Ocular Ferning Test – Effect of Temperature and Humidity on Tear Ferning Patterns

Abstract

Background: The ocular ferning test is used as a diagnostic aid to evaluate patients with dry-eye disease. The ferning phenomenon is a dendritic growth form of dried tear fluid. The influence of temperature and relative humidity (rH) on the morphology of tear ferning patterns was investigated. Methods: Two microliters of tear fluid of 5 volunteers with normal tear function were dropped onto a microscope slide with a pipette and were dried in a climatic chamber at four different temperatures (20, 22, 24 and 26°C) and at four different grades of rH (30, 40, 50 and 60%) at each temperature. The dried droplet was divided according to distinct morphological features into a center, transition zone and margin. The center of the dried droplet was classified into four types according to the system of Rolando. Results: In the temperature range between 20 and 26°C, rH has a strong influence on the ferning patterns. At these temperatures, increasing rH resulted in a deterioration of type I ferning obtained at 30% rH to type II or type III at 60% rH in all subjects. Otherwise, at rH of 30, 40 and 50%, no definite influence of temperature between 20 and 26°C was observed. At an rH of 60%, the ferning patterns changed with increasing temperature from 20 to 26°C from type II to type III. Conclusion: High humidity can modify and deteriorate the ferning patterns of tear fluid from subjects with normal tear function. To obtain reproducible results using the ocular ferning test, stable conditions are necessary. An rH not higher than 50% at a temperature range between 20 and 26°C produced ferning patterns without interstitial spaces which could be related to the best quality according to the system of Rolando.

Tear Osmolality and Ferning Patterns in Postmenopausal Women

“…When measuring tear osmolality, low molecular weight species, especially ionic solutes such as sodium, potassium, bicarbonate, and chloride, contribute to most of the osmolality value and organic solutes such as protein, glucose, and urea that have a large molecular weight contribute to the remainder of the signal. 42,43 Ferning patterns are because of the interaction of electrolytes with macromolecules such as proteins and mucous polysaccharides, 28,29,44 thus explaining why we obtained an insignificant correlation between tear osmolality and ferning. The spread of the data clearly shows that not all the participants who reported with higher osmolality values had poor ferning patterns.…”

“…However, care must be taken to maintain the room temperature and humidity levels while drying the tear drop on the glass slide, as this process can be greatly affected by environmental factors. 28 This must be ensured, especially when diurnal variation studies to study ferning patterns are being undertaken.…”

“…Tear fluid, when dried on a microscope slide, produces a specific "ferning pattern," which is believed to be due to an interaction between various electrolytes in the tears and macromolecules such as proteins. 28 An increased salt concentration in tears (as occurs in hyperosmotic tears) and other changes in tear composition may cause an alteration in the ferning patterns observed. 29 Studies have shown that an alteration in tear ferning patterns occurs in dry-eyed individuals and subjects aged over 40, 30 with a tendency for "less" ferning to be observed.…”

Freeze-controlled Crystallisation of the Aqueous Humour in Glaucomatous and Non-glaucomatous Patients

“…Since the result of the ferning test is strongly dependent on examination settings such as temperature and humidity, 10 The weakness of our study is that we did not investigate the influence of humidity in the freezer, but it might be assumed that the values should be relatively constant during the 24-hour freezing process. Furthermore, the aqueous humour of the control group was obtained from patients with cataracts, a disease caused by a certain amount of reactive oxygen species at least.…”

Stratification of Tear Components During Tear Microdesiccation on Vertical Glass Surfaces

“…6 Because the formation of this 4-zone structure while water is being evaporated in vitro must be a dynamic and complex process, a number of factors may influence such differential kinetic behavior of tear molecular components. 6,7 Apart from water, tear fluid is composed of large macromolecules (eg, mucins), medium-sized macromolecules (eg, proteins), and small organic molecules and ions (eg, glucose, Na + , Cl 2 , HCO 3 2 ). In addition, some of those components are highly hydrophilic (eg, mucins, most of the proteins, and abundant ions) or hydrophobic (eg, most of the polar and nonpolar lipids).…”