keratoconus vs pellucid marginal degeneration

Incidence is approximately equal in men and women. 1 Diagnosis is typically made between 20 and 40 years of age. Pellucid marginal degeneration is a rare, non-ulcerative peripheral thinning disorder involving the inferior cornea. Zywave wavefront analysis showed a Zernicke RMS of 1.40 µm in the right eye and 1.03 µm in the left eye with a 6-mm optical zone. This patient subsequently underwent successful LASIK, and is 20/20 OU 12 months postop with no evidence of a significantly increased posterior float or any other abnormality.įigures 7 and 8. However, the normal wavefront analysis prompted repeat Orbscan II testing, which confirmed our suspicion that the elevated posterior float was a spurious finding. Normally, this would have caused us to recommend against a refractive procedure. In this case, normal wavefront determined the inaccuracy of Orbscan II testing in the left eye, which was probably increased by transient dessication. Repeat testing showed a normal posterior float of 0.038 mm OS ( See Figure 12). Because wavefront analysis did not show increased HOAs, Orbscan II testing was repeated after the instillation of artificial tears. Wavefront analysis with the Bausch & Lomb Zywave aberrometer, however, showed a normal wavefront in the left eye with a Zernicke RMS of 0.67µm at 6 mm ( See Figure 11). A markedly increased posterior float of 0.064 mm was noted in the left eye ( See Figure 10). Orbscan II testing in the right eye was borderline normal, with a posterior float of 0.04 mm ( See Figure 9). Slit lamp and dilated fundoscopic examinations were normal OU. The patient's uncorrected visual acuity was 20/80 OD and 20/60 OS. The presence of significant HOAs noted on Zywave wavefront analysis confirmed our initial suspicion, which was based primarily on topography.Ī 60-year-old female with mild hyperopic astigmatism desired laser vision correction.

The patient was referred for contact lens fitting and was advised against refractive surgery because we felt he had previously undiagnosed pellucid marginal corneal degeneration. The Zernicke RMS at 6 mm was 1.40 microns OD and 1.03 microns OS ( See Figures 7 and 8). Wavefront analysis with the Bausch & Lomb Zywave aberrometer revealed significant HOAs, particularly vertical coma and trefoil, OU. Orbscan II testing revealed a posterior float of 0.049 and 0.038 in the right and left eyes, respectively (normal <0.040), with decentered corneal apices and inferior corneal thinning OU ( See Figures 5 and 6). Klyce/Maeda and Smolek/Klyce keratoconus detection programs were both positive for keratoconus and keratoconus suspect OD, and positive and negative for keratoconus OS ( See Figures 3 and 4). This revealed moderate against-the-rule astigmatism OU ( See Figures 1 and 2) with the crab's claw pattern characteristic of pellucid marginal degeneration. Slit-lamp and dilated funduscopic examinations were normal OU.Ĭorneal topography was performed with the Tomey TMS-1 unit (Tomey Technology, CBD Ophthalmic, Phoenix, AZ). The patient's uncorrected visual acuity was HM OU. He had previously obtained good vision with glasses, but had not been successful wearing soft contact lenses. Orbscan II testing revealed a posterior float of 0.049 mm and 0.038 mm in the right and left eyes, respectively (normal < 0.040 mm), with decentered corneal apices and inferior corneal thinning in both eyes.Ī 41-year-old male with myopic astigmatism was seen in consultation prior to LASIK. Klyce/Maeda keratoconus detection program was positive and Smolek/Klyce keratoconus detection program was negative in the left eye.įigures 5 and 6. Klyce/Maeda and Smolek/Klyce keratoconus detection programs were both positive for keratoconus and keratoconus suspect in the right eye.įigure 4. Corneal topography of the right and left eyes showing moderate against-the-rule astigmatism in both eyes with the crab's claw pattern characteristic of pellucid marginal degeneration.įigure 3. In addition, it may be used to rule out erroneous or conflicting test results, as evidenced by the following cases.įigures 1 and 2. Through wavefront analysis, we can now also measure higher-order aberrations, such as coma and trefoil, which can affect optical quality and subjective visual perception.Īlthough wavefront analysis was initially designed for and is primarily used in planning and delivering customized laser refractive treatments, it can also be a valuable diagnostic tool in detecting subtle disorders of the cornea or lens. Historically, refractive errors have been character ized by second-order Zernike polynomial aberrations (myopia, hyperopia and astigmatism).

Keratoconus vs pellucid marginal degeneration