Hemidivisional vector planning to reduce and regularize irregular astigmatism by laser treatment

Abstract

Purpose To demonstrate how hemidivisional vector planning of refractive laser treatments of astigmatism can be used to directly address idiopathic corneal irregular astigmatism that has an asymmetrical, non-orthogonal bow tie topography appearance. Design Case study. Methods The cornea is conceptually divided into two hemidivisions along the flat meridian of the corneal topographic astigmatism (CorT), which means that each hemidivision will approximately correspond to one lobe of the asymmetric, non-orthogonal topographic bow tie. An astigmatism reduction treatment can then be planned separately for each hemidivision using the vector planning technique, based on both its two hemidivisional CorT measures and common manifest refractive cylinder. The remaining irregularity is then regularized, and the junctional zone smoothed across the flat meridian. The final intended treatment thus combines hemidivisional astigmatism reduction and regularization of the corneal astigmatism and spherical refractive error in one treatment application. This could be applied to LASIK, PRK, SMILE, and Transepithelial PRK procedures using Designer Cornea® software. Results A theoretical treatment profile is derived from an actual example of a cornea with idiopathic asymmetric non-orthogonal astigmatism. The three steps of the derivation are as follows: (i) astigmatism reduction through the use of the vector planning technique; (ii) regularization, and (iii) smoothing across the hemidivisional midline. Conclusions Hemidivisional vector planning treatments could potentially both reduce and regularize asymmetric non-orthogonal astigmatism. These treatments can be systematically customized to account for qualitative and quantitative differences between the two corneal hemidivisions at the same time as correction of coexistent myopia or hyperopia.

Effectiveness of toric intraocular lens implantation for correcting irregular corneal astigmatism in cataract eyes

“…Certain eyes with irregular astigmatism could only achieve further improvement through limited and invasive refractive correction methods, such as corneal laser surgery and postoperative corneal contact lenses 5 . Today, treating the surface of irregular corneas with customized photoablation using an excimer laser is possible, aiming to eliminate high-order aberrations and expand the optical zone 6 . In recent years, some experts have broken the contraindication to use Toric IOL in such irregular cases, seeking to neutralize the low-order astigmatism component of preoperative corneal aberrations 7 – 9 .…”

Perfecting Laser Treatment for Regular and Irregular Astigmatism

“…Vector planning can now be applied to both halves of the cornea using the common refraction to both. 9,10 The cornea is conceptually halved using the flat orientation of the total corneal astigmatism. Any measure of total corneal astigmatism can be used; however, the example here is based on CorT Total.…”