Interconnections between diabetic corneal neuropathy and diabetic retinopathy:diagnostic and therapeutic implications

Diabetic corneal neuropathy and diabetic retinopathy are ocular complications occurring in the context of diabetes mellitus.Diabetic corneal neuropathy refers to the progressive damage of corneal nerves.Diabetic retinopathy has traditionally been considered as damage to the retinal microvasculature.However,growing evidence suggests that diabetic retinopathy is a complex neurovascular disorder resulting from dysfunction of the neurovascular unit,which includes both the retinal vascular structures and neural tissues.Diabetic retinopathy is one of the leading causes of blindness and is frequently screened for as part of diabetic ocular screening.However,diabetic corneal neuropathy is commonly overlooked and underdiagnosed,leading to severe ocular surface impairment.Several studies have found that these two conditions tend to occur together,and they share similarities in their pathogenesis pathways,being triggered by a status of chronic hyperglycemia.This review aims to discuss the interconnection between diabetic corneal neuropathy and diabetic retinopathy,whether diabetic corneal neuropathy precedes diabetic retinopathy,as well as the relation between the stage of diabetic retinopathy and the severity of corneal neuropathy.We also endeavor to explore the relevance of a corneal screening in diabetic eyes and the possibility of using corneal nerve measurements to monitor the progression of diabetic retinopathy.

An innovative bio-engineering retaining structure for supporting unstable soil

The paper presents a new prefabricated bio-engineering structure for the support of unstable soil.This prefabricated structure is made of a steel frame which is completely filled with soil and a face made of tree trunks among which scions or autochthonous bushes are planted.Due to the difficulties in interpreting the complex interaction between soil and structure during the installation and lifetime,an in situ test was carried out in order to evaluate the state of stress in the steel frame and to understand the global behavior of the structure under service loads.On the basis of the obtained results,a procedure for checking the structure safety was proposed and discussed.An easy design method was developed during the research.Moreover,the use of this type of prefabricated structure shows several advantages,such as good performances in terms of stabilizing effects,and easy assembly and transport.

Torrent Control and Stabilization through Bio-engineering Measures in North Western Himalayan Region

The study revealed that low cost bio-engineering measures using local grass （Saccharum munja）, shrubs （Vitex negundo and Ipomea spp.） and trees （Acacia nilotica and Acacia catechu） along with loose boulder structures （spurs, check dams and gully plugs） of suitable design and dimensions were very effective in channelizing the torrent water flow towards central line and its stabilization. In the catchment, small to medium sized gullies were treated with gully plugging by erecting loose boulder check dams along with suitable vegetative barriers ofSaccharum munja and Ipomea spp. to stop their further advancement. Different treatments of these combinations trapped the sediment to the tune of 5-15 tonnes and it was stabilized at the spur tails. In this, attractive type spur trapped the maximum sediment. The D-50 analysis of sediment deposited was also carried out and the value varied from 3.1-3.7 mm, implying deposition of higher percentage of finer fertile soil proportion and its stabilization. The mechanical as well as vegetative measures helped in the channelization of water course towards the central line to the tune of 10-80 m. The stream banks were stabilized by plantations and put to use under agro forestry systems. Different treatments in catchment, with regard to their efficacy to reduce runoff, ground water recharge, sediment and channel morphology resulted in reclamation of 43 ha area of the torrent bed.

