|Year : 1996 | Volume
| Issue : 1 | Page : 3-13
Donor corneal tissue evaluation
Jagjit S Saini1, Madhukar K Reddy2, Savitri Sharma2, Sangeeta Wagh3
1 Postgraduate Institute of Medical Education and Research, Chandigarh, India
2 L.V.Prasad Eye Institute, Hyderabad, India
3 Ruby Hall Clinic, Pune, India
Jagjit S Saini
Department of Ophthalmology, Postgraduate Institute of Medical, Education and Research, Chandigarh 160 012
Source of Support: None, Conflict of Interest: None
Proper evaluation of donor cornea is critical to the success of corneal transplantation. Attention must be paid to the cause of death and ocular condition as several general and ocular diseases constitute contraindications for donor corneal usage. Death to enucleation time should be noted. Gross examination and slit lamp biomicroscopy are mandatory for the evaluation of the donor eye while specular microscopy adds another useful dimension to information regarding donor cornea. This article provides a comprehensive review of all the aspects of donor corneal evaluation as practised today worldwide.
Keywords: Donor cornea evaluation - Indications - Contraindications -Bacteriology - Serology - Gross examination - Biomicroscopy -Specular microscopy.
|How to cite this article:|
Saini JS, Reddy MK, Sharma S, Wagh S. Donor corneal tissue evaluation. Indian J Ophthalmol 1996;44:3-13
In recent years, the number of donor corneas procured by eye banks is steadily increasing all over the world. Safety and viability of the donor cornea is an essential prerequisite for successful outcome of corneal transplant procedure. The medical standards and quality control measures followed by eye banks largely determine the quality of cornea supplied for surgery. The infrastructure should be optimal and the technical manpower should be properly trained in all aspects of eye banking. In this review, we discuss the guidelines for the proper selection of donors and methods of evaluation of donor eye and the cornea.
| 1. INDICATIONS AND CONTRAINDICATIONS FOR PROCUREMENT AND USE OF DONOR CORNEA|| |
Transplantation of human cornea involves potential risks of transmission of host disease to recipient and unsuccessful outcome because of poor quality of donor cornea or other complications. From extensive clinical and laboratory evaluations of corneal transplants, it was possible to increase the safety in the choice of donor cornea. Some of the listed contraindications have emerged from retrospective discoveries of transmission of disease. Other contraindications were based on either significant risk of transmission of disease or poor results. Although criteria for donor selection are more stringent for penetrating grafts, it is possible to be less restrictive for lamellar grafts. In eye banking all available donor eyes are harvested as a matter of policy except in the case of highly contagious diseases.
| 1.1 Disease transmission from donor cornea|| |
Diseases with the potential for transmission by corneal transplantation fall into three main categories: infections, neoplasms and corneal disorders. Eye Bank Association of America (EBAA) guidelines [1,2] make obtaining information on the cause of death of the donor mandatory.
| 1.1.1 Infections|| |
Among the medical contraindications [Table - 1],[Table - 2] are infectious diseases which are fatal when contracted.
It has been shown that corneal transplant resulted in transmission of rabies and death of recipients in few cases., Confirmed or suspected donor deaths because of rabies, is now a contraindication to harvesting of eye because of special precautions required in handling suspect rabies infected tissue and fatal outcome if transmitted.
b) Viral Hepatitis
Hepatitis B virus is known to have been transmitted via corneal tissue. Laboratory testing has demonstrated that donor tissue and tear fluid are hepatitis antigen positive in viral hepatitis. There is significant risk of transmission of hepatitis B virus to the enucleator and special precautions are required to be taken to handle hepatitis virus infected tissue. It is contraindicated to remove donor eyes from a donor known to have viral hepatitis. Hepatitis C seropositive individuals are also not safe for donor corneal procurement.
c) Human immunodeficiency virus (HIV)
Although donor seroconversion is not reported following corneal transplantation from HIV infected donors, there is enough evidence about its occurance following transplantation of other organs., There is further cause for concern in our current inability to screen donors who have been recently infected and may not have developed detectable levels of antibody response. Eye bank Association of America advises exclusion of all donors at high risk of HIV including homosexuals, intravenous drug abusers and haemophilics.
d) Creutzfeldt-Jakob disease
Only on one occasion, transmission of Creutzfeldt-Jakob disease resulting from corneal transplantation, has been documented. Screening of donor for slow virus causing Creutzfeldt-Jakob disease is not possible. The disease is however universally progressive and fatal. Any donor known to have died of progressive neurological ailment of Creutzfeldt-Jakob disease is a contraindication.
