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.

Zusammenfassung. Durch Ozon and UV-Licht werden dieProteine, Lipide and die Mucosubstanzen der Tranenfliissigkeit zerstort. Durch die Aufhebung der Wechselwirkung dieser Traneninhaltsstoffe kommt es zum Aufbrechen des Tranenfilms and zur Bildung trockener Bezirke an der Augenoberflache, wobei man vom umweltinduzierten trockenen Auge spricht.Setzt man in vitro lodid menschlichen Tranen zu, kommt es zu keiner Zerstorung des Hyaluronats der Tranen durch Ozon and UV-Licht. Diese schiitzende Wirkung des Iodids auf einen Traneninhaltsstoff kann mittels Viskosimetrie nachgewiesen werden. Die gunstige Beeinflussung des trockenen Auges durch Balneotherapie and Ophthalmoiontophorese-Behandlungen mit Iodsole in Bad Hall konnte auch auf die Wirkung des Iodids als Radikalfanger zuruckzufuhren sein. Schlusselworter: Iodid, Radikalfanger, Tranenflussigkeit, Iontophorese, Hyaluronat. Iodide protects tears from destruction by ozone and UV-lightSummary. By ozone and UV-light the proteins, lipids and the mucosubstances of the tear fluid are destroyed. By abolishment of the interaction of the tear fluid components a break up of the tear film and the formation of dry areas on the surface of the eye is provoked, leading to the environmental induced dry eye syndrome.By addition of iodide to human tears in vitro, the destruction of hyaluronate of tears by ozone and UV-light is prevented. This protective action of iodide on tear fluid hyaluronate can be determined by viscosimetry.The improvement by balneotherapy and ophthalmoiontophoresis of the dry eye syndrome with iodide solutions in Bad Hall/Austria may also be related to the action of iodide as a radical scavenger.

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Although rare in developed countries, ophthalmologists should consider xerophthalmia as differential diagnosis in night blindness and conjunctival and corneal xerosis. Early diagnosis and adequate treatment can prevent permanent visual loss.

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