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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-Aug16(4)407-13
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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

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PATIENTS AND METHODS

• Aberrometry with 6 mm diameter - WASCA
  aberrometer (Carl Zeiss Meditec)
• Keratotopography ATLASTM 995 (Carl Zeiss
  Meditec)
• Flap formation - Hansatome Excellus microkeratome
  (BL)
• 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.

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PATIENTS AND METHODS
Group 1
Group 2
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 0,050,02
• BCVA 1,00,06
• Z (4,0) 0,08 0,23 µm
• (Malacara notation)
• RMS HO 0,28 0,21µm

• UCVA 0,050,02
• BCVA 1,00
• Z (4,0) 0,01 0,19 µm
• (Malacara notation)
• RMS HO 0,24 0,07µm

Postoperative follow-up 6 months
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RESULTS
REFRACTIVE EFFECT (6 months)
Group 1 - wavefront-guided LASIK
Group 2 - combined LASIK
a c h i e v e d
p l a n n e d
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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.
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RESULTS
VISUAL ACUITY CHANGES
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RESULTS
HIGHER ORDER ABERRATIONS
RMS HO (µm) RMS HO (µm) Spheric aberration (Malacara notation,µm) Spheric aberration (Malacara notation,µm)
WAVEFRONT- GUIDED LASIK COMBINED LASIK 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
pgt0,05
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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).
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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) - 0.674 µm, Malacara notation)
compared to combined LASIK (Z(4,0) 0.000 µm,
Malacara notation).
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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