![]() 3,12-14 Increased expression of MMPs is widely observed in human tissue in which inflammation is present. 1,3 It has been suggested that this degradation could be related to alterations in enzyme activity from normal levels for example, matrix metalloproteinase (MMP) levels have been shown to be elevated in keratoconic corneas, demonstrating a possible role for these enzymes in collagen degradation. Essentially, corneal thinning in keratoconus occurs when corneal collagen degrades. Our knowledge about the causes of ectasia has come a long way since the condition’s discovery, largely because of advances in the way we measure the structure and composition of the cornea. Being knowledgeable about the causes of these conditions can help to enable better clinical decisions and increase the ease of delivering patient education. As such, optometrists trained in medical contact lenses are often the first line of care for this affected population. Today, the majority of patients with keratoconus or other forms of corneal ectasia are managed with specialty contact lenses, such as corneal or scleral rigid gas permeable lenses, rather than surgery. 1 Like primary keratoconus, the pathophysiologic and genetic etiology of pellucid marginal degeneration and keratoglobus remains unclear. Keratoglobus may be present early in life, or may be acquired. A rare corneal thinning disorder that is characterized by general thinning and protrusion of the cornea. 1 It is characterized by inferior peripheral corneal thinning and a ‘bow-tie’ topographical map appearance of the cornea. Considered the second most common form of ectatic disorders, pellucid marginal degeneration presents between the third and fifth decade of life. 2 Induced ectasia may be unilateral or bilateral and secondary to mechanical processes in a predisposed cornea. 1-2 According to the Global Consensus on Keratoconus and Ectatic Diseases, the pathophysiology of the condition likely includes genetic, biochemical, biomechanical and environmental components, but has no primary pathologic explanation. 1 Mandatory clinical findings to diagnose keratoconus include abnormal posterior ectasia, in addition to corneal thinning and abnormal corneal thickness distribution. 1-3 Usually, keratoconus presents in the second or third decade of life. Considered to be the most common form of ectatic disorder, primary keratoconus affects at least one out of every 2,000 members of the general population. 10 In all cases, unilateral presentation of keratoconus contraindicates surgery for the other eye because keratoconus is currently understood to be a bilateral disease. 6,8-9 Other risk factors for iatrogenic corneal ectasia include thin baseline cornea, irregular corneal thickness, high myopia (due to the need for an increased amount of ablated tissue) and young age at the time of refractive surgery. ![]() 1-6įorme fruste (i.e., subclinical) keratoconus is an often-undiagnosed latent form of biomechanical instability in the cornea, which can be induced by refractive surgery and result in post-refractive surgery ectasia. 1-6 Overall, the prevalence of post-refractive surgery ectasia is estimated to be between 0.2% and 0.66%. However, post-refractive surgery ectasia can still occur in the absence of these findings. 11,12Ĭommon clinical findings in patients with post-refractive ectasia include a thicker resulting flap or thinner residual stromal bed than expected. In two recent isolated case reports, ectasia following this procedure was documented. 1-2 Additionally, small-incision-lenticule extraction (SMILE) is a relatively novel refractive procedure that uses a femtosecond laser to remove a disc-shaped portion of stroma with no flap lift, achieving similarly successful results to those of LASIK. ![]() Iatrogenic ectasia can occur post-laser-assisted in situ keratomileusis (LASIK) or after a photorefractive keratectomy (PRK) procedure. The central caliper measure of corneal thickness is 145µm. 1īecause ectasia describes a physiological finding rather than a particular disease process, it is used in the context of various clinical entities that can arise by mechanical, degenerative or genetic factors.Īnterior chamber segment optical coherence tomography image of thin, ectatic cornea in post-LASIK ectasia.Ĭentral 9mm segment optical coherence tomography image of thin, protruding cornea in keratoglobus. 1 Corneal ectatic disorders often result in decreased acuity, increased ocular aberrations and, in some cases, the need for surgical intervention. The visual consequences of keratoconus-which has historically been defined as a noninflammatory condition with hallmark progressive corneal thinning and steepening.-can be devastating for many patients.
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