These characteristic features help to differentiate this condition from other noninflammatory corneal thinning disorders such as keratoconus, posterior keratoconus, and keratoglobus. 4, 5 The topographic pattern described is distinctly different from that seen in keratoconus, in which a small area of high corneal power is surrounded by concentric bands of low corneal power. 4 This results in a relatively steep contour approximately 90° away. Stromal thinning is known to cause corneal flattening over the area of tissue loss, and steepening at the border of unaffected tissue. Topographic analysis in our case revealed a characteristic bow-tie appearance of marked against-the-rule astigmatism oblique-inferiorly, without peripheral steepening. This rare entity has been postulated to be an abnormality of the connective tissue, 2, 3 but the exact pathogenesis is still unknown. Pellucid marginal degeneration is a bilateral, slowly progressive condition classically described between the second and fourth decades. The left eye was normal, with no evidence of corneal thinning, striae, or abnormal protrusion ( Figure 1, bottom). The intraocular pressure by applanation tonometry was normal in both eyes. The rest of the anterior and posterior segment was normal. There was no evidence of iron lines, lipid deposition, or vascularisation. The portion between the thinned area and limbus was normal in thickness. On slit-lamp biomicroscopy, the cornea in the right eye showed an irregular contour with a thin band inferiorly, approximately 1.5 mm in width and 2 mm from the limbus, with bulging above the thinned zone ( Figure 1, top). Ophthalmic examination revealed best-corrected visual acuities of 6/18 OD with −1.0/−13.50 D×110° and 6/6 OS unaided. There was no history of redness, pain, or use of ophthalmic medication during this time. Case reportĪ 46-year-old healthy Indian man presented with painless progressive diminution of vision in the right eye for 6 years. Described here is such a case, in which the other eye was normal. Unilateral isolated PMD is extremely unusual, and corneal topography provides valuable clues in suspected cases. 1 It is differentiated from other peripheral corneal thinning disorders such as Terrien's marginal degeneration and Mooren's ulcer by the absence of vascularisation, lipid infiltration, or corneal ulceration. All rights reserved.Pellucid marginal degeneration (PMD) is a rare bilateral corneal disorder characterised by thinning in the peripheral portion of the inferior cornea with marked steepening just superior to the thinned zone. 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.
0 Comments
Leave a Reply. |