Clinical associations of corneal neuromas with ocular surface diseases

Corneal neuromas,also termed microneuromas,refer to microscopic,irregula rly-shaped enlargements of terminal subbasal nerve endings at sites of nerve damage or injury.The formation of corneal neuromas results from damage to corneal nerves,such as following corneal pathology or corneal or intraocular surge ries.Initially,denervated areas of sensory nerve fibers become invaded by sprouts of intact sensory nerve fibers,and later injured axons regenerate and new sprouts called neuromas develop.In recent years,analysis of corneal nerve abnormalities including corneal neuromas which can be identified using in vivo confocal microscopy,a non-invasive imaging technique with microscopic resolution,has been used to evaluate corneal neuropathy and ocular surface dysfunction.Corneal neuromas have been shown to be associated with clinical symptoms of discomfort and dryness of eyes,and are a promising surrogate biomarker for ocular surface diseases,such as neuropathic corneal pain,dry eye disease,diabetic corneal neuropathy,neurotrophic keratopathy,Sjogren's syndrome,bullous keratopathy,post-refra ctive surgery,and others.In this review,we have summarized the current literature on the association between these ocular surface diseases and the presentation of corneal microneuromas,as well as elaborated on their pathogenesis,visualization via in vivo confocal microscopy,and utility in monitoring treatment efficacy.As current quantitative analysis on neuromas mainly relies on manual annotation and quantification,which is user-dependent and labor-intensive,future direction includes the development of artificial intelligence software to identify and quantify these potential imaging biomarkers in a more automated and sensitive manner,allowing it to be applied in clinical settings more efficiently.Combining imaging and molecular biomarkers may also help elucidate the associations between corneal neuromas and ocular surface diseases.

Knockout of TMEM206 in mice associated with a loss of corneal transparency

AIM:To investigate the role of transmembrane protein 206(TMEM206)in corneal edema in mice by knockout the TMEM206 gene using CRISPR/Cas9 editing technology.METHODS:TMEM206-knockout mice were generated using the CRISPR-Cas9 system.Variations in ophthalmic pathology were observed using slit lamp microscope and optical coherence tomography(OCT),intraocular pressure(IOP)was measured using a TonoLab Rebound Tonometer,and the ultrastructure of the corneal was observed using a transmission electron microscope.RESULTS:Corneal opacity was observed in 4/18 homozygous TMEM206^(-/-)mice whereas a similar change was not observed in heterozygous TMEM206^(+/-)mice and wild-type littermates.OCT examination showed that the mean central cornea thickness was 125±5.4μm in 4 homozygous TMEM206^(-/-)mice developed corneal edema and 115±1.2μm in wild-type mice(t=3.468,P<0.05)at 43wk.The mean IOP was 12.08±0.07 mm Hg in four right eyes with corneal edema and 12.03±0.03 mm Hg in three normal left eyes(P>0.05).Transmission electron microscopy revealed a disruption in the organization of the collagen fibrils in the central part of the cornea in homozygous TMEM206^(-/-)mice.CONCLUSION:TMEM206 is associated with corneal edema which caused organizational disruption of collagen fibrils in corneas of mice.

Double intrastromal corneal ring segment implantation: a new approach for improved clinical outcomes in keratoconus patients

AIM:To evaluate the clinical outcomes after subsequent implantation of a new intrastromal corneal ring segment(ICRS)model followed by an additional short-arc ICRS implant in keratoconus patients.METHODS:This retrospective single-arm cohort study evaluated 25 eyes of 21 keratoconus patients implanted with the new ICRS followed by 140-arch length ICRS(140-ICRS)implantation.Uncorrected distance visual acuity(UDVA,logMAR),corrected distance visual acuity(CDVA,logMAR),sphere,astigmatism,keratometry,spherical equivalent(SE),and asphericity were compared preoperatively and postoperatively after both ICRS implantation.RESULTS:The average follow-up time after 140-ICRS implantation was 6.40±2.20mo.The mean preoperative UDVA improved from 1.27±0.14 preoperative to 0.52±0.26 after both ICRS implantation(P=0.03).The mean sphere value reduced from-5.34±2.74 preoperatively to-2.06±1.84 postoperatively(P<0.001)after the first ICRS implantation and decreased to-0.59±1.54 postoperatively(P<0.001)after 140-ICRS implantation.The mean preoperative astigmatism was-3.72±1.56 and improved to-2.82±1.08 after the first ICRS implantation,and following the 140-ICRS implantation,the mean astigmatism was-1.37±0.67(P=0.001).The SE and asphericity changes were statistically significant(P<0.001).The researchers did not find intraoperative or postoperative complications for both procedures.CONCLUSION:The combination of 2 different ICRSs can efficiently regularize the cornea,reduce the SE,and improve visual acuity in selected keratoconus patients.

