Thicker than average epithelium, highly irregular epithelial thickness distribution, and thin epithelium over a keratoconic protrusion are indicative of early ectatic changes that may not be evident with other imaging technologies. 11Įpithelial thickness mapping via anterior segment spectal-domain OCT may also be useful in identifying patients with early changes associated with keratoconus and those at risk of developing postoperative ectasia. These indices assist in the identification of individuals who may be at increased risk for ectasia after refractive surgery. These devices also provide indices that incorporate data such as central corneal thickness, thinnest corneal thickness, changes in corneal thickness over the entire cornea, anterior radius of curvature, and posterior radius of curvature. Corneal tomography imaging, with devices such as the Pentacam (Oculus Optikgeräte), Orbscan (Bausch + Lomb), or Gallei (Ziemer Ophthalmic Systems), produces a 3D image that characterizes anterior and posterior corneal curvature as well as thickness distribution.

Sensitive technologies to assess corneal structure should be used to identify findings that may increase risk for ectasia. 10Ĭorneal imaging is a crucial component of preoperative screening. Any value greater than 40% represents an increased ectasia risk. PTA is calculated as the combined flap thickness and ablation depth divided by central corneal thickness. Recently, percentage of tissue altered (PTA) has been proposed as a metric for calculating ectasia risk in individuals undergoing corneal refractive surgery. Approximately 15 µm of stromal tissue is ablated for every diopter of myopia correction, and a low residual stromal bed thickness (250–300 µm) increases the risk for postoperative ectasia. Refractive error must be considered in conjunction with corneal thickness to determine if the patient will have an adequate residual stromal bed thickness. It is possible that the inverse relationship between age and risk for ectasia is due to a natural age-related increase in stromal crosslinking and subsequent corneal stiffening. Younger age has been associated with increased risk for ectasia. Patient age and refractive error should be considered before any screening tests are performed. There is no infallible or universally agreed upon screening protocol to entirely eliminate postoperative ectasia development, but use of multiple imaging modalities and sensible patient selection criteria can reduce the risk for this potentially sight-threatening event. We must be diligent in identifying those at higher risk for complications. These individuals are intending to proceed with an elective surgery that they expect will improve their vision and their lives. Patients susceptible to development of ectasia must be identified preoperatively. Nevertheless, with improved screening protocols, enhanced understanding of corneal biomechanics, and judicious application of patient selection criteria, we can strive to reduce the incidence of postoperative ectasia as much as possible. Some individuals who undergo refractive surgery may have developed an ectatic condition such as keratoconus even in the absence of a corneal procedure. There may never be a way to completely eliminate this complication. 6 Despite this, cases of ectasia after SMILE have been reported. This theory is supported by mathematical models that predict a stronger postoperative tensile strength with SMILE compared with LASIK and PRK. SMILE is thought to reduce the incidence of ectasia in comparison with LASIK, through its greater maintenance of anterior lamellar fibers. 5 This is of no consequence for most patients, but a certain subset of individuals may have predisposing factors that make them more likely to develop ectasia. In LASIK, the stromal flap is functionally decoupled from the cornea and no longer provides tensile strength. 4 Postoperative corneal ectasia results from a loss of biomechanical integrity of the cornea with subsequent thinning and steepening of the tissue. 3 One large study found that 96% of cases of ectasia occurred as a result of LASIK and 4% as a result of PRK. Visual rehabilitation includes glasses, soft contact lenses, rigid gas permeable contact lenses, and scleral lenses, with corneal transplant as a last resort.Įctasia is a rare complication of corneal refractive surgery, occurring in just 0.04% to 0.6% of procedures.Identify ectasia early and halt the progression with corneal collagen crosslinking.Consider lens-based refractive procedures for those with risk factors associated with postoperative ectasia. Postoperative ectasia is a rare but potentially devastating complication of corneal refractive surgery.

Pellucid marginal degeneration ectasia