Transcript Title

Corneal power and wavefront aberrations
after PRK or LASIK for high myopia
Anders Ivarsen and Jesper Hjortdal
Department of Ophthalmology
Århus University Hospital
Denmark
Authors have no financial interests
Background
Few clinically controlled studies have examined long-term
changes in corneal aberrations after photorefractive
keratectomy (PRK) or laser in situ keratomileusis (LASIK).
This study reports seven-year changes in corneal power and
aberrations in patients randomized to PRK or LASIK for high
myopia.
Ivarsen and Hjortdal
Ophthalmology, Aarhus University Hospital, Denmark
Methods
Randomized controlled trial
• One eye of 45 patients (20 PRK and 25 LASIK eyes)
• Spherical equivalent refraction of -6 to -8 diopters
• Refractive astigmatism < 1.5 diopters
Surgery
•
•
•
•
Asclepion-Meditec MEL-70 G-scan excimer laser
6 mm optical zone
Same photoablation nomogram for PRK and LASIK
LASIK flaps cut with Schwind Supratome
Ivarsen and Hjortdal
Ophthalmology, Aarhus University Hospital, Denmark
Methods
Clinical examinations
•
•
•
•
•
•
Before surgery and at intervals for 7 years
Corneal topography (TMS-1, Tomey)
Manifest refraction
Ultrasound pachymetry
Pneumotonometry
…
• Only patients that attended the 7-year control and had
not been re-operated were included in the data-analyses
(7 LASIK and 9 PRK patients)
Ivarsen and Hjortdal
Ophthalmology, Aarhus University Hospital, Denmark
Methods
Topography
• Placido disk corneal topographer
• Topographical maps converted to height data
• Ray-tracings performed with Zemax-EE, 4-mm pupil
• Corneal power, total wavefront aberration, and Zernike
polynomial coefficients were calculated for 2, 4, and 6 mm
pupils.
• Defocus, Astigmatism, Coma, and Spherical aberrations
were reported individually. Other higher order aberrations
were pooled.
Ivarsen and Hjortdal
Ophthalmology, Aarhus University Hospital, Denmark
Results
Manifest refraction
Corneal thickness
PRK or LASIK induce significant refractive regression and increase in corneal
thickness in the first year after surgery
Ivarsen and Hjortdal
Ophthalmology, Aarhus University Hospital, Denmark
Results
Corneal power
• Corneal power increases
significantly in the first year after
PRK or LASIK
*
*
• Power remains stable from one
year after PRK but increases from 1
to 3 years and from 3 to 7 years
after LASIK (*, p < 0.05)
• Changes in optical power are not
correlated to changes in refraction,
CCT, or intraocular pressure
Ivarsen and Hjortdal
Ophthalmology, Aarhus University Hospital, Denmark
Results
Corneal power and wavefront aberrations, 4-mm pupil
PRK
Pre-op
3m
12 m
84 m
Power (D)
49.0 ± 1.9
44.2 ± 2.1*
44.7 ± 2.2
44.9 ± 2.0
Coma (µm)
0.07 ± 0.02
0.18 ± 0.07*
0.19 ± 0.06
0.14 ± 0.03‡
Sph. aberr. (µm)
0.05 ± 0.02
0.14 ± 0.07*
0.13 ± 0.07
0.13 ± 0.08
Other HOA (µm)
0.09 ± 0.02
0.15 ± 0.10
0.15 ± 0.13
0.12 ± 0.07
Pre-op
3m
12 m
84 m
Power (D)
49.3 ± 1.4
44.2 ± 1.9*
44.3 ± 1.7
45.0 ± 1.5‡
Coma (µm)
0.07 ± 0.04
0.15 ± 0.07*
0.15 ± 0.10
0.14 ± 0.07
Sph. aberr. (µm)
0.07 ± 0.03
0.17 ± 0.05*
0.17 ± 0.03
0.16 ± 0.04
Other HOA (µm)
0.10 ± 0.03
0.09 ± 0.02
0.12 ± 0.04
0.12 ± 0.02
LASIK
* pre-operative to 3 months, P < 0.01
‡ 12 months to 84 months, P < 0.05
Ivarsen and Hjortdal
Ophthalmology, Aarhus University Hospital, Denmark
Results
Defocus and astigmatism versus pupil size, 7 years after surgery
*
PRK or LASIK cause a pronounced increase in defocus during scotopic
conditions (p < 0.01) but cause no changes in astigmatism
Ivarsen and Hjortdal
Ophthalmology, Aarhus University Hospital, Denmark
Results
Higher order aberrations vs. pupil size, 7 years after surgery
*
*
*
*
PRK or LASIK increase coma and spherical aberration for 4 and 6 mm pupils
(p < 0.01) but cause no signifcant changes in other higher order aberrations.
Ivarsen and Hjortdal
Ophthalmology, Aarhus University Hospital, Denmark
Conclusions
Corneal power
• The continuing increase in corneal power after LASIK indicates that
corneal biomechanical properties may not be stable even after 7 years.
• PRK-treated eyes appear to be stable after 1 year.
Corneal Aberrations
• PRK or LASIK induce a persistent increase in coma and spherical
aberration but cause no changes in other higher order aberrations.
• Defocus and astigmatism are the most important contributors to
wavefront distortions after PRK or LASIK, amounting to almost 75 % of
the total wavefront distortion in dim light.
Results should be interpreted with caution due to few patients
Ivarsen and Hjortdal
Ophthalmology, Aarhus University Hospital, Denmark