I decided to post this thread in the Advanced Scuba Discussions forum rather than in one of the technical forums because the profiles which created a myopic shift during my last dives were within the realm of divers who use standard Nitrox32, double tanks, and maybe venture into a little bit of decompression on their dive computers. I'm also posting for advanced divers who may be thinking of moving into technical diving by taking advanced nitrox or triox courses in the future.
Hyperoxic myopia or oxygen-induced myopia has always been considered a rare event in sport scuba diving. More cases of patients having a change in their glasses or contact lens Rx have been reported in the world of hyperbaric medicine. The patient usually experiences an increase in myopia that may last for days, weeks, months or sometimes permanently after being exposed to higher partial pressures of oxygen in repeated frequent or daily treatments. Most cases tend to resolve themselves within a few days to a few weeks. Most of the time the patient's visual acuity or Rx will return to normal or the patient might require a slight Rx change.
In the sport of scuba diving, hyperoxic myopia has been on the radar of divers using closed-circuit rebreathers (CCR's) due to the ability of the diver to remain underwater for long exposures while being able to keep the partial pressure of oxygen higher throughout the course of a dive to reduce a decompression obligation or to use a higher partial pressure of oxygen during decompression to reduce decompression time. While open circuit divers have been doing the latter for quite some time, a CCR diver has the ability to maintain a constant oxygen partial pressure in the breathing loop due to the electronics controlling oxygen injection. Open-circuit divers do not have this ability because the pressure of oxygen decreases as the diver ascends. Simply put, a rebreather diver is exposed to more oxygen regarding both CNS and whole body oxygen toxicity.
Most advanced divers are familiar with the danger of CNS oxygen toxicity and know the importance of maintaining safe maximum operating depths. Some agencies and instructors do not spend much time covering whole body (pulmonary) oxygen toxicity because most single tank recreational divers are told they don't really need to worry about tracking OTUs (oxygen toxicity units) or UPTDs (unit pulmonary toxicity dose). Traditionally, the lungs have been used as the litmus test for whole body oxygen toxicity because they are often the first tissues injured by oxygen. Oxygen can inflame lung tissue and reduce the effectiveness of the lungs to filter out inert gases such as nitrogen and properly take in oxygen to fuel the cells of our bodies. If the lung tissue is inflamed long enough a permanent reduction in vital capacity may result.
While the lungs have always posed the greatest concern with cumulative exposure to higher oxygen, cumulative exposure is "whole body" but as divers we really haven't been paying much attention to other parts of the body. Oxygen hurts us through biochemical damage in our cells as a result of oxygen free radicals or radical oxygen species (ROS). Right! The same type of thing you hear about in commercials for foods and products that are "antioxidants", but we are giving oxygen steroids by taking it underwater and breathing in higher percentages and pressures.
After the lungs the eyes become one of the most noticeable areas of weakness to suffer the effects of oxidative stress and damage. I literally got to see this for myself, first hand, after having experienced definitely two and possibly as many as three or four hits of hyperoxic-induced myopia while diving on open-circuit.
In November 2014, I was teaching a stage cave diving class in North Florida and diving twice a day for a week. I noticed that I had great vision on my way to FL with my contacts having had a new Rx in October, but things were blurry during the drive home. We did one daytime dive and one night time or late afternoon dive with at least a 3 hour surface interval and run times from 90 to 120 minutes with depths no greater than 100 feet. My Rx jumped from -3.00 to -3.50. Prior to that, my Rx had been -2.25 during the summer and -1.75 before that.
I just returned from cave country in High Springs, FL where I taught a cavern instructor IQC, and intro to cave instructor course, two cavern/intro courses, a full cave course and cave DPV using the SUEX XK1's. The only systems we dove due to flooding were Devil's Ear/Eye at Ginnie Springs, Manatee upstream/downstream, and Peacock Springs. Maximum depth was 99 feet for cave and 65 feet for cavern, dive times were 60 to 90 minutes and the surface interval between dives was over 3 hours. But, I started diving around Jan 21 and dove consecutively until Feb. 8 then went to Crystal River to snorkel with manatees.
