EyeWorld Asia-Pacific December 2018 Issue

Pannet PANGPUTHIPONG, MD Deputy Director General, Department of Medical Services, Ministry of Public Health Nonthaburi 11000, Thailand Tel. no. +66-2-591-8239 Fax no. +66-2-591-8240 pannetp@hotmail.com Grooving Efficiency Modern cataract surgery involves breaking the nucleus into small pieces that can be easily and safely aspirated from the eye (except for soft nucleus). Many techniques are available to achieve this goal depending on the types of nucleus and the surgeon preferences and experiences. Each technique has advantages and disadvantages. Divide & Conquer / Cruciate Division Chop / Quick Chop / Prechop Stop & Chop Beginner’s Choice Spectrum of Nuclear Disassembly Techniques There are two bevel position we can use to make a groove: Bevel Up: A conventional position of the phaco tip to sculpt the nucleus and create the groove is bevel up. The efficiency of nucleus emulsification depends on the amount of U/S energy and the degree of the bevel of the phaco tip. The amount of nucleus covered with each passage and the velocity of the phaco tip forward movement must be adjusted according to the hardness of the nucleus. The most common setting is a 30-degree phaco tip with 50% U/S energy. In a hard nucleus, we can increase the efficiency of nucleus emulsification by increasing the U/S energy and slow movement covering small amounts of the nucleus at a time. Otherwise, there will be untoward stress on the zonules from excessive pushing of the nucleus. The surgeon may also choose to increase the angle of the bevel to 45 degrees. However the resulting larger bevel area will lead to more difficult occlusion. It will take longer to remove the segment. Bevel Down: In this technique, the surgeon points the bevel of the phaco tip downward, emulsifying the nucleus underneath. The surgeon constructs the groove by repeating emulsification in overlapping areas until the proper depth is reached. One may use a hook or chopper to help stabilize the nucleus during grooving. The advantage of bevel down is the forces on the zonule are equally distributed 360 degrees. The vitreous below the lens also provides further support against the downward forces. In contrast, only the zonules in the main incision area support the forces exerted during the bevel up sculpting. Furthermore, bevel down allows for phaco aspiration because the tip is mostly occluded. The built-up vacuum will help increase emulsification efficiency because the phaco tip can impact the nucleus with greater force. Normally, the vacuum is set lower than 100 mmHg to prevent engaging the phaco tip. In case of hard nucleus, the surgeon can increase both the vacuum and U/S power. The phaco tip should also be moved more slowly to emulsify and remove nucleus without excessive stress on the zonules. After making a nice, deep groove, the nucleus can be cracked and removed using bevel position sideways . I prefer bevel down phaco because of efficiency, especially in a hard cataract, but one has to learn how to safely adopt the technique. Emulsification Efficiency • Phaco Sculpting depends on :- • U/S power • Tip angle • Phaco aspiration depends on :- • U/S power • Vac Impact Force = Tip Impact ( U/S Power ) + Holding Force ( Vac ) Impact Force = Tip Impact ( U/S Power ) Emulsification is Enhanced by Vacuum Less U/S Energy is Needed Zonular Stress Zonular Stress Zonular Stress Zonular Stress During Bevel Up and Bevel Down Grooving Vitreous Support Editors’ note: Dr. Pangputhipong declared no relevant nancial interests. continued on page 46 EWAP CATARACT/IOL 43 December 2018