e) Other virus diseases
Several documented cases of transmission of cytomegalovirus (CMV) following transplantation of kidney, heart, liver and bone are available.Although no reports of transmission of CMV from corneal transplantation are known, in one prospective study, 9% of corneal transplant recipients demonstrated seroconversion. There is also potential for transmitting Herpes simplex virus,, zoster virus Epstein-Barr virus,adenovirus, and rubella virus. However, at the present time the risk of transmitting any of these viruses is not considered sufficient to warrant routine screening or contraindication to donor eye procurement.
f) Diseases of possible but unproved viral etiology
Because of unconfirmed evidence several diseases including Reys syndrome, subacute sclerosing panencephalitis, progressive multifocal leukoencephalopathy, pseudopresumed histoplasmosis are linked to a possible viral etiology. There is often a premortem diagnostic confusion because of clinical overlapping features of a typical rabies or Creutz feldt-Jakob disease.
All the above causes of death and deaths from unknown causes constitute absolute contraindications, according to EBAA. An important concern in keratoplasty is the possibility of transfer of infection from donor cornea to the host. There is evidence in literature of possible cultures of same organism from blood of donor or donor corneal rim and host cornea implicating direct transfer of infecting organism from donor to host eye. Such an evidence has been documented for Streptococcus pneumonia, Pseudomonas aeruginosa cryptococcus, and Torulopsis globorata.A positive corneal rim culture is associated with higher rate of postkeratoplasty infection in the host eye. The notion that sepsis in the donor is a risk factor for development of infection in the recipient, is the basis for EBAA to include donor septicemia as a contraindication for use in corneal transplantation. It remains however, impossible to quantitate the risk. Studies indicating lack of correlation between corneal rim positive culture rates and post keratoplasty infection rates are also reported in the literature. It has also been shown that eyes of donors on mechanical ventilation, did not demonstrate higher contamination rates.
Saini et al and Clark et al have presented evidences that in confirmed terminal septicemia, aqueous and vitreous culture from donor eyes remained negative. There is further difficulty because clinical septicemia as a terminal cause of death is often presumptive and not confirmed on blood cultures. Experience indicates that in most case of septicemia, there is no clinical evidence of external eye infection. It is believed that during the phase of septicemia, organisms may be circulating in the blood vessels in the eye. Avascular cornea is expected to remain free of any organisms however. Efficacy of donor eye decontamination by methods such as povidone iodine immersion may be more crucial than rejecting a cornea on suspected septicemia. The problem of contamination of donor tissue is unlikely to be resolved easily. It will be prudent to search for evidence of bacterial and fungal infection in potential donor.
| 1.2 Non infectious systemic disorders|| |
Theoretically lymphoproliferative disorders including leukemias (blast form), lymphomas and lymphosarcomas pose the greatest risk of transfer from donor to host. However till date there is no reported transfer of a systemic malignancy following keratoplasty. A single case report of transfer of ocular retinoblastoma has however been reported in 1939 and forms the basis of EBBA guidelines recommending not to use donor cornea when donor demonstrated systemic lymphoproliferative disorders or ocular malignancies of retinoblastoma or melanoma.
| 1.3 Corneal disorders|| |
Transmission of local corneal disorders is a definite risk of corneal transplantation. But literature contains very little information on this subject. It is rare in the current era of specular microscopy and careful examination of donor material that major corneal disorders will be missed. [Figure - 1] However anterior and posterior membrane dystrophies and keratoconus particularly in the early stages, may escape detection. It is also likely that corneas that are destined to develop Fuchs' dystrophy are being transplanted. Despite these comments it is reassuring to recognize the rarity of such an event. Possibly, the refined tissue evaluation techniques are responsible for this.
| 1.4 Donor characteristics|| |
| 1.4.1 Donor age|| |
Several studies have documented that graft survival is not dependent on age of donor. Most eye banks and corneal surgeons readily accept corneal tissue from donors of 70 years of age. Constraints to using infant cornea are technical because of small diameter, thinness, and elasticity. A majority of eye banks accept eyes of infants above the age of 6 months.
