Contact Lens Spectrum Supplements

Special Edition 2017

Contact Lens Spectrum

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56 C O N T A C T L E N S S P E C T R U M S P E C I A L E D I T I O N 2 0 1 7 c l s p e c t r u m . c o m sphere or cylinder powers, large or small diameters, etc. They may be manufactured individually (lathe-cut or cast-molded), but their design choice is still somewhat limited. A number of companies are offering several lens di- ameters and different base curves, if desired. These can be ordered for a monthly replacement schedule and in either conventional or silicone hydrogel materials. One company in the United States even offers a daily dispos- able lens in three different diameters. Following up on the discussion of sagittal height, it can be stated that diameter and sagittal height are more closely correlated than base curve radius and sagittal height. If anything, diameter would be a better alterna- tive than base curve. Measuring corneal diameter ac- curately is not particularly simple or accurate, though, as we are typically measuring the horizontal visible iris diameter (HVID). Researchers found the average cor- neal diameter based on OCT and on the actual transi- tion in shape between the cornea and the limbus to be 13.4 mm instead of the 11.8 mm to which we typically adhere when using HVID. 18,19 From a clinical perspective, however, if you have a larger than average corneal diameter (whatever way that is measured) and the central curves are steep, this indi- cates we are dealing with a large overall sagittal height, and a standard lens most probably will not fit. Out-of- standard lenses would be a viable option. CUSTOM-MADE LENSES These lenses are made individually and specifically for each eye. With these lenses (typically lathe-cut), there are no limits to shape, power, and design, and they may be made in a silicone hydrogel material to benefit from the latest technology in material development. A true tailored fit can be achieved to accommodate the shapes and patterns that may be present on the ocular sur- face. Some companies, for example in conjunction with academia, have developed effective eye modeling based on ocular surface profilometry to develop the best suit- able (literally) soft lens fit. CLOSING REMARKS As one of my former students said, "You can't mea- sure a toe to determine shoe size." The limitations in soft lens fitting are clear, but unfortunately this article doesn't deliver the answers to many of the questions and issues raised. This article is more about understanding soft lens behavior on-eye and maybe more about finding the right question in a way. What is it that we want to achieve? Or as a famous quote, widely believed to come from Mark Twain reads, "It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so." From an educational standpoint, it seems we need to go back to the drawing board to redefine how we teach our students in a plausible way. It appears that in the near future we will see more soft lens parameters from a variety of sources. Without trying to be over-dramatic, I believe, to some degree, the future of our profession as contact lens fitters is at stake. In other words, it is about the survival of the fitting. Many questions remain. It's a learning curve, or perhaps more accurately, it is beyond (base) curves. Microns of height and elevation may be better ways to educate our students to understand soft lens fitting and on-eye behavior. CLS SOFT LENSES REFERENCES 1. Van der Worp E, Mertz C. Sagittal height differences of frequent replacement silicone hydrogel contact lenses. Cont Lens Anterior Eye 2015;38(3):157-162. 2. Papas EB, Tilia D, Tomlinson D, et al. Consequences of wear interruption for discomfort with contact lenses. Optom Vis Sci. 2014;91(1):24-31. 3. Sulley A, Young G, Hunt C. Factors in the success of new contact lens wear- ers. Cont Lens Anterior Eye. 2017;40(1):15-24. 4. Stapleton F, Tan J. Impact of Contact Lens Material, Design, and Fitting on Discomfort. Eye Contact Lens. 2017;43(1):32-39. 5. Caroline PJ, Kojima R. Sagittal Height Calculator Based on Peripheral Cor- neal Angle Measurement. World Wide Vision XIV. Soft Special Edition Newslet- ter. http://www.softspecialedition.com/. Accessed September 2017. 6. Hall LA, Hunt C, Young G, Wolffsohn J. Factors affecting corneoscleral topography. Invest Ophthalmol Vis Sci. 2013;54(5):3691-3701. 7. Sorbara L, Maram J, Fonn D, et al. Metrics of the normal cornea: anterior segment imaging with the Visante OCT. Clin Exp Optom. 2010;93(3):150-156. 8. Van der Worp E, Graf T, Caroline PJ. Exploring beyond the corneal borders. Contact Lens Spectrum. 2010;6:26-32. 9. Wolffsohn J, Hall L, Mroczkowska S, et al. The influence of end of day silicone hydrogel daily disposable contact lens fit on ocular comfort, physiology and lens wettability. Cont Lens Anterior Eye. 2015;38(5),339-344. 10. Caroline PJ. Clinical indications for custom soft lenses. Poster presented during the Global Specialty Lens Symposium; January 2017 in Las Vegas. 11. Michaud L, Tremblay C, Grégoire S, van der Worp E, Mertz C, Wolffsohn J. Relationship between ocular sagittal height and soft contact lens sagittal depth to improve fitting and comfort. Poster presented during the American Academy of Optometry meeting; 2017 in Chicago. 12. Plainis S, Charman WN. On-eye power characteristics of soft contact lenses. Optom Vis Sci. 1998;75(1):44-54. 13. Young G. Mathematical model for evaluating soft contact lens fit. Optom Vis Sci. 2014; 91(7):e167-176. 14. Young G, Hall L, Sulley A et al. Inter-relationship of Soft Contact Lens Diameter, Base Curve Radius, and Fit. Optom Vis Sci. 2017;94(4):458-465. 15. Young G, Potts M, Sulley A. The Effect of Temperature on Soft Contact Lens Diameter. Eye Contact Lens. 2016; 42(5):298-302. 16. Montani G, Van der Worp E. BCE vs SAG vs DIAM. Global Contact. 02/2016: 34-39. 17. Lampa M, Andre M. What is a Custom Soft Contact Lens? Soft Special Edition Newsletter. Fall 2010. http://www.softspecialedition.com/. Accessed September 2017. 18. Hall L, Young G, Wolffsohn J, et al. The influence of corneoscleral topogra- phy on soft contact lens fit. Invest Ophthalmol Vis Sci. 2011; 52(9):6801-6806. 19. Bergmanson JP, Martinez JG. Size does matter: what is the corneo-limbal- diameter? Clin Exp Optom. 2017 Sep;100(5): 522-528. Dr. van der Worp is an educator and researcher from Amsterdam (the Netherlands) and is affiliated with the University of Maastricht as an associate researcher, an adjunct professor at the University of Montreal College of Optometry (Canada), and an adjunct as- sistant professor at Pacific University College of Optometry. He has received educational grants from Bausch + Lomb Boston, Johnson & Johnson Vision, and Contamac.

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