The clinical diagnosis for PMD is the same as Keratoconus where the patient is examined by doctor on a slit lamp microscope and checked with patient’s history and supported by corneal topography & pachymetry. Patients are also commonly asymptomatic except for the gradual worsening of vision that is unaided by glasses. Some of the different signs of PMD may include drastically reduced uncorrected visual acuity that usually cannot be improved with glasses (usually for astigmatism), roughly normal pinhole visual acuity, and refraction/keratometry that shows against the rule astigmatism (where the astigmatism on a corneal topography is seen horizontally). Protrusion of the cornea occurs above a band of thinning, which is located 1 to 2 mm from the limbus and measures 1 to 2 mm in width. PMD is caused by a thinning of a narrow band of the cornea between 4 and 8 o’clock, approximately 2mm in from the edge of the cornea and the white of the eye. Hallmarks of PMD supposedly included a crab-claw or butterfly patterned corneal topography, a diagnostic measurement which generates a color map representing the light-bending power of the cornea. They do not know if the three eye diseases are different diseases, or just different phenotypic (expression) variations of one disease. Pellucid marginal degeneration of the cornea is a bilateral, clear, inferior, peripheral corneal-thinning disorder. Pellucid marginal degeneration (PMD) is characterised by non-ulcerative, non-inflammatory, clear thinning of the inferior portion of the peripheral cornea. Pellucid marginal degeneration, or PMD, is often confused with keratoconus, and indeed it is a type of irregularity affecting the cornea which results in visual impairment. Pellucid Marginal Degeneration Researchers and eye doctors used to believe that PMD was a separate disease from keratoconus. The answer is that doctors are not sure either. Now you may ask if there is an actual difference between Keratoconus and PMD and Keratoglobus or if the three diseases are the same. There is a third disease called Keratoglobus that like the previous two also causes corneal thinning (more about this disease will be discussed in a future post). The difference between Keratoconus and Pellucid Marginal Corneal Degeneration is that PMD causes a crescent shaped band of thinning in the lower region of the eye, while the central cornea is usually of a normal thickness as well as the cornea appearing transparent in PMD. Corneal Topography shows the characteristic, but not.

What is Pellucid Marginal Corneal Degeneration (PMD)? In short it is an eye disease very similar to Keratoconus in that it also causes thinning of the corneas. There is protrusion of the cornea above the thinning area, resulting in high irregular astigmatism.

Pellucid corneal degeneration