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Purpose: To quantify the total eye astigmatism that is not accounted for by measurement of anterior corneal astigmatism and posterior corneal astigmatism and knowledge of intraocular lens (IOL) astigmatism and assess whether it is correlated with candidate sources of or correlates with leftover astigmatism., Methods: Vector subtraction of anterior corneal, posterior corneal, and IOL astigmatism from total eye astigmatism as represented by spectacle astigmatism to yield a value of "leftover" astigmatism that is neither corneal nor lenticular. This value was derived in a series of eyes following cataract surgery. This novel entity was examined for correlation with candidate sources of or correlates with leftover astigmatism., Results: In 103 pseudophakic eyes with known IOL toricity, mean leftover astigmatism was 0.71 ± 0.43 diopters. This was significantly correlated with against-the-rule anterior corneal astigmatism ( P < .001)., Conclusions: Leftover astigmatism is clinically substantial. Because it is included in IOL cylinder power calculations based on refractive outcome, it may explain why methods of IOL cylinder power calculation using refractive outcome-based adjustments to anterior corneal astigmatism (previously described as adjustments for "posterior corneal astigmatism") are more successful than adjustment on the basis of measured posterior corneal astigmatism. [ J Refract Surg. 2022;38(9):559-564.] .

Purpose: To compare "total keratometry" measurements with Goggin nomogram adjusted anterior keratometry (GNAK) for toric intraocular lens calculation., Methods: Routine biometry provided measured total keratometry values from which astigmatism was derived. The Goggin nomogram was applied to anterior keratometry values on the same eyes to provide nomogram-adjusted anterior keratometry values (GNAK) that estimate total corneal astigmatism. The agreement between total keratometry and GNAK was analyzed., Results: Overall, in 46 eyes there was no statistically significant difference between median GNAK and total keratometry power values (P = .746). No statistically significant difference remained in against-the-rule and oblique subgroup analyses. Absolute and signed steep axis of astigmatism was statistically significantly different for GNAK and total keratometry in the overall analysis (P < .001 and = .029, respectively) and for against-the-rule and oblique subgroup analyses. The with-the-rule subgroup showed a statistically significant difference in astigmatic power and no significant signed steep axis difference between GNAK and total keratometry., Conclusions: Total keratometry appears able to measure total corneal astigmatism to match closely (clinically and statistically) GNAK estimation of that parameter. This indicates that it would be safe and reasonable to use total keratometry data for planning of cataract surgery with toric IOLs. [J Refract Surg. 2018;34(8):521-526.]., (Copyright 2018, SLACK Incorporated.)

Purpose: To evaluate age-related changes in anterior, posterior, and total corneal astigmatism by comparing simulated keratometric astigmatism to total corneal astigmatism., Methods: Corneal topography of the anterior and posterior surfaces was evaluated using three-dimensional optical coherence tomography in 419 patients with normal eyes (218 men and 201 women) with ages ranging from 8 to 93 years (mean ± standard deviation: 49.5 ± 23.1 years). Keratometric astigmatism was calculated using the keratometric index (1.3375) and radius of the anterior corneal curvature; anterior and posterior corneal curvature measurements were used to calculate total corneal astigmatism., Results: The keratometric and total astigmatism were 1.08 ± 0.71 diopters (D) and 1.03 ± 0.69 D, respectively. Vector analysis revealed a mean difference between keratometric and total astigmatism of 0.24 ± 0.09 D, which showed a significant correlation to age (P < .0001). In eyes with with-the-rule astigmatism, keratometric astigmatism overestimated total astigmatism. In eyes with against-the-rule astigmatism, keratometric astigmatism underestimated total astigmatism., Conclusions: The anterior corneal surface shifts from with-the-rule to against-the-rule astigmatism with aging, whereas the posterior corneal surface remains as against-the-rule astigmatism in most cases. The variation in the anterior astigmatism is the most important factor contributing to this change. Total corneal astigmatism is a better predictor than keratometric astigmatism for selecting toric intraocular lenses., (Copyright 2014, SLACK Incorporated.)