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  • Title: [The cornea in high axial myopia].
    Author: Touzeau O, Gaujoux T, Sandali O, Allouch C, Laroche L, Borderie V.
    Journal: J Fr Ophtalmol; 2014 Jun; 37(6):449-61. PubMed ID: 24878175.
    Abstract:
    PURPOSE: To compare corneal characteristics of eyes with high myopia with those of eyes with no spherical ametropia using Orbscan and ultrasonic pachymetry. METHODS: Orbscan and ultrasonic pachymetry values were prospectively recorded in a study group of 105 patients with high myopia (i.e., axial length greater than 26mm in both eyes) and in a control group of 105 patients with no spherical ametropia (absolute value of spherical equivalent less than 1.25D regardless of cylinder value). Astigmatism data were expressed by rectangular coordinates in a dioptric plane. Axis was decomposed in 2 components (WTR/ATR and oblique) which were analyzed by Cos2axis and Sin2axis trigonometric functions. Enantiomorphism (mirror-image symmetry) between fellow eyes was quantified by a Euclidean distance for the location of the thinnest point and by the difference (in absolute value) between 180° and the sum of both axes for astigmatism. RESULTS: In the study group, the mean axial length and subjective spherical equivalent were, respectively, 27.82±2.14mm (26.00 to 34.06) and -9.00±3.46D (-4.71 to -19.82). The mean corneal astigmatism was +0.92D×91.3° in the study group and +0.65D×89.3° in the control group. The mean corneal cylinder was higher in the study group (1.44D versus 0.91D; P<0.001) whereas axis showed no significant differences between both groups. The mean maximal keratometry was steeper in the study group (44.53D versus 44.13D; P=0.03) whereas the mean keratometry and minimal keratometry displayed no significant differences between both groups. No significant differences in central corneal thickness (540.2μm versus 546.9μm; P=0.10), peripheral corneal thickness, corneal diameter, corneal irregularity, asphericity, and irregular astigmatism were found between both groups. There were no significant differences in enantiomorphism parameters between both groups. In the study group, correlation with axial length was significant only for spherical equivalent (r=-0.86; P<0.001) and corneal cylinder (r=0.16; P=0.04). CONCLUSION: High myopia exhibits corneal characteristics similar to corneas of eyes with no spherical ametropia, except for toricity. While the posterior segment elongates, development of high myopia appears not to affect corneal characteristics. Corneal toricity may be associated with evolution toward high myopia by perturbing mechanisms of emmetropization.
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