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Impact of the epithelial remodelling on anterior corneal and stromal surface topography and on choice of surgical technique in topography-guided therapeutic refractive surgery

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First Author: F.Stojanovic NORWAY

Co Author(s):    W. Zhou   A. Stojanovic                 

Abstract Details

Purpose:

To identify and analyze optical and therapeutic impact of epithelial remodelling in irregular corneas and to establish the treatment guidelines for different surface ablation techniques in topography-guided therapeutic refractive surgery.

Setting:

Eye department, University Hospital of Northern Norway, Tromso, Norway

Methods:

Corneal topo/tomography and epithelial thickness mapping (ETM) were simultaneously acquired on eyes with pronounced epithelial remodeling by a novel high definition rotating-Scheimpflug device capable of ETM. The measurements were analyzed in 10 eyes with keratoconus. Topography-guided treatment simulations aimed at correcting total corneal astigmatism (TCA) and corneal higher order aberrations (CHOAs) were also performed. Three different surface ablation techniques were simulated. Conventional topography-guided PRK (photo refractive keratectomy) and anterior stromal-topography-guided PRK applied on top of the stroma simulated the situation after mechanical epithelial removal, while topography-guided ablation applied on top of the intact epithelium simulated transepithelial PRK.

Results:

A significant difference in morphology and optics of the anterior corneal surface and the stromal surface was found. Simulated transepithelial topography-guided PRK and stromal-topography-guided PRK both resulted in correction of both TCA and CHOAs, while the traditional topography-guided PRK delivered after simulated mechanical epithelial removal resulted in a significant residual corneal irregularity and astigmatism.

Conclusions:

Incongruence between the epithelial and stromal surface shapes was found in irregular corneas, which may be a significant source of treatment error if topography-guided ablation is not based on the data from the very same surface that is ablated. Anterior corneal topography-guided ablation should be performed transepithelially, while stromal-topography-guided ablation should be performed after epithelial removal.

Financial Disclosure:

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