EyeWorld China September 2019 Issue

Comparison of Wavefront-optimized vs Topography-guided vs TMR LASIK Prof Tae-Young Chung Prof Chen Yueguo Chairman, Department of Ophthalmology Peking University Third Hospital, China Prof Tae-Young Chung Associate Professor, Department of Ophthalmology Samsung Medical Centre, South Korea Dr. Arthur Cheng Consultant ophthal- mologist and refractive surgeon Hong Kong Sanatorium Hospital Prof Zhai Changbin Tongren Eye Center, Beijing Tongren Hospital, China 3 When performing topography-guided LASIK, if CA< MRA, treating CA with TMR- TG is a preferred choice. If the CA > MRA, treating MRA with FDA-TG seems to be a more suitable option. Using modified TMR (treating midpoint between MRA and CA) when CA > MRA may also result in astigmatic over-correction. A comprehensive pre-operative evaluation, excellent topography, appropriate patient selection, high quality images with Topolyzer VARIO and understanding biomechanical properties of the cornea are crucial for successful treatment with Contoura TM Vision. Capturing high-quality images with Topolyzer VARIO is another crucial determinant of treatment success. It is recommended to have at least 4-8 images before the day of surgery. “Sometimes, the VARIO images do not work well when the cyclotorsion fails to register, in which case a manual marking or manual alignment (with the red cross-line projector under the EX500) of astigmatism is needed,” added Dr. Ryu. Another consideration for topography- guided Contoura TM Vision is to understand the biomechanical properties of the cornea. Patients with Tomographic/Biomechanical Index (TBI) > 1 should be excluded from laser refractive surgery. TBI cut-off value of 0.79 provides 100% sensitivity for detecting clinical ectasia with 100% specificity. 2 Adding accelerated cross-linking inborderlinepatients and converting to phaco surgery is the surgeon’s personal preference, noted Dr. Ryu. An active customer relationship management, ensuring patient satisfaction and results is another reason for selecting Contoura TM Vision. Dr. Ryu continued “My aim is to convert LASIK and PRK to customized ablation to provide accuracy and satisfaction to the patients”. “The challenge with wavefront-optimized ablation is that the human wavefront aberration is dynamic and constantly changes with accommodation (leading to aspherical ablation), whereas topography-guided ablation aims to target the aberration at the anterior surface of the cornea, which is relatively constant regardless of accommodation. This is why we should treat corneal aberration rather than ocular aberration,” said Prof. Tae-Young Chung. However, since treatment of corneal HOA has an effect on refractive outcome, it is believed that treating refractive astigmatism and corneal HOA would result in over-correction or under- correction of refractive astigmatism depending on the axis difference. Therefore, the concept of topography-modified refraction (TMR) was introduced, which involves treating corneal HOA and topography-based corneal astigmatism instead of treating corneal HOA and the manifest refraction (FDA-TG). In addition, in sub-group analysis of TMR-TG, astigmatic over-correction was more when corneal astigmatism (CA) was greater than manifest refractive astigmatism (MRA). Astigmatic over-correction was associated with pre-operative magnitude difference between CA and RA, which is quantified by ocular residual astigmatism (ORA). “Since a higher ORA is associated with poor visual outcome it needs to be detected early to avoid suboptimal visual outcome,” highlighted Prof. Chung.