HA was used with success in assisting excimer laser surgery for the correction of irregular astigmatism resulting from previous corneal refractive surgery.
During corneal healing after excimer laser surgery, a variable degree of irregular astigmatism can occur. Most of the time, its effect on visual acuity and refraction is minimal but sometimes the corneal surface irregularity can cause light dispersion, which is responsible for the occurrence of decreased visual acuity and visual discomfort.
To obtain correction of the irregular corneal surface resulting from the previous surgery, photo-therapeutic keratectomy (PTK) has been used since 1994 (91). This procedure proved to be effective. Furthermore, the use of a viscous masking agent, such as 0.25% HA, was able to increase the efficiency of the procedure through protection of the valleys between the irregular corneal peaks, leaving these irregular peaks exposed to laser treatment (92). In fact, HA is able to cover the depressions of the corneal surface so effectively, masking them from the photoablation, that only protruding, irregular areas can be ablated. This characteristic is depending on HA physical properties, which are responsible for a photoablation rate of HA similar to that of the corneal tissue.
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