Ultramarathon-Induced Corneal Edema
Key points at a glance
Section titled “Key points at a glance”1. What is Ultramarathon-Induced Corneal Edema?
Section titled “1. What is Ultramarathon-Induced Corneal Edema?”Ultramarathon-induced corneal edema (UMICE) is corneal edema that occurs during prolonged physical exertion such as ultramarathons (over 42.2 km) 1. It is a transient condition that usually resolves within hours after stopping exercise 2.
It has been reported mainly in ultramarathon-distance foot races, but may also occur in other endurance sports such as cycling and cross-country skiing 1. In a survey of 173 ultramarathon runners by Høeg et al., the average distance at onset of visual impairment was 73 ± 40 km, and the most frequently reported race distance was 161 km (46.8%) 2.
Risk Factors
Section titled “Risk Factors”- History of corneal refractive surgery: Previous LASIK and other procedures are suspected risk factors. In Høeg et al.’s survey, runners who experienced visual impairment had nearly twice the rate of refractive surgery history compared to controls (23.7% vs 12.1%, P < .001) 2.
- Wind exposure: External environmental factors that stress the cornea are risk factors 1.
- Corneal dystrophy / decreased corneal endothelial cells: Their involvement as risk factors has not been investigated.
UMICE is mainly reported in ultramarathon-distance races (over 42.2 km). It cannot be ruled out that it may also occur in regular marathons (42.195 km) or shorter endurance sports, but reported cases are concentrated in ultramarathons. Prolonged physical exertion is thought to be necessary to raise lactate accumulation to sufficient levels, making the duration of exercise an important factor.
2. Main Symptoms and Clinical Findings
Section titled “2. Main Symptoms and Clinical Findings”Subjective Symptoms
Section titled “Subjective Symptoms”- Blurred vision: Progressive painless blurred vision occurs in one or both eyes 2. It can lead to severe visual loss 3.
- No pain or photophobia: This is an important feature of UMICE and a clue for differential diagnosis 2.
Clinical Findings (Findings Confirmed by Physician Examination)
Section titled “Clinical Findings (Findings Confirmed by Physician Examination)”- Corneal edema: Slit-lamp microscopy reveals opacity and thickening of the corneal stroma 3.
- Descemet’s membrane folds: Mild Descemet’s membrane folds may be present along with corneal edema 1.
- Mild conjunctival injection: The eye usually does not appear red, but mild bulbar conjunctival injection may be present.
- Transient: Findings resolve within hours after cessation of exercise (median 3.5 hours, range 0–48 hours), so recovery is often seen at the time of examination 2.
3. Causes and Risk Factors
Section titled “3. Causes and Risk Factors”Lactate Accumulation Theory
Section titled “Lactate Accumulation Theory”According to the current leading hypothesis, UMICE is caused by lactate accumulation within the cornea 1. Lactate is a known metabolite of corneal metabolism, and its accumulation in the corneal stroma has been shown to increase osmotic pressure and draw in water 1.
Hypothesis of Pathogenesis
Section titled “Hypothesis of Pathogenesis”External corneal stress, such as wind and sweat, increases lactate production inside the cornea. This, combined with systemic lactate elevation in the blood and aqueous humor due to prolonged physical exertion, is thought to lead to corneal lactate accumulation and edema. Moshirfar et al. proposed a multifactorial hypothesis in which increased glycolysis, elevated aqueous humor lactate, and oxidative stress act additively to impair the normal regulatory function of the corneal endothelium 1.
4. Diagnosis and Examination Methods
Section titled “4. Diagnosis and Examination Methods”UMICE is diagnosed clinically based on the characteristic situation (onset during an ultramarathon), symptoms (painless progressive blurred vision), and rapid recovery after stopping exercise 2. By the time endurance race participants seek medical attention, symptoms have often largely resolved, with only slight residual Descemet’s membrane folds 3. In a report measuring corneal thickness, intraocular pressure, and visual acuity before and after a 161 km race in 8 asymptomatic finishers, no significant changes were observed in any of these parameters 4.
