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G Hu, P Challa, T Kim, A Carlson; Nomogram-guided Adjustment of IOP Measurement Following LASIK for Myopia, Based on the Amount of Refractive Correction . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2107.
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Purpose: The diagnosis and management of glaucoma in patients following LASIK is challenging, as excimer laser ablation artifactually lowers IOP readings. Although this reduction in IOP has been correlated with changes in central corneal thickness, preoperative pachymetry measurements are often not available to the consulting physician. This study aims to develop a nomogram to estimate the true IOP in post-LASIK, myopic patients based solely on the amount of refractive correction, which is often the only available historical data. Goldmann applanation, the choice of intraocular pressure measurement modality by most glaucoma specialists, is employed exclusively. Methods: A review of 228 LASIK cases performed for myopic correction at the Duke Aesthetic Center from 4/1997 to 1/2001 was undertaken retrospectively. Preoperative refraction, IOP measurement by Goldmann applanation, and other variables were recorded at the initial consultation. Manifest refraction and IOP were again recorded during follow-up visits 3 to 29 months postoperatively (mean=10.1 months). The correlation between the change in IOP and the amount of myopic correction was evaluated by regression analysis. Other parameters, including visual outcome and thickness of ablation, were also analyzed to establish the comparability of LASIK technique employed in this series and other published studies. Results: LASIK induced a mean refractive shift of +4.64 D (SD=1.9 D), a mean stromal ablation of 57.2 mm (SD=24 mm), and a mean decrease in IOP of 3.24 mmHg (SD=2.4 mmHg). A nomogram for adjusting IOP measurement based on the amount of myopic correction is described. For every 1 D of myopic correction induced by LASIK, IOP reading is artifactually lowered by 0.4 mmHg postoperatively (P<0.00000), comparable to other published studies. In addition, an initial reduction of 1.5 mmHg is observed and thought to be the result of flap creation alone (P<0.00000). Conclusion: This study shows that, even in the absence of preoperative pachymetry readings, the amount of myopic correction can be independently used to estimate the true IOP following LASIK. This is of particular relevance to the diagnosis and managmement of glaucoma suspects, ocular hypertention and glaucoma patients.
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