The vitreous or vitreous body is a clear, clear gel, which is located in the space between the crystalline lens (lens that is removed in the case of cataracts) and the retina (the area where the image we see is formed). For the most part, the vitreous is made up of 98% water. The remaining 2% contains collagen, hyaluronic acid, sugars and proteins.
The vitreous, because of its compactness, helps the bulb to maintain its shape within the cavity of the skull. Also, because of its individual materials, it helps to circulate nutrients throughout the eye.
Over time the vitreous undergoes changes in its structure. Similar changes also occur in the other organs of our body. In particular, the vitreous loosens and loses its gelatinous texture. Medically, this condition is called vitreous liquefaction or syneresis and can occur simply due to advanced age (Figure 1). Common symptoms of vitreous liquefaction are myopes (flies) and photopsies (flashes). This event is not treated surgically, except in the case where the patient's symptoms are severe. Ophthalmologists usually recommend regular follow-up.
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Figure 1: Vitreous detachment
However, there are also cases where the liquefied vitreous pulls on the retina or its vessels during eye movements (movements that the patient makes as he or she turns his or her eyes to look at various objects in everyday life). This results in the formation of cracks or even detachment of parts of the retina and holes in the macula. (The macula is located in the center of the retina and is responsible for central, color vision and recognizing details of a face. It is the most sensitive area of the eye).
Vitrectomy or vitrectomy is a widely used technique, which is applied for a variety of conditions that may be caused secondarily by vitreous liquefaction, as mentioned above. Essentially, during vitrectomy, the cause of the traction on the retina (vitreous) is removed. Also, the surgeon in this way gains access to the retina in order to manage the problem caused by the vitreous traction.
After the removal of the vitreous it is necessary to refill the cavity it was occupying, as it does not have the ability to regenerate itself. Despite the high success rates of vitrectomy, many surgeons and researchers argue that the secret to a successful restoration is the material that will replace the vitreous within the eye. There have been many suggestions and experiments on these materials over the years and the search for the ideal ’substitute“ continues. It is widely known that the ideal material should have structurally and functionally similar properties to the vitreous itself.
For over a century we have had the first reports on the materials that can be used instead of the vitreous after a vitrectomy procedure. The first material used was gas by injection in order to regrow a patient's retina. Later on, the use of silicone, long-acting gases and special liquids that are denser than water were introduced. The purpose of these materials is to cause tamponade and thus seal areas where there are detached parts or cracks in the retina. However, these materials cannot be used for a long time as they have certain disadvantages.
For example, in the case of gas placement at the vitreous site, the patient should be bent over (head down) for a few days in order for the affected area of the retina to stabilize with the gas and adhere to the wall. Also, patients should avoid high altitudes and airplane flights until their doctor indicates that they should travel.
On the other hand, silicone is a good option for patients who cannot maintain the correct head position according to their surgeon's instructions. However, silicone cannot be used for a long time in the eye as it causes problems. However, studies are being carried out to modify the materials of which silicone is made in order to prolong its use as a “substitute” for the vitreous.
Materials such as hyaluronic acid and collagen could be considered ideal replacements for vitreous, due to their natural presence in its structure. However, research to date has not yielded any significant results as these are unstable substances which do not provide a sufficient and stable effect on the retina.
Finding new materials, but also the evolution of those already in use that can replace the vitreous, is a challenge for both ophthalmic surgeons and researchers. Everything indicates that the future lies in the polymers that form the natural structure of the vitreous. Undoubtedly, the length of time the material has to be in the eye and its compatibility with the tissue play an important role, because we must not forget that any material is a foreign body to the body.
In the coming years we expect the vitrectomy- vitrectomy procedure to improve the postoperative quality of life of patients, as we believe that the success of the procedure will not depend mainly on the patient's compliance with the doctor's instructions regarding the correct head position (as is the case today), but on the safety and tissue compatibility of the materials used during the procedure.
