Articles about Eye Health and Disease 2001
 

Refractive Changes Caused by Hypoxia (reduced atmospheric oxygen) after Lasik

(From ML Nelson, MD et al. Refractive Changes Caused by Hypoxia after Laser In Situ Keratomileusis Surgery. Ophthalmology 2001;108:542-544.)

Reduced atmospheric oxygen levels (hypoxia) are found at altitudes over 9000 feet. This has found to lead to a prominent and dangerous hyperopic shift (farsightedness) in corneas that have had radial keratotomy. In eyes that have not had refractive surgery, and in eyes that have had PRK (photorefractive keratectomy), no change in refractive status has been demonstrated. This study looks at the effects of reduced oxygen on corneas which have had the Lasik procedure.

In this study, 20 patients who had bilateral Lasik previously were compared to 20 nearsighted patients who had not had surgery. Each subject had one eye exposed to ocular surface hypoxia (humidified nitrogen) by use of an airtight goggle system at sea level for 2 hours. The other eye was simultaneously exposed to humidified compressed air (21% oxygen) with the same goggle system. Corneal curvature, dilated refraction (glasses prescription), and corneal thickness were compared before and after the exposure.

It was found that Lasik eyes exposed to hypoxia had a statistically significant shift towards nearsightedness with an average shift of -.312 D (ranging from +.25 to -1.5 shift). Keratometry (curvature) showed a trend towards steepening in the hypoxia exposed eyes, but this was not statistically significant. There was virtually no change in refraction in the control eyes (no surgery), or in the eyes exposed to normal oxygen levels. All eyes exposed to hypoxia over 2 hours developed increased corneal thickness.

This study suggests that hypoxia may lead to a myopic shift in refraction in eyes that have had Lasik. The clinical significance of this study is unknown, since 2 hours of nitrogen exposure does not correspond to a specific altitude. Many studies and reports in the past have demonstrated that the refractive shift occurring after radial keratotomy surgery does not occur immediately, but rather after a few days. Thus, those individuals encountering high altitudes for an extended amount of time (mountain climbers, skiers, etc.) may experience a change in refraction after Lasik.

 

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