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Victor Sicam, Stijn Klijn, Maarten Huijbregtse, Annette JM Geerards, Nicolaas J Reus; Color LED corneal shape analysis of aberrations and irregularity indicators in healthy and keratoconus eyes. Invest. Ophthalmol. Vis. Sci. 2016;57(12):1925.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate Color LED corneal shape measurements of corneal aberration and irregularity indicators in healthy and keratoconus eyes.
Cassini Color LED corneal shape analyzer (Cassini BV, The Hague, Netherlands) measurements were done for 63 Healthy (38 OD, 25 OS) and 24 Keratoconus (9 OD and 15 OS) eyes. Corneal aberrations (coma – RMS 3rd order, trefoil – RMS 3rd order, spherical (SA) – Z(4,0) and quadrafoil – RMS 4th order) were characterized using Zernike convention @ 6mm diameter. Surface Regularity Index (SRI) and Surface Asymmetry Index (SAI) as described by Klyce and Wilson (Refract Corneal Surg 1989) were evaluated @ 4.23 mm diameter. Mann Whitney test was used to compare measurements between normal and keratoconus eyes. Pearson correlation coefficient, R, of each aberration and index compared to SRI and SAI were calculated. Sensitivity and specificity of corneal aberrations and indices were determined with respect to its performance in diagnosing keratoconus.
Coma is strongly correlated to SAI for both healthy and keratoconus eyes (see Table 1). For healthy eyes the correlation to SRI/SAI gets stronger/weaker with more complexity on the irregularity of the aberration (coma < trefoil < quadrafoil / coma > trefoil > quadrafoil. This pattern seems to disappear with Keratoconus eyes which may be attributed to the dominance of coma in the shape of keratoconus eyes. SA does not correlate with either SRI and SAI for healthy eyes, however for keratoconus eyes the correlation is strong.
SAI and coma agrees well for both healthy and keratoconus eyes indicating that coma aberration may well be an alternative for SAI in measuring corneal asymmetry. The correlations confirm and give insights that SRI is an indicator of local irregularity which could be a contribution of the actual corneal shape and tear film distribution. Correlations found for SA suggest that corneal dystrophy in keratoconus eyes involves simultaneous increase in SA, SRI and SAI. There is a similar statistical significant difference between corneal aberrations and irregularity indices of healthy and keratoconus eyes as measured by color LED corneal shape and there is no statistical significant difference between sensitivity of keratoconus diagnosis . However, coma aberration , SRI and SAI are superior to trefoil, spherical and quadrafoil aberration in specificity of keratoconus diagnosis.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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