The fundus makes up the central part of your retina, which is a very thin layer at the back of your eye which is able to recognise light. Think off it like the sensor in a camera. Within your fundus, there is the macula, the optic disc, the fovea and the posterior pole of the eye.
We have mentioned the fovea in the section on binocular vision. The optic disc, also known as the "blind spot", is the area in which the optic nerve leaves the eye and heads towards the brain. It is known as the blind spot as there are no light receptors in this area, meaning that it cannot "see" anything. However, since our vision overlaps between the two eyes, we tend not to notice the blind spot while we have both eyes open. The optometrist will look at the shape and colour of your optic disc to help assess the health of it. You can try and find your blind spot by closing one eye, holding 1 finger up in front of the open eye, and slowly moving the finger outwards whilst looking forward. You should reach a point where you can no longer see your finger!
The macula is the area directly behind your pupil, and includes the fovea. It is the part with the most light receptors, and is what gives us the sharp vision we use to see fine details. It also has the highest concentration of receptors which help us see colour. Again, the optometrist will assess the health of this area.
The will do this using a technique called Ophthalmoscopy, and they may sometimes take a fundus photograph. Ophthalmoscopy can be done by either using a handheld direct ophthalmoscope, a head mounted indirect ophthalmoscope, or by using the slit lamp with a Volk lens. These are all good methods of assessing the back of your eye, and all have different strengths and weaknesses.