Some clinical morphopatological aspects of lumbar intervertebral formations

Introduction: Degenerative-dystrophic damages in human spinal column are quite frequent. In 90% of the cases they manifest themselves through disorders in peripheral nervous system with growth tendency at young people, capable to work. According to the latest information from the National Center of Public Health Statistics in the USA, persons over 45 years old often limit their activities due to pain in the thorax and lumbar part of the vertebral column, and these people constitute about 26-32% of the population of the “second age”. Structural changes in the tissue in the lumbar area of the vertebral column as a rule become irreversible with time. Materials and methods: We studied the structure of the intervertebral disc with pathology of the vertebral column in 123 patients, who underwent surgical intervention at the Vertebrology Section of Public Medical Sanitary Institution Traumatology and Orthopedy Hospital in 2009 and compared cadaver material (lumbar vertebral segments) from 7 cases with different somatic pathologies from the Hospital „Sfinta Treime”. Results and discussions: The nucleus pulposus is primarily affected by a series of mechanisms with disintegration of collagen fibers, fragmentation, loss of liquid, thus forming multiple crevices at the level of fiber ring, which leads to decrease of their ability to absorb the shocks, and makes them less flexible, which decreases the disc resistance significantly. One of the ethiopathogenetic factors is circulation disorders of the disc irrigated by the vertebral arteries. In case of senior people, atherosclerosis at advanced stage intensifies degenerative-dystrophic changes of intervertebral disc. Conclusions: The results obtained during this study show that normally people at the age of 40-50 years old suffer from discogenic pain, mostly female (55%), most of them accusing of discal hernia at the level of lumbar area, segment L5. Histologically 14 patients (16,6%) have incipient forms of degenerescence of intervertebral disc with aspects of myxoid degenerescence, centrally chondroblastic wtih condrocites, in cases of 70 patients (83,3%) in medium forms of degenerescence of intervertebral disc the following were detected: fibrosed tissue, with zones of interfibrilar edema; discal cartilaginous tissue with chondrocytes in chondroblast, papillary aspect and hemorrhagic zones, hyalinization zones. In case of 39 patients (30,5%), after 51 years old in advanced forms of intervertebral disc the following were discovered: hyalinized discal cartilage, intradiscal calcifications or ossification zones, lymphocitar infiltrate

Конгруэнтность дегенеративных изменений, обнаруженных посредством магнитной резонансной томографии и гистологического исследования поясничного межпозвоночного диска

Catedra Morfopatologie, USMF N. TestemiţanuSummary. The lumbar intervertebral disc degeneration is the most important cause of low back pain. The purpose of the paper was to highlight the herniated lumbar disc and degenerative change in patients with clinical accusations by MRI that pleads for the diagnosis and staging them in relation to Modic classification and correlative histological examination of the material according to the postoperative lumbar disc degeneration degree, performed in 173 patients admitted in Vertebrology department of PMSI SCTO January 2008 – December 2009, of which 87 patients were operated for osteochondrosis with herniated lumbar compression and spondylolisthesis. The first type of change evidenced by MRI, histopathological, it was demonstrated the recent forms of the intervertebral disc degeneration, identified in 10 (11.49%) operated patients. The type II changes by MRI, similar histopathological correspond with two-phase – the medium forms of the intervertebral disc degeneration, detected in 32 (36.78%) operated patients. The type III changes by MRI, histopathological, correspond with the type three, the advanced forms of the intervertebral disc degeneration, discovered in 45 cases (51.72%): myxoid degeneration and intradiscal calcification, discal cartilage hyalinization with intradiscal calcification areas and the presence of young cells, fibroblasts, and chondroblasts, cartilage tissue with areas of fibrosis and chronic inflammatory infiltrate.Резюме. Дегенеративные процессы в поясничных межпозвонковых дисках являются наиболее важной причиной болей в пояснице. Целью работы было подчеркнуть дегенеративные изменения, обнаруженные с помощью магнитной резонансной томографии на уровне межпозвоночного диска поясничного отдела позвоночника у этих больных с клиническими жалобами, которые важны в диагностике грыжи диска. Были произведены стадиализация данных изменений по отношению к классификации по Модику и корреляционный анализ результатов гистологического исследования послеоперационного материала в соответствии со степенью дегенерации диска. Материал набирали от 173 пациентов, поступивших в Республиканскую клиническую больницу, отделение вертебрологии, в период январь 2008 – декабрь 2009 г., из которых 87 больных были оперированны с диагнозом «остеохондроз поясничного отдела с компресивной грыжей» и «спондилолизтез». В первом типе изменений, обнаруженных с помощью магнитной резонансной томографии посредством гистологического исследования, у 10 (11,49 %) оперированных пациентов были выявленыранние формыдегенерации межпозвонкового диска. Второй тип изменений, обнаруженных с помощью магнитной резонансной томографии после гистопатологического исследования, соответствовал со второй фазой – средней формой дегенерации межпозвонкового диска, обнаруженной у 32 (36,78 %) оперированных больных. Третий тип изменений после магнитной резонансной томографии и гистопатологического анализа свидетельствовал о тяжелой форме дегенерации межпозвонкового диска, обнаруженной в 45 случаях (51,72 %). Соответсвенно третьему типу были обнаружены следущие изменения: миксоидная дегенерация, внутридисковая кальцификация гиалинизированного хряща диска, присутствие молодых клеток-фибробластов и хондробластов, хрящевая ткань с зоной фиброза и воспалительным хроническим инфильтратом

