Okay. This was a bit of a “Whoa” moment. Many studies list an email address for at least one of the authors… this one didn’t, so I’ll have to do a little digging for some follow-up.

For those who need a little background to understand this:

HA is a Good Thing for the cornea. It is a key ingredient in many artificial tears - from the Hylo products so popular in Europe to Oasis Tears Plus, Blink, Refresh Relieva and others in the US. HA = hyaluronic acid, which you’ll usually see listed as sodium hyaluronate.
BAK is a Bad Thing for the cornea. It is a toxic preservative in most prescription eye drops. Short term exposure is not believed to be harmful. Long term exposure causes or exacerbates dry eye. BAK is in most glaucoma medications still.
This study is suggesting that when HA is on the eye, the way it interacts with BAK is not just a Bad Thing, it’s a Much Worse Thing.

So what I want to know is, what are the implications for people with compromised corneas who are using HA-based artificial tears AND prescription eye drops such as glaucoma drops (or even just a steroid). The AAO says we only need to leave 5 minutes between dosing different drops, but does this study mean people using HA drops might need to wait much, much longer in between? And how does HA compare with common polymers used in drops like CMC?

Hungry for info. I will follow up.

Topical hyaluronan alone promotes corneal epithelial cell migration whereas combination with benzalkonium chloride impairs epithelial wound healing. Seino S, Matsuoka R, Masuda Y, Kunou M, Okada Y, Saika S. Cutan Ocul Toxicol. 2019 Oct 14:1-8.

Purpose: To evaluate the effects of topical hyaluronan (HA) on corneal epithelial wound healing when administered with or without benzalkonium chloride (BAC).
Methods: A cultured human corneal epithelial cell line (HCE-T) was subjected to in vitro scratch assays and in situ epithelial migration was evaluated in organ-cultured rabbit corneas. The corneal epithelium of C57BL/6J mice was also evaluated to determine in vivo wound healing. An in vivo imaging system was also used to evaluate the effects of HA on eye drop retention on the ocular surface.
Results: The findings revealed the promotion of HCE-T migration, in situ rabbit corneal epithelial migration, and in vivo wound healing in mouse corneal epithelium by HA. Pre-treatment with HA also protected against delayed epithelial wound healing in BAC in vitro. However, pre-treatment with 3 mg/mL HA did not show a protective effect against BAC in vivo, but instead delayed epithelial wound healing and increased detection of cleaved caspase-3. This suggested that HA promotes the retention of BAC on the ocular surface. The instilled HA was retained after 15 min, at a significantly higher rate than for phosphate-buffered saline.
Conclusions: The combination of HA and BAC impaired wound healing in the corneal epithelium.