Ocular ferning test - Effect of temperature and humidity on tear ferning patterns

Background: The ocular ferning test is used as a diagnostic aid to evaluate patients with dry-eye disease. The ferning phenomenon is a dendritic growt h form of dried tear fluid. The influence of temperature and relative humid ity (rH) on the morphology of tear ferning patterns was investigated. Metho ds: 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 cl imatic chamber at four different temperatures (20, 22, 24 and 26 degreesC) and at four different grades of rH (30, 40, 50 and 60%) at each temperature . The dried droplet was divided according to distinct morphological feature s into a center, transition zone and margin. The center of the dried drople t was classified into four types according to the system of Rolando. Result s: In the temperature range between 20 and 26 degreesC, rH has a strong inf luence on the ferning patterns. At these temperatures, increasing rH result ed in a deterioration of type I ferning obtained at 30% rH to type II or ty pe III at 60% rH in all subjects. Otherwise, at rH of 30, 40 and 50%, no de finite influence of temperature between 20 and 26 degreesC was observed. At an rH of 60%, the ferning patterns changed with increasing temperature fro m 20 to 26 degreesC from type II to type Iii. Conclusion: High humidity can modify and deteriorate the ferning patterns of tear fluid from subjects wi th normal tear function. To obtain reproducible results using the ocular fe rning test, stable conditions are necessary. An rH not higher than 50% at a temperature range between 20 and 26 degreesC produced ferning patterns wit hout interstitial spaces which could be related to the best quality accordi ng to the system of Rolando. Copyright (C) 2001 S. Karger AG, Basel.