![]() , Tummanapalli and colleagues, in a large study of 1133 patients with corneal ectasia, documented keratoconus in 97% of patients and PMD in 3%. PMD is also less commonly seen than keratoconus, with incidence depending on the geographic location, ranging from 0.0003% in Russia to 2.3% in Central India. Patients with PMD, however, typically present later, between the second to the fifth decades of life, compared with keratoconus, wherein patients present from puberty to the third decade of life. PMD is often misdiagnosed as keratoconus, because they may closely resemble each other in clinical presentation. Both are typically bilateral and asymmetric at presentation, although unilateral PMD has been reported. Like keratoconus, PMD is a degenerative disorder characterized by progressive corneal thinning and ectasia. The latter is easily identifiable once a history of laser vision correction (LVC) is obtained. These include pellucid marginal degeneration (PMD), keratoglobus, and postrefractive surgical ectasia. The most important conditions to consider are the other ectatic disorders. Hence, the differential diagnoses of keratoconus can be classified into other corneal ectatic diseases, and nonectatic conditions mimicking keratoconus. Newer diagnostics such as epithelial thickness mapping, corneal aberrometry, and corneal biomechanical measurement such as with the Corvis ST (Oculus Optikgeräte GmbH, Wetzlar, Germany) may help detect early ectatic disease. Any family history of keratoconus or other corneal and ocular conditions must also be elicited. The presence of other ocular and systemic comorbidities such as vernal keratoconjunctivitis, atopy, and connective tissue disease are also important to establish. An accurate diagnosis can often be made after consideration of corneal findings on slit lamp biomicroscopy, corneal tomography, and respectively generated keratoconus indices in relation to the ocular history, including details of contact lens wear and any prior corneal ablative or incisional procedure. Identifying underlying ectatic disease is also critical when screening candidates for laser refractive surgery, to avoid inadvertent acceleration of any underlying ectasia. Keratoconus must be differentiated from other forms of keratectasia and other causes of irregular or asymmetric corneal astigmatism, because the management and prognosis are specific for each condition. Patients with equivocal findings must be followed up regularly with repeat corneal imaging. Newer imaging with biomechanics can help differentiate tomographic normal cases. In suspicious cases, repeat scanning may be done to confirm results. ![]() Tomographic maps of both eyes must always be analyzed in relation to each other. Nonectatic conditions to consider include corneal warpage, measurement artifacts, corneal scars, asymmetric and irregular astigmatism, and tear film instability and dry eye. Other ectatic disorders include pellucid marginal degeneration, keratoglobus, and postrefractive surgery ectasia. These can be classified as ectatic and nonectatic disorders. All rights reserved.Pertinent medical (systemic and ocular) and family history must be elicited. This review describes the clinical features of PMD, its differential diagnosis and various management strategies presently available.Ĭopyright © 2010 British Contact Lens Association. Since patients with PMD make poor candidates for laser vision correction, an awareness of the topographical and slit-lamp features of PMD will be useful to clinicians screening for signs of corneal abnormality before corneal refractive surgery. Several surgical procedures have been used in an attempt to improve visual acuity when spectacles and contact lenses do not provide adequate vision correction. The vast majority of PMD patients are managed using spectacles and contact lenses. In rare cases, patients may present with a sudden loss of vision and excruciating ocular pain due to corneal hydrops or spontaneous perforation. Visual signs and symptoms include longstanding reduced visual acuity or increasing against-the-rule irregular astigmatism leading to a slow reduction in visual acuity. Unless corneal topography is evaluated, early forms of PMD may often be undetected however, in the later stages PMD can often be misdiagnosed as keratoconus. Ocular signs and symptoms of patients with PMD differ depending on the severity of the condition. The prevalence and aetiology of this disorder remain unknown. The condition is most commonly found in males and usually appears between the 2nd and 5th decades of life affecting all ethnicities. Pellucid marginal corneal degeneration (PMD) is a rare ectatic disorder which typically affects the inferior peripheral cornea in a crescentic fashion.
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