Back of the eye

The ocular fundus is the posterior part of the eyeball which can be made visible in case of drug-induced pupil dilation. The Latin name for the fundus oculi is Fundus oculi. In order to be able to look at it more closely, one looks through the transparent vitreous body and can illuminate various structures, such as the retina (also called retina), the exit of the optic nerve (blind spot), arterial and venous vessels and the so-called yellow spot (macula lutea).

The retina develops from a part of the forebrain and is of central importance for actual vision. It contains various light-sensitive photoreceptors. These are cells in which an electrochemical reaction takes place when light arrives, which is converted into an electrical signal and then transmitted further into the brain.

There the visual impressions are finally processed into visual information. In addition, cross-links between the photoreceptors already serve to enhance contrast in the retina. The retina is divided into a light-sensitive and a light-insensitive part.

In the middle is the yellow spot (macula lutea), the point of sharpest vision, since this is where the density of photoreceptors is highest. This is where only so-called cones are located, which are responsible for daytime vision as well as colour perception. A distinction is made between blue, red and green cones.

In total, humans have about 6-7 million cones, which are mainly located in the macular region. Around the yellow spot are the 110-125 million rods that are responsible for vision at dusk or at night. This is because the messenger substance in the rods is about 500 times more light-sensitive than that in the cones.

Vitamin A is of outstanding importance for the production of this messenger substance. A deficiency of this vitamin is therefore associated with impairments in twilight vision. The place where the extensions of all photoreceptors bundle and enter the brain is the exit of the optic nerve.

This is also where there are no longer any light-sensitive cells, which is why it is called a blind spot. The retina is supplied by arterial and venous vessels. However, pain-sensitive nerves are missing, which is why diseases of the retina are usually not perceived as painful.

The examination of the back of the eye is called ophthalmoscopy or ophthalmoscopy. There are two different procedures for this purpose, we speak of direct and indirect ophthalmoscopy. In direct ophthalmoscopy, the ophthalmologist uses an ophthalmoscope that shines light on the back of the eye and displays it at a magnification of 14 to 16 times.

The physician looks with his right eye into the patient’s right eye and thus sees the fundus of the eye as an upright image, which is why this type of examination is also known as an “upright image”. The same applies to the left eye only in reverse. This examination is easy to perform and shows a relatively small portion of the fundus of the eye in high magnification.

This allows the individual structures within it, such as the exit of the optic nerve or individual vessels, to be assessed particularly well, but an overall view can only be obtained by means of indirect ophthalmoscopy. In indirect ophthalmoscopy, the physician holds a magnifying glass in front of the eye to be examined with an outstretched arm and with the other hand a light source, such as a flashlight. With this type of examination, he sees the back of the eye as an upside-down image, which is why the examination is also referred to as an “inverted image”.

The magnification here is considerably lower than in direct ophthalmoscopy, about 4.5 times. This examination is therefore better suited to obtaining an overall view of the back of the eye and requires more practice on the part of the examiner. With the help of the slit lamp examination, i.e. a binocular microscope, it is possible to examine both eyes simultaneously. If this is not possible, other examination options are available, such as an ultrasound examination.