Anatomy of The Eye
Before considering diabetic eye disease we need to understand a little of how the anatomy of the eye and how the eye works.
- Iris – This regulates the amount of light that enters the eye. It is the coloured part of the eye across the front of the lens. Light enters through a central opening called the pupil.
- Pupil – Is the circular opening in the centre of the iris through which light passes. The iris controls dilation and constriction of the pupil.
- Cornea – Is the clear circular part of the front of the eyeball. It refracts the light entering the eye on to the lens, which then focuses it on to the retina. The cornea is extremely sensitive to pain.
- Lens – Is a transparent crystalline structure behind the pupil of the eye. It helps to refract incoming light and focus it on to the retina. A cataract is when the lens becomes cloudy, and then the lens can be removed and replaced with a plastic intra-ocular lens.
- Vitreous – Is a clear jelly-like material in the middle of the eye.
- Retina – Is a light sensitive layer that lines the interior of the eye. It is made up of light sensitive cells known as rods and cones. The rods are necessary for seeing in dim light. And the cones best in bright light and are essential for receiving a sharp accurate image. Cones can also distinguish colours. The retina works much in the same way as film in a camera.
- Macula – Is the yellow spot on the retina at the back of the eye with the greatest concentration of cone cells. It provides the greatest acuity of vision, such as reading.
- Optic disk – Is the visible portion of the optic nerve on the retina. The optic disk is the start of the optic nerve where messages from cone and rod cells leave the eye and pass along nerve fibres and so transfer all the visual information to the brain. The optic disk is also known as the ‘blind spot’.
How we see
For sight to take place light must be able to pass to the retina at the back of the eye. The light passes through cornea and enters the eye through the pupil. It then passes through the lens and the vitreous to be focused on the retina. The focused light or images of what we have been looking at, are then passed down the optic nerve to the brain.