Eyeworld

EW NEWS & OPINION 24 January 2017 Pulse of ophthalmology: Survey of clinical practices and opinion by Mitchell Gossman, MD uncorrected visual acuity, our most common goal, assuming no mean- ingful astigmatism is present. When looking at the biometry printout, we are faced with a deci- sion. How often is there a lens pow- er that is projected to produce a final postoperative refractive outcome of 0.00? Not very often (see Figure 1 for example). So what to do? The first question in the survey was, "You are planning cataract surgery. With your biometry in hand for both eyes, you apply your favorite formula, and your target is emmetropia for best unaided dis- tance correction. Generally speak- ing, do you choose the lens power that targets: absolute value closest to 0.00; least minus; or absolute value closest to 0.00, but if this projects hyperopia exceeding 'X,' opt instead for least minus?" As Table 1 shows, not very many —only 8%—selected the IOL power that is most likely, on average, to give a result closest to emmetropia and thus the best distance uncor- rected vision. Most choose the IOL power that produces the smallest myopic result even if that myopia is greater in degree than the smallest hyperopic result. Why is this? 0.25 refraction steps and regard em- metropia as –0.125 through +0.125. Experience and studies have shown that approximately 80% of patients fall in the +0.50 to –0.50 range (inclusive) spherical equivalent, and 95% fall in the +1.00 to –1.00 range; this leaves 5% who fall outside the +1.00 and –1.00 range. It is likely that most ophthalmologists agree that being in the range of +0.50 and –0.50 is good enough in the sense of maintaining satisfactory distance variations and biases present in your specific equipment, you can be confident that the average residual refractive error for your own pa- tients, when enough are pooled, will be very close to 0.00 with "normal" eyes. Unfortunately, there is impre- cision, with a spread of results. In fact, if we could measure refractive error with great precision, almost no one would achieve exactly emmetro- pia defined as, say, 0.000+/–0.005. However, we do work generally in Part 1 in a series on the complexities of everyday IOL decisions T he optical coherence tomography (OCT) revolu- tion as applied to biometry with its greater precision as well as advancements in theoretical IOL power formulas have made IOL power calculations much more precise and accurate. However, when planning surgery, we still face decisions where lens power selection can seem more art than science. It is my hope that this series of articles will be a useful journey, and food for thought, in the day-to-day power selection situations cataract surgeons face. A survey was performed of 74 ophthalmologists who volunteered to participate from the EyeConnect online community in North Amer- ica. Responses are anonymous to encourage candor. Totals may not equal 100% due to rounding. Assuming you have optimized your A-constant and thus have accounted for surgical technique Art of IOL power selection: Fudge factors Mitchell Gossman, MD Figure 1. LENSTAR biometry example Source: Mitchell Gossman, MD Absolute value closest to 0.00 8% Least minus 74% Absolute value closest to 0.00, but if this projects hyperopia exceeding "X," opt instead for least minus. Specify your "X." For example, say your cutoff for maximum projected hyperopia is +0.10. If a +21.50 IOL projects +0.15 outcome and a +22.00 projects –0.21 outcome, you will use the +22.00 lens targeting –0.21 even though this is greater in absolute value than +0.15. On the other hand, if your cutoff maximum projected hyperopia +0.18, you would go with the +21.50 lens targeting +0.15. 19% Table 1: Results of question 1

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