The Limbal Niche and Its Role in Maintaining Corneal Regeneration

In recent years, stem cells have been a focal point in research designed to evaluate the efficacy of ophthalmologic therapies, specifically those for corneal conditions. The corneal epithelium is one of the few regions of the body that maintains itself using a residual stem cell population within the adjacent limbus. Stem cell movement has additionally captivated the minds of researchers due to its potential application in different body regions. The cornea is a viable model for varying methods to track stem cell migratory patterns, such as lineage tracing and live imaging from the limbus. These developments have the potential to pave the way for future therapies designed to ensure the continuous regeneration of the corneal epithelium following injury via the limbal stem cell niche. This literature review aims to analyze the various methods of imaging used to understand the limbal stem cell niche and possible future directions that might be useful to consider for the better treatment and prevention of disorders of the cornea and corneal epithelium. .

Surgical approaches to correct corneal astigmatism at time of cataract surgery: a mini-review

Among refractive errors,astigmatism is the most common optical aberration,where refraction changes in different meridians of the eye.It causes blurred vision at any distance and includes corneal,lenticular,and retinal astigmatism.Cataract surgery used to cause a progressive increase in the pre-exisiting corneal astigmatism because of creating a surgically induced astigmatism,for example,a large size surgery incision.The development of surgical techniques during last decades has made cataract surgery interchange to treat preoperative corneal astigmatism at time of surgery.Nowadays,three surgical approaches can be used.By placing a sutureless clear corneal incision on the steep meridian of the cornea,a preoperative corneal astigmatism less than 1.0 D can be corrected.Single or paired peripheral corneal relaxing incisions(PCRIs)provide 1.0-3.0 D corneal astigmatism correction.PCRIs are typically used for treating 1.0-1.5 D of regular corneal astigmatism,if more than 2.0 D,the risk of overcorrection and irregular astigmatism is increased.When toric intraocular lenses(IOLs)are unavailable in markets,PCRIs are still a reasonable option for patients with up to 3.0 D of pre-existing corneal astigmatism.Toric IOLs implantation can correct 1.0-4.5 D of corneal astigmatism.Several IOLs are approved to correct a high degree of corneal astigmatism with cylinder power up to 12.0 D.These approaches can be used alone or in combination.

Thiel-Behnke Corneal Dystrophy in a Young Man in Denmark—A Case Report

Background: This case report presents a case of bilateral Thiel-Behnke corneal dystrophy in Denmark. Thiel-Behnke is an autosomal dominant inherited epithelial-stromal TGFBI dystrophy causing visual impairment. Methods and Results: This case study presents a 24-year-old Lithuanian man, with no previous ocular history, who had experienced slowly progressive visual impairment since his childhood. He was examined at the Department of Ophthalmology at Vejle Hospital and Aarhus University Hospital, where he was diagnosed with bilateral Thiel-Behnke corneal dystrophy. Histology confirmed the diagnosis. A lamellar corneal transplantation was performed in the right eye;however, due to epithelial growth under the corneal graft, it was later decided to redo the operation. Following the operations, the patient experienced a visual improvement in best corrected visual acuity (BCVA) from 0.1 (20/25 Snellen equivalent) to 0.3 (20/40 Snellen equivalent) in his right eye. Conclusions: This case of Thiel-Behnke corneal dystrophy is to our knowledge the first reported case in Denmark.

