Vision and 3D movies

Ganesh returned home, complaining of  nausea and headache after watching a 3D movie, while his friends enjoyed every bit of the technologically brilliant film. Ganesh works on a computer, for over 12 hours a day, and enjoys regular movies, so he was baffled about his reaction to the 3D film. Maria, a young movie buff, said she had to remove the 3D glasses and rest, with her eyes closed, at regular intervals during the film. Supreeta, a call centre executive, reported that she did not enjoy the movie as she was unable to spot the 3D effect. The screen was all blurred and dim, she claimed.  What could be their problem?

What is 3D vision?
The right and left eyes see objects from different angles. The right eye sees more objects on the left, while the left eye sees more objects on the right. The two  images are then sent to the brain separately. The objects, which are near, are seen more vividly than other objects. The brain assesses this minute disparity and indicates the distance of objects. This is called stereo vision. If you close one eye, you are left with only a false look at 3D dimensions, which is not accurate.  

3D movies use this technique to create dramatic effects. There are two movies projected on the screen, with a disparity. The rays are polarised, so when you wear  the 3D glasses, the right eye sees one image and the other eye sees the projected image. The images are dim due to polarisation.

To enjoy a 3D movie, both your eyes should be good, the muscle balance between the two eyes needs to be good, and convergence should be adequate.Here’s why some people have difficulty in enjoying a 3D movie: Supreeta suffers from amblyopia. Her problem should have been treated when she was about three or four years old. Amblyopia cannot be treated after the age of 9. The correction process involves wearing glasses and applying a patch on the good eye so as to exercise the defective eye. Supreeta cannot enjoy 3D movies or 3D comics.

Maria is affected with anisometropia, where one eye has higher power than the other. Although her vision is fairly clear, her eyes send images of different sizes to the brain. The brain can usually take on additional work, but in an artificial scenario, like a 3D movie, it becomes far too much work for the brain. Advanced EpiLasik treatment can correct such a condition in most cases. Ganesh’s condition is called ‘convergence insufficiency’. His eyes are unable to move inwards when they spot an object which is close by. Although his muscles are used to focussing on a computer screen,  the 3D movie was a strain on his convergence. Convergence exercises can help treat cases such as his to a large extent. If the problem persists and affects his work, he could opt for a minor surgery.
Another common problem is phoria. It is a type of squint, where the eyes have a tendency to deviate but are kept together by binocular effort. There is a continuous strain on the eye muscles to keep them straight.

Phoria can be caused due to nerve palsy, diabetes, tumour, trauma, minor head injury, congenital disease, myasthenia, thyroid etc. Some conditions are treatable. A squint eye is ideally corrected before the age of 5 years to get the best results.