Dust particles retained in the upper fornix.

Minute multiple dust particles enclosed in long stick mucous filaments may remain hidden in the recesses of the upper fornix for considerable periods of time. They produce the subjective sensations of grittiness or smarting. After repeated maneuvers of eversion of the upper eyelid and blinking, the nasal end of the mucosities lodged in the upper fornix may become visible over the plica semilunaris or caruncle. When drawing them from the lacus lacrimalis with thin moist cotton-tipped applicators, long mucous filaments will be seen gliding out from under the nasal end of the upper eyelid.