Eyeworld Supplements

EW MAY 2017 – Sunday – Supported by Alcon A Novartis Division

This is a supplement to EyeWorld Magazine.

Issue link: https://supplements.eyeworld.org/i/824595

Contents of this Issue


Page 5 of 7

6 –4.99 –0.31 x 34. However, Contoura is detecting astig- matism along an axis of 10 degrees. (Figure 1). Double checking the Contoura against another topographer, the Orbscan, shows it too detects corneal astigmatism along axis of 10 degrees. (Figures 2 and 3). The surgeon now faces a decision: choose the astigmatic axis based off manifest or measured? Figure 4 shows that there is a 48 degree difference between these two and an 0.62 D dif- ference in magnitude. A lot of difference! Why are they so different? What should be treated? The answer lies in the influence that the topograph- ic abnormalities have on how light is being focused. The manifest is the optical image as it strikes the retina. It is the sum total of the effects of the smaller topographic abnormalities and the true corneal astigmatism. Figure 5 shows just the topographic correction for this eye after removing the cylinder and sphere from treatment. It is the effect of these smaller topographic abnormalities that "bend" the manifest cylinder away from the true corneal measured astigmatism. Once you remove these abnor- malities, the true corneal cylinder measured by Contoura is at 10 degrees. This is the cylinder that should be treat- ed with Contoura topographic LASIK. By treating all of the corneal abnormalities, vision sharpness and better than normal manifest results can be obtained. It seems to be a leap of faith for the surgeon at first to treat a different axis than manifest refraction but the optical physics here are real and can and should be trusted to gain the best possible results. T opographic-guided LASIK is available in the United States as Contoura from Alcon. It is a versatile and powerful new tool for refractive surgery. However, it does require refractive surgeons to rethink their treat- ment calculations and to consider the patient's total refractive error in a new way. In the past, LASIK surgeons would simply target the patient's astigmatic axis and magnitude off the patient's manifest refraction. As surgeons begin to become more precise and target the small topographic imperfections of the cornea, they must treat the astigmatic axis and magni- tude that the advanced Contoura topographer detects. It be- comes disconcerting when the Contoura astigmatism differs from the manifest. At this point, the surgeon needs to resist his or her experience-based knowledge and trust the technol- ogy, treating measured and not the refraction axis. This case highlights these issues. The patient is a 23-year-old woman. Pre-LASIK MRx is –5.00 –0.50 x 35 20/15. Wavefront PPR is in good agreement with this at Case study: Trust the technology by Mark Lobanoff, MD Figure 1 Figure 2 Figure 3 Figure 4 Figure 5: Topographic abnormalities to be treated in this eye Figure 6: MRx cylinder axis vs. Vario measured axis Mark Lobanoff, MD, is in private practice at North Suburban Eye Specialists in Minneapolis. He can be contacted at mlobanoff@gmail.com.

Articles in this issue

Links on this page

Archives of this issue

view archives of Eyeworld Supplements - EW MAY 2017 – Sunday – Supported by Alcon A Novartis Division