Exposure to excessive oxygen can impair distance vision.
This phenomenon, called hyperoxic myopia, is a form of oxygen toxicity that affects the lenses of the eyes.1,2 It is a known risk of hyperbaric oxygen treatment (HBO), where oxygen partial pressure (PO2) is 2 to 2.4 Atm,1–10 but also has been documented after exposures to PO2 of 1.3 Atm which is within PO2s traditionally encountered in diving activities.11–14
The first diving-related report of hyperoxic myopia was a case study in an underwater film maker and his partners, with three divers affected.11 Later documented cases occurred at the U.S. Navy Experimental Diving Unit (NEDU) in four divers exposed for six hours per day across five or six days,12, 13 and in one exposed for four hours per day for five days,12 caisson workers exposed to similar PO2s have also experienced hyperoxic myopia.14 A closer look at the published reports may help divers to assess their own risks.
The underwater film maker11 noticed a general blurriness of vision about 18 days into a 21-day, rebreather dive series in which his exposure totaled 84.8 hours with PO2 of 1.3 Atm. His optometrist confirmed a myopic shift after the end of the dives. Six weeks later his vision had recovered. On his next dive trip he carried an eye chart and checked his vision regularly. He measured changes after nine days and about 36 hours of bottom time. Once again, his vision returned to normal after time. A third dive series of 15 days duration and with approximately 45 hours with a PO2 of 1.3 Atm again caused a temporary myopic shift, a change that also was measured in the diver’s two buddies.
The NEDU dives after which hyperoxic myopia was noted involved six hours per day with PO2 between 1.3 and 1.4 Atm, either for five consecutive days (surface interval 18 hours),12,13 or for six days of diving every other day (surface interval 42 hours).12 The four cases documented with refractive measurement resolved in a few weeks. Other divers with similar oxygen exposure may have been affected, but only subjective measurements, not refraction measurements, were available,12 and approximately 50 other divers underwent six-hour daily exposures for five consecutive days with no measurable changes in visual refraction. After five days with 4-hour exposures (20-hour surface intervals), one of 28 divers had a very small but measurable refraction change after resting in the water,12 but none of 16 divers had measurable refraction changes after exercising during dives.15
Hyperoxic myopia is caused by a change in the angle at which light bends on crossing into or out of the lens tissue in a process similar to that of aging,1, 2, 11 but few other details are known.
Known:
1) Changes can be expected to be self-correcting.
2) Myopic changes are delayed in onset (for example, four days after the end of a five-day dive series).
3) Changes in the lens accumulate over repeated dives.
4) Divers who have age-related stiffening of their lenses, that is, those who need reading glasses, are more likely than younger divers to experience a refractive shift.
Unknown (among many questions):
1) What is the minimum surface interval to prevent cumulative effects?
2) Is there a threshold PO2 or exposure time below which hyperoxic myopia does not occur?
3) Does repeated exposure to elevated oxygen partial pressure influence the age at which a person first needs reading glasses?
Divers who accumulate many hours of bottom time during a dive series, say, more than 20 hours in a week, should be alert for changes in their distance vision. It is probably wise to back off a bit on the oxygen exposure if visual changes are noted. (A myopic shift may also show up as an improvement in near vision without reading glasses.) But what is your personal acceptable risk? You’ll have to decide!
References:
1. Khan B., Evans A.W., 2003. Refractive Changes in Patients undergoing Hyperbaric Oxygen Therapy: a Prospective Study
2. Evanger, K., Vaagbø, G., Thorsen, E. and Haugen, O.H., 2011. Phakic and pseudophakic eyes in patients during hyperbaric oxygen therapy. Optometry and Vision Science, 88(6), pp.691-696.
3. Anderson Jr, B. and Farmer Jr, J.C., 1978. Hyperoxic myopia. Transactions of the American Ophthalmological Society, 76, p.116-124.
4. Lyne, A.J., 1978. Ocular effects of hyperbaric oxygen. Transactions of the ophthalmological societies of the United Kingdom, 98(1), pp.66-68.
5. Palmquist, B.M., Philipson, B. and Barr, P.O., 1984. Nuclear cataract and myopia during hyperbaric oxygen therapy. British Journal of Ophthalmology, 68(2), pp.113-117.
6. Anderson Jr. B. and Shelton D.L., 1987. Axial length in hyperoxic myopia. In: Bove A.A., Bachrach A.J. and Greenbaum L.J. (eds). Underwater and Hyperbaric Physiology IX. Proceedings of the Ninth International Symposium on Underwater and Hyperbaric Physiology. Bethesda, Maryland: Undersea and Hyperbaric Medical Society: 607–611.
7. Ross, M.E., Yolton, D.P., Yolton, R.L. and Hyde, K.D., 1996. Myopia associated with hyperbaric oxygen therapy. Optometry & Vision Science, 73(7), pp.487-494.
8. Krott, R., Roessler, G., Heller, R., Krauss, D. and Krieglstein, G.K., 2001, March. Short term hyperbaric oxygenation does not alter ocular refraction (Abstract). In Investigative Ophthalmology & Visual Science (Vol. 42, No. 4, pp. S896-S896). Bethesda, MD, USA: Assoc. Research Vision Ophthalmology Inc.
9. Fledelius, H.C., Jansen, E.C. and Thorn, J., 2002. Refractive change during hyperbaric oxygen therapy. A clinical trial including ultrasound oculometry. Acta Ophthalmologica, 80(2), pp.188-190.
10. Evanger, K., Haugen, O.H., Irgens, Å., Aanderud, L. and Thorsen, E., 2004. Ocular refractive changes in patients receiving hyperbaric oxygen administered by oronasal mask or hood. Acta Ophthalmologica, 82(4), pp.449-453.
11. Butler Jr, F.K., White, E. and Twa, M., 1999. Hyperoxic myopia in a closed-circuit mixed-gas scuba diver. Undersea and hyperbaric medicine, 26(1), pp.41-45.
12. Shykoff B.E., 2008.Pulmonary effects of submerged oxygen breathing in resting divers: repeated exposures to 140 kPa. Undersea Hyperb Med 35(2):131-143.
13. Brugger J.W., Gupta A., Shykoff B., and Florian J., 2015. Hyperoxic Myopia: A Prospective Study of Twelve Divers with Six Hours of Exposure to 1.35 ATM PO2 for Five Consecutive Days (abstract). Invest. Ophthalmol. Vis. Sci., 56 (7):2176.
14. Onoo, A., Kiyosawa, M., Takase, H. and Mano, Y., 2002. Development of myopia as a hazard for workers in pneumatic caissons. BritisJournal of Ophthalmology, 86(11), pp.1274-1277.
15. Shykoff B.E., 2008. Pulmonary effects of submerged exercise while breathing 140 kPa oxygen. Undersea Hyperb Med. 35(6):417–426.
