Comparison of the Topographic Optical Zone After LASIK for Myopic Astigma-tism With 2 Excimer Laser Platforms

Ik Hee Ryu, Hun Yang, David S. Kang, Jin Kuk KimBS Clean Vision Eye center

The authors have no financial interest in the subject matter of this e-poster.

• By technical advance in excimer laser platform, pro-grammed ablation zone gains it’s maximal boundary▫ Night vision symptoms such as halo and glare due to

larger scopotic pupil in relation of ablated corneal optical zone being dramatically decreased

• Different manufacturer produce a variety of laser plat-forms, yielding various degree of effective optical zone zone under identical ablation zone and parameters▫ Several papers previously reported a difference between

intended ablation zone and actual effective optical zone regardless of excimer laser platforms

Purpose• In our study

▫Two types of excimer laser : Allegretto-Q 400 Hz & Schwind Amaris being used

▫Comparison after laser refractive surgery in ablation parameters (short & long axis, abla-tion area) between two platforms

▫Investigating preoperative parameters relation to postoperative optical zone

Patients & Methods• Between Feb. to Mar., 2010, 99 patients (198 eyes) with fem-

tosecond laser-assisted LASIK enrolled; retropective study un-dergone▫ Allegretto group: 50 patients (100 eyes)▫ Amaris group : 49 patients (98 eyes) ▫ Identical programmed ablation zone of 6.5 mm applied to all

cases of LASIK regardless of laser platforms • After certain period of time (mean: 19.4 days), topographic

measurements performed▫ Short and long axis of optical zone identified on the topography

were measured▫ Area of optical zone was calculated via short/long axis

• Measurement of optical zone▫ Short and long axis identified as an imaginary line connecting

the boundary margin at least 1 diopter difference from the center

▫ Optical zone being elliptical in all cases, short and long axis can be identified

• Area of Optical zone▫ Area = ∏ × long axis × short axis/4

• Contributing factors▫ Investigate to identify statistical correlation between optical

zone and preoperative sphere, cylinder, sphere-cylinder ratio, keratometric value (K1, K2, mean K)

▫ Statistical comparison by spearman correlation (SPSS 12.0 ver.)

Long axis

Short axis

ResultsAllegretto Amaris

Short axis (mm) 4.58 ± 0.40 4.21 ± 0.49 p=0.031*

Long axis (mm) 5.23 ± 0.40 4.93 ± 0.48 p=0.039*

Area (mm2) 18.89 ± 2.65 16.37 ± 2.83 p=0.652

*: statistically significant

Allegretto groupSpearman Correlation Coefficients, N = 100Pre_Sph Pre_Cyl Pre_SE Pre_SC_ratio Pre_K1 Pre_K2

Short axis 0.3489 0.8270 0.3858 0.9082 0.6573 0.9046

Long axis 0.0358 0.0008 0.1307 <.0001 0.8276 0.1516

Area 0.5049 0.0557 0.6999 0.0065 0.9252 0.3780

Spearman Correlation Coefficients, N = 98Pre_Sph Pre_Cyl Pre_SE Pre_SC_ratio Pre_K1 Pre_K2

Short axis 0.1109 0.1232 0.1002 0.1348 0.5203 0.4967Long axis <.0001 <.0001 <.0001 <.0001 0.0021 0.0792Area 0.0004 0.2312 0.0016 0.0893 0.0280 0.0918

Amaris group

Pre: preoperative; sph: spherical; cyl: cylinder; SE: spherical equivalent; SC: sphero-cylinder ratio; K1: lower K value; K2: higer K valuered blanks: statistically significant

Conclusions• Topographical optical zone

▫Diameters (long and short axis) A statistical significance in Allegretto group In short and long axis, longer diameter observed

▫Calculated area of optical zone Larger in Allegretto group, but not statistically signifi-

cant• No linear correlation between preoperative pa-

rameters and optical zone in both diameters and calculated area regardless of laser platforms

• Allegretto group▫ Correlation with diameters (long/short axis)

Preoperative spherical/cylindrical amount, sphero-cylinder ra-tio affecting long axis

▫ Correlation with area Preoperative sphero-cylindrical ratio affects caculated area of

optical zone• Amaris group

▫ Correlation with diameters (long/short axis) Preoperative spherical/cylindrical amount, spherical equiva-

lent, sphero-cylinder ratio and flatter K-value affecting long axis

▫ Correlation with area Preoperative spherical amount, spherical equivalent and falt-

ter K-value affects caculated area of optical zone

• Under the identical circumstances, different optical zone in diameters and area was ob-served with different types of laser platforms

• To reduce night vision complaints such as glare and halo, preoperative refractive errors, pupil size, corneal thickness and keratometric value must be considered for selecting a proper laser platform and ablation zone