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Janine Lenk, Michael Haustein, Eberhard Spoerl, Lutz E Pillunat; Characterization of Corneal Biomechanical Response Parameters in Pellucid Marginal Dystrophy, Keratoconus and Normal Corneas. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3710.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate corneal biomechanical response parameters in patients with normal cornea, keratoconus (KC) and pellucid marginal dystrophy (pmD), measurements of the Ocular Response Analyzer (ORA, Reicherts ®) and the newer device CorVis ST (Oculus®) were compared.
107 right eyes of 107 patients were included in this prospective observational study. We investigated corneal biomechanical response parameters using ORA and CorVis ST. Parameters of interest regarding ORA: corneal hysteresis (CH), corneal resistance factor (CRF), and 37 ORA specific parameters; for CorVis ST: radius (COR Wmax r), corneal thickness (COR CCT), and 10 other parameters, describing deforming response of the cornea during measurement. Three patient groups were analyzed: normal (n=49), keratoconus (n=38) and pellucid marginal dystrophy (n=20). Statistical analysis was performed using SPSS: Students t-test and ANOVA were used to determine which parameters differed between the 3 groups. Statistical significance was considered as P<0.05.
Patients with keratoconus are younger than those with pellucid marginal dystrophy (31.8±13 yrs, 48.5±14.2 yrs; P=0.001). CH and CRF and all the 37 specific parameters do not differ between KC and pmD (P>0.05), but CH is higher in the control (CHn=10.03±2 mmHg, CHpmD=8.33±2.6 mmHg; P=0.05) and most of the 37 ORA specific parameters differ between pmD and control (P<0.005). Central corneal thickness (COR CCT) is almost significantly lower in KC than in pmD (482.3±46 µm, 511.4±30 µm, P=0.068). Of the other 11 CorVis parameters, COR A2t, COR A2v are different between KC and pmD (P=0.015, P=0.022) and the radius of the maximal depression (COR Wmax r) is higher in pmD than in KC (7.49±1.56mm, 5.96±1.3; P=0.016), because it is measured in the corneal center, which is rarely changed in pmD. There is no difference between CorVis parameters of normal and pmD (P>0.05).
We could show for the first time, that both ORA and CorVis ST are useful to distinguish between different corneal pathologies: CorVis parameters do not differ between normal and pmD, so one cannot detect this pathology with CorVis alone, whereas ORA can differentiate between normal and pmD, but not between pmD and keratoconus. Using both devices, one can reliably discriminate patients with normal cornea from marginal pellucid from keratoconus.
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