Computational modeling of mechanical anisotropy in the cornea and sclera

PURPOSE: To determine the biomechanical deformation of the cornea resulting from tissue cutting and removal by use of a new computational model and to investigate the effect of mechanical anisotrophy resulting from the fibrillar architecture. SETTING: Department of Mechanical Engineering, Stanford University, Stanford, California, USA. METHODS: A mathematical model for a typical lamella that explicitly accounts for the strain energy of the collagen fibrils, extrafibrillar matrix, and proteoglycan cross-linking was developed. A stromal model was then obtained by generalized averaging of the lamella properties through the stromal thickness, taking into account the preferred orientations of the collagen fibrils, which were obtained from x-ray scattering data. RESULTS: The model was used to predict astigmatism induced by a tunnel incision in the sclera, such as is used for cataract extraction and intraocular lens implantation. The amount of induced cylinder was in good agreement with published clinical data. Results show it is important for the model to incorporate preexisting corneal physiological stress caused by intraocular pressure. CONCLUSIONS: The mathematical model described appears to provide a framework for further development, capturing the essential features of mechanical anisotropy of the cornea. The tunnel incision simulation indicated the importance of the anisotropy in this case.     

Melatonin receptor expression in the cornea and sclera

The scornea and sclera have been shown to exhibit circadian rhythms in cellular proliferation, wound healing and extracellular matrix synthesis. The distribution of melatonin Mel1a and Mel1c receptors was examined in the cornea and sclera of the Xenopus laevis eye in order to determine whether melatonin may potentially influence the growth and/or development of these ocular tissues. Sections of adult X. laevis eyes were analyzed by immunocytochemistry and confocal microscopy, using antibodies prepared against specific peptide sequences of the Xenopus Mel1a and Mel1c receptor proteins. Antibodies were pre- incubated with their appropriate antigenic peptides to control for non-specific labelling. Analysis of the distribution of Mel1a and Mel1c receptor immunoreactivity in the Xenopus eye revealed that both the Mel1a and Mel1c receptors were located in the outer fibrous layer (OFL) of the sclera, with Mel1c labelling being the most prominent. Similarly, Mel1a and Mel1c (Mel1c mostly) were also located in cells of the inner fibrous layer (IFL) with Mel1c being most abundant. The chondrocytes of the cartilaginous layer also appeared to express Mel1a, Mel1c, or both receptors. Both Mel1a and Mel1c receptor immunoreactivity were observed in the corneal epithelium and endothelium. Whereas the Mel1a antibody labelled the entire corneal epithelial layer, the Mel1c antibody labelled only the most superficial layer of epithelial cells. Cell processes of fibroblasts of the corneal stroma were immunoreactive for either Mel1a or Mel1c receptors. The identification of Mel1a and Mel1c receptors in restricted distributions in the cornea and sclera suggests that melatonin may play a role in the cellular physiology of these ocular tissues.     

Electron microscopic study of distribution of proteoglycans in bovine cornea and sclera.

To study differences in the distribution of proteoglycans and their relationships to collagen fibrils in the cornea and sclera, bovine cornea and sclera were examined histochemically using the ruthenium red (RR) staining method. RR-positive granules (30 nm in diameter) were present in association with fine filamentous materials (3 nm in diameter and 30-100 nm in length) in the interfascicular spaces of collagen bundles in both the corneal stroma and sclera. The amount of these materials was smaller in the sclera than in the cornea. The characteristic band-like arrangement of RR-positive granules connected by filamentous materials at intervals of 80-100 nm was found only in the cornea. In enzyme digestion experiments, tissue sections were treated by chondroitinase ABC, AC, and keratanase before RR staining. The RR-positive granules and their associated filamentous materials were darkly stained after chondroitinase AC or keratanase digestion, but displayed markedly lighter staining after chondroitinase ABC digestion. These results indicate that RR-positive granules and filamentous materials contain dermatan sulfate proteoglycan.     

异体巩膜用于无眼球结膜囊成形术的实验研究

目的　为异体巩膜结膜囊成形用于临床探索科学依据。方法　将经酒精灭活处理的兔保存巩膜进行兔部分结膜囊成形及全结膜囊成形术 ,对巩膜移植后的组织学变化进行光镜 ,电镜系统观察。结果　无论是光镜还是电镜均显示植入后 1～ 2周出现细胞反应阶段 ,2周～ 2个月为细胞浸润和纤维替代阶段 ,植入后 2～ 3个月出现瘢痕组织形成阶段。即异体巩膜在结膜囊成形术中开始作为支架 ,此后随着自身的溶解 ,同时也诱导自体新生结缔组织移入 ,最终被结缔组织完全替代 ,形成新的结膜囊。结论　异体巩膜用于结膜囊成形术方便、安全、可行     

Some characteristics of the c-wave of ERGs recorded by a pair of electrodes on the cornea and sclera

Summary Light-evoked responses of the rabbit retina in situ were recorded between the electrode on the longitudinal line of the nasal side (positive) and the electrode on the opposite longitudinal line of the temporal side (negative). The c-wave was negative and the a-, b-wave was reversed when the negative (temporal) electrode was closer to the corneal center than the positive (nasal) electrode. The c-wave decreased its amplitude as the positive electrode came to the same latitudinal position as that of the negative one. Then, the c-wave was cancelled out in appearance on the recordings. When the negative electrode moved further into the posterior pole, the polarities of the c-wave as well as of the a-, b-wave were returned to those of routine ERGs.     

