This Newsletter aims to promote communication between schools and the Student Health Service of the Department of Health

Sept 2013 Issue No.60

Published by the Student Health Service, Department of Health


Continuous improvement in technology has made 3D film and 3D television programme available. It rewards our life with more advance visual experience. But at the same time, we should be aware of the risk factors of 3D films when we are enjoying them.

In this issue, we would like to provide some information on “Evolution of Binocular vision”, “Principal of 3D Films” and “Common Side Effects of Viewing 3D Films”. Most important, we would like to enhance readers’ awareness on taking necessary precautions. We hope our readers could enjoy 3D films as well as keep our eyes healthy.

Health Decoding

Optometrist: Lam Kin Shing, Wallace Cheung, Rita Wong, Roy Wong

The Effects of 3D Movies to Our Eyes


3D movies are becoming more popular nowadays. The brilliant box record of the 3D movie “Avatar” has led to the fast development of 3D technology. 3D technology not only affects the film industry but also extends to home televisions, video game products and many other goods. It certainly enriches our visual perception and gives us entertainment.

Evolution of Binocular vision

Mammals have two eyes. Some prey animals, e.g. rabbits, buffaloes, and sheep, have their two eyes positioned on opposite sides of their heads to give the widest possible field of view. For these animals, their eyes often move independently to increase the field of view but they do not have the ability to judge the depth of focus of the objects accurately.

Other predatory animals, e.g. human beings, eagles, wolves, and snakes etc., have their two eyes positioned on the front of their heads, allowing the overlapping of fields of views of the left and right eyes creating good binocular vision (stereopsis). Thus these animals have the ability to judge the position of objects more accurately.

Binocular Vision (Stereopsis)

Stereo vision, or 'Stereopsis', is a result of good binocular vision, wherein the separate images from two eyes are successfully combined into one 3D image in the brain.

The impression of depth is perceived when an object is viewed with both eyes by someone with normal binocular vision. Binocular viewing of an object creates two slightly different images in the brain because of the different positioning of the eyes on the head. These differences give information to the brain for calculating the depth of the object, thus providing a major means of depth perception.

Principle of 3D Movie

Unlike general movie, when shooting a 3D image, two cameras at fixed viewpoints are used to capture separate images of the same object from slightly different angles.

When played back on a plano-stereoscopic display, the image taken by the left camera is shown only to your left eye and the image taken by the right camera is shown only to your right eye through the 3D eyeglasses. Your brain then fuses these two images to give you a stereoscopic image.

Common Side Effects of Viewing 3D Movies

  • The eyes get dried and tired easily.

  • Long exposure to 3D movies can reduce vision, or may even cause dizziness, headache or nausea. Pregnant women, elderly and people who are drunk or exhausted are not encouraged to watch the 3D movies.

  • Viewing 3D movies is more tiring than watching TV. Children may feel uncomfortable and they should be accompanied by adults when viewing such movies.

  • It may trigger latent squint.

  • The flashes of the images may induce the attack of stroke or epilepsy for patients having these diseases.


  • Choose a seat with greater viewing distance from the screen. It should be at least 15-20 meters from the screen.

  • Rest and relax your eyes intermittently when viewing the 3D movie.

  • Select theaters with good video facilities.

  • People with shortsightedness, long-sightedness and astigmatism should have their corrective glasses on before wearing the 3D glasses for special effects.

  • For regular contact lens users, it is better to wear contact lens rather than spectacle if the difference between two eyes are greater 2.5 Diopter.

  • If you have eye coordination problems, you should take a break when you feel tired.

  • People over the age 40 and with a family history of glaucoma should avoid staying in dimly lit environment for too long. They should take a rest of 5 minutes under normal lighting for every 30 minutes exposure of 3D movie.

Eye practitioners suggest that it is best to check your eyes first before watching 3D movies , as this may cause headache. Under normal circumstances, our brain can regulate some minor eye problems. However, when viewing 3D movies, ours eyes and brain require extra effort, which may cause headache.


