角膜后弹力层剥除内皮移植术治疗大泡性角膜病变的初步疗效观察

目的 探讨角膜后弹力层剥除内皮移植手术的适应证、手术方法以及对大泡性角膜病变的疗效与并发症的处理.方法 非随机回顾性系列病例研究.选择2006年9月至2007年10月于中山大学中山眼科中心住院的8例(8只眼)大泡性角膜病变患者行角膜后弹力层剥除内皮移植术.术中剥除患眼角膜中央部直径7.75 mm的后弹力层和病变的内皮层,再将植床周边部基质表面刮粗糙,然后按常规角膜内皮移植术的方法植入内皮植片.术后观察植片与植床贴合和植片移位等情况.随访3～9个月,记录患者视力、植片透明度、角膜散光及内皮细胞密度.结果 8例患者术后植片与植床贴合良好,未出现植片移位.术后第1天,1例患者出现继发性闭角型青光眼,术后48 h后缓解.8例患者术后植片透明,术前存在眼痛的6例患者术后眼痛缓解.8例患者术后视力均提高,最好矫正视力为0.3～0.7,平均角膜散光度数为(1.90±0.70)D,平均内皮细胞密度为(2014±192)个/mm2.结论 与深板层角膜内皮移植术比较,角膜后弹力层剥除内皮移植术的操作较简单,对受体角膜和前房的创伤更小.术中将植床周边部基质表面刮粗糙,可有效预防术后植片移位.     

不剥除后弹力层的深板层角膜内皮移植术治疗大泡性角膜病变的初步临床观察

目的 探讨不剥除后弹力层的深板层角膜内皮移植术治疗大泡性角膜病变的可行性和临床疗效.方法 前瞻性系列病例研究,收集自2007年9月至2009年1月在我院住院的大泡性角膜病变患者,进行不剥除后弹力层的深板层角膜内皮移植术.术中均未处理患眼角膜内皮.直接用植入镊将制作好的直径为8.5mm的角膜内皮植片植入受体前房,气体顶压植片进行固定.术后随访6～20个月,观察植片贴附和植片移位等情况,对手术前后的视力进行比较,检查植片透明度和角膜内皮细胞密度.结果 5例患者术后植片与受体内皮面始终贴附良好;1例患者术后第2天出现层间裂隙,经改俯卧位后植片贴附良好.6例患者植片均透明,其中5例患者术后最佳矫正视力均有不同程度的提高;1例患者术后视力同术前,视力不提高的原因为眼外伤造成的视神经萎缩.6例术后平均角膜内皮细胞密度为(1648±384)个/mm~2.随访过程均未发现有免疫排斥反应发生.结论 不剥除后弹力层的深板层角膜内皮移植术治疗大泡性角膜病变具有安全、有效、操作简便等特点,有望成为治疗该病的手术方式之一.     

小切口深板层豚鼠角膜内皮移植伤口愈合的组织病理学研究

目的 探讨小切口深板层角膜内皮移植术后角膜伤口愈合的组织病理学特点。方法 45只豚鼠分为受体组30只（30只眼）和供体组15只（30只眼）,进行同种异体深板层角膜内皮移植。受体组豚鼠右眼为术眼,左眼的正常角膜作为组织病理学对照。于术后1、2周、1、2、3、4个月分别处死受体组2只角膜恢复透明的豚鼠,取左、右眼角膜组织经内皮细胞茜素红染色、苏木素-伊红和（或）高碘酸希夫染色后行光镜检查,计数角膜基质内细胞。结果 受体组有22只眼术后角膜透明,角膜内皮细胞经茜素红染色后显示植片上内皮细胞形态和排列正常,在植床与植片间存在环形的内皮细胞异型区域。光镜检查显示,术后早期在角膜板层分离的径路上,基质内细胞明显增多;植床与植片的交接处,后板层胶原纤维和后弹力层中断,后者的残端卷起;交接处的空隙由结构紊乱、细胞成分较多的组织填充;而板层界面上胶原排列整齐。术后1个月时,出现新生的后弹力层。术后3～4个月时,后弹力层和后板层连续性恢复。结论 小切口深板层角膜内皮移植术的基质创口愈合特点与损伤形式有关,板层界面上胶原排列整齐,纤维化的愈合方式见于植床与植片的连接处。（中华眼科杂志,2006,42：694-698）     