角巩膜栗刺异物伤诊治分析

目的探讨角巩膜栗刺异物伤的临床特点,治疗方法及其临床效果。方法对71眼角巩膜栗刺异物伤采取剔出或巩膜切开摘出异物。结果巩膜异物1次摘出32眼,2次摘出16眼,3次摘出9眼,11眼经4次摘出,3眼经5次全部摘出。无眼内炎及视力改变。结论栗刺所致巩膜异物多而隐匿,采取恰当方法彻底清除异物是治疗成功的关键。     

保存异种巩膜移植的实验研究

目的：比较经过保存的异种(猪)巩膜与同种异体(兔)巩膜及人工合成材料作为埋藏材料的术后效果，为眼科手术探寻新的应用材料。方法：在白兔背部及眼睑皮下分别植入甘油保存的猪巩膜、甘油保存的兔巩膜、酒精保存的猪巩膜、医用硅橡胶片。术后1、4、12周取出，进行大体观察和组织学检查，部分植片还进行电镜检查。结果：同种异体巩膜和异种巩膜植片在受体内的转归相似。结论：保存猪巩膜有希望成为人同种异体巩膜的代用品。     

准分子激光原位角膜磨镶术后角膜瓣及瓣下角膜厚度对角膜强度影响的实验研究

目的　研究准分子激光原位角膜磨镶术 (laserinsitukeratomileusis ,LASIK)后角膜瓣及瓣下角膜厚度对角膜强度的影响。方法　选取成年家猫 2 8只随机分成 4个组 ,建立LASIK动物模型。A组 8只 ,制作厚度为 16 0 μm的角膜瓣 ,激光切削至剩余瓣下角膜厚度为 30 0 μm ,复位角膜瓣。B组8只 ,弃去角膜瓣 ,剩余瓣下角膜厚度为 30 0 μm。C组 6只 ,处理方法同A组 ,但剩余瓣下角膜厚度为180 μm。D组 6只 ,处理方法同B组 ,但剩余瓣下角膜厚度为 180 μm。分别于术前 ,术后 1周 ,1、2及3个月行中央角膜厚度及前房深度的测量 ,并分析角膜后表面地形图。术后 3个月行组织病理学及透射电镜检查。结果　术后 3个月时 ,A、B、C及D组前房深度增加量分别为 ( 0 16± 0 0 8)、( 0 2 1± 0 16 )、( 0 33± 0 0 9)及 ( 0 41± 0 10 )mm。A组与B组、C组与D组相比 ,差异无显著意义 (t=0 6 85 ,1 45 7;P >0 0 5 ) ;A组与C组、B组与D组相比 ,差异有显著意义 (t=3 45 8,2 5 97;P <0 0 5 )。A、B、C及D组角膜后表面前突的增加量分别为 ( 2 7 78± 9 5 2 )、( 39 5 7± 7 6 8)、( 5 8 5 7± 8 6 6 )及( 6 8 14± 19 6 9) μm。A组与B组、C组与D组相比 ,差异无显著意义 (t=2 36 1,1 0 90 ;P >0 0 5 ) ;A组与C组、B组     

Multilayered amniotic membrane transplantation for severe ulceration of the cornea and sclera

PURPOSE: To examine the efficacy of amniotic membrane transplantation in the treatment of deep corneal and scleral ulcers. PATIENTS: A total of 11 patients were recruited for this study: four patients (four eyes) with corneal perforation, five patients (five eyes) with a deep corneal ulcer and descemetocele, and two patients (two eyes) with a scleral ulcer. METHODS: Ulcers were treated by amniotic membrane transplantation. Separate amniotic membranes were transplanted as material to fill the stromal layer (amniotic membrane filling), as a basement membrane (amniotic membrane graft), and as a wound cover (amniotic membrane patch). After surgery, all cases were treated with artificial tears, autologous serum drops, antibiotic eyedrops, topical corticosteroids, and sodium hyaluronate eyedrops. RESULTS: Eight eyes (72.7%) healed with epithelialization in 16.5 +/- 8.0 days (range, 7 to 29 days), with five and three eyes showing corneal epithelialization and conjunctival epithelialization, respectively. A persistent epithelial defect was noted in one eye with corneal ulcer after limbal allograft transplantation for a chemical burn and in two eyes with corneal ulcers as a complication of rheumatoid arthritis. CONCLUSION: Multilayered amniotic membrane transplantation may be effective for the treatment of deep ulceration of the cornea and sclera. In some eyes with total corneal limbal dysfunction or autoimmune disorders, amniotic membrane transplantation alone is not effective.