Apple of patient’s eye a sign of pellucid marginal degeneration
An apple-shaped topographic pattern appears to be a useful sign for discriminating early pellucid marginal degeneration (PMD) from keratoconus (KCN)
An apple-shaped topographic pattern appears to be a useful sign for discriminating early pellucid marginal degeneration (PMD) from keratoconus (KCN), said Mohammadreza Jafarinasab MD, Iran.
“The apple pattern observed in corneal topographic map, especially in sagittal and instantaneous map, is a useful sign for the early diagnosis of PMD,” said Dr Jafarinasab.
In a cross-sectional study involving 120 patients referred with a primary diagnosis of subclinical keratoconus or pelllucid marginal degeneration, computerised corneal topography and dual-Scheimpflug analyser revealed a topographic pattern that looked like an apple (apple sign) and consistently had two portions, a flat stem and a steep core portion.
“The most important finding in the early pellucid marginal degeneration
group was an inferior flattening surrounded by steep areas inferior to the horizontal axis surrounded by steep areas inferior to the horizontal axis, which created an apple-shaped pattern instead of the usual pear-shaped pattern that is common in keratoconus,” Dr Jafarinasab said.
An additional distinguishing feature of eyes with pellucid marginal degeneration was against-the-rule astigmatism – the presence of steep meridians within the horizontal quadrant – in contrast to with-the-rule astigmatism that occurs in keratoconus.
Changes of steep and flat areas inside the apple pattern appeared to be a good indication of disease progression. In early pellucid marginal degeneration eyes the inferior flat area was less than 3mm, in mild disease it was 3mm, in moderate disease it was 5.0mm and in severe disease it was 7mm.