自动板层刀辅助的后弹力层前膜角膜内皮移植术

角膜内皮移植已成为治疗角膜内皮病变的首选方法.作为目前主流的2种角膜内皮移植手术——后弹力层剥除自动板层刀制备的角膜内皮移植术和后弹力层角膜内皮移植术,前者手术操作易于掌握,但角膜植片仍带有部分基质;后者术后视觉质量好,但手术操作较难掌握,二次手术率较前者高.大气泡和自动板层刀辅助的后弹力层前膜角膜内皮移植术在自动板层刀制备角膜内皮植片的基础上,用大气泡法暴露中央6.5 mm直径的后弹力层前膜,本术式既有后弹力层角膜内皮移植术后的视觉效果,手术操作又易于掌握,值得推广.     

临时锚状缝线在无晶状体眼后弹力层剥除内皮移植术中的应用

目的 探讨在无晶状体眼后弹力层剥除内皮移植术(DSEK)中采用临时锚状缝线固定内皮植片的可行性、疗效及并发症.方法 回顾性系列病例研究.2007年4至12月期间中山大学中山眼科中心对12例(12只眼)无晶状体眼大泡性角膜病变患者采用临时锚状缝线固定内皮植片进行后弹力层剥除内皮移植术.12例患者均为白内障术后,最佳矫正视力(BSCVA)均低于或等于0.04,8例有眼痛.术前与术后3、6及12个月行BSCVA、角膜散光、角膜曲率、角膜厚度测量,术后6和12个月行角膜内皮显微镜检查.术后随访12～20个月.结果 12例患者均顺利行DSEK.术后12只术眼植片均位于受体植床中央,无植片移位.术后第1天,2例患者出现瞳孔阻滞性青光眼,予20%甘露醇静脉滴注,术后第2天,随前房中空气减少眼压降至正常.术后12只术眼内皮植片均出现轻至中度水肿,术后8～15 d,植片恢复透明.随访期间,12只术眼角膜均透明.术后12个月,有2例BSCVA为0.7,有3例为0.5,有4例为0.4,有3例为0.3.术后12个月,平均角膜散光度数为(2.40±0.70)D,平均角膜曲率为(45.40±1.50)D,平均角膜厚度为(591.5±20.4)μm.术后6和12个月,平均角膜内皮细胞密度分别为(2088±146)个/mm~2和(1857±101)个/mm~2,内皮细胞损失率分别为(28.9±3.9)%和(36.7±3.1)%.结论 临时锚状缝线能有效地固定内皮植片,防止植片移位和滑入玻璃体腔.     

兔角膜后弹力层剥除联合深板层内皮移植术后植片与植床愈合的观察

目的 探讨小切口下兔角膜后弹力层剥除联合深板层内皮移植(DSEK)术后不同时间植片与植床的愈合情况.方法 30只新西兰大白兔,供体组10只(20只眼),受体组20只(20只眼),右眼为实验组,行同种异体DSEK手术,左眼为正常对照组.术后裂隙灯定期观察角膜透明度;应用SL-OCT观察植片与植床的贴附情况及角膜厚度;分别于术后1、2、3、4、8周各取兔4只,制作角膜组织病理学切片,光镜下观察植片与植床的愈合情况.结果 实验组中1只眼由于植片严重卷曲未与植床贴附导致角膜持续混浊水肿,其余19只眼全部恢复透明.裂隙灯下见术后第1d角膜水肿严重,以后逐渐减轻,术后4周角膜完全透明.SL-OCT见各个时间点植片与植床均紧密贴附,术后第1d角膜明显增厚,以后逐渐变薄,至第4周角膜恢复到正常的厚度和形态.光镜下组织学观察,术后早期植片与植床界面清晰易辨,胶原纤维间缝隙增宽,排列紊乱.术后4周植片与植床的界面辨认不清,胶原纤维结构和排列基本恢复正常,角膜中央光学区无瘢痕形成.结论 DSEK术后,植片与植床能迅速达到无瘢痕的组织学愈合,该愈合对角膜透明度的恢复起重要作用.     

