Monday, 7 March 2016

The Eye - Muscles of the Iris

There are two muscles in the iris: the circular muscle and the radial muscle, the diagram below shows both of them

Courtesy of http://georgi-georgiev.com/
These muscles control the iris, and incase you've forgotten, the iris controls how much light is let into the pupil.

The two muscles work antagonistically, meaning that when one constricts the other relaxes and when one relaxes the other constricts.


What happens in low light concentrations (dark)?

The pupil will widen when it is dark, allowing more light into the eye.
The radial muscle fibres constrict, widening the eye and the circular muscle relaxes due to the constriction of the radial muscle.


What happens in high light concentrations (light)?

The pupil will narrow when its light, allowing less light into the eye.
The circular muscle fibres constrict, reducing the pupil size and the radial muscle relaxes due to the constriction of the circular muscle.


Please note that this is a reflex.

Read about RODS AND CONES next!

The Eye - Rods and Cones

There are hundreds of millions of rods and cones covering the surface of the retina of the eye.


Cones

Cones detect colours.
There are around 7 million cones in the human eye.
There are three types of cones, each type detects a different colour, red, green or blue.
When all three types of cones are stimulated equally, we see white.


Rods

Rods detect shapes.
Rods help us see at night, when there isn't enough light for the cones to work.
There are around 120 million rods in the human eye.



Courtesy of http://littlewebgiants.com
You don't have to know what rods and cones look like for the exam, but it might be helpful to see what they look like.


Look at the FOVEA next!

The Eye - Fovea

The fovea is the area in the retina where the cones are concentrated. It is also the part of the eye where images are examined in detail.

Objects within a 2° angle of the eye are the only objects that can be seen in detail. By scanning across scenes, the eye builds up an accurate picture of the object or scene.

Image courtesy of www.studyblue.com