Naked Science Forum

Life Sciences => Physiology & Medicine => Topic started by: annie123 on 29/09/2016 22:12:50

Title: Why can we see peripherally?
Post by: annie123 on 29/09/2016 22:12:50

If light travels in straight lines, how can light rays enter the pupil from an angle so far to the right or left of us? Surely they should just continue on their path past the eye?

Title: Re: Why can we see peripherally?
Post by: chiralSPO on 29/09/2016 22:48:03

The lenses of our eyes capture a pretty wide angle of image from the outside world--no magic involved (see attached schematic).

I believe the difference between peripheral and and central vision has more to do with the density of light detectors (the resolution) on the back part of the eye, where the image is projected and collected.

Title: Re: Why can we see peripherally?
Post by: annie123 on 30/09/2016 00:59:15

I can see further behind my eye than the diagram shows and it would seem to me that a light ray coming from there would by pass my pupil or only touch it tangentially, never mind going in to interact with the lens...?

Title: Re: Why can we see peripherally?
Post by: chiralSPO on 30/09/2016 01:39:40

Yeah, the picture doesn't really indicate the actual angle. If I look directly forward and move my hands around the side of my face, I can see almost 180° (probably like 165° or 170°... but barely. Just detecting motion or color.

Title: Re: Why can we see peripherally?
Post by: alancalverd on 30/09/2016 15:02:22

The front surface of the lens actually bulges slightly from the near-spherical eyeball. This one eye can accept light from a cone of about 100 - 120 degrees. There is a central area where both eyes can coordinate to provide full stereoscopic vision, but the axes are slightly offset each side of your nose so you can detect movement from anywhere in a horizontal arc of up to 220 degrees.

Title: Re: Why can we see peripherally?
Post by: evan_au on 30/09/2016 23:40:33

I have seen the angle of vision quoted as 110°, but I guess the fact that your eyes are pointing in slightly different directions extends that angle. Towering, curved IMAX screens try to fill your entire visual field. 

Unless you are a sheep, where the eyes are pointing in totally different directions, and produce almost 360° vision...

Title: Re: Why can we see peripherally?
Post by: annie123 on 04/10/2016 06:46:19

Thanks everyone. tried the say thanks button- didn't get the hang of it.WIthdraw thanks turned up when I clicked on it etc.