角膜后弹力层剥除联合自动角膜刀取材内皮移植术的临床研究

目的 探讨角膜后弹力层剥除联合自动角膜刀取材内皮移植术的术后疗效、并发症、处理及适应证的选择.方法 临床病例系列研究.2007年9至12月期间,北京大学第三医院、北京大学眼科中心选择9例角膜内皮失代偿的患者行角膜后弹力层剥除自动角膜刀取材及角膜内皮移植手术,术后观察视力、角膜透明性的恢复、植片的脱位率、角膜厚度、角膜曲率及角膜内皮细胞数,随访时间3～7个月.结果 手术中1例虹膜角膜内皮综合征患者的角膜内皮植片植入失败,改行穿透性角膜移植术;其余8例患者术后植片明显脱位1例,再处理后复位.术后8例手术成功患者视力全部提高,植片透明,角膜厚度为(775±30)μm;角膜曲率为(44.19±2.28)D;角膜散光度数为(2.20±0.83)D;角膜内皮细胞数为(1439±296)个/mm~2.结论 角膜后弹力层剥除联合自动角膜刀取材内皮移植术有可能成为一种治疗角膜内皮失代偿的重要术式.     

兔血管内皮细胞对角膜后弹力层代谢的影响

目的:检测移植后生长于角膜内皮面的自体血管内皮细胞对角膜后弹力层代谢的影响.方法:家兔26只随机分成3组:实验组10只,将培养的自体血管内皮细胞移植到无后弹力层的角膜内皮面;实验对照组10只,移植无角膜内皮层的自体植片;空白对照组6只,移植带角膜内皮细胞的自体植片,术后观察3组角膜植片的水肿变化.术后15d,取下各组角膜植片做病理切片HE染色观察各组植片的角膜后弹力层变化及其上的细胞分布情况.结果:实验组角膜植片的内皮面长满培养的自体血管内皮细胞.病理切片显示,生长的细胞呈单层分布,内皮面未见明显的后弹力膜样物质形成;实验对照组角膜植片高度增厚,内皮面无细胞生长和后弹力膜样物质形成;空白对照组角膜植片内皮面可见明显的后弹力层,其上可见单层细胞分布.结论:血管内皮细胞具有一定的角膜内皮细胞样功能,但不能产生角膜后弹力层样物质.     

角膜内皮板层移植术治疗角膜内皮病变的初步报告

探讨角膜内皮板层移植术 (endotheliallamellarkeratoplasty ,ELK)治疗角膜内皮病变的临床效果。方法 :对 6例 ( 6眼 )因角膜内皮病变导致的角膜水肿、混浊患者施行了ELK术。其中 ,白内障术后大泡性角膜病变 2例 ,Fuchs角膜内皮营养不良 1例、外伤性角膜内皮失代偿 3例。用 6 0～ 7 5mm环钻切取前 1/ 2厚度供眼板层角膜片 ,保留后 1/ 2厚度 ,包括后基质、后弹力层和内皮细胞层的后板层角膜片。用比供体角膜片小 0 2 5～ 0 5mm的环钻钻切患眼角膜 ,深度达 1/2厚度 ,用角膜板层刀剖切下前板层备用 ,再钻切后板层角膜。将异体后基质角膜植片和自体前基质角膜植片重叠用 10 / 0尼龙线连续缝合。术毕结膜下注射庆大霉素和地塞米松 ,术后局部滴环孢霉素。随访 6～ 15个月。结果 :植片平均上皮化时间 6 5天 ,无新生血管侵入异体后基质植片 ,5例植片透明 ,1例排斥反应。裸眼视力 0 0 8～ 0 3 ,1例因白内障需进行手术 ,2例分别因原有的青光眼和老年性黄斑变性而视力不能矫正 ,1例层间积液 (粘弹剂 )经冲洗而消失。结论 :ELK具有植片上皮化时间短、水肿消失快、手术反应轻、排异反应率低等特点 ,对治疗内皮失代偿的病变是一种较理想的替代手术。     

