BLOG: What is ‘ultra eye?’
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“Ultra eye,” more formally known as “ultramarathon-induced corneal edema,” is a rare but fascinating condition that presents only in athletes during very long-distance events.
Understanding this issue could not only be useful during an emergency, but also illuminate the complex metabolism of the cornea.
Ultramarathons are races that last any distance longer than the standard marathon distance of 26.2 miles; races can cover anywhere from 30 miles to 3,000 miles and are typically held in wild and mountainous areas. The sport has been growing rapidly, with more than 131,000 ultramarathon finishes in North America last year. Runners suffer from a variety of physical challenges, including extreme fatigue, difficult weather, dehydration, loss of electrolytes and calories, and sleep deprivation.
The longer races can also result in the onset of visual impairment; in 100-mile races, progressive vision loss occurs in 5.7% of racers (Hoffman MD, et al). Despite this, more than a third of these runners went on to finish their race.
For years, ultrarunners traded reports of painless progressive vision loss during long runs. The condition happened more often in those who’d had LASIK, presented at an average of 70 miles and resolved without intervention after hours or days. Although runners can suffer from many ocular issues, eight out of 10 of the few runners who were able to get a professional eye exam were diagnosed with corneal edema. This presented as a diffuse corneal edema spreading from the periphery to the center, often with Descemet’s folds and usually bilateral (Høeg et al.).
The condition was eventually given the name ultramarathon-induced corneal edema, or UMICE. Although UMICE is poorly understood, the current theory states that it is a result of systemic lactate saturation. All cells produce lactate during work as a byproduct of glucose metabolism, but during normal activities, the lactate is rapidly broken down. During significant exercise, however, lactate cannot be cleared rapidly enough, and levels rise throughout the body.
Endothelial cells also produce lactate during their constant effort to keep the corneal from overhydrating, and normally this lactate is flushed via facilitated transport into the aqueous humor. During an endurance race, however, systemic lactate levels can rise so high that even the aqueous humor becomes flooded, and corneal lactate cannot be pushed out against this uphill concentration gradient. Unable to flush its lactate, the endothelium struggles to pump, and the cornea begins to swell.
In addition, the buildup of lactate in the stroma may lead to an osmolar influx of water from the aqueous. Both effects push the cornea into edema.
The increased incidence of this condition in post-LASIK eyes may be a reason to avoid LASIK in serious ultramarathon runners. Contact lenses, on the other hand, may actually be protective against UMICE. There is anecdotal evidence that hypertonic saline drops can help with UMICE mid-race.
Readers of this blog may notice some similarities with the condition described in the piece Is LASIK safe at altitude?, wherein a cornea starving for airborne oxygen floods with bicarbonate and lactate, and the endothelial pumps begin to fail. In UMICE, the cornea floods with lactate because it cannot pump against an unfavorable concentration gradient.
If ultramarathoners suffer from new-onset blurred vision during a long race, it’s important to rule out corneal abrasions, contact lens-related problems, vascular issues, pigment dispersion and dry eye. But if the vision loss is not accompanied by pain, photophobia or darkness, they are likely experiencing UMICE, and they should feel comforted knowing their blindness will be transient. And ultramarathon runners, being who they are, they’re going to try to finish that race regardless.
References:
- Høeg TB, et al. Wilderness Environ Med. 2015:doi:10.1016/j.wem.2014.10.003.
- Hoffman MD, et al. Int J Sports Physiol Perform. 2011;doi:10.1123/ijspp.6.1.25.
- Lindström BE, et al. Curr Sports Med Rep. 2021;doi:10.1249/JSR.0000000000000796.
- Moshirfar M, et al. Ophthalmol Ther. 2018;doi:10.1007/s40123-018-0125-y.
For more information:
Oliver Kuhn-Wilken, OD, practices at Pacific Cataract and Laser Institute’s Tualatin Clinic in Oregon.
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