To the Editor:
I am writing to respond to the January 2019 article, “Amniotic Membrane Use in Pterygium Surgery” (Thomas John, MD). The article contains inaccuracies related to the processing, protein profile and clinical effectiveness of dehydrated amniotic membrane technologies (such as Ambio Amniotic Membrane Grafts [Katena]).

Dr. John states that dehydration of the amniotic membrane “involves high-temperature processing to remove the water content of the tissue; this has been shown to potentially cause protein denaturation, loss of function and possibly irreparable damage to the tissue, with the possible loss of active components and, hence, their associated biological functions.” 

The process employed to clean and dehydrate the Ambio Amniotic Membrane grafts does not expose the native tissue to high temperatures. Additionally, laboratory tests have been conducted to prove that the Ambio graft does contain native growth factors and cytokines. These data were published by Koob et al.¹ 

Dr. John also claims that, when compared to dehydrated amniotic grafts, “cryopreserved amniotic membrane is usually a preferred choice for clinical use in ophthalmology and pterygium surgery.” Ambio grafts have been widely used by eye surgeons since 2002 to treat pterygium and a range of other ocular surface disorders and diseases. According to Katena, more than 125,000 Ambio grafts have been supplied to the ophthalmic surgical community.

I have used both dehydrated and cryopreserved amniotic membrane to treat thousands of patients with pterygium and other forms of ocular surface disease. Both methods of membrane preparation and both types of product work well to preserve the anti-inflammatory, anti-fibrotic properties of this special tissue. There are no published studies that demonstrate the clinical superiority of one preparation method or one product over another. Like many colleagues, I prefer dehydrated amniotic membrane grafts because they can be stored at room temperature for five years. The dry configuration of the tissue also allows for easier cutting, manipulation, placement and fixation. And finally, the cost of dehydrated amniotic membrane is considerably lower than cryopreserved tissue.  

I will appreciate your sharing these facts with your readers to provide more accurate reporting on this topic.

John Hovanesian, MD
Harvard Eye Associates
Laguna Hills, Calif.

Financial Disclosure: Dr. Hovanesian serves Katena as its medical director.

^{1. T. Koob, J. Lim, N. Zabek, M. Massee. “Cytokines in single layer amnion allografts compared to multilayer amnion/chorion allografts for wound healing.” Journal of Biomedical Materials Research B: Applied Biomaterials. 2014.}

Dr. John responds:
I thank Dr. Hovanesian for his interest in my recent article which reviews pterygia and the best surgical approach in managing them. 

As I mentioned in the article, amniotic membrane grafts possess anti-inflammatory and anti-scarring properties that theoretically make it an optimal tissue graft during pterygium surgery. Although the aforementioned is true in general, different processing techniques (e.g. cryopreservation and dehydration) of the amniotic tissue have varying impacts on the biochemical composition and anti-inflammatory properties of the tissue.¹ In fact, cryopreservation, but not dehydration, was shown to retain the HC-HA/PTX3 complex, which has been identified as an active matrix component responsible for the observed anti-inflammatory and anti-scarring properties of amniotic tissue.² This is one potential reason why, in one study, dehydrated amniotic membrane (Ambiodry 2) was not effective in controlling inflammation and scarring in rabbit eyes after extraocular muscle surgery, as the authors of the study mention.³ Hence, despite the presence of some growth factors and the ability to “work well,” dehydrated amniotic tissue lacks the maximal properties that one would expect with amniotic tissue. As such, cryopreserved amniotic tissue is usually preferred by many clinicians when seeking optimal outcomes for patients and is FDA-recognized as demonstrating anti-scarring and anti-inflammatory functions.⁴ 

Thomas John, MD 
Thomas John Vision Institute
16532 South Oak Park Ave Suite 201
Tinley Park, IL 60477

Financial disclosure: Dr. John has a small equity interest in, is consultant/advisor to, and has received lecture fees and grant support from Bio-Tissue and Tissue Tech.

 

^{1. Cooke M, Tan EK, Mandrycky C, He H, O’Connell J and Tseng SC. Comparison of cryopreserved amniotic membrane and umbilical cord tissue with dehydrated amniotic membrane/chorion tissue. J Wound Care 2014;23:465-76.}

^{2. Tseng SC. HC-HA/PTX3 Purified from amniotic membrane as novel regenerative matrix: Insight into relationship between inflammation and regeneration. Investigative Ophthalmol Vis Sci 2016 Apr 1;57:5:ORSFh1-8.}

^{3. Chun BY, Kim HK and Shin JP. Dried human amniotic membrane does not alleviate inflammation and fibrosis in experimental strabismus surgery. J Ophthalmol 2013;2013:369126.}

^{4. Bio-Tissue 2001 RFD, available at: https://www.fda.gov/downloads/CombinationProducts/JurisdictionalInformation/RFDJurisdictionalDecisions/Redac tedDecisionLetters/UCM113701.pdf}