Biological skin tissue engineering for wound dressings

Introduction. Modern and smart dressings are becoming more and more sought after. Their values consist not only in a protective barrier but also in a beneficial environment for healing, biocompatibility, selfdissolving, the possibility of realising therapeutic agents, minimal human involvement, that would actively support the healing process of wounds. Dressings with extracellular matrix, hydrogel, collagen are an example of such innovative products that facilitate wound healing, providing an humid environment in which cells can thrive, while the wound can still breathe and exudate can be self-drained. Aim of study. To create the tissue engineering, decellularized extracellular sheets, sponges, hydrogels from the porcin derma, small intestinal submucosa, for the wound dressing. Methods and materials. For one year period, from the pigs’ tissues, were obtained: decellularized extracellular matrix from dermis; collagen suspension from dermis; hydrogels from dermis; decellularized scaffolds from mucosa and submucosa of small intestine; collagen suspension from mucosa with small intestine submucosa; hydrogels from the mucosa with small intestine submucosa. Extracellular matrices from skin and intestine were obtained by decellularization with 4% sodium deoxycholate, 0.1% sodium dodecyl sulphate solution, 0.25% Trypsin, sodium hydroxide, Triton X-100. Collagen extraction was performed by treating with 0.1 M NaOH and 0.5 M acetic acid containing porcine pepsin. Preparation of the hydrogel was performed in HCl solution with porcine pepsin. The products obtained were compared with non-treated native tissue samples. Tissue evaluation included examination of the decellularized samples with hematoxylineosin and DNA quantification assays. For the morphological evaluation H&E staining was performed. Results. Histological examination has not revealed any presence of cells in tissues, decellularized in accordance with the protocols. More than 99% of the nucleic acids were removed from the decellularized bovine matrix. Conclusion. Regenerative medicine is advancing from a wound healing approach based on obtaining smart dressings. Hydrogels, sponges, foils, collagen can play a key role in wound care and facilitating the tissue engineering strategies, acting as a scaffold for stem cells and carrier, source of bioactive molecules and drugs

Management of the cornea grafts in the tissue and human cells bank of the Republic of Moldova during the years 2013-2019

Nicolae Testemitanu State University of Medicine and Pharmacy of the Republic of Moldova, Laboratory of Tissue Engineering and Cells Cultures, Congresul consacrat aniversării a 75-a de la fondarea Universității de Stat de Medicină și Farmacie „Nicolae Testemițanu” din Republica Moldova, Ziua internațională a științei pentru pace și dezvoltareIntroduction: Tissue Bank serves with corneal grafts a population of 4 million people, which offers over 40 corneas per year for transplant in the Republic of Moldova. The high quality of the cornea due to international standards (based on both the standards of the American Eye Bank Association and the European Eye Bank Association) described in all areas of operation, including donor selection and screening, corneal collection, storage, testing, evaluation and transport to transplant centers. A standard protocol is the National Corneal Transplant Protocol of 2019, which includes maintaining a comprehensive database, supported by ophthalmic surgeons in the Republic of Moldova, in which potential data are collected on all aspects of corneal donation and transplantation. The authors previously published data on the indications for the corneal transplantation and in this study we analyzed this database to evaluate the source and management of donor corneal tissue in the Republic of Moldova. • Purpose: Evaluation of the cornea transplant application rate in the Republic of Moldova the period of years 2013 - 2020. • Material and methods: Prospective study, electronic database of Tissue Bank for the period of 7 years 2013 - 2019 were analyzed for each year in terms of the donor number, the indications for the sampling, cause of death, interval from death to corneal preservation, storage methods, endothelial evaluation, bacteriological contamination and distribution. Results: During the study period, 306 corneas were taken from 153 donors (69,8% male, 30,2% female), with a mean age of donors 59,4 years (18,3 years SD) and between 18 and 91 years old. Donors were from forensic medicine (23,5%), public hospitals (67,6%) and multi-organ donors (7.1%). The most common causes of the donor deaths were the cardiovascular disease, trauma and the cerebrovascular diseases. The average storage time increased from 3,5 to 11,8 days, from when the culture medium replaced hypothermic storage. Invalidation of the corneas was in 22,8% of cases, of which were determined by serological infections ( HBsAg - positive, HCV positive, HIV / AIDS) - 15%, and biological contamination occurred in 7,8% of all donor corneas. The most common bacterial and fungal isolates were coagulase-negative staphylococci and Candida spp., respectively. A significant decrease in the contamination rate was identified during the study years. Overall, 77,2% of the corneal tissue taken was used for corneal transplantation (74,8% for penetrating keratoplasty, 2,1% for lamellar keratoplasty and 1.3% for unspecified transplants) and 22,8% were destroyed. The most common reasons for tissue settlement were biological contamination, serology, and endothelial cell integrity assessment. Conclusions: 1. The analysis of the Tisue Bank database provides valuable information about corneal transplantation in the Republic of Moldova. 2. The rate of corneal utilization increased during each year of the study, reflecting improvements in all areas of Tissue Bank operation, in particular, corneal storage and decreased microbiological contamination. 3. The Human Tissue and Cell Bank, founded is the main supplier of the corneas graft for the transplantation in the Republic of Moldova

Impact of differently processed amniotic membrane grafts on the outcome of corneal ulcers in rabbit models

Introduction. Thanks to its regenerative properties, the human amniotic membrane (AM) is extensively used in ophthalmology to treat a wide range of eye surface conditions. Despite the vast amount of studies justifying its ophthalmic use, there is lacking scientific data on the effectiveness of differently processed AM in the treatment of corneal ulcers. In this paper, we aim to compare the effectiveness of cryopreserved, lyophilized and decellularized amniotic membrane transplantation (AMT) in the management of corneal ulcers in a rabbit model. Material and methods. Corneal ulcers were surgically induced in the left eyes of 28 rabbits. Four groups, each containing 7 specimens, were formed: group A (control) – rabbits treated conservatively, with no AMT; group B – rabbits operated with cryopreserved AM; group C – rabbits operated with decellularized AM; and group D – rabbits operated with lyophilized AM. The rabbits were clinically observed for a 3-month period, with the assessment of objective signs, the evolution of the corneal lesion and/or complications. After the follow-up period, the rabbits were euthanized; the left corneas were excised, fixed in 10% formaldehyde and then embedded in paraffin, cut into thin sections, stained with hematoxylin-eosin, and studied by light microscopy. Results. The cornea regenerated the slowest in the control group (28 days), the fastest in group B (15 days), followed by group D (18 days) and then group C (21 days). The highest rate of infectious complications was found in rabbits from group A (57%, n=4), and the lowest – in the group operated with cryopreserved AM (14%, n=1). Corneal neovascularization and opacification were most intense in the control group. In the groups operated with AM, corneal transparency was relatively uniformly recovered, with a slightly poorer outcome in the group C. In conservatively treated corneas (A), histological examination revealed a thickened and deformed epithelium, patchy connective tissue and epithelial cell depletion; in corneas treated with cryopreserved AM (B), fibroblast proliferation and solitary lymphocytic infiltrate below Bowman's membrane were revealed; in corneas treated with decellularized (C) and lyophilized (D) AM, polymorphic and atrophied epitheliocytes were found. Conclusion. While there were significant differences between the control group and the eyes treated with AMT, the clinical signs did not differ significantly between groups operated with cryopreserved, decellularized and lyophilized AM. Still, the cryopreserved AM showed the best results in terms of post-operative complications, regenerative capacities and restoration of corneal transparency

Disorders circulation in osteochodrosis of the lumbar intervertebral disc

Atherosclerosis is one of the etiological factors to initiate the degeneration disc studied in detail by histological investigations stained with haematoxylin-eosin, silver impregnation and immunohistochemical examination with antibodies CD34, CD68 and MCT (mastocyte cell tryptse) in immunohistochemicalLoboratorul Timisoara, leaded by Marius Raica. All are made on a sample of 20 cases where prevailed the L1-L5 vertebral arteries in people with different pathologies somatic cardiac death, age and sex of MCH “Sfânta Treime”. Atherosclerosis with vascular wall thickening has a structural impact on the viability of intervertebral disc, initially being affected nucleus pulposus, annulus and then through a series of mechanisms for splitting fragmented collagen fi bers, and fi nally proliferation with sclerosis. The vertebral arteries affected are 5, lacking intimate vascular event (5%), 3 cases, faint, moderate in 10 cases – handed (50%), and 6 cases – preserved.Атеросклероз является одним из этиологических факторов для начала дегенеративных изменений в позвоночных дисках. Подробно изучены гистологические исследования с окрашиванием гематоксилин-эозином, oрсеином, пропитка серебром, а также иммуногистохимические исследования с антителами CD34, CD68 и MCT (mastocyte cell tryptse) в Лаборатории г. Тимишоара, руководитель – Marius Raica. Все они исследованы в 20 случаях на поясничных позвоночных артериях (1-5 позвонки) у людей умерших от различных соматических заболеваниях, разные по возрасту и полу, в МКБ «Sfânta Treime». Атеросклероз с утолщением стенок влияет на структурную жизнеспособность межпозвоночного диска, первоначально на студенистого ядро, потом на фиброзное кольцо, а затем, через ряд механизмов, ведёт к фрагментированию коллагеновых волокон, и, наконец, фибробласты распространяются со склерозом. В позвоночных артериях пораженных атеросклерозом, в 5-ти случаях отсутствует интима в стенках сосудов (5%), в 3-х случаях – слабо-умеренное, в 10-ти случаях – умеренное (50%), а также в 6 случаях интима сохранилась

Grafts of the cornea in pediatrics

Tissue Engineering and Cells Cultures, Tissue Bank, Nicolae Testemitanu State University of Medicine and Pharmacy of the Republic of MoldovaIntroduction. Transplantation of the cornea in pediatrics remains a challenge. In 2008, Edward Wilson, from South Carolina, relates that the keratoplasty with the stem cell transplantation around the cornea induces the immune modulation and allows only a part of the cornea to be grafted and being more beneficial in the adults. All these advances improve the transplantation of the cornea in the children. However, new surgical methods are not available for the small pacients. In 2007, Edward J. Holland, a professor at the Department of Ophthalmology, University of Cincinnati, USA, says that the children are difficult to investigated because they do not complain about their symptoms as an adult, and their immune system increases the chance of a transplant rejection. That's reason of the keratoplasty in the adults is in progress. He also mentions that the endothelial keratoplasty can be used whether the Descemets base layer is intact. Currently, in the Republik of Moldova, from 2012, specialists prepare the various grafts in the Bank of Human Tissues, such as bone, tendon, skin, amniotic membrane, stem cells and cornea,. In 2013, the first transplant of the cornea was successful in the Municipal Clinical Hospital "H. Trinity". The most of the grafts of the cornea was transplanted in the adults using the transfexing and endothelial lamellar keratoplasty. The children are less likely to have surgery, the causes of which are the technical deficits. In the Medical Center "Ovisus" two children with the age over 11 years old were operated. The diagnoses was "Penetration of the cornea with the foreign bodies". The cornea were released from the Human Tissue Bank and had a number of over 2700 endothelial cells per mm2, useful for transfusion keratoplasty. The dynamic results of transplantation are positive with the restoration of the vision. Conclusions. The development of the associations of eye banks enables us to promote new techniques of the sampling and preservation of the cornea, which allow us to maintain the quality of the graft, and the pediatric ophthalmology will increase the spectrum of the surgical interventions

Antigenic and biodegradable characteristics of the extracellular matrices from the pig derm