| 1.4.2 Death to enucleation, excision and preservation time|| |
Acceptable time intervals from death, enucleation or excision to preservation time may vary according to the circumstances of death and interim means of storage of the body. It is generally recommended that corneal preservation occurs as soon as possible after death. All time intervals for each donor i.e. the time of death to time of enucleation, preservation and surgical use should be recorded. Generally eye banks develop their own acceptable time limits. Traditional limits of 6 hours post-mortem time have, however, not been found critical to graft survival. Many eye banks routinely accept tissue upto 12 hours post-mortem or even later.Studies have now demonstrated that post-mortem time is not a critical contributor to graft survival although immediate postoperative graft swelling varied according to post-mortem time.
| 1.4.3 Cause of Death|| |
Corneal graft outcome generally does not depend upon cause of death of donor. However, donor material from acute trauma related death was found better in terms of graft survival as compared to donor material from natural causes of death. Corneas from patients who died suddenly including cardiac infarction have good metabolic status even 24 hours after death.Compared to ATP/ADP ratio of 3 in fresh cornea, it was 1.0118 at 24 hrs post-mortem in acute deaths. ATP/ADP ratios in corneas at 24 hrs post-mortem following deaths due to renal insufficiency (0.6010), sepsis (0.1434) and cancer(0.3539) were significantly low indicating the variable extent of catabolic changes which will take variable time post-mortem to recover. From studies of primary graft failures no correlation could be found to the cause of death. At the current stage of information corneal surgeons do not generally choose corneas depending upon the cause of death but lean towards donor tissue from acute deaths if tissue supply is in plenty.
| 1.4.4 Health of donor endothelium|| |
Attrition of corneal endothelium commences immediately after death and continues during transplant surgery and for atleast 5 years postoperatively. There are constraints to our ability to precisely quantitate the extent of functioning endothelium. Eye banks follow routine procedures of slit lamp and specular microscopic evaluation in order to assess the quality of endothelium.
Slit lamp evaluation of whole globes is the most commonly employed assessment method. In practice for each of the assessed slit lamp parameter a grade is assigned on an empirical scale of excellent to poor (1 to 5) [Table - 3]. Given that the slit lamp gradation is clinical and not precise, each eyebank is expected to develop its own experience and guidelines employing more stringent criterion for optical penetrating grafts initially.
Specular microscopy of endothelium is a more precise way of evaluating donor cornea. An endothelial count of more than 1500 cells/mm is considered empirically adequate to cover for almost 50% cell loss following corneal transplantation. In a recent study, 3%of corneas assessed to be excellent on slitlamp evaluation were rejected on specular microscopy. In the USA 58% of eye banks are routinely evaluating donor corneas by specular microscopy. Experience has demonstrated that in the majority of corneas of any age, endothelial cell counts are adequate. Some eyebanks (7% in USA) are therefore employing specular microscopic evaluation on selective basis in extremes of donor age or longer death to enucleation time or any situation where endothelial cell counts are suspected to be low such as diabetes melitus. This reduces the eye bank workload. It is left to the discretion of corneal surgeons to use the specular microscopic data.
| 2. DONOR EYE EVALUATION: BACTERIOLOGY|| |
The standards followed by the eyebank and the quality of the tissue obtained is of paramount importance in reducing the incidence of endophthalmitis caused by contaminated donor tissue. The incidence of positive donor corneoscleral rim contamination varies from 12.4% to 47.9 %. The isolates included Staphylococcus aureus, Staphylococcus epidermidis, hemolytic and nonhemolytic Streptococci, Pseudomonas and Propionbacterium[Table - 4]. The variable incidence of positive cultures depends on the methodological differences in various studies.,Polack et al reported the flora in living individuals, where staphylococcus epidermidis were present in 69.7%, staphylococcus aureus in 30.2% and diphtheroids in 73.1%. Donor corneas have a significantly higher incidence of Streptococcus and gram negative bacteria in cultures.Numerous studies indicate that the occurance of post penetrating keratoplasty endophthalmitis is far less than the frequency of positive cultures.,, Cases of bacterial endophthalmitis, where the same organism was cultured from the donor and recipients are very few. A large population of bacteria are eliminated by techniques like donor eye immersion in antibacterial solutions, tissue preservation in media containing anti biotics, antbiotics administered intra and postoperatively and finally the host immune mechanisms.,,
Donors with documented or suspected sepsis at the time of death have not demonstrated a higher aqueous humour contamination, although an earlier report indicated that donor eyes from septicemic donors may harbour organisms in the eye. There is no clear association of organisms cultured from blood and aqueous.
