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Reports have been made that corneal aberrations of all orders, including astigmatism, often significantly increase with the use of night orthokeratology lenses. In this study the dynamic changes of total and corneal astigmatism in myopes using orthokeratology lenses was evaluated by different methods. The study enrolled 38 patients (76 eyes) with low and medium myopia (28 and 48 eyes correspondingly) and initial astigmatism less than 2 diopters. The assessment was made before and in different terms after the patient started to wear orthokeratology lenses. Induced astigmatism (or =1 diopter) was found in more than 50% of cases. The degree of astigmatism gradually increased from the centre to the periphery within the papillary zone. The maximum values were found within a 4-mm zone ("uptake zone") and minimal - within a 8-mm zone ("equalization zone"). In all patients, despite the presence of induced astigmatism and residual myopia (0.83+/-0.09 diopters in average), distance visual acuity was high enough without an additional correction (0.82+/-0.05 in average). Apparently, in these patients the aberrations (astigmatism in particular) exceed the focal depth.

The authors have studied a response of the cornea (a change in its thickness, shape, refraction, and endothelium) to nocturnal orthokeratotology - a procedure for temporarily diminishing or removing myopic refraction, which is accomplished by wearing rigid gas-permeability contact lenses that change corneal shape and optical strength. The orthokeratological technique has been ascertained to be an effective modality for the temporary reversible reduction of mild and moderate myopic refraction. In some cases, the refractive effect of the technique may run up to 7.5 diopters. The mechanism of action of orthokeratological contact lenses is to form an epithelial diverging biolens onto the corneal surface by transferring epithelial cells from the center to the paracentral parts. Wearing of orthokeratological contact lenses does not cause clinically significant symptoms of damages to the epithelium and corneal stroma or lead to altered endothelial cell density.