The most common type of oxygen toxicity is lenticular or affecting the lens. This phenomenon is called progressive myopia, a condition represented by defective vision of distant objects, also called nearsightedness. The number of hyperbaric treatments administered increases its occurrence and this is usually not seen when less than 20 treatments are given. Treatments are usually 90 to 1 20 minute in length and given on a daily basis at 2.0 ATA or higher. The incidence is reported to be between 20 to 40% and more often seen in diabetic and elderly patient. The good news is that when hyperbaric therapy is finished the condition is reversed. Complete recovery usually takes about 6 weeks although it may take longer in some cases. This condition is always discussed with patients so they realize that is not uncommon and that it is reversible. For this reason, patients are told not to get a new eyeglass prescription until about 6 weeks after therapy has ended. For patients with presbyopia, their condition may improve. They normally have an inability to focus sharply on items that are close (like with us middle-aged people who have trouble reading). Unfortunately this improvement will also reverse itself after therapy is terminated.
Cataract formation is a potential side effect of prolonged hyperbaric therapy and is discussed with patients. It has been found that new cataracts can develop and existing cataracts may worsen. Unfortunately this condition of lens opacity (reduction in light reflective properties) does not reverse itself and may require surgery for repair.
There are ocular contraindications to hyperbaric oxygen therapy. Patients who have had placement of an orbital prosthesis called a hollow silicone orbital implant should not be exposed to changing ambient pressures. There is a potential for a pressure-induced collapse of the prosthesis in this case. Fortunately the hollow design is rarely used today. The second contraindication is an intraocular gas bubble when introduced by surgeons as an internal stent to maintain position of the retina. In this case an air space in the eye can change in volume and cause barotrauma. However, if the gas bubble is due to decompression sickness, hyperbaric treatment is still indicated. Another relative contraindication is with patients who have a history of optic neuritis. Although very rare, blindness has been reported anecdotally in this group of patients. One might think that glaucoma is a contraindication but it is not. This disease is marked by increased pressure in the eyeball that can lead to damage of the optic disk (area in the retina where the optic nerve enters the eye, also called the blind spot) and gradual loss of vision. In the case of refractive surgeries, hyperbaric oxygen therapy has not been shown to pose a problem.
There are differing opinions on the use and frequency of eye examinations in the hyperbaric setting. Drs. Butler and Hagan in "Physiology & Medicine of Hyperbaric Oxygen Therapy", recommend a pretreatment eye examination for any patient when a large number of treatments are indicated. The eye exam should consist of checking for changes in visual acuity, refraction, color vision, and status of the lens. A fundus (part of eye opposite the pupil) exam should also be performed. Other references appear to pay less attention to the use of ophthalmologist examinations in the hyperbaric setting and therefore I think this is a topic that deserves more discussion to guide hyperbaric center practices.
The last point to be made is that patients must be made aware of the potential effects that treatment may have on their vision. This should be an important topic in patient education and also a part of the signed patient consent. In most cases, vision changes are temporary and reversible and are not contraindications for therapy.
by Kenneth Capek RRT, CHT, MPA
Ken Capek, RRT, CHI, MPA is Director of Respiratory Care and Hyperbaric Oxygen Therapy at Englewood Medicai Center in Englewood, NJ. He can be reached at Ken.Capek@ehmc.com
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|Title Annotation:||HYPERBARIC MEDICINE|
|Publication:||FOCUS: Journal for Respiratory Care & Sleep Medicine|
|Date:||Nov 1, 2008|
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