Experiences

Optic - human eye

Mária Fabianová

Slovakia

Lower Secondary School

Chemistry

Teaching in class

Direct

It is totally normal for students that they can see but they do not have any idea how difficult process it is. Eye is exceptionally perfect “optical tool” which is considered to be salient part of the brain. Students are usually surprised that the end of eye perception is in the brain.
We draw the eye on the blackboard but not from the anatomical point of view. On the picture are shown only parts which are connected with the physical process. Converging lens is emphasized because the light is broken on it and according to the law of refraction it incidents on the back wall of the eye which is called retina. There are placed the cells which allow black and white and colour seeing. All colours that we can perceive are only combination of three basic colours: red, green and blue. Colour perception which is so obvious to us, is very difficult phenomena. On retina is reflected the image which is inverted and this image is rotated to an upright position in brain. Muscles to which is retina attached play a dominant role. Those are so called ciliary muscles which are flexible like a rubber and they enable us to see into various distances. If this was not like this our eye would be set to some constant distance and if we wanted to see some distant object we would have to get to it closely.

Then we compare our eye with eyes of various animals because they differ in many things. For example insects have mosaic eye and perceive in other way colours of plants. Birds of prey have more precise vision because they are looking for they prey from very big height. Interesting is the vision of dogs, they very well developed smell but no so perfect vision.
In comparison with animals is human eye very poor. For example when we want to see further away we need to have telescope which will get the image to our eye, or when we want to see in details we have to do it by microscope. In one publication is showed structure of grey hair in this way and students were shocked.
Humans have to compensate all their imperfections by brain. They have to ebe surrounded by things which increase their speed, power, hearing, vision. Lastly we mention disease of the eye, blindness and I say to students to try at least 10 minutes in unknown environment with their eyes closed.
Vision is getting worse as we age but it is also connected with how we use it.
Human eye has so called inertia which means that the subject stays in eye for the tenth of the second longer even we do not see the object any more. Screening of the films is based on this principle because the film strip is moved at speed 25 frames per second.