Decompression-induced ocular tear film bubbles reflect the process of denitrogenation

To confirm that the tear film bubbles observed after decompression from hyperbaric exposure are due to denitrogenation and to assess the time course of denitrogenation based on the number of ocular tear film bubbles.

The study comprised two parts. In the first, subjects (n = 8) were compressed to a pressure of 2.0 ATA (atmospheres absolute; depth of 10 meters of sea water [msw]) for 60 minutes in a hyperbaric chamber on two separate occasions. On one occasion they breathed air, whereas on the second occasion they inspired pure oxygen. Before and within 30 minutes after each dive, the subjects' tear film was examined with a slit lamp microscope and the average number of bubbles recorded. Ultrasound reflectivity of the lens-vitreous humor compartments was also examined. In the second part of the study, subjects (n = 8) participated in two simulated dives in the hyperbaric chamber: 4.0 ATA (30 msw) for 15 minutes and 2.5 ATA (15 msw) for 180 minutes. The former was a no-stop decompression dive, whereas the latter required a 43-minute decompression stop at 3 msw. Ocular tear film examinations were conducted before the dive, as well as 30 minutes and 1 day, 2 days, and 3 days after the dives.

The number of tear film bubbles increased significantly (P < 0.05) after the air dives to 2.0 ATA for 60 minutes, whereas there was no significant postdecompression increase in tear film when oxygen was inspired by the subjects during the dive. Posterior lens-vitreous humor reflectivity increased significantly after decompression from 2 ATA, when air was the breathing mixture, whereas no change in reflectivity was observed when oxygen was inspired during the dive. In the second part of the study, there was a significant elevation in tear film bubbles for 2 days after the two dives (P < 0.05). There was no significant difference in the number of ocular tear film bubbles between the two dives.

After a hyperbaric air exposure, tear film bubbles reflect the process of denitrogenation, which may persist for up to 2 days after the decompression.