Ren D H, Petroll W M, Jester J V, Cavanagh H D
Department of Ophthalmology, The University of Texas Southwestern Medical Center at Dallas, 75235-9057, USA.
CLAO J. 1999 Jul;25(3):136-41.
To study the effect of rigid contact lens oxygen transmissibility on cell proliferation of the corneal, limbal, and conjunctival epithelium in vivo following 2 days of extended wear in the rabbit model.
Fourteen adult New Zealand White rabbits were divided equally into two groups. Each group was assigned to one of two test rigid gas permeable (RGP) contact lenses (Dk/Ltotal = 10 and 97) with uniform thickness (0.15 mm) and diameter (14.0 mm). One eye of each rabbit randomly received a contact lens for two days (48 hrs) extended wear, and the fellow eye was used as a control. Rabbits were injected intravenously with 5-bromo-2-deoxyuridine (200 mg/kg) in sterile phosphate buffered saline (pH 7.4) 24 hours before being killed. Corneas with a limbal rim of episclera and overlying conjunctiva were fixed in situ and excised. Nuclei labeled with BrdU were detected with a monoclonal anti-BrdU antibody and an FITC-conjugated secondary antibody. Digital images were collected and BrdU-labeled nuclei of whole-mount corneas were counted from superior limbus to inferior limbus using epifluorescence microscopy.
Twenty-four hours after intravenous injection of BrdU, labeled nuclei were confined to and appeared as pairs in the basal epithelial layer. The density of BrdU-labeled nuclei were found to be 258 +/- 42, 167 +/- 43, 372 +/- 64, and 310 +/- 46 (pairs/mm2, mean +/- SD, n = 14) in normal controls for adjacent conjunctiva, limbus, peripheral cornea, and central cornea, respectively. By contrast,there was significant 81.35% (low Dk)and 22.46% (ultra-high Dk) suppression of cell proliferation in the central cornea after two days lens wear (n = 7). In addition, significant increases in the labeling of limbal and conjunctival epithelium were also noted.
Significantly less BrdU labeling of epithelial cells at the normal rabbit limbus was noted as compared to the peripheral and central cornea (P < 0.05) and is consistent with the presence of slow-cycling limbal basal cells and the limbal stem cell theory; however, this is the first report of up-regulation of limbal cell proliferation induced by contact lens wear. This study also revealed, for the first time, that short-term extended wear of RGP lenses inhibits central corneal epithelial cell proliferation. This effect was significantly more pronounced for a low-oxygen vs. a hyper-oxygen transmissible test lens. This data also suggests that corneal epithelial layer thinning seen following extended contact lens wear may be explained, in part, by suppression of basal epithelial cell proliferation. Further study is clearly necessary to validate and extend these preliminary findings.
在兔模型中，研究硬性接触镜透氧性对连续佩戴2天后角膜、角膜缘和结膜上皮细胞增殖的影响。
将14只成年新西兰白兔平均分为两组。每组被分配佩戴两种测试用的硬性透气（RGP）接触镜（Dk/Ltotal = 10和97）中的一种，两种镜片厚度均一（0.15毫米），直径相同（14.0毫米）。每只兔子的一只眼睛随机佩戴接触镜连续2天（48小时），另一只眼睛作为对照。在处死兔子前24小时，给兔子静脉注射无菌磷酸盐缓冲盐水（pH 7.4）溶解的5-溴-2-脱氧尿苷（200毫克/千克）。将带有巩膜缘和上方结膜的角膜原位固定并切除。用单克隆抗BrdU抗体和异硫氰酸荧光素（FITC）偶联的二抗检测标记有BrdU的细胞核。采集数字图像，使用落射荧光显微镜从角膜上缘到下缘计数全层角膜中BrdU标记的细胞核。
静脉注射BrdU后24小时，标记的细胞核局限于基底上皮层并成对出现。在正常对照组中，相邻结膜、角膜缘、周边角膜和中央角膜BrdU标记细胞核的密度分别为258±42、167±43、372±64和310±46（每平方毫米的对数，平均值±标准差，n = 14）。相比之下，佩戴镜片2天后，中央角膜细胞增殖受到显著抑制，低透氧镜片组抑制率为81.35%，高透氧镜片组为22.46%（n = 7）。此外，还观察到角膜缘和结膜上皮标记显著增加。
与周边和中央角膜相比，正常兔角膜缘上皮细胞的BrdU标记显著减少（P < 0.05），这与缓慢循环的角膜缘基底细胞的存在和角膜缘干细胞理论一致；然而，这是首次报道接触镜佩戴诱导角膜缘细胞增殖上调。本研究还首次揭示，RGP镜片短期连续佩戴会抑制中央角膜上皮细胞增殖。低透氧性测试镜片的这种抑制作用比高透氧性测试镜片更显著。这些数据还表明，接触镜连续佩戴后观察到的角膜上皮层变薄，部分原因可能是基底上皮细胞增殖受到抑制。显然需要进一步研究来验证和扩展这些初步发现。
