Hi, I am Dr Thomas Whitelaw, welcome back to Espisode 65 of Basic Sciences in Ophthalmology.In thiks episode we're exploring one of the most remarkable abilities of the human visual system: the ability to see in darkness.

Imagine walking out of a brightly illuminated room into a dark garden.

At first, you can barely distinguish the objects around you.

Gradually, however, shapes begin to emerge. You become aware of movement,outlines and objects that were initially invisible.

Your eyes have not simply become accustomed to the darkness.

A complex series of biochemical, physiological and neural changes has occurred within your visual system.

At the centre of these changes are the rod photoreceptors, the specialised retinal cells responsible for vision at low levels of illumination.

The process by which visual sensitivity increases afterentering darkness is known as dark adaptation.

And when the rod system or its supporting pathways become dysfunctional, patients may experience nyctalopia, commonly called night blindness.

Today, we'll explore three interconnected subjects:

First: rod photoreceptors.

Second: dark adaptation.

And third: disorders affecting night vision.

We'll examine the anatomy, physiology, biochemistry and clinical consequences of these systems, using exclusively the ophthalmology textbooks uploaded for this podcast project.