Patterned corneal collagen crosslinking for astigmatism: Computational modeling study

Abstract

PURPOSE To test the hypothesis that spatially selective corneal stromal stiffening can alter corneal astigmatism and assess the effects of treatment orientation, pattern, and material model complexity in computational models using patient-specific geometries. SETTING Cornea and Refractive Surgery Service, Academic Eye Institute, Cleveland, Ohio, USA. DESIGN Computational modeling study. METHODS Three-dimensional corneal geometries from 10 patients with corneal astigmatism were exported from a clinical tomography system (Pentacam). Corneoscleral finite element models of each eye were generated. Four candidate treatment patterns were simulated, and the effects of treatment orientation and magnitude of stiffening on anterior curvature and aberrations were studied. The effect of material model complexity on simulated outcomes was also assessed. RESULTS Pretreatment anterior corneal astigmatism ranged from 1.22 to 3.92 diopters (D) in a series that included regular and irregular astigmatic patterns. All simulated treatment patterns oriented on the flat axis resulted in mean reductions in corneal astigmatism and depended on the pattern geometry. The linear bow-tie pattern produced a greater mean reduction in astigmatism (1.08 D ± 0.13 [SD]; range 0.74 to 1.23 D) than other patterns tested under an assumed 2-times increase in corneal stiffness, and it had a nonlinear relationship to the degree of stiffening. The mean astigmatic effect did not change significantly with a fiber- or depth-dependent model, but it did affect the coupling ratio. CONCLUSIONS In silico simulations based on patient-specific geometries suggest that clinically significant reductions in astigmatism are possible with patterned collagen crosslinking. Effect magnitude was dependent on patient-specific geometry, effective stiffening pattern, and treatment orientation.

Advances in Refractive Surgery

“…In the ectasia group, PTA of 40 or greater was the most prevalent factor (97%), followed by age younger than 30 years (63%), residual stromal bed of 300 μm or less (57%), and ectasia risk score of 3 or greater (43%) (P < 0.001 for all). Percent tissue altered of 40 or greater had the highest odds ratio (223), followed by residual stromal bed of 300 μm or less (74) and ectasia risk score of 4 or greater (8) (Fig. 1).…”

“…This study presents a new, noninvasive alternative for corneal refractive correction of astigmatism. 74 …”

Slowing the Progression of Keratoconus - Turning to Corneal Crosslinking

“…[4,5] Since its introduction, the CXL technique was developed and evolved in order to shorten the treatment time and to extend the indication to thin corneas (Raiskup-Spoerl-Hafezi hypotonic solution CXL, Mazzotta's epithelial island CXL, Jacob's contact-lens-assisted CXL), to the more advanced and decentered cones, alone or in combination with excimer laser photo-ablation, intra-corneal rings segments (ICRS) and phakic intraocular lenses (CXL plus). [6][7][8][9][10][11][12][13][14] According to current evidences of CXL safety and efficacy, the National Institute for Health and Care Excellence in the UK, since September 2013, recommended only the cross-linking with epithelium removal as a benchmark for this conservative treatment of progressive ectasia.…”

“…[40] More topographic flattening occurs in eyes with centrally located cones and the least flattening effect of the cone occurs when the cone is located peripherally. [9][10][11] A great challenge today is the management of the keratoconus in patients with more advanced or decentered ectasia, intolerant to rigid gas permeable contact lenses and poor spectacles corrected visual acuity. [40,41] The refraction of these patient is always difficult because spectacle correction is unable to correct HOA and irregular astigmatism, especially in peripheral cones, and a comfortable contact lens fitting sometimes is hard to reach or not possible at all and could cause corneal scarring or infection.…”

“…The protocol showed in Table 1 is based on patient-specific computational modeling of keratoconus progression and differential responses to CXL. [9][10][11] According to computational analysis, smaller-diameter-simulated CXL treatments centered on the cone provided greater reductions in corneal curvatures and HOA than conventional broad-beam CXL patterns. [9] In our experience, by using energy doses higher than standard 5.4 J/cm 2 (7.2, 10 and 15 J/cm 2 ), the keratocytes apoptosis was detected between 250 and 300 µm.…”