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SM Ahmad, M Fuhrman, MM Fahim, IJ Dualan, SA Haji, ML Nedjar, PA Asbell; Calculation of IOL Power following INTACSTM . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4125.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: INTACS are an accepted method to correct mild to moderate myopia. One concern with this procedure is that in the future, when the patients develop age-related cataracts it may be difficult to determine IOL power, as has been reported in LASIK patients. This may be especially true, because at the time of cataract surgery pre-refractive keratometry, axial length, and refraction are usually unobtainable. To determine if this is an issue with INTACS, IOL power was calculated utilizing pre and post- INTACS operative data. Methods: Data was collected in 38 consecutive patients (55 eyes) who underwent INTACSTM placement as part of a FDA Phase II safety and efficacy trial. Pre and post-operative values, including average keratometry (K) and axial length (AL) were determined for each eye. Using a standard IOL power formula (SRK II), a comparison of pre and post -operative IOL power calculations was performed and the results analyzed. Results: Comparison of post-operative keratometry readings demonstrated flattening of the central cornea by an average of 2.16 D ± 1.12, as would be expected in refractive surgery for myopia. Axial length measurements before and after refractive surgery varied, but not always in the same direction: a decrease was observed in 42% (n=23) with an average change of -0.37mm ± 0.23 and a increase observed in 58% (n=32) with an average change of 0.25mm ± 0.27. Changes in AL did not correlate with ring segment sizes. Utilizing a standard IOL formula, SRK II, 75% (n=41) required a higher IOL power (average increase 2.16D ± 1.06), while 16% (n=9) required a lower IOL power (average decrease 0.89D ± 0.42). No difference in IOL power was observed in 9% (n=5). Conclusion: In post-INTACS patients, using standard information for IOL power calculations (AL, K) the results seemed to vary in a non-predictable way, when compared to calculations where pre-operative data was used. The changes in IOL power calculations did not correlate with induced refractive changes. Previous studies have advocated the use of a refraction-derived method to increase accuracy after refractive surgery, but this method requires pre-refractive data. Our results showed that the placement of INTACSTM may create, similar to LASIK, difficulties in calculating appropriate IOL power. However, with INTACS surgery the ring segments can be explanted and typically measurements return to the pre-operative values; then, standard and accurate IOL power determinations could be performed.
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