Simple hypermetropic and mixed astigmatism correction using LASIK at «MicroScan»PIC» device

Purpose
To assess the effectiveness and safety of modified ablation algorithm at simple hypermetropic and mixed astigmatism correction from 3.5D and higher using LASIK at excimer laser «MicroScan»PIC» device.

Materials and methods
237 patients (365 eyes) having simple hypermetropic and mixed astigmatism from 3.5D to 8.75D were operated by LASIK at excimer laser «MicroScan»PIC» device using primary and modified ablation algorithms.

Results
The following uncorrected visual acuity measurements were reached in groups studied after LASIK: in «Hm ast mod.» group — 0.63±0.08, «Hm ast bas.» group — 0.61±0.09, group «Mixt ast mod.» — 0.60±0.07, group «Mixt ast bas.» — 0.58±0.08. Eyes rate (in %) with corrected visual acuity decrease by 2 lines was nearly the same in each group and didn’t exceed 2.7%. In «Hm ast mod.» group astigmatism rate decreased from 4.2±1D to 0.77±0.42D, in «Hm ast bas.» group - from 3.93±1.12D to 0.73±0.36D, in mixed astigmatism groups «Mixt ast mod.» and «Mixt ast bas.» from 4.9±1.1D to 0.92±0.47D and from 4.6±1.2D to 0.95±0.39D appropriately. Statisticallyvalid difference (Р<0.001) was defined by ablation depth comparative analysis using primary and modified algorithms in hypermetropic astigmatism groups — in central cornea, in mixed astigmatism groups — both in central and transitional ablation areas. Evaluation of «slight» visual functions research results showed: LASIK allows to achieve practically normal contrast sensitivity data in low and average frequencies range; the improvement (P<0.001) was also defined in high spatial frequencies area.

Conclusion
Modified ablation algorithm use at «MicroScan»PIC» device provides: ablation depth decrease; corneal surface physiologic form with transitional area smooth profile. Modified ablation algorithm allows to correct simple hypermetropic and mixed astigmatism effectively and safely from 3.5D and higher.