Stereopsis is a complicated but interesting visual ability. It requires the coordination of the two eyes and the accurate interpretation of the images at the visual cortex of the brain. Stereopsis helps us to judge the depth of objects and distances between objects more accurately. However, we do not notice its existence very often.

We need to wear Polaroid 3D eye glasses to generate stereospic views when watching 3D movies. The 3D eye glasses help us receive 2 different images from the eyes so that the visual cortex of the brain can generate the fusion of them and produce a stereospic image.

Though 3D technology brings us entertaining stimulations, it has certain side effects to our health. We have to make extra effort in focusing and coordinating the mobility of our eyes. People who are weaker in these areas may experience blurred vision, double vision, dizziness, headache or nausea. Moreover, people with eye coordination problems like squinting or amblyopia may not be able to see the stereospic view when watching the 3D movies with the 3D eye glasses. Therefore, it is best for them to have an eye examination first before going for the first 3D movie or buying a 3D television.

Bridge Blog

My view on 3D Film:

It is so real! But I felt dizzy and hard to concentrate after watching it.

Very dynamic, it’s good.

Lively and interesting! But better not watch it too often, it is bad to the eyes.

I felt dizzy, nauseous and have a headache.

I became dizzy and got tears in my eyes

Shocking! Awesome! The 3D film lingers in my mind.

Long hours of watching 3D movies stresses our eyes and might worsen our eyesight.

Very exciting! However, it was not comfortable to wear glasses while watching it.

Bridge Chats

+852 1256 7890 Sa
Last night I watched a 3D film. It was excellent! The aeroplane was flying towards me as if it was crashing into my face.

+852 1234 5678 Tim
My mom did not think so. She felt dizzy and nausea as if she got motion sickness. Her eyes were very uncomfortable.

Elderly people, people with Presbyopia or dry eyes should not watch 3D films.

+852 1256 7890 Sa
Oh yeah! It’s very exciting but I felt tired.

If you want to enjoy the film, you should have adequate sleep. You should also apply eye drops prescribed by doctors before watching 3D film.

+852 1256 7890 Sa
Oh! Thanks!

After watching the film, you better not use your smart phone. You should look at distant objects to let your eyes have a good rest.

+852 1234 5678 Tim
Oh! Let me tell my mom so that we can watch 3D film together.

Junior Health Pioneer

The content of this issue is the sharing between Yuen Yuen and Junior Health Pioneer about the experience of watching 3D film with their family.

Yuen Yuen: Yesterday, I went to cinema with my mum and dad. We watched a cartoon wearing special glasses. The cartoon characters seemed to be running toward us. Compared with other cartoons, it was more vivid and realistic.
Junior Pioneer: You must be watching the latest 3D cartoon. 3D film pictures are more vivid and appeared three-dimensional. It enriched our entertainment lifestyle.
Yuen Yuen: But my mum said she felt a little dizzy and it was inconvenient to wear two set of glasses at the same time.
Junior Pioneer: On that day, you might be sitting too close to the screen. That’s why you have this feeling. When we are enjoying the visual experience from 3D technology, we have to beware of some factors. In this issue, optometrists would explain more on this issue.
Yuen Yuen: It is not just watching a movie, there are other issues we need to consider.
Junior Pioneer: To learn and use new technology smartly, our life will be more enjoyable.

For enquiries of student's health problem, please write to "Health Box"

4/F, Lam Tin Polyclinic, 99 Kai Tin Road, Kwun Tong, Kowloon

E-mail Address:

Editorial Board Members: Dr. HO Chun-luen, David, Ms. LAI Chiu-wah, Phronsie, Ms. CHAN Shuk-yi, Karindi, Ms. CHOI Choi-fung, Ms. CHAN Kin-pui
Tel : 2349 4212 / 3163 4600
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Last Revision Date : 9 December 2014