Avatar

Seems like most of the world has seen Avatar; it just passed Star Wars for the third highest grossing film of all time.  Avatar does have one advantage; they get to charge a significantly higher price to go see it.  If you see it in 3-D of 3-D IMAX plan on paying at least two dollars extra.  But everyone wants to see it that way (myself included) because lets be honest, the story is very predictable.  Do you realize that somewhere between 4 and 10 percent of the people going are wasting their money and don’t appreciate the 3-D?

This is really a question of stereopsis vs depth perception.  Look at the photo below.  It is a stock photo from Venice.  You get a sense of depth from this photo.  You know that the boats in the left are in front of the house; because of course they block some of the house.  You can tell that the houses in the middle are further away than the ones in the periphery because they are smaller and you can see less detail.  Now close one eye, does anything change?  Of course not, nothing changes.  It does not matter if you use one or two eyes; you have depth perception either way.

Now hold up two fingers one about 6 inches from you nose and one about a foot from your nose (go ahead, do it, I won’t watch).  Look at the further finger.  If you have stereopsis you should see two closer fingers. Now if you look at the closer finger you should see two further fingers.  If you now close one eye you will only see one finger on either hand.  This is normal.  This ability allows us to judge small distances with extreme accuracy.  Try threading a needle with one eye closed, or simply cap a pen.  It is a lot harder than with both eyes open.

Going back to our original point, Avatar has some amazing scenes.  But between 4 and 10 percent of the population does not have stereopsis.  Without stereopsis those individuals appreciate the movie exactly the same if they go to the 3-D and wear the glasses vs. going to the non-3-D showing without the glasses. They appreciate a sense of depth from depth perception but they do not appreciate the stereopsis.  If they went to the non 3-D they would save a few bucks.

If you ever went to an amusement park and enjoyed a 3-D movie one of the things that always happens is someone throws something out of the screen and startles the audience.  Many people would even duck.  However some people never reacted and these people generally were not impressed with those 3-D movies.  Many of them lacked stereopsis and therefore didn’t actually perceive anything different.  Avatar very carefully avoided any of those scenes, you never saw someone shoot an arrow and have it come off the screen at you.  I would guess they wanted to avoid people saying they didn’t notice that affect.

To have steopsis you need to have a couple things:

• Two eyes

• The eyes need to line up

• Both eyes have to see clearly
   

Stereopsis, like all of vision is a learned skill.  If you had all the above traits as a child you probably have stereopsis.  We used to believe that after the age of 14 we could never teach you stereopsis however Susan Berry is professor of neurobiology, she was an adult when she first appreciated stereopsis and her book, Fixing My Gaze is about her experience with vision therapy and learning to see in 3-D.  This example has really changed the way we think about vision but the key point is with vision therapy we can teach stereopsis.

“Dodge”

William Dodge Perry, OD