Refractive change in response to acute hyperbaric stress in refractive surgery patients Enoch T. Huang, MD, Michael D. Twa, OD, David J. Schanzlin, MD, Karen B. Van Hoesen, MD, FACEP, MaryAnn Hill, PhD, Mark I. Langdorf, MD, FACEP Purpose: To determine whether acute hyperbaric stress affects visual acuity or refractive power after keratorefractive surgery. Setting: Clinical multiplace hyperbaric chamber and ophthalmology clinic, Univer- sity of California, San Diego, California, USA. Methods: This prospective convenience sample study included 3 groups: 3 pa- tients who had had bilateral myopic radial keratotomy (RK); 2 who had had bilat- eral myopic laser in situ keratomileusis (LASIK); and 4 control subjects who had no previous corneal refractive surgery or ocular pathology but had a myopic re- fractive error (-1.25 to -8.38 diopters [D]) similar to that in the treated patients before refractive surgery. One additional patient had had unilateral LASIK only and was included in the LASIK and control groups. Best spectacle-corrected vi- sual acuity (BSCVA), manifest spherocylindrical refractive error, and intraocular pressure were measured at baseline, at 4 atmospheres absolute (atm abs), and on return to ambient pressure. Corneal pachymetry and keratometry were mea- sured at baseline and on return to ambient pressure. Results: The mean BSCVA changed from 0.06 logMAR (20/25 Snellen equivalent) at baseline to 0.10 logMAR (20/25) at 4 atm abs in the RK group and from 0.00 logMAR (20/20) to -0.06 logMAR (20/15) in the LASIK group; it did not change in the control group. The mean refractive error changed from 0.25 D at baseline to 0.50 D at 4 atm abs in the RK group, from -0.90 to -1.02 D in the LASIK group, and from -4.58 to -4.53 D in the control group. Conclusion: Acute hyperbaric stress did not appear to alter refractive power after corneal surgery. J Cataract Refract Surg 2002; 28:1575–1580 © 2002 ASCRS and ESCRS T he intent of this study was to quantify the change in visual acuity in the postsurgical cornea compared to that in the natural cornea under the increased atmo- spheric pressures of scuba diving. Radial keratotomy (RK) and laser in situ keratomileusis (LASIK) are com- mon treatments for moderate to severe myopia. These procedures, however, alter the structural integrity of the cornea to varying degrees, and changes in environmental conditions may adversely affect the postsurgical cornea. 1,2 A hyperopic shift has been observed in postopera- tive RK patients ascending to altitudes of 9000 to 18 000 feet. 3–11 The cause of this loss of vision was initially attributed to direct pressure differences between the orbit and the ambient atmosphere. 3 Recent studies indicate that these visual changes occur when corneal edema caused by the hypoxic atmospheric conditions at high altitudes produces a change in the corneal curva- ture. 4–8 Preliminary reports of LASIK at high altitudes are contradictory. Two reports claim that LASIK is sta- ble at high altitudes (“Parting Glance: LASIK Stable at an Altitude of 18,500 Feet,” Ocular Surgery News, Sep- Accepted for publication February 27, 2002. Reprint requests to Enoch T. Huang, MD, Hyperbaric Medicine, Insti- tute for Environmental Medicine, One John Morgan Building, 36th and Hamilton Walk, Philadelphia, Pennsylvania 19104-6068, USA. © 2002 ASCRS and ESCRS 0886-3350/02/$–see front matter Published by Elsevier Science Inc. PII S0886-3350(02)01362-7