Eyeworld

EW RESIDENTS 44 December 2011 Instrument and microscope myopia: What's all the focus about? Chi-Wah Rudy Yung, M.D., professor of ophthalmology, Eugene and Marilyn Glick Eye Institute, Department of Ophthalmology, Indiana University School of Medicine, Indianapolis Instrument myopia is the overac- commodation that occurs when looking through an optical instru- ment such as an operating micro- scope. Possible causes of instrument myopia include limited field of view, perceived proximity of the target, and improper setup of the micro- scope. Many factors can affect the magnitude of instrument myopia and thus accommodation. These in- clude pupillary distance (distance between the eyepieces), image mag- nification, how the microscope is fo- cused (direction of focus), and the user's microscopy experience. Set- ting the distance between the two eyepieces based on the surgeon's dis- tant pupillary distance will mini- mize convergence since the visual axis of both eyes will be close to par- allel. This helps to reduce the ac- commodation that occurs when looking into the microscope. Higher magnification is believed to induce higher accommodation under the microscope. Operating microscopes are de- signed to be parfocal (remain in focus) with change of magnification. However, the microscope must be set up properly before surgery in order for this to occur without in- ducing excessive accommodation. Parfocus procedure is outlined as below: 1. Set proper eyepiece distance based on distant interpupillary dis- tance. 2. Set both eyepiece diopter set- tings to "0." 3. Set the microscope on its highest magnification setting. (This will induce the highest accommoda- tion from the user, thus setting the highest accommodation amplitude that is required during surgery. Dur- ing surgery, lower magnifications will most likely be used and there- fore any induced accommodation should be well within the pre-set amplitude.) 4. Reset the fine focus control so that it is in neutral position. 5. Bring the microscope down to focus on the object, for example, at the iris plane. 6. Without changing the up and down focus of the microscope, change the magnification to its low- est position. Each eyepiece should be focused in turn by dialing out- ward to fog and then turning inward until best focus is attained. 7. Make sure the patient's posi- tion is not changed after the micro- scope is set. Parfocality is assured by this technique, and microscope myopia (accommodation) during surgery is minimized. Talia Kolin, M.D., associate clinical professor of ophthalmology, University of Southern California, Los Angeles, and chief of ophthalmology, Veteran's Administration Los Angeles Outpatient Clinic Accommodative excess is the exer- tion of more accommodation than is necessary and is sometimes seen with prolonged near work such as cataract surgery. This is more com- monly seen in younger surgeons, es- pecially residents who are anxious or doing a stressful case. When the sur- geon overaccommodates, the micro- scope setting prevents the assistant surgeon from being able to focus. While some residents may complete cases without assistance, it is prefer- able that the attending monitoring the case be able to see every step. This requires a solution to the excess accommodation. The first step in ensuring that the microscope setting is suitable for both the young surgeon and older attending is accurate alignment of the operating microscope. Before the surgical procedure begins, the oper- ating microscope must be focused precisely. The surgeon should posi- tion him or herself in a comfortable, natural position with a straight back, flat feet, and relaxed shoulders. The oculars should then be zeroed, an- gled, and positioned for the sur- geon's viewing comfort. High power magnification should be used to ad- just the scope manually. Manual ad- justment of the microscope at high magnification by the surgeon allows a more accurate focus because of the narrowed depth of field. Once the surgeon has set the microscope, the assistant should adjust the oculars as needed in order to have a clear view of the field. The magnification should then be reduced by the sur- geon to a power appropriate to the procedure by using the zoom pedal. This method of microscope adjust- ment will usually prevent unneces- sary accommodation during surgery. In fact once this adjustment is made, fine focusing is rarely needed, and only the zoom pedal should need to be used. When excess accommodation occurs in spite of proper microscope setup, there are various techniques that can be used to overcome this problem. The attending will quickly realize that he can no longer clearly see the operating field. Sometimes verbal reassurance alone is enough M icroscope myopia refers to the tendency of novice and anxious surgeons to ac- commodate when using the operating microscope. This blurs the image for the assisting and often more sen- ior instructor, who may be limited in his ca- pacity to compensate through adjusting the fine focus at the oculars and by his own presbyopia. Visualization is paramount to safe surgery, and the distraction of con- stantly refocusing interferes with the atten- tion that should be paid to the surgery at hand. We've asked Drs. Yung, Kolin, and Bailey for their advice on addressing this common issue. Sherleen Chen, M.D., and Roberto Pineda, M.D. Sherleen Chen, M.D. Assistant professor of ophthalmology Harvard Medical School Director of Cataract and Comprehensive Ophthalmology Massachusetts Eye and Ear Infirmary Roberto Pineda, M.D. Assistant professor of ophthalmology Harvard Medical School Director of Refractive Surgery Massachusetts Eye and Ear Infirmary Cataract tips from the teachers Chi-Wah Rudy Yung, M.D. Talia Kolin, M.D. Robert S. Bailey Jr., M.D.

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