Quantitative tear ferning. Methodologic and experimental investigations.
The reproducibility of different tear-ferning methods has been investigated by double tests on 122 subjects. Rough grading according to Rolando gives identical recovery in only 42 to 50%. Quantitative test (mm2 ferning per 1 microliter) of conjunctival fluid drawn with a glass rod according to Rolando gave a coefficient of variation of 99 to 128%. Aspiration with a quantitative pipette acc. to Norn 79%, and 55% for a standardized dilution (2.5 microliters of water) in the same pipette. The coefficient of variation was lower between tear samples aspirated through a thin capillary tube (1 mm = 0.5 microliter) from the lateral part of the tear meniscus (35%), and with a standardized tear volume (2.5 microliters) only 6.4%. Ferning is obstructed by ointment, fat emulsion dropped on the conjunctiva and mucous thread, but not by a glass slide rubber with stearin. A quantitative test with a capillary tube (2.5 microliters of aspirated lacrimal fluid) showed reduced ferning 30 sec after instillation of methylcellulose (2.5%) and arachis oil, and after expression of meibomian gland secretion. No significant alteration was observed after instillation of water or stimulation of the tear secretion by nasal inhalation of NH4OH.
Norn
M
M
Eye Department, Hvidovre Hospital, University of Copenhagen, Denmark.
D003460:Crystallization; D006801:Humans; D008722:Methods; D013048:Specimen Handling; D013666:Tears / Q000032:analysis / Q000502:physiology*