REG增强的脱细胞猪角膜/聚甲基丙烯酸羟乙酯原位一体式全层复合人工角膜

背景:目前用于全层移植的人工角膜缺乏生物活性及力学适配性,组合式人工角膜存在镜柱和周围组分间的界面问题。目的:在脱细胞猪角膜原位固化制备具有多肽增强、匹配自然角膜机械强度、良好透光性的一体式全层人工角膜。方法:使用非离子型脱细胞试剂Triton X-100与超声冻融及超级核酸酶相结合的方法制备脱细胞猪角膜,将聚甲基丙烯酸羟乙酯单体与光引发剂同时引入脱细胞猪角膜中,通过紫外滤光片遮住除中心区域以外的部分,使用275 nm紫外光引发中央区域聚合,除去未反应的单体及引发剂后得到中央光学区,同理在后板层固化隔水区,最后引入REG活性多肽,得到原位一体式全层人工角膜,表征人工角膜的物理性能、力学性能、透光性、降解性能及体内外生物相容性。结果与结论:①实验在脱细胞猪角膜的中央区域采用聚甲基丙烯酸羟乙酯原位构建了一个具有聚合物和胶原纤维共存的光学区,扫描电镜下可见人工角膜的上表面较为粗糙且轮廓不规则,具有明显的凹陷和突起结构,下表面相对光滑;该人工角膜具有接近于天然角膜的力学性能,光学区透光率达到自然角膜的80%,浸泡于含胶原酶的PBS无菌溶液中可较好地保留固化光学区和隔水区,维持角膜的基本结构;该人工角膜具有良好的细胞相容性,能够为细胞提供适宜的黏附生长环境,有利于角膜上皮细胞的迁移和黏附,促进血管内皮细胞的生长和新生血管的形成,促进上皮化过程;人工角膜植入SD大鼠皮下12周后具有良好的生物相容性和安全性,可降低植入初期的急性炎症反应;②结果表明,实验制备的一体式全层人工角膜具有作为全层人工角膜支架材料的潜力。

生物材料促进角膜碱烧伤修复的作用机制和应用途径

背景:在角膜碱烧伤治疗中,传统治疗方法存在多种局限,尤其在控制炎症、预防新生血管形成和抑制角膜瘢痕化方面表现不佳。天然材料、合成材料或复合材料为治疗提供了多元化的选择,然而生物材料促进角膜碱烧伤修复的相关机制尚未形成系统深入的认识。目的:对目前生物材料促进角膜碱烧伤修复的国内外研究进行梳理,综述生物材料修复角膜碱烧伤的机制及其应用途径。方法:第一作者以“角膜,碱烧伤,羊膜,透明质酸,胶原,壳聚糖,高分子材料”“Amniotic membrane,Hyaluronic acid,Collagen,Chitosan,Polymer,Cornea,Alkali burn”为关键词在Pub Med、Web of Science、中国知网和万方文献数据库内检索,根据纳入标准和排除标准,最终纳入符合要求的76篇文献进行综述。结果与结论:(1)在角膜碱烧伤修复领域,羊膜、透明质酸、胶原、壳聚糖和可降解高分子材料等生物材料被广泛研究和应用,这些生物材料各有其特点和优缺点,在不同方面都有所突出。(2)首先,羊膜因含丰富的生物活性因子而被认为是最有前景的生物材料之一,其生物相容性良好,并且能够调节角膜炎症反应,但是存在供体短缺和易感染疾病的问题。(3)透明质酸具有良好的保湿性和生物相容性,并且能够提高角膜细胞的生存率和增加角膜透明度。(4)胶原具有良好的生物相容性和支架结构,能够促进角膜细胞的黏附和增殖,促进角膜组织结构的重建。(5)壳聚糖具有良好的生物相容性和可降解性,可作为载体用于药物递送和细胞移植。(6)可降解高分子材料具有较好的降解可控性,可为角膜碱烧伤的修复提供良好的支持和递送平台,但其稳定性和生物相容性仍需进一步研究。(7)综合来看,目前还没有一种生物材料能够完全解决角膜碱烧伤的修复问题,每种生物材料都有其特定的适用场景和局限性。(8)未来的研究方向应该是通过进一步改进生物材料的性能和结构,探索更有效的组合应用方式,以及深入了解生物材料与角膜组织的相互作用机制,以提高角膜碱烧伤的治疗效果和患者的生活质量。

