treatment of vision disturbances due to corneal irregularities by trans-epithelial optical phototherapeutic keratectomy (te-optk)

Conditions: Corneal Astigmatism

Summary: this study sets out to evaluate the epimaster application software for use in predicting the refractive change induced by a trans-epithelial phototherapeutic keratectomy (te-ptk) procedure in eyes with irregularly irregular astigmatism. if validation criteria are met during the observational phase, the software refractive prediction will be used to plan the refractive correction in te-ptk treatments.

complications after laser eye surgery can often result in the front surface of the eye (the cornea) becoming irregular, which causes visual symptoms such as halos, glare, starbursts, double vision, and reduced contrast sensitivity. for the past 20 years, corneal irregularities have been treated using wavefront-guided ablation, topography-guided ablation or trans-epithelial phototherapeutic keratectomy (te-ptk). topography-guided ablation is the most effective treatment for certain types of irregularity and works by using a laser to remove tissue from the cornea in a pattern derived from a topography scan (a measurement of the shape and curvature of the front of the eye) designed to make the corneal surface more regular. however, topography-guided ablation is less effective for other types of irregularity. in these cases, the corneal epithelium (the layer of skin on the surface of the cornea) has changed in thickness to partially hide the irregularity on the body of the cornea under the epithelium (the stroma). the epithelium does this by becoming thinner over peaks and thickening over troughs in the stroma. therefore, the topography measurement can only detect the proportion of the irregularity that has not been hidden by the epithelium, hence reducing its effectiveness. the preferred treatment option is te-ptk; the laser treatment is applied onto and through the epithelium, breaking through to the stroma where the epithelium is thinnest, thus removing tissue from the peaks on the stroma resulting in a more regular surface. the main weakness of te-ptk is that it may unpredictably change the refraction to become more short-sighted or more long-sighted or change the astigmatism. to improve this, we have developed the epimaster software that simulates a te-ptk treatment and predicts the change in refraction. the aim of the study is to validate the refractive prediction produced by the epimaster software by comparing this to the achieved result in the patients treated. the treatment received by the patient will be the same as has been used routinely for the past 20 years.

Eligibility criteria:
inclusion criteria: * patient presents with topographic irregularly irregular astigmatism and associated quality of vision issues, where te-ptk would be a more effective treatment than topography-guided ablation or other therapeutic treatment options. medically suitable for corneal laser refractive surgery. * calculated residual stromal thickness ≥250 µm. * subjects should be 21 years of age or older. * contact lens wearers must stop wearing their contact lenses one week per decade of wear before baseline measurements in case of hard contact lenses and one week before baseline measurements in case of soft contact lenses. * patient will be able to understand the patient information and willing to sign an informed consent. * patient will be willing to comply with all follow-up visits and the respective examinations. exclusion criteria: * patient not being able to tolerate local or topical anesthesia * autoimmune diseases * sicca syndrome, dry eye * herpes viral (herpes simplex) infections * herpes zoster * diabetes * pregnant or nursing women (or who are planning pregnancy during the study) * patients with a weight of \> 135 kg * any residual, recurrent or acute ocular disease or abnormality of the eye, e.g. * cataract * suspected glaucoma or an intraocular pressure \> 21 mm of hg * corneal disease * corneal thinning disorder, e.g. keratoconus, * pellucid marginal corneal degeneration * dystrophy of the basal membrane * corneal oedema * exudative macular degeneration * infection * any residual, recurrent, or active abnormality of the cornea to be treated, e.g. * existing corneal implant * corneal lesion * unstable refraction * connective tissue disease * dry eye

Keywords: trans-epithelial phototherapeutic keratectomy ptk te-ptk corneal epithelium excimer laser