As a contact lens wearer, I noticed my vision was a little blurry in the evenings, but most people get a little near-sighted at night and contact lens wearers know that the quality of vision is lessened as the lenses are a bit dry after diving or after longer wear times when the eye has been dealing with a piece of soft plastic all day. On the way to Crystal River I noticed that my vision in my left eye was really off and a little bit off on the right. I thought I goofed and put the wrong lenses in each eye. I switched lenses, then I opened new disposables twice. Yep. Rx changed. I went to the optometrist in Gainesville and he thought oxygen was responsible for a jump to a -4.00 diopter. Generally, cumulative oxygen exposures affect the lens while CNS would affect the retina.
In hindsight, I believe that diving nearly daily for my job as a full-time instructor, teaching mostly tech and cave classes, and teaching intensive days diving 2 to 3 times a day for recreational depths, and 1 to 2 times for technical depths on open-circuit has been responsible for recurrent bouts of ocular oxygen toxicity since summer. I would just leave this as a "technical diving" issue if not for a DAN case of a 23 year-old experiencing myopia after 5 days of air diving (7 dives) no deeper than 78 feet. I think we are going to hear about more and more cases of this rare phenomenon on OC not just CCR as more divers end up primarily diving nitrox, getting into technical diving, diving on consecutive days, and getting older.
In my case I think it is the getting older part. As free radicals are connected with breaking down as we age, the age range of many of the CCR divers who've had hyperoxic-induced myopia are definitely "middle" and at age 46, despite taking care of myself, I'm getting up there. I probably haven't healed enough so I'm going to take a few months off diving. It's reported that once you get ocular oxtox you are more likely to get it again. This may simply be because one's body broke down enough in the first place. Ocular oxtox might stem from something wrong in the body like repeated DCS is often tied to a PFO. Perhaps the aging lens? Oxygen is also tied to cataract formation. I have the beginnings of posterior subcapsular cataracts, but most likely due to floater-only vitrectomy surgery I had in 2009 and 2011 to remove eye floaters. Cataracts normally form within 5 years following FOV surgery. Mine are very small and are not related to any myopic Rx change.
Here are some thoughts:
1. As we get older we probably cannot tolerate oxygen the same as in our youth. Older divers may want to be more careful about tracking OTUs/UPTDs, doing less repetitive dives, and taking a day off diving during week-long dive trips. Be aware that most cases of oxygen-induced myopia seem to come after a week to 10 days of exposure and if you are anticipating multiple days of diving keep your daily doses low.
2. Try to keep the ppO2's low. I may run more triox than nitrox for bottom mix to reduce my open-circuit bottom ppO2 to well below 1.0 ata when possible this season. While it is known that spiking the ppO2s at the end of the dive for deco isn't always the best practice on a rebreather depending upon the bottom ppO2 and the dive time, for open-circuit diving the few minutes of high ppO2's to speed off-gassing will probably be less of a problem than a higher ppO2 throughout the bottom portion. For example, I might try 21/10 rather than Nitrox32 at 100 feet.
3. Report any visual changes to DAN. Be aware of your visual acuity and log it if you notice something might be wrong. See a doctor right away if you think it could be from DCS. If you know something is going related to oxtox discuss it with DAN and your eye doctor. Don't discount oxtox just because you are a recreational nitrox diver.
4. After speaking to DAN, Gary Taylor at PSAI and reading in detail about myopia due to oxygen, I'm going to add more antioxidants into my diet and take it as easy on my eyes when diving as I do on my knees when running. I may also switch back to an Rx facemask rather than dive in contacts.
5. Take oxygen as seriously as nitrogen. As a diving community we have become pretty complacent about oxygen exposure, but the old salts who used to track their oxygen weren't foolish.
I'd be very interested to hear of any other incidents of this or any advice from the medical community since there have been very little studies of this matter related to diving.
Hyperoxic myopia or oxygen-induced myopia has always been considered a rare event in sport scuba diving. More cases of patients having a change in their glasses or contact lens Rx have been reported in the world of hyperbaric medicine. The patient usually experiences an increase in myopia that may last for days, weeks, months or sometimes permanently after being exposed to higher partial pressures of oxygen in repeated frequent or daily treatments. Most cases tend to resolve themselves within a few days to a few weeks. Most of the time the patient's visual acuity or Rx will return to normal or the patient might require a slight Rx change.
In the sport of scuba diving, hyperoxic myopia has been on the radar of divers using closed-circuit rebreathers (CCR's) due to the ability of the diver to remain underwater for long exposures while being able to keep the partial pressure of oxygen higher throughout the course of a dive to reduce a decompression obligation or to use a higher partial pressure of oxygen during decompression to reduce decompression time. While open circuit divers have been doing the latter for quite some time, a CCR diver has the ability to maintain a constant oxygen partial pressure in the breathing loop due to the electronics controlling oxygen injection. Open-circuit divers do not have this ability because the pressure of oxygen decreases as the diver ascends. Simply put, a rebreather diver is exposed to more oxygen regarding both CNS and whole body oxygen toxicity.
Most advanced divers are familiar with the danger of CNS oxygen toxicity and know the importance of maintaining safe maximum operating depths. Some agencies and instructors do not spend much time covering whole body (pulmonary) oxygen toxicity because most single tank recreational divers are told they don't really need to worry about tracking OTUs (oxygen toxicity units) or UPTDs (unit pulmonary toxicity dose). Traditionally, the lungs have been used as the litmus test for whole body oxygen toxicity because they are often the first tissues injured by oxygen. Oxygen can inflame lung tissue and reduce the effectiveness of the lungs to filter out inert gases such as nitrogen and properly take in oxygen to fuel the cells of our bodies. If the lung tissue is inflamed long enough a permanent reduction in vital capacity may result.
While the lungs have always posed the greatest concern with cumulative exposure to higher oxygen, cumulative exposure is "whole body" but as divers we really haven't been paying much attention to other parts of the body. Oxygen hurts us through biochemical damage in our cells as a result of oxygen free radicals or radical oxygen species (ROS). Right! The same type of thing you hear about in commercials for foods and products that are "antioxidants", but we are giving oxygen steroids by taking it underwater and breathing in higher percentages and pressures.
After the lungs the eyes become one of the most noticeable areas of weakness to suffer the effects of oxidative stress and damage. I literally got to see this for myself, first hand, after having experienced definitely two and possibly as many as three or four hits of hyperoxic-induced myopia while diving on open-circuit.
In November 2014, I was teaching a stage cave diving class in North Florida and diving twice a day for a week. I noticed that I had great vision on my way to FL with my contacts having had a new Rx in October, but things were blurry during the drive home. We did one daytime dive and one night time or late afternoon dive with at least a 3 hour surface interval and run times from 90 to 120 minutes with depths no greater than 100 feet. My Rx jumped from -3.00 to -3.50. Prior to that, my Rx had been -2.25 during the summer and -1.75 before that.
I just returned from cave country in High Springs, FL where I taught a cavern instructor IQC, and intro to cave instructor course, two cavern/intro courses, a full cave course and cave DPV using the SUEX XK1's. The only systems we dove due to flooding were Devil's Ear/Eye at Ginnie Springs, Manatee upstream/downstream, and Peacock Springs. Maximum depth was 99 feet for cave and 65 feet for cavern, dive times were 60 to 90 minutes and the surface interval between dives was over 3 hours. But, I started diving around Jan 21 and dove consecutively until Feb. 8 then went to Crystal River to snorkel with manatees.
