EyeWorld India December 2018 Issue

CHEONG Fook-Meng, MD Head of Ophthalmology Department, Gleneagles Kuala Lumpur 282 Jalan Ampang 50450 Kuala Lumpur Malaysia Tel. no. +60-3-42570299 Fax no. +60-3-42570298 fmcheong@gmail.com A ppropriate utilization of preoperative diagnostics forms the basis for attaining the ever-increasing standards for refractive outcomes that are expected today. An important element in preoperative diagnostics in my practice is the evaluation of ocular surface/tear film quality. These will affect the accuracy of diagnostic corneal measurements, impacting on eventual refractive outcomes. A second element is the OCT-assisted macula evaluation. These are performed in every patient undergoing cataract surgery and are especially relevant when considering presbyopia-correcting IOL implantations. For IOL power evaluations, I use a combination of devices consisting of an autokeratometer, an optical biometer, a digital image-guided toric marker, and a corneal topographer. My current preferred IOL formulas are the Barrett Universal II and Hill-RBF, with bias towards the former when there are disparities between the two. Landmark papers by Prof. Douglas Koch’s team on the contribution of posterior corneal astigmatism (PCA) to total corneal astigmatism and its effect on refractive outcomes led to the practice of preoperative PCA measurements. However, recent studies presented within the past year have indicated that the outcomes from updated toric IOL formulas which incorporate population-based estimations of PCA, such as the Barrett toric calculator, were as good as, if not better than that gained from direct measurements of PCA using the current generation of devices. As astigmatism management has been shown to improve visual quality and patient satisfaction, I now use the Barrett toric calculator on virtually all patients. Any eye with anterior corneal astigmatism of more than 0.4 D measured on any one of my diagnostic devices will have calculations performed on the Barrett toric calculator. Eyes with 0.3 D to 0.4 D astigmatism will be assessed individually to decide if they require toric calculations, depending on the axes, IOL types, and patients’ needs. As stated in the article, the online calculator has a useful feature that takes the median of several different K-readings computed from multiple diagnostic devices that I use. Finally, I use the digital image marker and its microscope overlay in every cataract operation, not just in toric IOL implantations. It ensures consistent placement of my incisions in every case by compensating for cyclotorsion that can occur when patients are supine. The capsulorhexis overlay helps guide the performance of appropriately sized and centered capsulorhexis so that the anterior capsule edge is consistently within the optics of the IOLs. Transitioning to the methods described above has helped raise the bar even higher for refractive outcomes in my practice. Editors’ note: Dr. Cheong declared no relevant financial interests. Rohit SHETTY, MD Vice chairman and Head of Cornea and Refractive Department, Narayana Nethralaya, Bangalore Tel. no. +96111-2568 drrohitshetty@yahoo.com C ataract surgery is becoming more like a refractive procedure with patients wanting perfect outcomes and 20/20 vision every time. For optimal postoperative results, the preoperative evaluation has to include not only an accurate IOL calculation but also measurement of the corneal biomechanics and evaluation of the ocular surface and optics of the eye. One important consideration is the contribution of the posterior cornea to the total corneal astigmatism. It is essential to keep this in mind to avoid errors in IOL power calculation, especially for irregular corneas. Relying solely on the anterior corneal curvature measurements could result in residual astigmatism after toric IOL implantation due to over correction or under correction. The keratometers and Placido based topography systems assume a fixed ratio between the anterior and posterior curvature and may show errors in keratometry estimation. The slit scanning systems, Scheimpflug imaging, and OCT measure both the anterior and posterior corneal curvature and are more accurate in this regard. Evaluation of the ocular surface and the optics of the eye prior to cataract surgery is another mandatory step to improve postoperative comfort and visual outcomes. A detailed dry eye workup including Meibomian gland assessment both clinical and Meibography and a tear film assessment adds value to this. An abnormal tear film is also known to affect the quality of vision which can be assessed by the Optical Quality Analysis System (OQAS, Visiometrics SL, Spain) based on an asymmetric double pass technique. This enables the detection of both symmetric and asymmetric aberrations (such as coma). The optical scatter index (OSI), modulation transfer function, and Strehl ratio are good measures of the quality of vision of the patient both pre- and postoperatively. Corneal Biomechanics also have a very important role to play in perfecting post cataract surgery outcomes. They can be measured using the Corneal Visualization Scheimpflug Technology tonometer (Corvis ST tonometry: CST, Oculus, Wetzlar, Germany). In addition to the effect of incision size on surgically induced astigmatism, biomechanics also modulates the refraction and optical changes. Taking into account the biomechanical features of the cornea preoperatively helps us predict the postoperative refractive outcomes better. The role of preoperative ocular surface inflammation cannot be underestimated in postoperative wound healing. Inflammatory markers such as MMP9 can be used to predict which patients are likely to have more dry eye or ocular surface issues after surgery and preemptively treat them. These few important extra steps go a long way in making patients happy post cataract surgery. Editors’ note: Dr. Shetty declared no relevant financial interests. continued on page 50 EWAP CATARACT/IOL 49 December 2018