Correlations in a change in aqueous tear evaporation with a change in relative humidity and the impact.

PURPOSE: To establish scientific relationship between relative humidity (RH) and aqueous tear evaporation to elucidate possible significance of this relationship in normals and aqueous tear deficiency patients. DESIGN: Prospective experimental laboratory study. METHODS: Ocular surface evaporation was determined using evaporometry and calculated for two ranges of RH, 25% to 35%, and 35% to 45% in a randomized clinical patient population. RESULTS: Average evaporative rate in the higher humidity range was between 0.029 +/- 0.009 through 0.043 +/- 0.016 microl/cm2/min. At lower humidity, range was between 0.044 +/- 0.013 through 0.058 +/- 0.018 microl/cm2/min. Differences in the corresponding evaporative rates were statistically significant (between P < .003 through P < .043) for each analysis. CONCLUSIONS: A decrease of 10% RH resulted in an average difference of between 28.33% to 59.42% increase in evaporation. The increase in evaporation at lower humidity has significant clinical implications for patients with aqueous deficient dry eyes, and possibly those undergoing laser-assisted in situ keratomileusis (LASIK).

Increased evaporative rates in laboratory testing conditions simulating airplane cabin relative humidity: an important factor for dry eye syndrome.

PURPOSE: To quantitatively explore the relationship between low relative humidity conditions, as experienced in airplane cabins during flight, and increases in aqueous tear evaporation as a potential explanation for increased dry eye symptoms noted by people when in low humidity environmental conditions. METHODS: Prospective experimental laboratory study. Evaporative rates under two different ranges of increasing relative humidity, from 20% to 25% (similar to the relative humidity in airplane cabins or arid regions) and from 40% to 45% (similar to the relative humidity in nonarid regions), were obtained from 18 patients with dry eye and 11 healthy subjects. RESULTS: Statistically significant differences were found within all groups: patients with dry eye (divided into keratoconjunctivitis sicca [P=0.001] and meibomian gland dysfunction [P=0.007]) and healthy subjects (P

Pattern of vital staining and its correlation with aqueous tear deficiency and meibomian gland dropout.

PURPOSE: To assess the relationship between the degree and anatomic location of ocular surface vital staining and the degree of aqueous tear deficiency in patients with dry eye, as measured by the Schirmer test, and the presence of meibomian gland dropout. METHODS: Twenty-two patients with dry eye (nine men and 13 women; mean age, 60 years) were prospectively enrolled in the study. Eleven subjects with no ocular disease were considered control subjects. Lissamine green vital staining, Schirmer test, and meibomian gland dropout were evaluated. RESULTS: Patients were stratified based on their vital staining pattern (presence or absence of corneal staining). A progressive decrease in the Schirmer test result was found when the vital staining score increased (r = -0.655; P<0.0001). Patients with dry eye showed an increase in meibomian gland dropout when compared to control subjects (P

Impact of evaporation on aqueous tear loss.

PURPOSE: To determine the impact of evaporation on preocular aqueous tear (AT) loss in normal subjects (controls) and patients with keratoconjunctivitis sicca (KCS). METHODS: Eighteen patients (32 eyes) with KCS with or without associated meibomian gland dysfunction (MGD) and 11 sex-matched controls had AT evaporation determined between relative humidity (RH) of 20% and 45% using an evaporometer. AT volume, flow, and turnover were determined with a fluorophotometer. RESULTS: Evaporative rates increased significantly when the RH was changed from 40%-45% to 20%-25% (P < .001). This change was similar in all groups and on average accounted for a 99.43% increase. There were no statistically significant differences in evaporative rate between controls, the KCS alone group, and the KCS/MGD group. Dry eye patients exhibited a decreased tear turnover when compared to controls. Evaporative contribution to tear loss at 40%-45% RH was 23.47% for controls, 30.99% for "classic" KCS patients, and 25.44% for KCS/MGD patients. At 20%-25% RH, the evaporative contribution was 41.66% for controls, 57.67% for classic KCS patients, and 50.28% for KCS/MGD patients. CONCLUSIONS: RH significantly impacts evaporation regardless of the presence of dry eye disease and probably accounts for the increased dry eye symptoms in people (controls and dry eye patients) in conditions of low RH (eg, deserts, airplane cabins, cold dry seasons). Contribution of evaporation to tear loss tends to be higher than previously described. The percent contribution is dependent on environmental conditions such as RH. There was a trend toward increased contribution to AT loss in dry eye patients vs controls, but statistical significance was not reached.