体外培养角膜内皮细胞移植的实验研究

目的　探讨体外培养角膜内皮细胞移植的手术方法及移植后在活体的生理功能。方法　植片 :以直径 7 5mm、厚 10 0 μm、冷冻脱水保存的猪角膜后弹力膜 (Descemet′smembrane ,DM ) /基质为载体 ,原代接种兔角膜内皮细胞 ,体外培养 7～ 10d ,用于移植。受眼 :新西兰兔 3 0只 ( 3 0眼 ) ,实验组 2 0眼 ,对照组 10眼 ,全角膜范围去除术眼内皮细胞 ,5周后施行手术 ;做直径 9mm、3 / 4角膜厚的带蒂前层角膜瓣并掀置一侧 ,再用直径 7 2 5mm的环钻钻去中央后层角膜 ,形成植床 ;将植片置于植床 ,8-0可吸收线间断缝合 ,10 -0尼龙线间断缝合前层角膜瓣 ,术后观察 1～ 12个月。结果　术后角膜持续透明 6个月 14眼 ( 14 / 18、 77% ) ,12个月 8眼 ( 8/ 14、 5 7% ) ;术后 6个月内皮细胞密度 ( 193 4± 3 0 7)个 /mm2 ,角膜厚度平均为 ( 3 92± 3 9) μm。 结论　以异种DM /基质为载体培养的兔角膜内皮细胞 ,行同种异体移植后 ,能够在活体上成活 ,并具有正常内皮细胞的生物学功能 ,维持角膜透明 ,深板层角膜内皮移植术是体外培养内皮细胞移植的一种有效术式。     

Descemet's stripping with endothelial keratoplasty in 200 eyes: Early challenges and techniques to enhance donor adherence

PURPOSE: To describe early challenges and techniques to promote donor tissue adherence in Descemet's stripping with endothelial keratoplasty (DSEK). SETTING: Price Vision Group, Indianapolis, Indiana, USA. METHODS: The first 200 consecutive cases of DSEK performed by a single surgeon were analyzed retrospectively. Follow-up was 7 to 20 months for 124 eyes and 2 to 6 months for 76 eyes. The surgical technique consisted of stripping Descemet's membrane and endothelium from the recipient's central cornea and transplanting an 8.0 to 9.0 mm disc of donor endothelium and posterior stroma through a 5.0 mm incision, with sutures used only to close the incision. RESULTS: The most frequent challenge was inadequate donor attachment. Using techniques to remove fluid from the donor-recipient graft interface, the donor detachment rate in the last 64 cases was 6%, with half attributable to patient eye rubbing. Detached grafts were reattached by injecting an air bubble to press the donor against the recipient cornea. There were 7 primary graft failures, with only 1 occurring in the second 100 cases, which primarily used microkeratome-dissected donor tissue. Other complications were infrequent and included pupillary block glaucoma (1), aqueous misdirection syndrome (1), and cataract development in 2 of 27 phakic eyes. The DSEK procedure was performed safely before and after laser in situ keratomileusis (1 each). CONCLUSIONS: Early outcomes in the initial 200 consecutive DSEK procedures suggest the technique provides significant advantages over penetrating keratoplasty, including more rapid healing, more predictable refractive outcomes, and better retention of corneal strength and integrity. Although donor adherence was more challenging, DSEK was technically easier and should be less traumatic to anterior chamber structures than earlier posterior grafting techniques.     

Outcomes of endothelial keratoplasty with descemetorhexis (DSEK)

PURPOSE: Analysis of morphologic and functional outcomes of endothelial keratoplasty with descemetorhexis technique for recipient Descemet's membrane removal (DSEK). MATERIAL AND METHODS: We analyzed patients treated for chronic endothelial dysfunction with DSEK technique. For the study 12 patients (12 eyes) with follow up at least 9 months, were qualified. Study group consisted of 9 women and 3 men, in age from 53 to 83 years, mean 72.9 +/- 7.82 years. All surgery were performed by one surgeon (EW). Anterior chamber was opened through 5 mm wide and 3 mm long sclero-corneal tunnel. Before descemetorhexis incision points on the endothelial side of cornea were done with radio-frequency diathermy. Descemet's membrane stripping was done with the forceps. Endothelial grafts were fixed with anterior chamber by air tamponade. We analyzed postoperative visual acuity (on Snellen's charts), corneal transparency, endothelial cell density, total central corneal thickness and endothelial button (with OCT Visante), and complications of the surgery. RESULTS: 9 months postoperatively VA ranged from 0.1 to 0.5 (mean 0.28 +/- 0.15), BCVA ranged 0.1-0.9 (mean 0.43 +/- 0.30). Endothelial cell density ranged from 982 to 2781 cells per square millimeter (mean 1848.5 +/- 550.7). Total central corneal thickness ranged from 642 to 998 microm (mean 791.6 +/- 38.0 microm) before surgery and from 536 to 789 microm (mean 645 +/- 61.3 microm) 12 months postoperatively. Total central thickness of the endothelial graft 12 months postoperatively ranged from 42 to 163 microm (mean 89.1 +/- 38.2 microm). One penetrating keratoplasty was made for graft failure. Due to endothelial graft detachment or dislocation in anterior chamber, air tamponade was made in 5 cases with satisfactory final result. Only one case of the rejection was observed. CONCLUSIONS: Endothelial keratoplasty (DSEK) is safe and effective procedure in treatment of the endothelial cell dysfunction. Surgery supported by descemetorhrexis is easy and quick and results in smooth endothelial graft bed. The DSEK technique decreases surgery time and number of corneal graft dislocations.     