Irrigation of the eyes reduces the yield of positive cultures. Use of nonsterile procedure to remove donor eyes substantially increases the contamination.
| 2.1 Bacteriological Evaluation and Surface Decontamination|| |
Following death, exposure, dehydration and desiccation along with prolonged death to enucleation time increase the risk of donor contamination. [39,48]Application of an antibiotic solution or ointment and patching the eyes after death and storing the body below 15°C, helps to reduce microbiological contamination. Gross examination of the eyes at the site of enucleation would include ruling out exposure, conjunctivitis, injuries or the presence of foreign bodies. A careful search for other local injuries, contaminated wounds or splashing of secretions on the face should be made. In addition, presence of infection anywhere in the body including open tracheostomy and burns may be important. As against the living state, Staphylococcus aureus, Pseudomonas, E.Coli, Streptococcus viridans and Klebsiella are recovered more frequently. Staphylococcus epidermidis continues to be the most prevalent post mortem organism.
Once the eyes are brought to the eyebank, they are processed in the laminar flow hood. The surface is irrigated with normal saline taking care to work all around the limbus. Limbal swabs are plated onto blood agar and thioglycollate broth. Foreign particles, if any, are noted and removed. Excessive tissue, conjunctiva, muscles and Tenon's sheaths are trimmed. The eyeball is subsequently dipped in antibiotic solution for 3 to 10 minutes, followed by a thorough saline rinse.
Besides the limbal swabs, culturing of the donor corneoscleral rim and the medium at the time of surgery is recommended after thorough irrigation.
The antibiotics used vary in many studies [Table - 5]. Neosporin and gentamicin have been most widely used.,, The use of providone iodine has been recently reported. Topical thiomersal upto 2% has no deleterious effect on the conjunctival or corneal epithelium. Mindrup and colleagues assessed the efficacy of diluted betadine. The whole eye was immersed in 1:1 dilution of povidone iodine for three minutes, followed by vigorous irrigation with saline. They reported a significant reduction in positive limbal cultures.
| 2.2 Decontamination in Storage Media:|| |
Transfer of the corneoscleral button into preservation media at the earliest possible time is preferred over moist chamber preservation by most surgeons.,,Besides allowing time for serology, planned surgery, maintaining a compact stroma and the endothelial viability, it allows removal of the cornea from the deleterious effects of a rapidly changing aqueous environment and autolysis. Besides exposure of the cornea to antibiotics, the preserving media may have a significant effect in reducing bacterial contamination,,
Several studies have reported on the efficacy of storage media in sterilising the corneoscleral button prior to penetrating keratoplasty.,,,] Microbial contamination can take place at any stage during preparation, handling transportation of the medium from contaminated tissue, instruments or the atmosphere. Numerous antibiotics have been studied for their efficacy and safety in storage media. Some of these include penicillin G, streptomycin, cefazolin, Gentamicin, Vancomycin. Penicillin G and Cefazolin are demonstrated to be ineffective in decreasing the colony counts.
Gentamicin resistance is emerging for both gram positive and gram negative organisms. Strepococci show a resistance in 84.6% of isolates and pseudomonas as much as 86.2%. The use of 100ug/ml gentamicin in storage media reduced the donor contamination from 43% in the whole eyes to 14% in preserved corneas.The corneal button absorbs antibiotic and continues to release this into the tissues of the recipient over the early postoperative period. Donor buttons in storage media should be stored at 4°C to inhibit the growth of gentamicin resistant organisms and be allowed to warm upto room temperature one hour prior to the surgery to allow gentamicin to act on the gentamicin sensitive bacteria. Baer and colleagues demonstrated that warming the globe one hour prior to surgery may not always eliminate sensitive organisms. In the face of emerging gentamicin resistance, supplementation with another bactericidal agent could increase the safety of tissue utilisation. Steinemann et al studied vancomycin (100 ug/ml) in optisol (Chiron ophthalmics), for its efficacy and toxicity and noted that, vancomycin inhibits Streptococcus, without any deleterious effect on the endothelium. In view of the fact that, antibiotics fail to sterilise the medium in all instances, Poole and colleagues, suggest administration of broad spectrum antibiotics intravenously at the time of surgery and postoperatively.
