Introduction
The examination of the retina not only serves to detect diseases of the eye at an early stage and to regularly monitor their course, but also diseases that can affect the entire body, such as high blood pressure or diabetes, can manifest themselves and be recognized in the eye. Through early detection, possible consequential damage can often be avoided or reduced.
Examination methods of the retina
The retina itself can best be assessed by using the slit lamp. In order to get the best possible view of the eye, the patient is given eye drops beforehand. These drops dilate the pupil.
However, this causes a high degree of glare for the patient, since the pupil cannot contract after the administration of these drops to regulate the incidence of light. The effect, however, only occurs after 20 to 30 minutes and lasts a few hours until it subsides. When examining the retina with a slit lamp, a distinction is made between direct and indirect reflection.
In the case of direct reflection, a three-mirror glass is placed directly on the eye as part of an eye test after instillation of a local anaesthetic eye drop preparation. This glass cancels out the refractive power of the cornea and one can view the back of the eye. With the help of the mirrors it is also possible to look “around the corner” and assess the periphery of the retina.
This method is particularly suitable for seeing cracks in the retina. The slit lamp is also needed for indirect reflection. In indirect reflection, magnifying glasses are used to look inside the eye.
They are held in front of the eye at a certain relatively short distance. The magnifying glasses produce an inverted image of the retina, which is magnified by the slit lamp. In reflections in general, the retina can be examined for various changes.
For example, water retention (edema), excavations of the optic nerve papilla (the central dent in the papilla is too deep) and much more. These features indicate possible clinical pictures. The deepened dent of the optic nerve exit point can indicate an increased intraocular pressure.
High blood pressure can also be detected in the eye vessels. If there is a suspicion of retinal hemorrhage or other vascular diseases, an examination method is used which specifically depicts the vessels of the retina: Fluorescence angiography. A fluorescent dye (no contrast agent) is injected into a vein, which is distributed over the blood and also flows into the vessels of the eye.
The vessels of the choroid fill first, as the blood supply to the choroid is stronger, and shine through the retina. The distribution of the dye is recorded by a special camera. The photos then allow the diagnosis of water retention, bleeding, occlusion and much more.
All articles in this series:
