Thanks Bob,

This is an interesting study.  I've a couple related observations on oxygen therapy and some anecdotal first-hand data to add on my experience with Optical Coherence Tomography (OCT).

Military pilots have been flying with 100% oxygen since the late 1930s and early 1940s.  Mission length and time above 10,000 feet altitude where 100% oxygen is required, averaged out to 7 hours a day.   

All Navy and Marine Corps pilots flying ejection seat equipped fighter and attack aircraft have been required to breathe 100% oxygen from takeoff to landing from the early 1950s through 2005 when LOX systems, that provide pilots and air crew with 100% oxygen, were phased out and On-board Oxygen Generating System (OBOGS) were phased in. 

OBOGS are like a home oxygen concentrator on steroids.  They use a molecular sieve fed by bleed air from a jet engine's 17th stage compressor section to supply a two-man crew with oxygen flow rates in excess of 40 liters/minute and oxygen concentrations of 93% to 94%.  Many OBOGS are rated at 60 LPM flow rates. 

Long story made short... Several hundred thousand aviators and hundreds of astronauts have been breathing 100% oxygen for over 70 years and all of them had annual flight physicals with eye exams.  In all that time there were no reports of loss of vision or loss of visual acuity attributed to repeatedly breathing 100% oxygen for extended periods... 

I'll qualify that finding by saying Optical Coherence Tomography didn't come into widespread use until the mid 1990s and it's not part of an aviators annual flight physical.

Now for the personal anecdotal OCT evidence...  I was a participant in an interventional study of people with uveitis at the National Eye Institute (NEI) at the National Institutes of Health (NIH), in Bethesda Md. 

Uveitis is an inflammation of the uvea, the middle layer of the eye... basically, my retina were trying to reject my body... 

The 24 month study protocol called for Daclizumab as the method of intervention.  Daclizumab is a therapeutic humanized monoclonal antibody produced in a lab environment that's used to prevent organ rejection after transplants. 

Like nearly all of the monoclonal antibody (MAB) biological treatments, daclizumab carries a long list of onerous side effects starting with a compromised immune system, several types of infections and skin cancer.  As these were the lesser of the evils compared to a potential loss of vision due to uveitis, I signed the study consent form.

The study protocol called for monthly eye exams, and labs where they checked my T-Cell receptors for the presence of daclizumab antibodies, with OCT and Intravenous Fluorescein Angiography (IVFA) conducted every 3 months... 

The OCT procedure is a relatively non-invasive, easy do, that takes a few minutes per eye... They give you a light dot to follow that moves the eye in a pattern allowing OCT imaging of the entire retina.  The results are printed out and they look much like bottom returns you see in a high quality depth/fish finder color display. 

The IVFA is a different story...  They put in an IV line, shoot you up with fluorescein dye, then start taking a series of photo's of the retina using a very bright and painful flash with each photo.

You're effectively blind and recoil from the pain of the first flash.  It takes a lot of will power to open your eye next to the eyepiece for the next of up to 10 or more photo flashes per eye...  As a side note, the first time you urinate after this procedure, you're treated to a very bright yellow stain in the urinal or commode.

I'd been diagnosed with episodic CH years earlier and was in the process of turning chronic when this study started.  Other than prednisone, none of the standards of care CH preventatives were acceptable due to onerous side effects and as oral imitrex was my abortive of choice, it was the only means of controlling my CH. 

I took imitrex daily during the first year of this study during which I received the six daclizumab injections called for in the protocol, one every other month.

Half way through the study protocol, having endured a year of non-stop CH, my neurologists at NIH agreed I had turned chronic and finally prescribed oxygen therapy as an abortive.  At that point I discontinued imitrex and used oxygen therapy as my only method of controlling my CH.

A team of at least four ophthalmologists analyzed my labs and test results including the OCT and IVFA each month.  As oxygen therapy was not part of the study protocol, they paid particular attention to any possible changes in my labs and test results that could possibly be attributed to its use on a daily basis.

As luck would have it, a little over half way through the 24 month protocol, I developed a small lesion on my forehead that was surgically excised by one of the staff surgeons at NIH and biopsied.  The biopsy came back squamous carcinoma.

A few weeks later, I experienced a raging bilateral headache so drove to the NEI.  When I explained it was clearly not a cluster headache, they took my temperature.  It was 103º so they sent me straight to radiology for an MRI.

As I was walking back to the NEI clinic after the MRI, I was met by one of the NEI ophthalmologists, the Principal Investigator for the study, and the NIH, Chief of Study Protocols.  They put me on a gurney and rolled me back to radiology for a lumbar puncture under flouroscopy and CSF draw. 

The MRI had indicated meningitis and analysis of the CSF indicated it was eosinophilic meningitis. 

Needless to say they admitted me for a few days and a heavy course of antibiotics.  I'd started the second half of the study protocol that didn't include daclizumab so I vowed to refuse treatment with any of the MABs after that.

In all, I had eight OCTs, four while taking daclizumab and imitrex and the second four while using only oxygen therapy as my abortive.  The OCTs indicated the daclizumab had reduced the inflammation and stopped the progress of uveitis after the second month of treatment. 

The last four OCTs revealed there was no change and no indication of deterioration after switching to oxygen therapy as my CH abortive...

Epilog...  In November of 2011, a year after starting the anti-inflammatory regimen and nearly 3 years after the NEI study concluded, I was invited back to the NEI for a followup eye exam, labs, and tests including an IVFA and OCT. 

The Principal Investigator and a staff ophthalmologist, were pleased to find my vision had improved. I no longer need reading glasses when at the computer...  Moreover, the IVFA and OTC results indicated a slight improvement when compared to the previous IVFA and OTC from three years earlier.

Again, although my experience with OTC is anecdotal, it is relative.

V/R, Batch