| 3. SEROLOGICAL SCREENING OF DONOR|| |
The first serologic test required by the Medical Advisory Board of the Eye Bank Association of America was donor HIV-1 testing in 1985. This was followed by the requirement to screen for Hepatitis B antigen in 1986, Hepatitis C (HCV) antibody testing in 1991 and serologic testing for syphilis in 1992. The reason for donor syphilis testing emerged from the suggested correlation between syphilis and HIV seropositivity and the possibility that a positive syphilis serology might identify recently infected HIV-positive donor who had not yet converted to HIV seropositivity. A recent study, however, reported? positive syphilis serology to be a poor marker for HIV-1 infection and recommended re-evaluation of the decision of screening of potential cornea donors for syphilis. Testing for HCV antibody was deemed important when seroconversion (positive HCV antibody) was demonstrated in renal transplant recipients. However, to date no seroconversion has been shown following corneal transplantation.
| 3.1 Serological Screening tests|| |
Blood samples from the donor can be collected by several methods. A 20 mL syringe with 18 G needle is preferred. A 3.5 inches spinal needle is ideal for cardiac puncture. Blood can be collected from the jugular vein, left ventricle or femoral artery. Blood is collected in a plain sterile tube and submitted to the laboratory. Blood should be preserved at 4°C until serum is separated and must never be frozen before that, in order to prevent lysis. However, it is common to find haemolysis in cadaver blood. This normally does not interfere with the present systems available for serological testing. Serum can be kept frozen until tested.
Enzyme linked immunosorbent assay (ELISA) is the commonly used screening method for HIV, HBsAg and anti-HCV. Commercial kits can be obtained from several companies. Presently the recombinant antigen used for immunoassay for HIV includes that of HIV 1 and 2. Because of the epidemiological situation of HIV-2 in Europe routine screening for HIV-2 was deemed necessary recently. The seroprevalence in a population is an important parameter for determining the relevance of a serological screening test. Presence of 'reagin' antibodies can be detected by any of the rapid tests for detection of syphilis. RPR card antigen test is commonly performed in the United States. The VDRL test also detects 'reagin' antibodies. Detailed descriptions of the serological tests is beyond the scope of this review.
| 3.2 Status of serological screening of eye donors|| |
Most eye banks currently mandate screening for HIV and Hepatitis virus. ELISA test kits are upto 97.1.% specific and upto 99.6% sensitive leaving scope for improvement as has been demonstrated in studies involving polymerase chain reaction tests for HIV-I, Hepatitis B and C virus in the eye tissue., The carrier rate of HBsAg among general population is 0.2% to 8% and in hospital personnel between 8% and 18% which leaves no place for complacency. The HIV infection rate in female commercial sex workers has risen from 0.5% in 1986 to 34.5% in 1990 in Tamil Nadu (India). It is now estimated that there are more than half-a-million persons infected with HIV in India alone which is likely to rise to 2 to 3 million by the year 1996. The serosurveillance for AIDS was initiated in India in 1985 and the Indian Council of Medical Research has reported the seroprevalence rate as 0.7% in 1992.Therefore, all donors must be tested for HIV and HBsAg for a reasonably safe corneal transplantation.
In India, the Government of Maharashtra state has made serological screening of donors mandatory by law. Currently all eye banks in Maharashtra state release corneal tissue after serological screening for HIV and HBsAg. Several eye banks in Bangalore, Madras, Delhi and Hyderabad are also following the procedure.
| 4. DONOR CORNEA VIABILITY EVALUATION METHODS|| |
Donor corneal tissue evaluation has to begin before the eyes or corneoscleral rims are excised from the donor. Donors older than 75 years generally may be considered for transplantation after specular microscopic endothelial assessment.
Donor corneal tissue may be available as
- a) Whole globes stored in a moist chamber
- b) Corneoscleral rims in storage media, which could be
- i) In situ excisions
- ii) Laboratory excisions
| 4.1 In Situ Examination|| |
The eyes of the donor are to be examined with a bright torch and preferably a portable slit lamp. The conditions/structures looked at in donor eyes are listed in [Table - 6].
| 4.2 Gross Examination|| |
Once the whole globes arrive at the eye bank, the condition of packing and the presence of ice in the styrofoam container is to be noted to know whether the cold chain is broken. Sometimes the jar containing the eyes may be filled with water causing excessive stromal hydration, such eyes are to be discarded unless a specular microscopy can be done to prove the presence of adequate endothelium. The jar and the cap are to be examined for organic debris. The globe is to be examined for scleral lacerations, and excess retention of orbital tissue indicating a poor enucleation. In an eye bank, initial examination similar to that indicated in [Table - 6] should be carried out on a slit lamp biomicroscope. The sclera is to be examined for any yellow discoloration indicating a jaundiced donor.
