EyeWorld Asia-Pacific March 2017 Issue

March 2017 EWAP refractive 45 Views from Asia-Pacific Xiuming JIN, MD, PhD Director of Cornea and Ocular Surface Department of Eye Center Second Affiliated Hospital, School of Medicine, Zhejiang University 88 Jiefang Road, Hangzhou, China Tel. no. +86-571-87783897 Fax no. +86-571-87783897 lzyjxmi@zju.edu.cn I t is well known that the use of crosslinking protocols is very effective in the treatment of keratoconus and halting the progression of keratoconus. Using CXL, ophthalmologists can reshape the corneal structure without the use of invasive surgeries such as penetrating keratoplasty or lamellar keratoplasty. Residual corneal thickness of less than 400 μm was once an absolute contraindication for CXL, but Dr. Hafezi expands indications for corneas thinner than 400 μm by swelling the cornea using a hypo-osmolar riboflavin or using a contact lens. He treated patients with this method and those patients didn’t have any surgical complications. Therefore, swelling the cornea can be used in some patients with thin corneas originally not suitable for this treatment. In Dr. Kling’s study, he used porcine eyes and murine eyes to represent standard corneas of 400 μm in thickness and thinner corneas; dependency on oxygen and the amount of UV absorption were evaluated using different CXL protocols, including standard CXL, contact lens-assisted CXL (caCXL), and CXL after corneal swelling. This research confirmed that standard CXL was most efficient. Dr. Kling also concluded that the higher oxygen availability in thin corneas potentially increases the overall efficacy of riboflavin UV-A CXL compared to corneas of standard thickness. However, clinical efficacy remains to be seen. If this method is clinically proved to be effective, it will be a major step forward in the treatment of keratoconus. Currently, iontophoretic collagen crosslinking (I-CXL) has been found to be as effective as the standard technique in some studies. Finally, I want to present some of my views: 1. Some methods should be used to speculate the relationship among the content of oxygen, and the amount of UV absorption and the swelling cornea using a hypo-osmolar riboflavin or using a contact lens. 2. The safety and efficacy need to be followed closely for corneas thinner than 400 μm at swelling cornea using a hypo-osmolar riboflavin or using a contact lens. 3. Ultraviolet rays can damage the corneal epithelium, and may cause corneal epithelial haze. In visible light, thermal radiation that is longer than ultraviolet rays may be used in the crosslinking protocols. 4. Besides, CXL is also used to prevent corneal ectasia after laser surgery; I wonder if CXL can be used for astigmatism treatment directly by changing UV energy, riboflavin, and oxygen content? These views require further experimental studies to confirm. Editors’ note: Dr. Jin declared no relevant financial interests. Sri GANESH, MD Chairman, Nethradhama Hospitals Pvt Ltd 256/14, Kanakapura Main Road, 7th Block Jayanagar, Bangalore – 560070 Tel. no. +91-80-26088000 Fax no. +91-80-26633770 C orneal crosslinking with riboflavin and UV radiation has become a popular procedure to treat ectatic corneas to stabilize and prevent progression of ectasia. Since the original Dresden protocol was described in the 1990s, there have been a number of protocols which have evolved since then to improve patient comfort and reduce treatment time. These include accelerated crosslinking, pulsed accelerated crosslinking, and transepithelial crosslinking. Accelerated crosslinking is based on the law of reciprocity which increases energy to reduce treatment time. However, some of these new protocols have not had as good a success rate as the original Dresden protocol. This could be due to the role of oxygen in the process of crosslinking. This article by Hafezi et al. demonstrates the role of oxygen in crosslinking and biomechanical stability and conclude that thicker corneas have poorer crosslinking than thinner corneas due to lesser oxygen diffusion using the same UV energy per volume. Accelerated crosslinking uses up the available oxygen in the first few seconds of high energy UV radiation and poor availability of oxygen during the rest of the treatment may not result in the desired stiffening of the cornea. In the standard Dresden protocol, lower energy longer duration treatment results in better oxygen diffusion and thus better biomechanical strengthening. The available oxygen or the depletion of oxygen is very significant while applying the law of reciprocity. However, in clinical practice we see that accelerated crosslinking appears to stabilize the cornea in ectatic conditions and prevent progression in majority of cases. This may be due to the fact that individual patients may have different biomechanical responses to crosslinking depending upon age, stage of ectasia, corneal thickness and other related factors like eye rubbing and inflammation. We see that the accelerated crosslinking or transepithelial crosslinking may not be as effective in the pediatric age group as the standard Dresden protocol. Hence, there is a need to ideally take into consideration age, stage of ectasia, corneal thickness, and probably measure corneal biomechanics before considering the protocol of corneal crosslinking to use. Editors’ note: Dr. Sri Ganesh is a consultant for Carl Zeiss Meditec (Jena, Germany) and Abbott Medical Optics (Abbott Park, Illinois). continued on page 46