无缝线深板层角膜内皮移植术的研究进展

角膜内皮失代偿可严重影响视力,以往多采用的穿透性角膜移植手术(PKP)具有术后高度散光、移植片排斥等并发症,严重限制了术后视力的提高.如果能够单纯地进行后弹力层和内皮细胞层的移植,将减少手术操作所带来的受体角膜损伤并能更好地恢复术后视力.近年来,无缝线深板层角膜内皮移植手术的优点已逐渐获得公认;其中深板层角膜内皮细胞移植手术(DLEK)手术难度较大,限制了其在临床的广泛开展.而通过剥除受体角膜的后弹力层和内皮层来制作植床的角膜内皮移植手术即角膜后弹力层剥除内皮细胞移植手术(DSEK)已经取得了较好的手术效果.本文归纳、分析了DSEK的手术方法、效果及并发症等.     

利用后弹力层撕除术建立兔眼角膜内皮失代偿模型的评估

目的利用后弹力层撕除术建立一种新的角膜内皮失代偿模型以便更好地了解该手术的组织反应。方法根据手术方法的不同将40只新西兰成年兔平均分为4组：角膜内皮刮除组、后弹力层撕除组、后弹力层撕除角膜内皮移植术（DSEK）组及DSEK供体组;右眼为手术眼。每组定期通过角膜内皮活体染色,眼前节照相和UBM至少观察2个月。结果后弹力层撕除组角膜始终保持混浊,角膜内皮刮除组和DSEK组角膜逐渐透明,角膜厚度逐渐降低。活体染色显示角膜后弹力层撕除组术后2个月仍无角膜内皮生长。结论后弹力层撕除术建立的角膜内皮失代偿模型显示了后弹力层撕除后角膜内皮愈合过程,可用于角膜内皮移植的研究。     

Diagnosis of residual Descemet's membrane after Descemet's stripping endothelial keratoplasty with anterior segment optical coherence tomography

We present a patient with residual Descemet's membrane diagnosed by anterior segment optical coherence tomography (AS-OCT) after Descemet's stripping endothelial keratoplasty (DSEK). Postoperatively, persistent partial corneal edema and interface fluid without dislocation of the donor button were observed. No improvement of interface fluid was found during the follow-up period. A primary donor graft failure was diagnosed within 4 months, and the patient was regrafted with penetrating keratoplasty. Pathology examination of the specimen revealed the presence of residual Descemet's membrane in the recipient corneal button, confirmed using AS-OCT imaging. This case report demonstrates that inadequate Descemet's stripping in the recipient button could be a potential cause of DSEK failure; AS-OCT is a useful and noninvasive instrument for diagnosing and monitoring this post-DSEK complication.     

Histologic evidence of retained fetal layer of the descemet membrane after presumed total removal for endothelial keratoplasty: a possible cause for graft failure

