Not long ago, riboflavin/UV-A corneal crosslinking (CXL) was introduced to ophthalmic practice. Initially aimed for the treatment of ectatic corneal conditions, including keratoconus, pellucid marginal degeneration, and postlaser keratectasia, it is now also used to treat for bullous keratopathy, infectious keratitis, and corneal melting, and for the stabilization of post-radial keratotomy hyperopic shifts. Crosslinking forms new covalent bonds between collagen fibrils; hence, corneal rigidity improves.
The standard protocol for CXL requires mechanical removal of the epithelium. The drawbacks of this step include prolonged surgical time, increased incidence of herpetic activation and haze development, corneal edema, postoperative pain and discomfort, and reduced visual acuity until epithelialization is complete and corneal edema is resolved. We have been motivated to develop a variant technique in which the epithelium is not removed.
In our technique, riboflavin containing benzalkonium chloride (BAK) is applied directly onto the intact epithelium. As a tensioactive substance, BAK changes the surface tension value, facilitating penetration of other substances through biological membranes. In CXL, BAK allows riboflavin to penetrate into the corneal stroma without removal of the epithelium.
We have demonstrated the results of tensioactive CXL in rabbit corneas (Figure 1) and compared it with the standard CXL protocol (control group).1,2 With our treatment, the epithelial surface retained its curvature due to increased stiffness and was more compact. In the stroma, the fibers not only showed more compact arrangement but were also straighter than the wavy fibers of the control corneas. This effect was noticed in the upper 50% of the stroma. Additionally, the deep stroma adjacent to the endothelium looked the same as the control.
BAK, which is contained in many eye drops prescribed to patients, can cause lifting and peeling of some superficial epithelial cells, exposing the second layer of cells; however, it does not cause change in the basal epithelial or endothelial cells. We conclude that the benefits of using BAK to avoid epithelial removal in CXL outweigh the drawbacks of epithelial removal. Tensioactive CXL is a less invasive procedure with fewer complications and increased patient comfort.
Roberto Pinelli, MD, is the Scientific Director of ILMO, Brescia, Italy. Dr. Pinelli states that he has no financial interest in the products or companies mentioned. He may be reached at tel: +39 030 24 28 343; e-mail: pinelli@ilmo.it.
Hytham Ib El-Shawaf, MD, is a Fellow of Research and Development at ILMO, Brescia, Italy. Dr. El-Shawaf states that he has no financial interest in the products or companies mentioned. He may be reached at tel: +39 030 24 28 343.
