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P.C. Lai, H.I. Savage, A.S. Payman; Refractive Suprise after Contact Ultrasonography (RESCU) . Invest. Ophthalmol. Vis. Sci. 2003;44(13):212.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: This study sought to determine if there was a meaningful and significant difference between postoperative refractive results when IOL powers were determined with immersion ultrasonography rather than contact ultrasonography. We also compared these two measurements with a linear regression analysis of clinical characteristics of our patient population to determine if there was a substratification of patients for whom one technology would be superior to the other. Methods: Fifty consecutive cataract patients underwent axial length measurements by contact ultrasound (CU) and immersion ultrasound (IU). CU [Mentor A/B Systems] was performed manually. IU was performed using the Prager Shell through sterile saline. Keratometry was performed using a calibrated manual. Axial length measurements were used to calculate a predicted postoperative spherical equivalent refractive error using the SRK-T formula. We determined the predictability of refractive outcomes derived from each of the two ultrasonographic techniques and compared them employing the Wilcoxon Rank Sign test. Univariate analysis [SAS, Cary, NC] was used to determine whether central corneal thickness (CCT), intraocular pressure (IOP), mean corneal thickness (mean K), astigmatism, axial length (AL), intraocular lens power (IOL), or patient age correlated with predictability of refractive outcomes from each measurement technique. Results: The correlation between IU and refractive outcome (R=0.67, p=0.001) was significantly better than CU (R=0.59, p=0.001). The mean absolute value difference between predicted and actual postoperative spherical equivalent was 0.6 +/- 0.6 D by IU, and 0.9 +/- 1.0 D by CU. Two factors correlated with refractive predictability using CU and IU. Flatter corneas (lower mean K) correlated with worsening refractive predictability for both CU (R= -0.43, p=0.002), and IU (R= -0.30, p=0.04). Higher IOL power was associated with a significant correlation with poorer refractive predictability (R=0.28, p=0.05). No correlation was found for CCT (R=-0.13, p=0.39), IOP (R=0.06, p=0.7), axial length (R=-0.21, p=0.15), astigmatism (R=-0.14, p=0.34), or age (R=0.006, p=0.97). Conclusions: IU more successfully predicts postoperative cataract surgery refraction than CU. This is true even for one new to the technology. Significant markers for poor refractive predictability by CU and IU include flatter corneas, and higher power IOL implants. CCT, IOP, axial length, astigmatism, and patient age did not correlate with predictability by either CU or IU.
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