![pellucid like keratoconus pellucid like keratoconus](http://image.slidesharecdn.com/keratoconus2016-151211135102/95/keratoconus-2016-6-638.jpg)
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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). They do not know if the three eye diseases are different diseases, or just different phenotypic (expression) variations of one disease. The answer is that doctors are not sure either. He complained of a progressive decrease in visual acuity greater in the right eye than the left, which started more than a year prior to presentation. He has sleep apnea and a history of myocardial infarction. Now you may ask if there is an actual difference between Keratoconus and PMD and Keratoglobus or if the three diseases are the same. F.Q is a 42-year-old male with no known family history of keratoconus or pellucid marginal degeneration (PMD). 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. 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.