As a contact lens wearer, I noticed my vision was a little blurry in the evenings, but most people get a little near-sighted at night and contact lens wearers know that the quality of vision is lessened as the lenses are a bit dry after diving or after longer wear times when the eye has been dealing with a piece of soft plastic all day. On the way to Crystal River I noticed that my vision in my left eye was really off and a little bit off on the right. I thought I goofed and put the wrong lenses in each eye. I switched lenses, then I opened new disposables twice. Yep. Rx changed. I went to the optometrist in Gainesville and he thought oxygen was responsible for a jump to a -4.00 diopter. Generally, cumulative oxygen exposures affect the lens while CNS would affect the retina.
In hindsight, I believe that diving nearly daily for my job as a full-time instructor, teaching mostly tech and cave classes, and teaching intensive days diving 2 to 3 times a day for recreational depths, and 1 to 2 times for technical depths on open-circuit has been responsible for recurrent bouts of ocular oxygen toxicity since summer. I would just leave this as a "technical diving" issue if not for a DAN case of a 23 year-old experiencing myopia after 5 days of air diving (7 dives) no deeper than 78 feet. I think we are going to hear about more and more cases of this rare phenomenon on OC not just CCR as more divers end up primarily diving nitrox, getting into technical diving, diving on consecutive days, and getting older.
In my case I think it is the getting older part. As free radicals are connected with breaking down as we age, the age range of many of the CCR divers who've had hyperoxic-induced myopia are definitely "middle" and at age 46, despite taking care of myself, I'm getting up there. I probably haven't healed enough so I'm going to take a few months off diving. It's reported that once you get ocular oxtox you are more likely to get it again. This may simply be because one's body broke down enough in the first place. Ocular oxtox might stem from something wrong in the body like repeated DCS is often tied to a PFO. Perhaps the aging lens? Oxygen is also tied to cataract formation. I have the beginnings of posterior subcapsular cataracts, but most likely due to floater-only vitrectomy surgery I had in 2009 and 2011 to remove eye floaters. Cataracts normally form within 5 years following FOV surgery. Mine are very small and are not related to any myopic Rx change.
Here are some thoughts:
1. As we get older we probably cannot tolerate oxygen the same as in our youth. Older divers may want to be more careful about tracking OTUs/UPTDs, doing less repetitive dives, and taking a day off diving during week-long dive trips. Be aware that most cases of oxygen-induced myopia seem to come after a week to 10 days of exposure and if you are anticipating multiple days of diving keep your daily doses low.
2. Try to keep the ppO2's low. I may run more triox than nitrox for bottom mix to reduce my open-circuit bottom ppO2 to well below 1.0 ata when possible this season. While it is known that spiking the ppO2s at the end of the dive for deco isn't always the best practice on a rebreather depending upon the bottom ppO2 and the dive time, for open-circuit diving the few minutes of high ppO2's to speed off-gassing will probably be less of a problem than a higher ppO2 throughout the bottom portion. For example, I might try 21/10 rather than Nitrox32 at 100 feet.
3. Report any visual changes to DAN. Be aware of your visual acuity and log it if you notice something might be wrong. See a doctor right away if you think it could be from DCS. If you know something is going related to oxtox discuss it with DAN and your eye doctor. Don't discount oxtox just because you are a recreational nitrox diver.
4. After speaking to DAN, Gary Taylor at PSAI and reading in detail about myopia due to oxygen, I'm going to add more antioxidants into my diet and take it as easy on my eyes when diving as I do on my knees when running. I may also switch back to an Rx facemask rather than dive in contacts.
5. Take oxygen as seriously as nitrogen. As a diving community we have become pretty complacent about oxygen exposure, but the old salts who used to track their oxygen weren't foolish.
I'd be very interested to hear of any other incidents of this or any advice from the medical community since there have been very little studies of this matter related to diving.
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