Analysis of basal and reflex human tear osmolarity in normal subjects: assessment of tear osmolarity.

PURPOSE: The aim of this study is to evaluate the difference between reflex and basal tear osmolarity among healthy normal subjects. METHOD: The right eyes of 20 healthy normal male subjects aged 20 to 40 years were recruited for this study. The inclusion criteria for the subjects were the Ocular Surface Disease Index questionnaire score of less than 12 and wetting length of the phenol red thread of more than 10 mm. Tear film osmolarity was assessed using TearLab osmometer. Basic tear osmolarity was measured normally without inducing any irritation to the eye. In order to stimulate reflex tear, subjects were asked to open their eye as long as they can till they feel ocular surface irritation (minimum 20 s). RESULTS: The mean score on the Ocular Surface Disease Index questionnaire was 5.5 ± 3. The mean value obtained from the phenol red thread was 21 ± 4.5 mm. There were no statistically significant differences between the osmolarity readings of basal and reflex tear osmolarity (p > 0.05). The mean value was 308 ± 12 and 306 ± 9 mOsm/l for basic and reflex tear osmolarity, respectively. CONCLUSION: This study found that the osmolarity of the basal and reflex tears fell within the same range. The values found in this study are in agreement with published results for normal subjects.

Care solution effects on contact lens in vivo wettability.

BACKGROUND: The aim of the study was to evaluate the effect of care solutions on contact lens in vivo wettability using Doane's interferometric technique. METHODS: Thirteen subjects (aged 26.6 ± 6.3 years) participated for contact lens wettability evaluation after soaking in five care solutions namely Opti-Free EverMoist (now called puremoist), Opti-Free Express (Alcon), COMPLETE (AMO), ReNu and Biotrue (Bausch & Lomb). A new pair of lenses was soaked in the solutions for eight hours (prior to wear) or taken directly from pack solutions (as control) and worn by the subjects. The total number of pairs of lenses tested was 13 by six (78 lenses; 13 pairs of lenses wetted in five care solutions plus the pack solution). Doane's interferometer was used to capture images of the pre-lens film on a single type of contact lens, Acuvue Oasys (Johnson & Johnson). The lens in vivo wettability was evaluated after 15 minutes and eight hours of wear by each subject. Four parameters: onset latency, drying duration, maximum speed and peak latency were used to assess the lens wettability. RESULTS: After eight hours, the solutions showing significant reduction in contact lens wettability were the following. For onset latency: Pack solution, Biotrue Opti-Free EverMoist and Express; for drying duration: pack solution, ReNu and Opti-Free EverMoist; for peak latency; pack solution, Biotrue and Opti-Free EverMoist. Regarding the maximum speed, lenses soaked in Pack solution, ReNu and Opti-Free EverMoist showed a significant increase (worsening). The comparative study showed that there were significant differences among the performance of the care solutions. CONCLUSION: This novel thin film interferometric technique was able to measure, objectively, contact lens in vivo wettability, following the use of care solutions. COMPLETE was the only solution that showed no significant change in the lens wettability (with the all parameters) between the initial and the end of day.

Changes in blink rate and ocular symptoms during different reading tasks.

BACKGROUND: Reading from tablets is fundamental to modern culture. This study measured differences in the blink rate and symptoms of ocular discomfort in healthy participants during reading from a tablet and a paper book. METHODS: Forty healthy, normal males subjects were recruited for this study. Subjects were video recorded during reading a text presented on an electronic device (9.7 inch tablet) and a hard copy format, for 15 min. Ocular discomfort experienced during reading was scored using a visual analog scale. Each participant was examined performing one of the two tasks (randomized) on one visit and the other on a separate visit (crossover design). All subjects were evaluated before the reading tasks and every 5 min during 15 min of reading. RESULTS: The mean ± standard deviation blink rate was 19.74 ± 9.12/min at baseline. The blink rate decreased significantly under both reading conditions (to 11.35 ± 10.20 and 14.93 ± 10.90/min when reading from a book and a tablet, respectively). There was no significant difference in the blink rate over 15 min during either type of reading. The mean discomfort symptom scores were 148 for the book and 134 for the tablet; both were significantly higher than baseline. A gradual increase in symptoms was found every 5 min during both types of reading. CONCLUSION: The study confirmed that both the blink rate and ocular discomfort symptoms were strongly affected during performance of close visual tasks. Both reading conditions affected blinking; this may interfere with tear film dynamics. Such effects were reflected in the immediate development of ocular symptoms, which increased significantly during both types of reading.

Effect of Ambient Temperature on the Human Tear Film.

PURPOSE: During everyday life, the tear film is exposed to a wide range of ambient temperatures. This study aims to investigate the effect of ambient temperature on tear film physiology. METHOD: A controlled environment chamber was used to create different ambient temperatures (5, 10, 15, 20, and 25°C) at a constant relative humidity of 40%. Subjects attended for two separate visits and were exposed to 25, 20, and 15°C at one visit and to 10 and 5°C at the other visit. The subjects were exposed to each room temperature for 10 min before investigating tear film parameters. The order of the visits was random. Tear physiology parameters assessed were tear evaporation rate, noninvasive tear break-up time (NITBUT), lipid layer thickness (LLT), and ocular surface temperature (OST). Each parameter was assessed under each condition. RESULT: A threefold increase in tear evaporation rate was observed as ambient temperature increased to 25°C (P=0.00). The mean evaporation rate increased from 0.056 µL/min at 5°C to 0.17 µL/min at 25°C. The mean NITBUT increased from 7.31 sec at 5°C to 12.35 sec at 25°C (P=0.01). A significant change in LLT was also observed (P=0.00), LLT median ranged between 20 and 40 nm at 5 and 10°C and increased to 40 and 90 nm at 15, 20, and 25°C. Mean reduction of 4°C OST was observed as ambient temperature decreased from 25 to 5°C. CONCLUSION: Ambient temperature has a considerable effect on human tear film characteristics. Tear evaporation rate, tear LLT, tear stability, and OST were considerably affected by ambient temperature. Chronic exposure to low ambient temperature would likely result in symptoms of dry eye and ultimately ocular surface disorders.

The effect of low humidity on the human tear film.

PURPOSE: To investigate the effect of exposure to a low relative humidity (RH) environment on tear film physiology. METHOD: A controlled environment chamber was used to create 2 different environmental conditions. Ambient temperature was constant in both conditions (21°C) while the RH was set at 40% at the normal condition and at 5% in the desiccating environment. Tear evaporation, noninvasive tear break-up time, lipid layer thickness (LLT), osmolarity, ocular comfort, tear production, and ocular surface temperature were assessed in normal humidity and over a period of 60 minutes in the dry environment. RESULTS: There was significant change in tear evaporation rate (P = 0.00), noninvasive tear break-up time (P = 0.00), LLT (P = 0.00), ocular comfort (P = 0.00), and tear production (P = 0.01) after exposure to the desiccating environment. No significant differences were observed between normal and dry environmental conditions in tear osmolarity (P = 0.09) and ocular surface temperature (P = 0.20). CONCLUSIONS: Evaporation rate, tear LLT, ocular comfort, tear stability, and production were adversely affected by low RH. The tear film parameters observed after exposure to a desiccating environment for 1 hour were similar to those of the dry eye patient. Therefore, to avoid tear film disruption and possible ocular surface damage, the environmental conditions of dry locations need to be improved or the tear film should be protected against adverse environmental conditions.