic movie Japanese OrthopshyticJournal 19881869-72

14 LambooijaM Fortuillii MF IJgtSIllsteijn WA Heyndenciltx I Visual discomlort assoctaled wlih 3D displays Ploceedshyings of tile Filth International Workshop 00 Video Processing and Quality Metrics for CQnsurrer Electronics VPQM-20 1 0 Available at hnogIlQub lullDO 3St edUiresoIYoar1JllrOOm101 Proceedinus VPQM2Ql ll1ltPqlll p44lliJ Awlssed July 2011 15 Iwasaki S KubotaT TavltIra The loleJance rilllge of billocular disparity on a3D display based on ttle ptryslologi cal characleristlcs 01 ocular accommodation Disntays 2009 Jan30(1)44-48 16 Yano S Ide S Milsuhashi T Thwaites H A study of visuallatigue and visual comfort fOr3 D HDlVlHDTV images Displays 2002 23(4) 191 -20 1 17 Hoffman OM GirshicK AR Akeley K BilnKs MS Vershygence-lCcommodalion conllicts hinder visual fJertorrnance and cause visual fatigueJVisioll 2008 Mar 288(3)33 1shy30 18 Lambooij M Fortuln M IJsselsteiin WA Heyndlicltx I Measuring visual discomlort aSSOCiated w1U1 3-0 display Proceooings 01 SPIEmiddotISampTEteclrooic lmagmg 2009 Avail shyableat MoropOllilmy ludell nlJyrgwftrl UldffO5~ 2342-4m-ae73-ti97etOd61906 Accessed AIJQus12011 19 Sh ibata T im J Hoilman OM snks MS nre zolle of comtort Predicting visual dlsoornforl willi stereo displals J Vision 2011 July 2111(8)11 1-29 20 MaHan LF De Land PN Nguyen AL Accommodative insulticiency is the primary source 01 SYTIPIOms In chllrnen diagnosed with conVErgence Insulticlency Oplom Vs Sci 2006 May83(5)281-9 21 Maino 0 The 3 0 Vision Syndrorrre Ii Case Reonrt labslracIJ American Academy 01 Optometry Annual Meeting Nov 2010 Sa FrancIsco CA Available at yen(IfN shdeshap netOMAINO31-vlsjoll-syndroflle Accessed July 2011

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