Differential Diagnosis
Section titled “Differential Diagnosis”| Differential Diagnosis | Key Differentiating Features |
|---|---|
| Acute corneal edema | Pain and photophobia present; recovery takes weeks |
| Acute angle-closure glaucoma | Pain and conjunctival injection present; elevated intraocular pressure |
| Pigment dispersion syndrome | Krukenberg spindle, iris atrophy |
| Uhthoff phenomenon | No corneal opacity; history of demyelinating disease |
| Dry eye | Foreign body sensation; no corneal opacity |
| Corneal freezing | Occurs in cold climates, accompanied by pain |
Pigment dispersion syndrome can present with a clinical picture similar to UMICE, as iris pigment is released during exercise, leading to elevated intraocular pressure and blurred vision. Clues for differentiation include Krukenberg spindle, wheel-shaped iris atrophy, and excessive pigmentation of the trabecular meshwork. Additionally, acute corneal hydrops in keratoconus presents with rapid corneal opacity but differs from UMICE in that it is accompanied by pain and photophobia and takes weeks to recover. Uhthoff phenomenon (exercise-induced visual disturbance associated with optic neuritis) is differentiated by the absence of corneal opacity.
5. Standard Treatment
Section titled “5. Standard Treatment”Acute Phase Management
Section titled “Acute Phase Management”If UMICE has already developed, cessation of exercise is the only known effective treatment1. After stopping exercise, corneal edema usually resolves spontaneously within a few hours (median 3.5 hours)2. Moshirfar et al. state that 5% hypertonic saline eye drops may promote recovery of corneal clarity if needed1.
Prevention
Section titled “Prevention”- Protective eyewear: Wearing goggles or sunglasses that protect the cornea from wind, UV light, and external environmental stress is considered the most effective preventive measure for endurance sports1.
- Lubricating eye drops: Used to protect the corneal surface3.
Recurrence Prevention
Section titled “Recurrence Prevention”UMICE is recurrent; affected runners experience the same symptoms at a median of 2 races2. Use of protective eyewear and lubricating eye drops is recommended.
Wearing protective eyewear (goggles or sunglasses) and using lubricating eye drops are recommended as preventive measures. Reducing exposure to wind is expected to decrease external stress on the cornea and suppress increased lactate production. However, no clinical trials have yet verified the effectiveness of these preventive measures. Participants with a history of corneal refractive surgery such as LASIK require particular caution.
6. Pathophysiology and Detailed Mechanism
Section titled “6. Pathophysiology and Detailed Mechanism”Lactate Metabolism in the Cornea
Section titled “Lactate Metabolism in the Cornea”The cornea is an avascular tissue, and oxygen supply is mainly from the tear film and aqueous humor. The corneal epithelium and stroma produce lactate through anaerobic glycolysis. Normally, the produced lactate is eliminated by the pump function of the corneal endothelium and diffusion into the aqueous humor 1.
Pathophysiological Hypothesis of UMICE
Section titled “Pathophysiological Hypothesis of UMICE”Prolonged physical exertion increases systemic lactate production, and elevated lactate concentration in the aqueous humor inhibits lactate elimination from the cornea into the aqueous humor 1. At the same time, external stressors such as wind, sweat, and decreased blinking increase local lactate production in the cornea. Accumulation of lactate in the corneal stroma raises osmotic pressure, drawing in water, and additionally, oxidative stress and hypoxia impair the regulatory function of the corneal endothelium, leading to progression of corneal edema 1.
When exercise is stopped, systemic lactate production rapidly decreases. Lactate in the cornea is also eliminated, endothelial pump function recovers, and corneal edema subsides 2.
8. References
Section titled “8. References”- Moshirfar M, Ding Y, Ronquillo Y, Birdsong OC, Murri MS. Ultramarathon-Induced Bilateral Corneal Edema: A Case Report and a Review of the Literature. Ophthalmol Ther. 2018;7(1):197-202. doi:10.1007/s40123-018-0125-y. PMID: 29536349; PMCID: PMC5997605.
- Høeg TB, Corrigan GK, Hoffman MD. An investigation of ultramarathon-associated visual impairment. Wilderness Environ Med. 2015;26(2):200-204. doi:10.1016/j.wem.2014.10.003. PMID: 25728559.
- Lindström BE, Høeg TB. Ultramarathon-induced Corneal Edema-A Case Report. Curr Sports Med Rep. 2021;20(1):13-15. doi:10.1249/JSR.0000000000000796. PMID: 33395125.
- Høeg TB, Corrigan GK, Hoffman MD. Eye function and physiology following a 161-km foot race. Res Sports Med. 2018;26(4):500-504. doi:10.1080/15438627.2018.1492394. PMID: 29957073.