Sammanfattning
Dry eye syndrome (DES) is a common condition causing dry eye sensation and ocular inflammation. The etiology is not fully explored, but clinical trials have demonstrated that the secretory functions of the eyelids can be compromised by microorganisms. Demodex are parasites which also can infest the follicles and glands of the lids, but their adverse effect is not equally documented. The purpose of this study is to examine these parasites and their potential implication in the development of DES and other ocular conditions. Transverse sections of the eyelids from 4 donors were processed through standard histochemical techniques, while 24 eyelashes were methodically extracted from the eyelids of a selected mature subject identified with DES. The sections and the eyelashes were analysed through light microscopy. Thirty-eight parasites were identified. They had a length of 300-555µm and diameter of 30-75µm. Histological examination of the donor eyelids suggested that follicles accommodate considerably more secretory substance (in which most parasites are embedded) than what is revealed through conventional methods of lash extraction. It is therefore legitimate to assume that a population of Demodex is arguably larger than indicated by most clinical methods. Furthermore, the tubular system inside the meibomian glands was found to have diameters that corresponded with the diameters of the parasites, which indicates tha the parasites are physically capable of blocking the secretory passageways. Finally, the parasites have eight segmented, claw-shaped legs with large ranges of motion. The mechanical and immunological provocation they inflict on houst tissues is arguably sufficient to cause inflammation.
This paper promotes the view that when a population of Demodex reaches a critical level it has the capacity to cause secretory dysfunctions in the eyelids and may hence be implicated in the etiology of DES and other ocular inflammatory conditions.