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Ashutosh Richhariya, Virender S Sangwan, Mengchen Xu, Sunil Punjabi, Renato Perucchio, Geunyoung Yoon; MULTIFACTORIAL ANALYSIS OF PENETRATING KERATOPLASTY. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):1558.
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© ARVO (1962-2015); The Authors (2016-present)
With empirical methods, management of post penetrating keratoplasty induced astigmatism and other aberrations (PKA) is a clinical challenge. The goal of this study is to quantify the cumulative effect of orientation of the donor cornea in the host and the suture tension on the corneal topography, this multifactorial study demonstrates induced PKA due to topographic changes.
Manipulating the above said parameters in vivo was difficult; hence, a finite element modelling software Abaqus was used for simulations. Cornea was considered as a geometrically symmetric, with anisotropic hyperelastic material property. The surgery was simulated in two steps, first step connected the donor and host cornea with intermittent suturing under tension, achieved by exerting tension load at 16 sutures located along the circumference of donor cornea. And then in second step applying 15mm of Hg of pressure force on the posterior side of donor and host cornea. This was repeated for different suture tensions and donor cornea orientation. For evaluating the impact of the factors on optical quality of the cornea, the anterior surface coordinates of the deformed shape from Abaqus were exported into custom-developed software to quantify the induced aberrations due to corneal surface changes. The aberrations were represented by Zernike coefficients and the wavefront maps were plotted for qualitative comparison.
The results after deformation show asymmetry, astigmatism and other aberrations due to suture tension and orientation. Furthermore, the steepness of the cornea matched the tight suture location in aligned corneas (figure 1). While, there was an offset between the tight suture location and the corneal steepness in misaligned corneas (figure 1). The normalized cross correlation (NCC) between corneas with equal suture tension was 0.94. For the same location of a tight suture, the average NCC was 0.69 between aligned and misaligned corneas, and finally for a sector of tight sutures it was 0.46.
We conclude that donor tissue orientation in host cornea, as well as the suture tension plays an important role in the PKA. The simulations demonstrated that suture tension is more critical for PKA. Through this, we have also challenged the clinical empirical method of removing sutures from the steep side of the cornea and have demonstrated the reason for its limited success.
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