毛木耳种质资源表型性状遗传多样性分析及综合评价

为研究毛木耳种质资源表型性状变异分布和多样性特征,分析性状间关系,筛选毛木耳评价指标和性状优异的种质,本研究以我国56份毛木耳种质为材料,对其18个表型性状进行精准鉴定,采用Shannon-Weaver多样性指数、变异系数等进行表型性状遗传多样性分析,综合运用相关性分析、聚类分析、主成分分析和逐步回归等方法对毛木耳种质进行综合评价。研究结果表明,毛木耳种质资源遗传多样性指数为0.090~1.978,数量性状变异范围为4.00%~40.39%。大部分表型性状间存在不同程度的相关性,性状信息重叠。经聚类分析,在遗传相似系数0.47处,可以划分为5个类群。主成分分析将18个表型性状转化为7个主成分/综合因子,累计贡献率为74.75%。56份种质的主成分综合得分(F值)范围为-3.91~2.21,将毛木耳种质资源划分为6个群组,部分群组与聚类分析的类群重合。基于F值筛选出5份表型性状优良的种质,可进一步发掘利用。结合逐步回归分析方法,经综合评估筛选出8个表型性状,可作为毛木耳的综合评价关键性指标,分别为菌丝体(栽培种)菌棒颜色变化、鲜耳片腹面主要颜色、鲜耳片背面颜色、干耳片腹面颜色、干耳片背面颜色、耳片质地、子实体成熟期和鲜耳片长度。本研究为毛木耳种质资源高效发掘利用和新品种选育提供了重要依据。

眼前节研究的融合与统一

著名生物学家爱德华·威尔逊(Edward O Wilson)在其名作《一致性:知识的统一》(Consilience:The Unity of Knowledge)中提出跨学科整合与协调的必要性。他将融合定义为“知识的‘跳跃式结合',即通过事实的相互关联……创造出一个共同的解释基础。”文章的假设是,与基础生物医学研究需要来源于最新技术的数据几乎一样,整合现有知识同样极其重要。这涉及到解决相互矛盾的发现、减少“信息孤岛”、以及承认复杂的必要性。我们以角膜和晶状体作为我们假设的案例研究。具体来说,在这种视角下,我们讨论蛋白质聚集、氧化损伤和纤维化方面相互矛盾和碎片化的信息。这些研究领域与眼前节研究紧密相关。我们的目的是强调威尔逊的知识融合统一的迫切需要,从而增强严谨性和可重复性,最重要的是,促进对知识的深入理解,而不只是知道。

Evaluation of novel decellularizing corneal stroma for cornea tissue engineering applications

AIM:To develop a new decellularization method depended upon the natural corneal structure and to harvest an ideal scaffold with good biocompatibilities for corneal reconstruction.METHODS:The acellular cornea matrix (ACM) were prepared from de-epithelium fresh porcine corneas (DFPCs) by incubation with 100% fresh human sera and additional electrophoresis at 4℃. Human corneal epithelial cells (HCEs) were used for the cytotoxicity tests of ACM. ACM were implanted into the Enhanced Green Fluorecence Protein (eGFP) transgenic mouse anterior chamber for evaluation of histocompatibility.RESULTS:HE and GSIB4 results showed fresh porcine cornea matrix with 100% human sera and electrophoresis could entirely decellularize stromal cell without reducing its transparency. ACM has no cytotoxic effect ex vivo. Animal test showed there was no rejection for one month after surgery.CONCLUSION:These results provide a decellularizing approach for the study of corneal tissue engineering and had the broader implications for the field of biological tissue engineering in other engineered organ or tissue matrix.

