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J. Pepose, J. Pepose; Wavefront Aberrations in Patients with Keratoconus and Pellucid Marginal Degeneration . Invest. Ophthalmol. Vis. Sci. 2004;45(13):2893.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To compare the ocular and corneal wavefront aberrations in control eyes to eyes with a clinical diagnosis of keratoconus (KCN) or pellucid marginal degeneration (PMD). Methods: A retrospective review identified patients with a clinical diagnosis of keratoconus (n=49), pellucid marginal degeneration (n=14), and a control group with central corneal power > 47 diopters in at least one meridian (n=11). Slit–scanning videokeratography (Orbscan II, Bausch & Lomb, Salt Lake City, UT) was performed on each eye. Hartmann–Shack wavefronts (Zywave, Bausch & Lomb, Rochester, NY) were statistically analyzed at a 5 mm pupil for 6 normal, 19 keratoconic, and 3 pellucid eyes. Some wavefront data was excluded because of poor centroid detail or due to small, undilated pupil size. Results: Compared to control eyes, keratoconic and pellucid corneas had a significantly wider distribution of corneal power within Orbscan–derived 3 and 5 mm central zones (p<0.01). Keratoconic eyes had thinner corneas on average (mean 461 + 122 µm KCN, 541 + 37 µm control, 493 + 81 µm PMD) than both control and pellucid counterparts (p=.03). Pellucid eyes were marked by against–the–rule astigmatism, which was not as readily seen in the other groups (p<.01), and an inferiorly displaced thinnest point (p<.01) identified via optical pachymetry (mean –1.5 mm position in the y–axis versus 0.0 control and –0.5 KCN). Analysis of corneal first surface elevation data differentiated keratonic and pellucid eyes from controls, but not from each other, as several cases had a forme fruste presentation. A review of total eye wavefront data showed that vertical coma is significantly increased in KCN (p=.02) but not PMD, and that vertical trefoil is selectively increased in PMD (p=.03). Conclusions: Keratoconus and pellucid marginal degeneration are characterized by inferior corneal thinning and steeping that induces third order coma–like and trefoil–like aberrations. A close review of these Zernike terms, in particular, can assist in the differentiation of pathologic steeping of the cornea from otherwise symmetric or regular astigmatism. Wavefront analysis of ocular and corneal aberrations is a useful adjunct to corneal topography in the diagnosis of keratoconus and pellucid marginal degeneration.
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