Introducere. Pansamentele moderne și inteligente devin din ce în ce mai căutate. Valorile lor constau în barieră de protecție, în mediu benefic, biocompatibilitate, autodizolvare, capacitate de absorbție a fluidelor, transfer de agenți terapeutici, implicare umană minimă, susțin vindecarea rănilor. Scopul lucrării. Scopul a fost evaluarea proprietăților antigenice și biodegradabile ale matricelor extracelulare obținute din dermul porcin. Material si metode. Examinarea probelor decelularizate s-a realizat prin examenul histologic cu hematoxilin-eozină, cuantificarea acizilor dezoxiribonucleici, testul de degradare a grefelor. În testul de absorbție a apei, a fost utilizat PBS cu pH 7,4. Greutatea probelor a fost de 87,9±3 mg pentru toate grupurile de studiu. Urmărirea dezorganizării in vitro a probelor s-a efectuat prin microscopie electronică cu scanare. Rezultate. Examenul histologic a evidențiat prezența a mai puține celule. Ca rezultat, am eliminat 80,5% din materialul genetic din structurile dermice porcine, demonstrat prin cuantificarea spectrofotometrică a ADN-ului. În studiul de degradare a grefei in vitro în soluție de PBS 0,01 M, am determinat o pierdere semnificativă (p < 0,05) a masei grefei cu 90,3% în pH 7,4 în ziua 28, 79,8% la pH 4,0 în ziua 21 și 74% în pH 10,0. în ziua 28 și 91,3% în PBS pH 7,4 combinat cu colagenază din Clostridium histolyticum la 35 de ore. În testul de absorbție am obținut o variabilă în funcție de timpul de expunere, respectiv probele înmuiate au ajuns să depășească de patru ori masa inițială de 87,9±3 mg la a 4-a oră de scufundare în lichid. Concluzii. Grefele acelulare din derma porcină pot juca un rol cheie în îngrijirea rănilor și în facilitarea strategiilor de inginerie tisulară, acționând ca o schelă acelulară și inertă imunologic, ca sursă de molecule bioactive cu trei proprietăți hidrofile și biodegradabile.Background. Modern and intelligent dressings are becoming increasingly sought after. Their values consist in a protective barrier, in beneficial environment, biocompatibility, self-dissolution, ability to absorb the fluids, transfer of therapeutic agents, minimal human involvement, and support the wound healing. Objective of the study. Purpose was to evaluate the antigenic and biodegradable properties of the extracellular matrices obtained from the porcine dermis. Material and methods. The examination of the decellularized samples was carried out by the histological examination with hematoxylin-eosin, quantification of deoxyribonucleic acids, and degradation test of the grafts. In the water absorption test, PBS with pH 7.4 was used. The weight of the samples was 87.9±3 mg for all study groups. In vitro disorganization of the samples followed by scanning electron microscopy. Results. Histological examination revealed the presence of fewer cells. As a result, we were able to remove 80.5% of the genetic material from the porcine dermal structures, demonstrated by spectrophotometric DNA quantification. In the in vitro graft degradation study in 0.01 M PBS solution, we determined a significant (p < 0.05) loss of graft mass by 90.3% in pH 7.4 at day 28, 79.8% at pH 4.0 at day 21 and 74% in pH 10.0 at day 28 and 91.3% in PBS pH 7.4 combined with collagenase from Clostridium histolyticum at 35 hours. In the absorption test, we obtained a variable depending on the exposure time, respectively the soaked samples ended up exceeding four times the initial mass of 87.9±3 mg at the 4th hour of immersion in the liquid. Conclusions. Acellular grafts from the porcine dermis can play a key role in the wound care and facilitating tissue-engineering strategies by the acting as an acellular and immunologically inert scaffold, as a source of the bioactive molecules with the hydrophilic and biodegradable properties

Selective wrist arthrodesis: standard vs combined graft with stem cells. Experimental research

