The human eye is an intricately composed, highly functional mechanism, whose operability depends on the nature and interaction of its individual parts. As is known, the eye, that is, the eyeball, is embedded in a bony, almost cone-shaped eye socket. The eyeball, which is supported in fat pads and surrounded by the eye muscles, is closed off to the front by the cornea, which merges into the conjunctiva, against the anterior chamber behind it, which is filled with a clear fluid and which, in turn, is bounded to the rear by the differently colored iris with the pupil opening.
Seeing through the eyes
Probably the most commonly used devices in ophthalmology are the slit lamp and the ophthalmoscope. Behind this iris, the lens divides the anterior chamber from the interior of the eye, which is completely filled by the clear vitreous body. This vitreous body ensures constant internal pressure and is located in front of the light-sensitive retina. Normal vision is now dependent on the size of the eyeball, the position of the lens, and so on. As is well known, errors in this interaction can be corrected by individually prescribed eyeglasses or spectacles. However, this requires precise knowledge of the conditions inside the eye. For an appropriate diagnosis, the doctor needs, in addition to sound knowledge, numerous technical aids, which fascinate some patients when they enter the examination room.
Treatment methods
Probably the most commonly used devices are the slit lamp and the ophthalmoscope. Many pathological changes in the anterior segment of the eye that are not visible to the eye alone become visible to the physician under the collected (focused) light beam of the slit lamp. Until the middle of the last century, it was not possible to see inside the eye to diagnose pathological changes here as well. It was not until Helmholtz’s revolutionary invention of the ophthalmoscope that doctors were able to examine the interior of the eye directly. Like many great inventions, this one is based on what is actually a quite simple, uncomplicated principle. Light is thrown into the eye to be examined through a round, slightly curved mirror, reflected at the back of the eye and directed through a small hole in the center of the mirror into the eye of the examining physician. Thus, the posterior wall of the eye spreads out in front of the physician. He can see the entrance of the optic cord into the eye, the retina containing the sensory cells, and the blood vessels, check their condition, and then determine his measures. Nevertheless, even the ophthalmoscope, without which the modern ophthalmologist is hardly imaginable, has limits to its scope of application. The prerequisite for an examination with an ophthalmoscope is a clear, transparent anterior segment of the eye. If, however, the cornea or the lens is clouded by disease or injury and has thus become opaque, the ophthalmoscope will also fail. Precise knowledge of the inner eye is particularly important, however, in the case of such diseases. For example, corneal transplantation, or cataract surgery is only useful and promising if the retina, the part of the eye that receives sensory impressions, remains unharmed. If the retina has been detached for a longer period of time and consequently has not been properly nourished, the eye would not regain its sight even after the clouding has been removed. In this case, the patient could be spared futile hopes and the burden of surgery.
Ultrasound examination
Just a few decades ago, there was no way for physicians to detect such a retinal detachment before surgery. Only the use of ultrasound diagnosis gave him an opportunity to “see” behind the clouded cornea, or lens. Ultrasound is the term used to describe sound waves that are beyond the limit of human audibility, i.e. have a higher frequency (number of oscillations per second) than 16,000. These high frequencies, we usually work with 8 to 15 million oscillations, per second, are generated by oscillating quartz plates that are set in motion with the help of electrical impulses. The application of ultrasound in medical diagnostics is based on
the findings of echo sounding. Unlike audible sound, ultrasound is difficult to conduct through air. It was therefore previously used in solid and liquid media, for example to determine the depth of the sea or to test materials.If an ultrasonic wave hits an interface between two media perpendicularly, for example water and the seabed, it is partially reflected, returns to the transmitter and can be read on a screen here. The time elapsed between the transmitted pulse and the return of the reflected wave can be used to calculate the sea depth. Ultrasound diagnostics in ophthalmology now also works according to this principle, since the eye is more easily accessible to this examination technique than any other human organ. In this case, the eye is to be regarded as a water-filled sphere with a very regular boundary, to which the aforementioned technique of echolocation can be transferred without difficulty. The ultrasound device that is used in medicine consists of the power supply part, the transmitter, the receiver and the display system. While the transmitter generates electrical impulses that are sent to the transducer placed on the eye, the latter converts the impulses into ultrasound and sends them to the object under examination. The reflected sound waves are again picked up by the transducer, converted and sent to the device. A monitor or computer makes the sound waves reflected from the back of the eye visible and displays them graphically as an echo curve. An ultrasound examination is harmless, since the eye does not need to be surgically
to open the eye. The patient lies down on a couch and fixes an arrow projected on the ceiling with the healthy eye so that the eye remains as still as possible during the examination. After the eye to be examined has been desensitized with some anesthetic drops, the transducer is placed lightly on the eye. The examination then proceeds in several directions, i.e. the transducer is placed successively at different points, but always in such a way that the sound beam, directed through the center of the eye, strikes the posterior wall of the eye perpendicularly. The result is immediately read on the device and recorded photographically or digitally. Among the diseases that can be diagnosed with ultrasound, one has already been mentioned, namely detachment of the retina, which can lead to the extinction of vision. In this case, fluid has penetrated between the detached retina floating in the vitreous body and the posterior wall of the eye, which does not give echoes on the computer, but makes the retinal echo appear in a place where it should not normally appear. Another condition that can be detected with ultrasound is tumors in the eye. They arise from the dense tissue of the tumor. The echogram of an old hemorrhage in the eye looks very similar. Both are distinguished from each other by appropriate examination methodology, e.g. by different transmission power. It is even possible to use echolocation to calculate the height of a tumor already detected in the eye and also to determine the total length of the eyeball. Furthermore, foreign bodies in the eye can be determined and other examinations can be performed. Thus, for some time now, this method has made it possible to reveal the interior of the eye, which was previously invisible in the case of an opacity, to precise examination, thus enriching ophthalmology with another valuable diagnostic option.
