Pellucid eye7/27/2023 They also noted that while progression often is associated with loss of uncorrected and best spectacle corrected visual acuity (BSCVA), this is not necessary. The group noted that the changes need to be consistent over time and above the normal variability of the testing system. Thinning and/or an increase in the rate of corneal thickness change from the periphery to the thinnest point.Steepening of the posterior corneal surface.Steepening of the anterior corneal surface.“Ectasia progression” by this group was defined by a consistent change in at least 2 of the following parameters where the magnitude of the change is above the normal noise of the testing system: In 2015, a group of international cornea specialists gathered in order to define key points in the global consensus on keratoconus and ectatic diseases. Topography is often used to diagnose post-refractive ectasia, displaying inferior steepening, thin corneas, and abnormal posterior elevation - findings similar to keratoconus. In advanced cases, the patients often appear similar to keratoconus. A careful history, with emphasis on patient's pre-surgery parameters, can help with suspecting post-refractive ectasia. This can occur as soon as months or as late as years after refractive surgery. Post-refractive ectasia is often suspected in patients with progressive myopia or astigmatism after refractive surgery. Besides geometric corneal parameters, new techniques permit a better understanding of the corneal bio-mechanics in order to get a better prediction of the corneal response to surgical or therapeutic interventions and to assist in the detection of early KC. Histologic and ultrastructural findings explain the pathophysiology of post-LASIK or post-PRK ectasia by interlamellar and interfibrillar biomechanics slippage induced by excimer laser disruption (interlamelar and interfibrillar fracture) and not to primary collagen fibrillar failure. Eye rubbing could explain the ectasia occurrence in some cases without other identified risk factors.Ĭorneal ectasia induced by excimer laser refractive surgery is thought to be the result of the alteration of the corneal surface and anterior stroma in corneas with previous biomechanical abnormalities. Įven when risk factors for ectasia after refractive surgery have been identified, reports of individuals developing ectasia without any of the proposed risk factors have emerged - this specific group of patients tend to be younger. Risk factors for the development of post-LASIK/PRK ectasia include a personal or family history of keratoconus (KC), abnormal corneal topography/tomography (form fruste keratoconus), high myopia, low-residual stromal bed (RSB 100 microns), high percentage of tissue altered (PTA >0.40), deep primary keratotomy resulting in a thick corneal flap and low preoperative corneal thickness (<500 microns). Although the general prevalence of postoperative ectasia is unknown, there are several reports that show a prevalence rate that vary from 0.02% to 0.6%. The disorder is considered irreversible and may reduce significantly uncorrected and spectacle-corrected visual acuity. It presents as a progressive eccentric thinning of the corneal stroma with consequent steepening of the anterior and posterior surface of the cornea. Refractive surgery induced ectasia is probably the most feared complication of laser in situ keratomileusis (LASIK), photorefractive keratectomy (PRK), and small incision lenticule extraction (SMILE).
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