Refractive, corneal, and ocular residual astigmatism: distribution in a German population and age dependency—the Gutenberg Health Study
Dear editor, We would like to thank Dr. Alpins and Mr. Stamatelatos [1] for their interest in our study [2]. Indeed, analysis of astigmatism is a challenging approach and these authors highly contributed to pave its path [3, 4]. In addition to the specific characteristics of astigmatism including amount and orientation, there are (unfortunately) different notations: while in most English-spoken countries a positive notation of astigmatism is in use (cylinder in plus diopters), Germany and other European countries commonly use negative measures of astigmatism (cylinder in minus diopters).While the absolute amount of astigmatism is the same, the orientation has a shift of 90° and spherical power is different. This is in contrast to measurement of velocity, an analogy been drawn byDr. Alpins andMr. Stamatelatos [1]: velocity is defined by the ratio of two units of the International System of Units (SI).
Corneal and Refractive Astigmatism in Adults: A Power Vectors Analysis
Purpose. In this article, we examine the relationship between corneal and refractive astigmatism (including with the rule, against-the-rule, and oblique astigmatism) in an adult population using power vectors. Methods. Refractive and keratometric measures of astigmatism were conducted on right eyes of 105 white subjects aged 18 to 59 years. We performed a linear regression of refractive astigmatic error on corneal astigmatism, using the J0 and J45 components of the astigmatism. Results. We obtained a statistically significant regression relationship between the corneal (C) and refractive (R) astigmatism for both J0 and J45 components, namely, RJ0 = 1.07 × CJ0 − 0.28; and RJ45 = 1.46 × CJ45 + 0.03. This results is a kind of generalized Javal rule for an adult population, because it is extended to include oblique astigmatism. We also found that the internal astigmatism is against-the-rule and uniform in our sample. Conclusions. This vector-based approach is equivalent to the traditional Javal rule, but it has the ability to make predictions about oblique astigmatism, rendering it more general and more accurate.
Photorefractive keratectomy for myopic astigmatism: Phase IIA of the Federal Drug Administration study (12 to 18 months follow‐up)
ABSTRACT Excimer laser photorefractive keratectomy was performed on eight eyes to investigate toric ablation of naturally occurring compound myopic astigmatism. Follow‐up ranged from 12 to 18 months. In each surgical case, the spherical component was reduced. The cylindrical component was reduced or eliminated in seven of eight eyes and remained unchanged in one eye. However, six of eight eyes had some residual astigmatism and three had 0.75 diopters of cylinder or more. In six of eight eyes the change in axis in the postoperative cylinder varied between 5 and 10 degrees of the preoperative cylinder axis. In one eye with an eccentric ablation, the axis changed by 40 degrees. In two eyes with loss of best corrected visual acuity of one line each, from 20/20 to 20/25, irregular astigmatism and subepithelial haze persisted 18 months after treatment. One eye gained a line of best corrected visual acuity from 20/20 to 20/15. Two eyes were overcorrected. Twenty‐five percent of patients achieved 20/20 or better uncorrected visual acuity, 62.5% achieved 20/40 or better uncorrected acuity, and 100% achieved 20/50 or better uncorrected acuity. These preliminary results of excimer laser photoastigmatic keratectomy compare favorably with reports of photorefractive keratectomy for myopia alone. There were no adverse reactions to treatment. The procedure was effective although some residual astigmatism was found in most patients.