Introduction. Selective arthrodesis is a surgical procedure used to be done in advanced wrist joint arthritis. The aim of the surgery is to achieve a stable joint, by intercarpal ankylosis, which removes the pain syndrome and restores the strength of the hand, unfortunately with the risk of decreasing the range of motion in the wrist joint. Aim of study. Comparative evaluation of the method of selective wrist arthrodesis using standard vs combined graft with stem cells. Methods and materials. Our study is based on experimental research on 10 New Zealand rabbits. In the first study group, on 5 laboratory animals was performed standard arthrodesis of wrist joint. In the second study group, on other 5 laboratory animals, was developed the new treatment technique using the combined graft with stem cells, obtained by tissue engineering. Results. In all cases, an immediate postoperative radiograph was performed. The clinical and radiological evaluation, performed at 4, 8 and 12 weeks after the surgery. Computer tomography of each operated wrist was done 12 weeks postoperatively. Imagistic results showed us, that the group were performed arthrodesis using combined graft with stem cells, the ankylosis were achieved faster. Preliminary histological examinations of experiments indicate more active involvement in the process of osteogenesis in the use of combined stem cell transplantation. Conclusions. Our experimental research highlights an innovative method of surgical treatment - arthrodesis using the combined graft with stem cells. It turned out to be a harmless and safe method. A comparative study with the standard treatment method was performed, the imaging and preliminary histological results are encouraging. The final analysis of the results is still in process

Managementul transplantului de cornee în banca de țesuturi și celule umane din Republica Moldova, pe parcursul anilor 2013-2019

Background. Tissue Bank serves with corneal grafts a population of 4 million people, which offers over 40 corneas per year for transplant in the Republic of Moldova. Objective of the study. Evaluation of the cornea transplant application rate in the Republic of Moldova the period of years 2013 - 2019. Material and Methods. Prospective study, electronic database of Tissue Bank for the period of 7 years 2013 - 2019 were analyzed for each year in terms of the donor number, the indications for the sampling, cause of death, interval from death to corneal preservation, storage methods, endothelial evaluation, bacteriological contamination and distribution. Results. During the study period, 306 corneas were taken from 153 donors (69,8% male, 30,2% female), with a mean age of donors 59,4 years (18,3 years SD) and between 18 and 91 years old. Donors were from forensic medicine (23,5%), public hospitals (67,6%) and multi-organ donors (7.1%). The most common causes of the donor deaths were the cardiovascular disease, trauma and the cerebrovascular diseases. The average storage time increased from 3,5 to 11,8 days, from when the culture medium replaced hypothermic storage. Invalidation of the corneas was in 22,8% of cases, of which were determined by serological infections ( HBsAg - positive, HCV positive, HIV / AIDS). Conclusion. The analysis of the Tisue Bank database provides valuable information about corneal transplantation in the Republic of Moldova. Introducere. Banca de țesuturi deservește cu grefe corneene o populație de 4 milioane de oameni, ce oferă peste 40 de cornee pe an pentru transplant în Republica Moldova. Scopul lucrării. Evaluarea ratei de solicitare a transplantului de cornee în Republica Moldova în anii 2013-2019. Material și Metode. Studiul prospectiv, înregistrările electronice ale BȚCU pentru perioada de 7 ani, 2013-2019, au fost analizate pentru fiecare an în ceea ce privește numărul donatorilor, indicațiile de prelevare, cauza morții, intervalul de la moarte până la conservarea corneei, metodele de stocare, evaluarea endotelială, contaminarea bacteriologică și distribuirea. Rezultate. În perioada de studiu, 306 de cornee au fost prelevate de la 153 de donatori (69,8% bărbați, 30,2% femei), cu vârsta medie a donatorilor 59,4 ani (18,3 ani SD) și între 18 și 91 de ani. Donatorii au fost de la medicina legală (23,5%), spitale publice (67,6%) și donatori multiorgan (7,1%). Cele mai frecvente cauze ale decesului donatorului au fost bolile cardiovasculare, traumatismele și bolile cerebrovasculare. Durata medie de depozitare a crescut de la 3,5 la 11,8 zile, de când mediul de cultură a înlocuit depozitarea hipotermică. Nevalidarea corneelor a fost în 22,8 % cazuri, din care din ei au fost determinate cu infecții serologice(AgHBs – pozitiv, HCV pozitiv, HIV/Sida). Concluzii. Analiza bazei de date a băncii de țesuturi oferă informații valoroase cu referire la transplantul de cornee în Republica Moldova. Rata de utilizare a corneei a crescut pe parcursul fiecărui an al studiului, reflectând ameliorări în toate domeniile de operare BȚCU, în special, depozitarea corneei