A comparison of three methods of decellularization of pig corneas to reduce immunogenicity

·AIM: To investigate whether decellularization using different techniques can reduce immunogenicity of the cornea, and to explore the decellularized cornea as a scaffold for cultured corneal endothelial cells(CECs).Transplantation of decellularized porcine corneas increases graft transparency and survival for longer periods compared with fresh grafts.·METHODS: Six-month-old wild-type pig corneas were cut into 100-200 μm thickness, and then decellularized by three different methods: 1) 0.1% sodium dodecyl sulfate(SDS); 2) hypoxic nitrogen(N2); and 3) hypertonic NaCl. Thickness and transparency were assessed visually. Fresh and decellularized corneas were stained with hematoxylin/eosin(H&E), and for the presence of galactose-α1,3-galactose(Gal) and N-glycolylneuraminic acid(NeuGc, a nonGal antigen). Also, a human IgM/IgG binding assay was performed. Cultured porcine CECs were seeded on the surface of the decellularized cornea and examined after H&E staining.· RESULTS: All three methods of decellularization reduced the number of keratocytes in the stromal tissue by 】80% while the collagen structure remained preserved. No remaining nuclei stained positive for Gal or NeuGc, and expression of these oligosaccharides on collagen was also greatly decreased compared to expression on fresh corneas. Human IgM/IgG binding to decellularized corneal tissue was considerably reduced compared to fresh corneal tissue. The cultured CECs formed a confluent monolayer on the surface of decellularized tissue.· CONCLUSION: Though incomplete, the significant reduction in the cellular component of the decellularized cornea should be associated with a significantly reduced in vivo immune response compared to fresh corneas.

In vitro tissue engineering of lamellar cornea using human amniotic epithelial cells and rabbit cornea stroma

AIM:To reconstruct the lamellar cornea using human amniotic epithelial(HAE) cells and rabbit cornea stroma in vitro using tissue engineering technology.·METHODS:Human amnia taken from uncomplicated caesarean sections were digested by collagenase to obtain HAE cells,and the cells were cultured to proliferate.Rabbit corneal epithelial cells were removed by n-heptanol to make lamellar matrix sheets.The second passage of HAE cells were cultured on the corneal stroma sheets for 1 or 2 days,then transferred to an air-liquid interface environment to culture for 2weeks.Tissue engineered lamellar cornea(TELC)morphology was observed by Hematoxylin-eosin(HE)staining;its ultrastructure was observed by transmission electron microscopy(TEM) and scanning electron microscopy(SEM);corneal epithelial cell-specific keratin3 and keratin 12 were detected with immunofluorescence microscopy.·RESULTS:HAE cells grew on the rabbit corneal stroma,forming a monolayer after 1-2 days.About 4-5 layers of epithelial cells developed after 2 weeks of air-liquid interface cultivation,a result similar to normal corneal epithelium.Rabbit corneal stromal cells were significantly reduced after one week,then almost completely disappeared after 2 weeks.TEM showed desmosomes between the epithelial cells;hemidesmosomes formed between the epithelial cells and the basement membrane.SEM revealed that the HAE cells which grew on the lamellar cornea had abundant microvilli.The tissue-engineered cornea expressed keratin 3 and keratin 12,as detected by immunofluorescence assay.·CONCLUSION:Functional tissue-engineered lamellar corneal grafts can be constructed in vitro using HAE cells and rabbit corneal stroma.

Clinical correlates of common corneal neovascular diseases: a literature review

A large subset of corneal pathologies involves the formation of new vessels(neovascularization), leading to compromised visual acuity. This article aims to review the clinical causes and presentations of corneal neovascularization(CNV) by examining the mechanisms behind common CNV-related corneal pathologies, with a particular focus on herpes simplex stromal keratitis,contact lenses-induced keratitis and CNV secondary to keratoplasty. Moreover, we reviewed CNV in the context of different types of corneal transplantation and keratoprosthesis, and summarized the most relevant treatment available so far.

