1. Kh.P.Takhchidi, O.A. Kostin1, A.A. Stepanov1 , A.I. Ovchinnikov1.
COMBINATION OF HYPEROPIC AND MYOPIC ABLATION ALGORYTHMS FOR CORRECTION OF SPHERIC ABERRATION APPEARING DURING CORNEA ABLATION FOR MYOPIA CORRECTION
Kh.P.Takhchidi, O.A. Kostin1,
A.V.Doga, S.V. Rebrikov,1,
A.A. Stepanov1 , A.I. Ovchinnikov1.
IRTC Eye Microsurgery State Enterprise named after S.N. Fyodorov, Moscow, Russia
Ekaterinburg Branch1

2. J Refract Surg. 2000 Jul-Aug;16(4):407-13

3. AIM
To develop the technology for correction of spheric aberration appearing during excimer laser cornea ablation for myopia correction
To compare refraction, visual acuity, and spheric aberration after wavefront-guided and combined excimer laser surgery

4. PATIENTS AND METHODS
Aberrometry with 6 mm diameter - WASCA aberrometer (Carl Zeiss Meditec)
Keratotopography – ATLASTM 995 (Carl Zeiss Meditec)
Flap formation - Hansatome Excellus microkeratome (B&L)
Excimer laser ablation with 6 mm diameter - MEL-80 excimer laser (Carl Zeiss Meditec)
Wavefront-guided ablation was performed with the use of CRS-Master (Carl Zeiss Meditec)
Combined ablation was performed in 2 steps during one operation:
Myopic ablation with the depth corresponding to the degree of myopia increased by 2.0 D for mild myopia and by 2.5 D for moderate myopia.
Hyperopic ablation with the depth corresponding to +1.0 D for mild myopia and +1.5 D for moderate myopia.

5. PATIENTS AND METHODS Group 1 Group 2 Postoperative follow-up 6 months
wavefront-guided LASIK
combined LASIK
20 patients (40 eyes)
14 patients (20 eyes)
SE – 4,67 D ± 1,94D
(range, -1,5 D to – 7,63D)
SE – 3,93 D ± 1,05D
(range, -2,75 D to – 7,00D)
UCVA 0,05±0,02
BCVA 1,0±0,06
Z (4,0) 0,08 ± 0,23 μm
(Malacara notation)
RMS HO: 0,28 ± 0,21μm
UCVA 0,05±0,02
BCVA 1,00
Z (4,0) 0,01 ± 0,19 μm
(Malacara notation)
RMS HO 0,24 ± 0,07μm
Postoperative follow-up 6 months

6. REFRACTIVE EFFECT (6 months)
RESULTS
REFRACTIVE EFFECT (6 months)
Group 1 - wavefront-guided LASIK
Group 2 - combined LASIK a c h i e v d
p l a n n e d

7. RESULTS REFRACTION CHANGES Group 1 - wavefront-guided LASIK
Group 2 - combined LASIK
before 1
month 3
mos. 6
mos.
before 1
month 3
mos. 6
mos.

8. RESULTS
VISUAL ACUITY CHANGES

9. RESULTS HIGHER ORDER ABERRATIONS RMS HO (μm)
Spheric aberration (Malacara notation,μm)
WAVEFRONT- GUIDED LASIK
COMBINED LASIK
Before
0,24 ± 0,07
0,28 ± 0,21
0,08 ± 0,23
0,01 ± 0,19*
6 months after
0,48 ± 0,23
0,33 ± 0,13
-0,53 ± 0,21
-0,01 ± 0,26*
* p>0,05

10. RESULTS
WAVEFRONT- GUIDED LASIK OD
COMBINED LASIK OS
Numerical keratotopographic map 6 months after surgery. A significant increase of corneal refraction (marked with red oval) from cornea center (0 mm) to the periphery (6 mm) is seen in wavefront – guided LASIK group (∆ 0,94 D) while it is almost absent in combined LASIK group (∆ 0,17 D).

11. RESULTS
WAVEFRONT- GUIDED LASIK OD
COMBINED LASIK OS
The value of spheric aberration 6 months after surgery (red arrow indicates the numeric value of spheric aberration). A significant increase of negative spheric aberration in wavefront – guided group (Z(4,0) µm, Malacara notation) compared to combined LASIK (Z(4,0) µm, Malacara notation).

12. CONCLUSIONS
During customized correction of higher order aberrations it is necessary to take into consideration not only preoperative wavefront aberration data, but also biomechanical changes of the cornea taking place during ablation
Combination of myopic and hyperopic ablation during correction of myopia is able to correct spheric aberration appearing due to ablation-induced biomechanical changes of the cornea