EyeWorld Asia-Pacific June 2013 Issue

44 EWAP rEfrActivE June 2013 Views from Asia-Pacific Myoung Joon KIM, MD Associate Professor, University of Ulsan College of Medicine, Asan Medical Center 88, Olympic-ro 43-gil, Songpa-gu, Seoul 138-736, Korea Tel. no. +82-2-3010-3975 Fax no. +82-2-470-6440 joon@amc.seoul.kr R ecently, wavefront technology has enabled precise measurement of wavefront errors in eyes and there have been attempts to correct higher order aberration in keratoconus using customized contact lenses. There are many challenges in the development of customized contact lenses for keratoconus. The first challenge was measuring a large magnitude of optical aberrations. Advanced keratoconic eyes have higher order aberrations which are several times that of normal eyes. The accuracy of wavefront sensors designed for normal eyes was questioned. The solution was the high dynamic range wavefront sensor. The second challenge was positional stability of the contact lens on the cornea. Positional instability of contact lens is commonly observed in keratoconus. Decentration and rotation of contact lens were the limitation to higher order aberration correction. Back surface modification of soft contact lenses is an example of an effort to improve positional stability. Recently, there was a study using a wavefront-guided scleral lens prosthetic device. Since the scleral lens prosthetic device with a diameter of about 20 mm has excellent positional stability, the lens movement is expected to be improved. The study showed that customized scleral lens prosthetic device reduced higher order aberration of advanced keratoconus patients to the level of the normal eye, but average visual acuity was still lower than that of the normal eye. Neural deficit by chronic exposure to blurred image may lead to such phenomena. The third challenge lies here in neural adaptation. The forth challenge is cost. The higher cost of customization is also a problem to consider. Also, since keratoconus is a progressive disease, aberration changes continuously. According to the change in aberration, the customized contact lens will need to be exchanged continuously as well. Despite all these challenges in customized contact lens for keratoconus, this technology seems to be very close to clinical application. It would be positioned in between intolerance to conventional gas permeable lens and surgical interventions or even as a primary treatment for keratoconus due to the potential to surpass gas permeable lens performance or surgical outcomes. Reference Sabesan R, Johns L, Tomashevskaya O, Jacobs DS, Rosenthal P, Yoon G. Wavefront- guided scleral lens prosthetic device for keratoconus. Optom Vis Sci. 2013;90:314-23. Editors’ note: Dr. Kim has no financial interests related to his comments. Robert Edward ANG, MD Senior Consultant, Asian Eye Institute 8th Floor Phinma Plaza, Rockwell Center, Makati City, Philippines 1200 Tel. no. +63-2-8982020 Fax no. +63-2-898-2002 RTAng@asianeyeinstitute.com , angbobby@hotmail.com P atients with keratoconus come for consult at different stages of the disease. Astigmatism and higher order aberrations increase as the disease progresses. Consequently, finding a solution to improve quality of vision becomes more elusive and difficult. Typically, we start a patient on rigid gas permeable lenses to improve vision. If the patient feels discomfort, the cornea develops scarring or vision gets worse as the disease progresses despite the RGP lens, then we recommend a surgical option such as collagen crosslinking or intracorneal rings. If any of these two surgical options prove successful in halting progression, stabilizing the cornea or improving the keratometry to more manageable levels, then we prescribe RGP lenses again to further improve vision. Corneal transplant is reserved as a last option when all these maneuvers fail. Having a soft contact lens option is welcome news indeed for our keratoconus patients. While we do not expect this lens to halt progression, it nevertheless can act as a substitute for RGP lenses and possibly offer better vision because of customization. The advantages of a soft contact lens option are less discomfort and less chance of corneal rubbing and scarring. Patients will want to try any and all lenses before proceeding to surgery. Even after crosslinking, intracorneal rings or corneal transplant, this customized lens can help fine-tune vision. We have been using aberrometers for the past 10 years in refractive surgery to do wavefront-guided LASIK with good success. Measuring highly aberrated eyes such as those with keratoconus or ectasia and customizing a contact lens is another great use for this technology. We congratulate Dr. Yoon and his lab for embarking on such a difficult project. The applications will start from keratoconus but once we are able to customize the lenses, we can expand its use to post-transplant, presbyopic, aphakic and post-traumatic patients. More indications may eventually lower the costs and make this special lens more affordable to a greater population Editors’ note: Dr. Ang has no financial interests related to his comments.