Pachymetry at planned incision sites if possible.Corneal topography to confirm axis of corneal astigmatism, and to classify as regular or irregular, symmetric or asymmetric.Keratometry to confirm diopters of corneal astigmatism.Close examination of the peripheral cornea, particularly in the areas where the incsions will be placed.Important items to note in the preoperative exam include: In adults, astigmatism can also be corrected surgically with LASIK, PRK, SMILE, or limbal relaxing incisions (LRI). Astigmatism, similar to myopia (nearsightedness) or hyperopia (farsightedness), is generally present and correctable at a young age with spectacles or contact lenses. The patient may present with a long history of astigmatism. Causes of irregular astigmatism include corneal dystrophy or degeneration, ocular surface disease, corneal ectatic disease such as keratoconus, or prior corneal surgery. Whenever the two main axes of astigmatism are not symmetric and/or do not lie 90 degrees apart (orthogonal), the astigmatism is considered irregular.Oblique: Steep axis of the cylinder is not within 15 degrees of the horizontal or vertical meridians (16-74 degrees and 106-164 degrees).Against-the-rule: Steep axis of the cylinder is within 15 degrees of the horizontal meridian (165 - 015 degree).With-the-rule: Steep axis of the cylinder is within 15 degrees of the 90 degree vertical meridian (75 - 105 degrees).Visit EyeSmart from the American Academy of Ophthalmology for a brief, patient-friendly description of astigmatism.Īstigmatism may also be classified as regular and irregular. Astigmatism typically results from curvature abnormalities of the front (anterior) surface of the cornea. This latter term generally refers to astigmatic incisions in the cornea that are placed in closer proximity to the visual axis compared to the peripheral placement of LRIs.Ībnormal curvature of the cornea with at least two axes of steeper and flatter curvature, which can result in abnormal focusing of light and impaired vision. Within this category, arcuate (or sometimes, 'astigmatic') keratectomy (AK) can also be included. LRIs are considered to fall under the spectrum of incisional astigmatism treatments known as Corneal Relaxing Incisions (CRIs). Limbal Relaxing Incisions (LRI) are partial thickness incisions made at the corneal periphery for the treatment of corneal astigmatism. 3.1.5 A simple breakdown of treatment options.3.1.3 Relative Contraindications for CRIs.

Limbo relaxing incision