Effect of corneal light scatter on vision: a review of the literature

The cornea is the transparent connective tissue window at the front of the eye.The physiological role of the cornea is to conduct external light into the eye,focus it,together with the lens,onto the retina,and to provide rigidity to the entire eyeball.Therefore,good vision requires maintenance of the transparency and proper refractive shape of the cornea.The surface structures irregularities can be associated with wavefront aberrations and scattering errors.Light scattering in the human cornea causes a reduction of visual quality.In fact,the cornea must be transparent and maintain a smooth and stable curvature since it contributes to the major part of the focusing power of the eye.In most cases,a simple examination of visual acuity cannot demonstrate the reduction of visual quality secondary light scattering.In fact,clinical techniques for examining the human cornea in vivo have greatly expanded over the last few decades.The measurement of corneal back scattering qualifies the degree of corneal transparency.The measurement of corneal forward-scattering quantifies the amount of visual impairment that is produced by the alteration of transparency.The aim of this study was to review scattering in the human cornea and methods of measuring it.

Relationship between contrast sensitivity and corneal shape following overnight orthokeratology

AIM: To evaluate the relationship between contrast sensitivity(CS) and corneal shape following overnight orthokeratology(OK). METHODS: We conducted a retrospective clinical study of 80 lens-wearing myopia patients, all of whom had undergone OK and had been evaluated by Orbscan II topography. We measured the surface irregularity index(SIRI) of corneal topography at 3 and 5 mm, the size of the flattened central corneal curvature of OK lens(zone A), the size of the cornea altered by OK lens(zone B), the size of the pupillary area at the corneal level(zone C), the area of crossover between zones A and C(zone AC), the area of crossover between zones B and C(BC), the ratio of BC to B(BC/B), and the ratio of AC to C(AC/C). CS was evaluated using the CSV-1000 with spatial frequencies of 3, 6, 12, and 18 cycles/degree(CPD). RESULTS: Multiple correlation analyses indicated significant negative correlations between CS, zone C, BC/B, and 3-mm SIRI(all P<0.01). There were no significant differences between CS, zone B, AC/A, or 5-mm SIRI(P=0.60, 0.94 and 0.11, respectively). Zone C was negatively correlated with 3, 6, 12, and 18 CPD. 5-mm SIRI were negatively correlated with 6, 12, and 18 CPD. BC/C was negatively correlated with 6 and 18 CPD. AC/C was positively correlated with 3 CPD. CONCLUSION: Zone C, 3-mm SIRI and BC/B affect the CS following overnight OK.

Evaluating alternative stem cell hypotheses for adult corneal epithelial maintenance

In this review we evaluate evidence for three different hypotheses that explain how the corneal epithelium is maintained. The limbal epithelial stem cell(LESC)hypothesis is most widely accepted. This proposes that stem cells in the basal layer of the limbal epithelium, at the periphery of the cornea, maintain themselves and also produce transient(or transit) amplifying cells(TACs). TACs then move centripetally to the centre of the cornea in the basal layer of the corneal epithelium and also replenish cells in the overlying suprabasal layers. The LESCs maintain the corneal epithelium during normal homeostasis and become more active to repair significant wounds. Second, the corneal epithelial stem cell(CESC) hypothesis postulates that, during normal homeostasis, stem cells distributed throughout the basal corneal epithelium, maintain the tissue. According to this hypothesis, LESCs are present in the limbus but are only active during wound healing. We also consider a third possibility, that the corneal epithelium is maintained during normal homeostasis by proliferation of basal corneal epithelial cells without any input from stem cells. After reviewing the published evidence, we conclude that the LESC and CESC hypotheses are consistent with more of the evidence than the third hypothesis, so we do not consider this further. The LESC and CESC hypotheses each have difficulty accounting for one main type of evidence so we evaluate the two key lines of evidence that discriminate between them. Finally, we discuss how lineage-tracing experiments have begun to resolve the debate in favour of the LESC hypothesis. Nevertheless, it also seems likely that some basal corneal epithelial cells can act as long-term progenitors if limbal stem cell function is compromised. Thus, this aspect of the CESC hypothesis may have a lasting impact on our understanding of corneal epithelial maintenance, even if it is eventually shown that stem cells are restricted to the limbus as proposed by the LESC hypothesis.