Floaters and Their Treatment with Chinese Herbs

The nature of floaters can be understood in terms of the fluid in which they occur, namely the vitreous. This is a gel matrix filling the vitreous cavity, making up about 2/3 the volume of the eye. In front of it is the lens structure, behind it is the retinal structure. The vitreous is a transparent gel, about 98% water, but it is 2-4 times more viscous than water, mainly due to the content of sodium hyaluronate (the salt of hyaluronic acid, a component of many fluid structures in the body). The hyaluronic acid molecules are large coils that hold water; in the vitreous they are entrapped in a matrix of collagen fibers (type II, the main fiber making up cartilage). Most of the collagen is at the surface region of the vitreous, where it comes in contact with the rest of the eye, giving it a somewhat more solid surface. There is less collagen in the central region, which is a more liquid portion, comprised of about 99% water. Collagen fibrils attach the vitreous gel to points around its margin, particularly to the retinal and lens structures.

The vitreous mainly functions as a transparent fill for the eyeball. The fluid maintains the shape of the eye, acts as a shock absorber, allows transmission of light to the retina, and helps maintain the contact between the retina and the back wall of the eye by applying a mild pressure. It contains no blood vessels and is essentially cell free. A few cells may be present near the retina, including hyalocytes that appear to be responsible for producing hyaluronic acid; these are similar to immune cells called macrophages. Aside from hyalocytes, there are other sources of the vitreous components among the various types of cells of the eye structure, though it is not yet established which ones play a key role.

The original three-dimensional net-like structure of collagen fibers begins to deteriorate once body growth has halted at adolescence. This deterioration is slow and involves having some strands of collagen clump up, and some of the original compartments of gel merge into larger compartments. At this point, "floaters" may begin to appear. Many people believe that these floaters are materials released into the eye, when, in fact, they are shadows on the retina from light encountering the irregularities in the gel matrix. Such irregularities are mainly caused by coalesced collagen filaments, forming fibrils. The floaters are especially visible while looking at a plain, well-lit background.

Diagram of our human eye, with floaters.

It is not until middle age, around age 40, that there are significant changes in the vitreous that generate floaters. The vitreous begins to slowly dry out, and the collagen becomes more clumped, leaving the vitreous almost entirely a free flowing fluid with some intervening gel lumps. These produce the floaters that are most frequently reported. They tend to "float" more easily because of the breakdown of the gel matrix. Nothing needs to enter the vitreous to make these floaters and nothing is present to break down the floaters, so they remain for many months. They may eventually degrade or settle out, or they may persist.

With further aging, the vitreous will dry, thicken, and shrink to an extent that it starts to pull away from the retina (the condition is called posterior vitreous detachment). This process may be the result of a sudden drying of the fluid, rather than the gradual drying that is normally expected. When a sudden vitreous shrinkage occurs, there can be a substantial appearance of floaters over a short period.

While vitreous detachment through a gradual process is common by age 70, it occurs more often and sometimes earlier in people who are nearsighted, have undergone cataract surgery or laser eye surgery, or who have an inflammatory disease of the inner portion of the eye, such as retinitis. When the vitreous gel pulls away from the retina, nothing may happen (vision remains basically the same), but this pulling can cause some retinal tears. Tearing of the retina may allow some blood cells to flow into the vitreous cavity, which accounts for some of the new floaters; other floaters may appear as a result of contraction of the fibers that had been attaching the vitreous to the retina.

When a retinal tear occurs, some of the vitreous fluid can penetrate into the torn areas and lift away the rest of the retina, which is extremely thin, leading to partial or full detachment. During retinal tearing or detachment, flashes of light (like flurries of fireflies) are detected by the patient, and the vision may be blurred, particularly in certain portions of the visual field. The torn retina should be examined carefully, as it may require treatment, such as laser photocoagulation, cryopexy (freezing), or surgery, to avoid complete retinal detachment or to treat a detached retina.

The condition of the vitreous fluid and the nature of floaters are observed by dilating the eye (applying eye drops to do so), and then examining the region through the pupil. There are no medical treatments for floaters. Some floaters, particularly those that occur as a young adult, will eventually disappear as the gel matrix changes. Other floaters, particularly those that occur in later years, may disappear as they settle out of the fluid. In persons suffering from severe disorders of the vitreous, which occurs in some cases of diabetes or where injuries have allowed blood into the vitreous, a vitrectomy may be performed; the vitreous is removed and placed with an artificial substitute liquid called hyaluronate.