The color of the tissue storage media is to be noted. If contents are colorless or yellowish in color it indicates an acidic PH which could be due to microbial contamination. The expiry date of the storage media mentioned on the vial is to be noted.
| 4.3 Biomicroscopic Examination|| |
This is the single most important step in the evaluation of donor corneas to assess their viability.
| 4.3.1 Whole Globe Examination|| |
The moist chamber stored tissue is to be examined as early as possible before the corneal edema increases. The tissue is to be thawed to room temperature for the endothelium to function and deturgesce the cornea. All handling of the globe should be done with sterile instruments/cotton tipped applicators. A low magnification is to be used initially to scan the globe for gross abnormalities with a wide slit beam held at 45°. A systemic examination of the anterior segment from the corneal epithelium to the lens is to be carried out with a slit.
| 4.3.2 Corneal Epithelium|| |
Epithelial microscytic oedema, defects and debris are to be looked for. Epithelial oedema is indicative of poor endothelial function. Epithelial oedema has to be carefully differentiated from surface irregularity of the epithelium by oblique illumination or retroillumination techniques.
| 4.3.3 Corneal stroma|| |
The corneal stroma is screened for opacities, infiltration, edema and Descemet's folds.
| 4.3.4 Corneal endothelium|| |
The specular endothelial reflection provides a gross estimate of the endothelium in terms of cell density, pleomorphism and presence of guttata. A drop or two of antibiotic solution on the surface of the cornea will improve endothelial viewing. Frequently, linear markings similar to snail tracks are seen on the endothelium. These are stress fractures of the endothelial sheet from the trauma of excision.
Crystals in the anterior chamber may indicate prior freezing of the eye and such globes are to be rejected.
| 4.3.5 Corneoscleral Rim Examination|| |
The glass vials may be placed in a special holder and viewed conveniently in a mirror placed below the vial or a special corneal storage viewing chamber provides a good view of the excised rim.
The tissue is allowed to be warmed to room temperature. As the cornea becomes compact due to the presence of dextran in the storage media, the presence of corneal oedema cannot be assessed correctly, hence the examination of whole globes before processing the tissue for media storage is very important.
| 4.4 Specular Microscopy|| |
A careful slit lamp examination provides an over all status of the endothelium better than specular microscopic examination as the area examined by specular microscopy is very small and cannot be extrapolated to the total endothelium.
The normal endothelium shows a pattern of cells of similar size and shape with no abnormal dark or bright structures being apparent as shown in [Figure - 1]. The cell density is between 2000 and 3500 cells/mm. Specular viewing of endothelium helps in better selection of corneas [Table - 7].
| 4.5 Documentation|| |
The details regarding a particular donor and the details of the donated tissue should be recorded meticulously and in detail on a form for the transplanting surgeon to evaluate the overall quality of the tissue. A model form is shown in [Table - 8]. We grade tissue into excellent, very good, good, fair and poor categories.
| Conclusion|| |
Eye banks discarded almost 8.76% of harvested corneal tissue and released only 44.4% of corneal buttons for optical corneal grafting in the USA in 1993,indicating the immense concern for failure to meet the acceptable safe criteria. EBAA guidelines recommend a mandatory record of donor history and screening for HIV, Hepatitis B, Hepatitis C and syphilis to limit the potential transfer to host of fatal disease. Guidelines also provide for mandatory slit lamp evaluation of donor tissue. While eyebanking in many parts of the world has adopted these mandatory provisions in the interest of recipient, other regions especially in Asia have not as yet adopted all the provisions because demand for corneas is outstripping supply at present, lack of diagnostic facilities, constraints of finances and trained manpower. It is however, prudent to upgrade eye banks and employ mandatory provisions at whatever cost.
There are practices of eyebanking where there is considerable flexibility in donor selection. In diabetics, endothelial viability is poorer and end up more often as primary graft failure. Again discretion can be employed based on specular microscopic evaluation. There is flexibility in donor tissue selection with regard to age of donor, post-mortem time and cause of death. When supply of corneas exceeds demand, corneal surgeons tend to choose younger donor, shorter post-mortem time and acute cause of death. Scientific evidence however demonstrates that empirical donor tissue selection based on donor age, death-enucleation time and cause of death, do not affect cornea graft survival. Each eye bank tends to set its own guidelines based on quality of surgical skill available, demand supply gap of corneas and operational constraints to harvest donor globes.
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[Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4]
[Table - 1], [Table - 2], [Table - 3], [Table - 4], [Table - 5], [Table - 6], [Table - 7], [Table - 8]