Commentary: The human amniotic membrane: Fortifying nature's gift to ophthalmology

The human amniotic membrane (hAM) is the innermost layer of the placenta. It consists of a superficial epithelial monolayer, a thick basement membrane, and an avascular stroma.[1] The hAM possesses anti-inflammatory, antiangiogenic, and antifibrotic properties while promoting epithelial cell migration and adhesion.[1] First popularized in the 1990's by Tseng and colleagues[2,3] the hAM now has an important role in ophthalmology, ranging from globe salvage in acute emergencies like chemical burns and Stevens–Johnson syndrome[1] to vision restoration in reconstructive procedures like limbal stem cell transplantation.[4]

The hAM also possesses antimicrobial properties against certain bacteria like Hemolytic streptococcus group A, Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa.[1] Antimicrobial factors like bactricidin, beta-lysin, lysozyme, transferrin, and 7S immunoglobulin have also been shown to be present in amniotic fluid.[1] However, hAM is generally not used to treat acute microbial keratitis, unless it is associated with ocular surface disease, since the antimicrobial properties are not specific and effective enough to treat virulent bacterial infection. Hence, the idea of hAM being a reservoir of antimicrobial drugs, as demonstrated in an article in this issue of the Indian Journal of Ophthalmology,[5] is particularly interesting. The use of hAM as a drug delivery system has been demonstrated previously where it has been soaked with a single drug such as an antibiotic, antiviral, or antifungal or a combination of two drugs and utilised in cases of diagnosed microbial keratitis.[6,7,8] In the present study, the authors show that hAM can be impregnated with an externally compounded fortified antibiotic, cefazolin effectively. Fortified cefazolin (5%) is a topical medication commonly used in bacterial keratitis caused by gram-positive organisms. However, this formulation is not available commercially and is prepared and dispensed to patients who require it. Also, the stability of these topical medications depends on multiple factors such as ambient temperature. In this study, the authors show that fortified cefazolin has significant entrapment within the hAM when it is treated for 3 hours at 4°C. Hence, hAM can be used as a drug reservoir for extended release of such fortified medications without affecting the stability of the formulation. Therefore, although this study paves the way for the clinical use of cefazolin impregnated hAM, further evidence in the form of clinical trials would still be required to establish its efficacy as compared to standard topical therapy in patients with gram-positive bacterial keratitis.

In India, several eye banks prepare and distribute the hAM to ophthalmic surgeons along with corneal tissues. The processing and preservation of the hAM is extremely simple and many ophthalmic surgeons mistakenly believe that they are limited by not having a clean room to prepare hAM, in case they are unable to source it from an eye bank. Every operating theater is a clean-room where the hAM can be processed by simple cleaning and mechanical separation of the amnion from the chorion. The hAM is usually preserved in Dulbecco's modified Eagle's minimal essential medium (DMEM) which is a popular inexpensive base-medium for tissue culture and easily procured commercially. If the placental tissue is obtained with proper informed consent from a reliable obstetrics clinic, where routine antenatal screening for HIV and hepatitis B/C is done, any ophthalmic surgeon can process, store and use the hAM with proper documentation and record keeping. An individual hAM can provide 30-40, 5 cm × 5 cm pieces which can each be preserved at 4°C (door/regular compartment of the refrigerator) for at least 1 month and at −20°C (deep freezer compartment of the refrigerator) for 3 months. It could be possible, therefore, for surgeons in the future to prepare and fortify the hAM themselves for application in patients, without having to depend on commercial preparations.