( CNN ) -- Take your thumb and hold it out directly in front of you , away from your face . Now close the left eye . Open it and close the right eye . Your thumb appears to have moved , even though you did n't move it with your arm . Three-D technology capitalizes on this effect , taking advantage of the brain 's ability to fuse two images into one . Those glasses that you have to wear when watching something in 3-D are basically helping your brain interpret two flat images as one object that has depth . With the success of `` Avatar , '' a cluster of 3-D movies , including `` Alice in Wonderland '' and `` How to Train Your Dragon '' , are making their mark in Hollywood . Martin Scorsese recently announced plans to direct a 3-D film later this year . Nintendo also announced plans for a 3-D gaming console , the 3DS . Many electronics companies have 3-D television models , bringing the opportunity for this enhanced viewing into the home as networks begin to air more 3-D programming . Comcast 's 3-D channel aired the Masters Golf Tournament earlier this month , and ESPN plans to launch a 3-D sports network this year . But doctors say that for eyes unaccustomed to watching 3-D for hours every day , there are some dangers , including mild symptoms such as disorientation and , in rare cases , seizures . The Samsung 3D LED TV comes with a substantial health warning . It cautions that certain flashing images or lights could induce epileptic seizure or stroke , and that `` motion sickness , perceptual aftereffects , disorientation , eye strain and decreased postural stability '' may result . Doctors say the percentage of people who should worry about significant adverse effects is small , especially the possibility of seizure . More commonly , people may experience dizziness or other discomfort after watching something in 3-D , including a feature film . One pair of 3-D glasses to rule them all . Symptoms of nausea , headache and fatigue may result because 3-D causes the eyes to move in an unnatural way , said an e-mail from Dr. Lisa Park , clinical assistant professor in the department of ophthalmology at New York University Langone Medical Center . Here 's how it works : The 3-D movie presents two slightly different perspectives of the same scene , superimposed but separated by a specific degree . Three-D glasses have a polarized filter that separates those two images , allowing each to be seen by a different eye . This happens so fast that you do n't see the transitions , said Steven Nusinowitz , associate professor of ophthalmology at the Jules Stein Eye Institute at the University of California , Los Angeles . In the brain , the two images are fused , creating the illusion of depth , he said . When you see something come toward you in the real world , your eyes slightly cross toward each other . At the same time , the lenses change shape in order to keep the object in focus as it moves in your direction , a process called accommodation . But when you see images on a screen , your eyes try to align the two images , but not `` accommodate , '' because the object is not actually moving toward you . `` The movie is telling you 'Hey , I 'm moving around in this scene , ' but your vestibular system is telling you , ' I 'm not moving anywhere , ' and that disconnect will make you feel sick , for some people , '' Nusinowitz said . Read about 3-D at CES . For those with certain underlying conditions , the artificial environment of a 3-D movie strains the ocular system , so when you take off the glasses it can be disorienting , said Dr. Norman Saffra , director of ophthalmology at Maimonides Medical Center in New York . People whose eyes are not perfectly aligned , or who have a weak eye muscle , will not be able to see in 3-D , Saffra said . Strabismus , a condition in which the eyes point in different directions , can be an impediment to seeing 3-D . Some people with amblyopia , or lazy eye , may also miss out on the depth perception effect when wearing 3-D glasses . Why I ca n't watch 3-D TV . Nusinowitz himself gets dizzy watching 3-D movies because his eyes have very different refractive errors -- he needs different prescription strengths in each lens of glasses . Still , based on experiences with patients , he said he believes he 's in the minority . `` I 'm willing to say that 80 percent of people will not have problems , '' he said . As for long-term effects of watching 3-D television instead of regular television , no one knows for sure because it 's too new . Park is concerned about serious consequences for children who watch 3-D television for long periods of time -- `` a continuous abnormal stimulus may possibly have long-term effects that are yet to be studied , '' she said .
In 3-D movies , glasses help the brain fuse two images , creating the illusion of depth . Symptoms of nausea , headache and fatigue may result when eyes move unnaturally . People with certain eye conditions can not see in 3-D .