<p>Posterior corneal astigmatism: a review article</p>

Abstract

Most human eyes show at least a small degree of corneal astigmatism and it can arise from both surfaces of the cornea. The shape of the anterior corneal surface provides no definitive basis for knowing the toricity of the posterior surface. In the previous studies, average astigmatism of the posterior corneal surface was −0.26 to −0.78 diopter. The radius of the posterior corneal surface is less than the radius of the anterior corneal surface. Most studies have found a clear correlation between the anterior and posterior corneal asphericities and the asphericity of the posterior surface is independent of the vertex radius of curvature, refractive error and gender. In contrast to the anterior corneal surface, the asphericity of the posterior corneal surface varies significantly between meridians. The anterior and posterior corneal surface would have approximately parallel principal meridians and both of these surfaces are often flatter in the horizontal meridian than the vertical one. This is especially true in the higher degrees of corneal astigmatism, and then about 10% of any anterior corneal astigmatism is neutralized by an astigmatism arising from the posterior corneal surface. Although the second corneal surface only contributes to about 10% of the total refractive power of the eye, a precise knowledge of its morphology is needed for the correct diagnosis and monitoring the corneal diseases or the surgical interventions and in many eyes neglecting the posterior corneal surface measurement may lead to significant deviations from the corneal astigmatism estimation. In this article, we have reviewed the shape and the toricity of the posterior corneal surface and also the effect of age on it. We investigated the contribution of posterior corneal astigmatism to the total corneal astigmatism and evaluated the accuracy of corneal astigmatism estimation by neglecting the posterior corneal surface measurement.

Analysis of Tear Ferning Patterns in Young Female Subjects with Refractive Errors

“…Subjects having uncorrected hyperopia might experience conditions including blurred vision, strabismus, or binocular dysfunction [ 4 ]. In astigmatism, the visual system's RE differ across different meridians [ 12 ]. Astigmatism is considered a higher level of myopia or hyperopia [ 13 ], characterized by blurred vision for both distant and close objects [ 4 ].…”

On the Relationship between Corneal Biomechanics, Macrostructure and Optical Properties

“…As shown in Results, the higher the OTI value the higher the corneal astigmatism and the lower the posterior eccentricity of the cornea. It is worth to mention that only posterior corneal eccentricity depends on corneal astigmatism [36] and even not shown in results, total corneal astigmatism and posterior corneal eccentricity were negatively correlated (R 2 =0.88, p=0.028) what implies that optical transparency and corneal macrostructure are related by means of the relative shape of the cornea independently of the thickness.…”

Analysis of corneal astigmatism and aberration in chinese congenital cataract and developmental cataract patients before cataract surgery

“…In the present study, there was also a negative correlation between PCA and age. Several studies of ARC patients manifested that the mean magnitude of PCA commonly ranged between 0 and 1.0 D [ 14 – 16 ]. However, PCA values of CC/developmental cataract patients in our findings were larger than 1.0 D, which may be due to the large age span of CC /developmental cataract patients in this study.…”