1 Comparison of bitoric with monotoric laser in situ keratomileusis for the correction of myopic astigmatism with the Nidek EC-5000 Laser. By Mohamed Abdul-Rahman Awadalla,FRCS Magrabi Eye Hospital Egypt

2 Nidek EC 5000 is a LASIK machine using the scanning slit technique So : When the Excimer laser uses the negative cylinder: Central ablation along the steepest meridian will flatten the steepest meridian but also will induce some flattening in the flattest meridian ((Coupling effect)) which will induce a positive sphere which has to be compensated by spherical hyperopic ablation While when the Excimer laser uses the positive cylinder: laser will steepen the flattest meridian with no significant effect on steepest meridian because ablation is not performed in the central area The princible of the Bitoric ablation profile is to steepen the flat meridian and to flatten the steep meridian by equal amounts which produce a spherical corneal profile then any residual spherical error is treated laser ablation. laser ablation (1) Evaluate the effectiveness, preditability & safety of Bitoric laser ablation. (2) Compare with that of Monotoric laser ablation Aim Introduction:

3 Retrospective study included a comparative analysis of 230 eyes of 135 patients with myopic astigmatism who underwent LASIK using the Nidek EC 5000 excimer laser and the Moria M2 microkeratome. With the Bitoric nomogram ( 105 eyes of 65 patients) and the monotoric nomogram ( 125 eyes of 70 patients) Preoperative evaluation: UCVA, BCVA, manifest and cycloplejic refraction, slit lamp exam, fundus exam, applanation tonometry, pachymetry and corneal topography Postoperative evaluation: UCVA, BCVA, manifest and cycloplejic refraction, slit lamp exam, corneal topography and total ablation depth Methods Inclusion criteria: older than 18 congenital astigmatism (-1.0 till -6.0 ) stable refraction Exclusion criteria: BCVA worse than 20/70 pupil bigger than 6 mm in dim light evidence of developing cataract history of uveitis corneal dystrophy, glaucoma, retinal disease or optic nerve pathology connective tissue disease

4 Nomogram used ( Modified Gimbel nomogram ) Calculation determined the laser parameters were 1) Calculate spherical equivalent 2) determine the PTK effect of the total astigmatism treatment ( Total cylinder X 35% ) this produce the hyperopic shift in refraction there for it is added to the sphere 3) apply spherical treatment adjustment the spherical component of the refractive correction is determined by: a) the spherical equivalent b) PTK effect (hyperopic shift) of the cylindrical treatment 4) divide the astigmatism by 2 and write hyperopic (plus) and myopic (minus) components separately 5) Write laser treatment stages a) Hyperopic cylinder with mm zone b) myopic cylinder with mm zone c) nomogram adjusted spherical refractive error 6) 6) for smoothing 3microns PTK are placed in 8 mm zone Example: -3.0 / X 180 S.E = PTK effect = - 4 X 35% = -1.4 Spherical treatment = - 4 – (-1.4) = -2.6 Astigmatism X 180 / +2.0 X 90 Laser treatment stages X X PTK 3 microns

5 The Mean age years +/- 6.3 (S.D) range years Preoperative refraction was to D of sphere with : astigmatism of to -2.0 D for monotoric ablation profile astigmatism of to -6.0 D for Bitoric ablation profile The mean preop.spherical equivalent (SE) was /- 0.7 range (-3.9 to D ) Follow up was 6 months in all patients Visual Acuity ( 6 months after LASIK ) The mean UCVA was 0.7 +/ (range ) was 20/40 or better in 120 eyes ( 88.3%) & 20/20 in 48 eyes (35.6%) in Monotoric profile was 20/40 or better in 101 eyes ( 92.6%) & 20/20 in 21 eyes (19.9%) in Bitoric profile The mean BCVA before LASIK was / after LASIK was / BCVA 20/40 or better was in 345 eyes ( 100%) in Monotoric profile: 7 eyes (5.1%) lost 1 Snellen line of BCVA, 13 eyes (10%) gained 1 line,2 eyes (1.5%) gained 2 lines,0 eyes (0%) gained 3 lines In Bitoric profile: 4 eyes (3.6%) lost 1 Snellen line of BCVA, 25 eyes (22.9%) gained 1 line,7 eyes (6.5%) gained 2 lines,2 eyes (2%) gained 3 lines l Retreatment for a significant residual refractive defect:, 24 eyes (17.1 %) needed after Monotoric LASIK 16 eyes (14.6 %) needed after Bitoric LASIK Results:

6 * Optically leads to a nearly spherical cornea as it ablates a cylindrical profile in the steeper meridian to flatten it and ablates midperipherally in the flat meridian to steepen it (unlike ablation in a single meridian which results in loss of physiological surface profile) * Reduces the effective optical zone and the edge profile by treating half the cylinder in the steep meridian and the other half in the flat meridian which creates a smooth transition between the treated and untreated cornea * Needs less tissue removal for the same refractive defect by balancing the negative and the positive ablation in turn this has the effect of treating high astigmatic errors predictably with a more stable result and with less haze and regression. Bitoric ablation for astigmatism appear to be safer, more effective, more tissue sparing and resulted in a decreased frequency of reablation than the standard treatment Conclusion: Why?

7