Mader T H, Blanton C L, Gilbert B N, Kubis K C, Schallhorn S C, White L J, Parmley V C, Ng J D
Madigan Army Medical Center, Ophthalmology Service, Tacoma, Washington, USA.
Ophthalmology. 1996 Aug;103(8):1188-95. doi: 10.1016/s0161-6420(96)30523-x.
The authors prospectively analyzed refractive and pachymetric parameters during exposure to high altitude after radial keratotomy (RK) and photorefractive keratectomy (PRK).
The authors measured manifest and cycloplegic refraction, keratometry, computed video keratography, and central and peripheral pachymetry in six subjects who have undergone RK (11 eyes), six who have undergone PRK (12 eyes), and nine with myopia (17 eyes) at sea level and on three consecutive days at 14,100 feet. All measurements were repeated 1 week after subjects returned to sea level.
Subjects who have undergone RK demonstrated a significant and progressive increase in spherical equivalence (+0.30 +/- 0.50 diopters on day 1 and +1.52 +/- 1.01 diopters on day 3; P < 0.001) and a decrease in keratometry values during exposure to altitude when compared with control subjects with myopia. Healthy subjects and those who have had PRK demonstrated no significant change in refractive error. Pachymetry measurements demonstrated significant peripheral corneal thickening in all three groups (RK, P < 0.004; PRK, P < 0.007; control subjects, P = 0.0006) by day 3 at high altitude. Refraction, keratometry, and pachymetry returned to baseline (P = 1.000) after return to sea level.
Seventy-two-hour exposure to high altitude in subjects who have had RK induces a significant, progressive, and reversible hyperopic shift in refraction with corresponding video keratographic and keratometric changes. The authors hypothesize that the high-altitude hypoxic environment causes increased corneal hydration in the area of the RK incisions, which may lead to central corneal flattening and a hyperopic shift in refractive error. Subjects who have had PRK and those with myopia are not susceptible to this refractive shift. The authors' RK data suggest that the time since surgery and the amount of surgery are related to the degree of hyperopic shift during altitude exposure.
作者前瞻性分析了放射状角膜切开术（RK）和准分子激光原位角膜磨镶术（PRK）后在高海拔环境下的屈光和角膜厚度参数。
作者测量了6例行RK手术的受试者（11只眼）、6例行PRK手术的受试者（12只眼）以及9例近视患者（17只眼）在海平面及海拔14100英尺连续三天的显验光和睫状肌麻痹验光、角膜曲率测量、计算机视频角膜地形图测量以及中央和周边角膜厚度。所有测量在受试者返回海平面1周后重复进行。
与近视对照受试者相比，行RK手术的受试者在海拔暴露期间等效球镜度显著且逐渐增加（第1天为+0.30±0.50屈光度，第3天为+1.52±1.01屈光度；P<0.001），角膜曲率值降低。健康受试者和行PRK手术的受试者屈光不正无显著变化。角膜厚度测量显示，到高海拔第3天时，所有三组（RK组，P<0.004；PRK组，P<0.007；对照受试者，P = 0.0006）周边角膜均显著增厚。返回海平面后，屈光、角膜曲率和角膜厚度恢复至基线水平（P = 1.000）。
行RK手术的受试者在高海拔环境下暴露72小时会导致显著、逐渐且可逆的远视性屈光偏移，并伴有相应的视频角膜地形图和角膜曲率变化。作者推测，高海拔低氧环境会导致RK切口区域角膜水化增加，这可能导致中央角膜变平以及屈光不正出现远视性偏移。行PRK手术的受试者和近视患者不易出现这种屈光偏移。作者的RK数据表明，手术时间和手术量与海拔暴露期间远视性偏移的程度有关。