PURPOSE: This is, to our knowledge, the first report of histology after failed Descemet-stripping endothelial keratoplasty (DSEK) surgery in a patient. We describe the interface histology found in a case of donor nonadherence and subsequent graft failure in a patient after DSEK. METHODS: An 83-year-old woman with a history of Fuchs dystrophy underwent DSEK surgery and subsequently underwent full-thickness penetrating keratoplasty (PKP) because of nonadherence of the donor disc and presumed graft failure. Specimens from the initial stripping of the Descemet membrane, the failed donor disc, and the full thickness of the patient's remaining cornea containing the recipient bed after her DSEK and PKP procedures were histologically evaluated by light microscopy. RESULTS: Microscopic examination of the initial stripped recipient Descemet membrane revealed a "delamination" of the Descemet membrane involving the fetal layer. After PKP, histopathologic study of the recipient button revealed residual fetal Descemet membrane retained on the recipient DSEK interface. Examination of the failed donor disc showed healthy tissue. CONCLUSIONS: In DSEK surgery, there are multiple reasons that the donor graft button may fail to adhere to the recipient posterior corneal surface. In this instance, histologic study revealed that the Descemet membrane was split by the stripping, and the fetal layer of the Descemet membrane was retained on the central part of the patient's posterior cornea. Despite histologically normal donor endothelial cells, the inability of the donor tissue to adhere may have been caused by the coating of the central recipient bed with retained fetal Descemet membrane.     

Experience and 12-month results of descemet-stripping endothelial keratoplasty (DSEK) with a small-incision technique

PURPOSE: To report our clinical experience and 12-month results of small-incision Descemet-stripping endothelial keratoplasty (DSEK). METHODS: Prospective study of 11 eyes of 9 patients who had DSEK. The DSEK technique consisted of stripping the Descemet membrane and endothelium from the recipient cornea. The donor button was prepared by manual dissection and inserted through a 5-mm incision. Air, sulfur hexafluoride (SF6), or perfluoropropane (C3F8) was used both at the end of surgery and in subsequent dislocations to promote donor tissue adherence. RESULTS: Mean age was 79.6 years (range, 66-91 years), and minimum follow-up was 12 months (range, 12-18 months). Nine eyes had donor tissue dislocation postoperatively, 8 of which received intervention with either SF6 (n = 4) or C3F8 (n = 4). In 1 patient with repeat dislocation, Tisseel glue in combination with C3F8 was used. Preoperative best-corrected visual acuity (BCVA) was 6/24 or worse in all patients. Postoperatively, 6/11 eyes (55%) achieved a BCVA of 6/12 at last follow-up. Mean preoperative cylinder was 1.875 +/- 0.906 D (range, 1-3 D) and postoperatively was 1.5 +/- 1.157 D (range, 0.25-3.25 D). At last follow-up, 6 grafts were clear and 5 had failed. Mean endothelial cell count in the clear grafts at 12-month follow-up was 1078 +/- 507 cells/mm. CONCLUSIONS: DSEK provided excellent refractive and reasonable visual outcomes in our limited series, but there were frequent problems with dislocation of the donor tissue, and the graft failure rate was high. The graft failures may be linked to excessive endothelial damage, and the high dislocation rate may be linked to not filling the anterior chamber totally with air after insertion of the donor. Further development of the procedure is necessary.     

Transplantation of corneal endothelium with Descemet's membrane using a hyroxyethyl methacrylate polymer as a carrier

AIMS: To evaluate the histology and function of Descemet's membrane transplanted with intact endothelium. METHODS: Japanese white rabbits and human eyebank eyes were used as donors and recipients of Descemet's membrane transplantation. Donor endothelium was hydrodissected by injecting indocyanine green from a limbal incision, and then processed as a corneal scleral button. A 6 mm diameter donor sheet was trephined, and folded in half using a 6 mm diameter polymer as a carrier. Recipient endothelium was also hydrodissected from the limbus using trypan blue to stain the Descemet's membrane. Continuous curvilinear descemetorhexis (CCD) was performed to remove a circular section of the Descemet's membrane using a 27 gauge cystotome. Donor tissue was inserted into the anterior chamber through a 5 mm limbal incision and apposed to the host stroma. Polymers were removed following transplantation. Similar surgical procedures were performed in both rabbits and eyebank eyes. Haematoxylin eosin stains were performed after 28 days in rabbits, and eyebank eyes were fixed immediately following surgery for endothelial cell counts. RESULTS: Rabbit control eyes demonstrated stromal oedema caused by loss of Descemet's membrane, whereas transplanted eyes had clear corneas. The mean (standard deviation) pachymetry of operated eyes was 376.6 (SD 32.5) mum compared with 389.6 (SD 25.1) mum in the unoperated eye. Mean endothelial density immediately following surgery in eyebank eyes was 2749 (SD 288) cells/mm(2). CONCLUSIONS: Transplantation of Descemet's membrane by CCD produces a functional graft with an optically clear interface similar to control cornea.