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First Safety Study of Femtosecond Laser Photodisruption
in Animal Lenses: Tissue Morphology and Cataractogenesis
R.R. Krueger1, J.R. Kuszak2, H.Lubatschowski3,
R.I. Myers4, T.Ripkin3, A.Heisterkamp3. 1Refractive
surgery, COLE EYE INSTITUTE, CLEVELAND CLINIC FOUNDATION, Cleveland, OH; 2Ophthalmology,
Rush-Presbyterian-St. Lukes Medical Center, Chicago, IL; 3Laser
Medicine, Lazer Zentrum Hanover, Hanover, Germany; 4Ophthalmology, University
of Missouri, St. Louis, MO.
Purpose: Refractive surgery is beginning to focus on presbyopia
correction. Photophaco-modulation is one attempt to restore accommodation by
modifying lens tissue with a laser. Safety studies in animal lenses can
determine the tissue effects and potential cataractogenesis.
Methods: Six fresh porcine lenses and 6 living rabbit eyes are
irradiated with a low energy femtosecond laser (Ti:Sapphire, 130 fsec). Several
hundred thousand pulses with an energy of 1-4 µJ/pulse are applied to the lens
epinucleus in one of two patterns: 3 concentric annuli or 8 radial slits. The
rabbit eyes are treated according to ARVO guidelines, leaving one eye as a
control. Both rabbit lenses are extracted and tested for light scatter with a
low power He-Ne laser 3 months after the treatment, and then photographed and
fixed for ultrastructure. Porcine eyes are fixed after lasing.
Results: After the laser treatment, all lenses display bubbles
which resolve with time. In the porcine eyes, the bubbles coalesce with a
spacing pattern of > 9µm with pulse energy > 2 µJ applied.
In the rabbit eyes, an energy of 1 µJ and spacing of 10µm is chosen for
transcorneal delivery. Ultrastructurally, the porcine eyes demonstrate a 0.5µm
electron dense border layer with adjacent normal lens architecture. After 3
months, the rabbit lenses demonstrate good transparency with only a fine
optical distortion at the site of laser treatment. One rabbit, in both eyes,
had cataract formation unrelated to the laser. In the other 5 rabbits, laser
scanning studies reveal essentially identical values for the back vertex
distance, sharpness of focus, and light scatter compared to the control.
Conclusion: Femtosecond laser photodisruption of the ocular lens
yields discrete lesions with a border zone of ~0.5µm, and bubbles which resolve
with time. In the living animal eyes, no cataract formation can be found after
3 months, and there is a similar depth of focus and value of scatter when
compared to fellow eyes. These preliminary results suggest that femtosecond
laser can be safely used in modifying the paracentral lens nucleus/epinucleus
for presbyopia correction.
Wavefront Analysis and its Correlation with Refraction
and Topography in Normal Eyes
S.H. Chavala, M.R. Chalita, S.Waheed, M.Xu, R.R. Krueger. Ophthalmology,
Cleveland Clinic Foundation, Cleveland, OH.
Purpose: To evaluate the information captured with the LADARWave
wavefront measurement device and correlate it with clinical findings of
refraction and computerized corneal topography.
Methods: Sixty eyes (30 patients) of healthy individuals having
preoperative exam for refractive surgery were enrolled. Complete ophthalmologic
exam, corneal topography and wavefront measurements were performed. Correlation
between the exams were made. Pearson’s correlation coefficient was assessed for
the two continuous variables, adjusting for the repeated measurements.
Results: In healthy virgin eyes, the mean values for all higher
order aberrations components were: coma = 0.35μm (SD = 0.29), spherical
aberrations = 0.36μm (SD = 0.31) and other terms of higher order
aberrations = 0.31μm (SD = 0.14). The wavefront sphere term was highly
correlated to manifest and cycloplegic sphere measurements (p<0.001), and
wavefront cylinder axis was highly correlated to the cycloplegic axis
(p=0.021). The mean match percentage was 85% and this value was used as the
cutoff point to divide the sample in to two subgroups and verify the influence
of match percentage. The high match subgroup had a higher correlation
coefficient than the low match subgroup when comparing refraction data, with
statistically significant correlation in almost all refraction components for
the high match subgroup. Topographic cylinder and axis were not strongly
correlated to manifest, cycloplegic or wavefront refraction, but there was a
statistically significant correlation between manifest axis and topographic
axis (p=0.046).
Conclusion: The LADARWave wavefront measurement device is a
valuable diagnostic tool in measuring refractive errors and ocular aberrations
in normal eyes. A strong correlation between both refraction and topography
measurements (cycloplegic cylinder axis with wavefront axis) with wavefront
measurements suggests that the LADARWave device may be helpful in preoperative
surgical planning.
Wavefont Analysis of Flap and Laser-Induced Aberrations in a Two-Step LASIK
Procedure
S.Waheed, M.R. Chalita, R.R. Krueger. Ophthalmology/Refractive,
Cleveland Clinic Foundation, Cleveland, OH.
Purpose: To identify aberrations created by making a LASIK flap
and by treating the refractive error with a flying-spot laser.
Methods: Twenty-two eyes underwent a two-step LASIK procedure
with the Autonomus LADARVision laser. In the first step, a flap was made, and 1
month later it was lifted and the laser correction was done. Aberrations were
measured with the LADARWave wavefront measurement device pre-operatively, after
making the flap (1 day, 1 week, 1 month post flap) and after laser treatment (1
week, 3 months post laser). Two different microkeratomes were used (Moria M2
and SKBM). With SKBM, all flaps were nasal. With the Moria M2 the flap was
randomly selected as superior or nasal.
Results: The difference between the preoperative and post-flap
measurements for lower and higher order aberrations was not statistically
significant for the two types of microkeratomes used and for hinge position
placement. A slight hyperopic shift after making the flap was noted in the
manifest refraction and in the wavefront refraction. Manifest sphere and
cylinder, wavefront sphere and cylinder and defocus decreased significantly
after laser ablation, but there was no statistically significant difference
between preoperative and post-flap measurements. When analyzing higher-order aberrations,
the only component that showed significant difference between preoperative and
post-flap values was other higher order terms at 1 day post-flap (p=0.001). All
higher-order aberrations showed statistically significant increment between
preoperative and post-laser treatment.
Conclusions: Making the flap creates changes in the aberrations,
but these changes seem to be transitory and not significant, returning close to
pre-operative levels 1 month later. This data suggests that customized laser
treatment as a two-step procedure may not be necessary. Laser treatment
increases aberrations, especially spherical aberration, and these changes seem
to be stable and permanent after 3 months.
Wavefront Analysis in Post-LASIK Eyes and its Correlation with Visual
Symptoms, Refraction and Topography
M.R. Chalita1A, S.Waheed1A, M.Xu1B,
R.R. Krueger1A. AOphthalmology, BBiostatistics,
1Cleveland Clinic Foundation, Cleveland, OH.
Purpose: To evaluate the information assessed with the LADARWave
wavefront measurement device and correlate it with visual symptoms, refraction
and corneal topography in previously LASIK treated eyes.
Methods: One hundred and five eyes (58 patients) of individuals
that underwent LASIK surgery were evaluated. Wavefront measurements were assessed
using the LADARWave wavefront measurement device. Complete ophthalmologic exam,
corneal topography and wavefront measurements were performed. Correlations
between the exams and symptoms were made. Manifest, cycloplegic refraction and
topographical data were compared to wavefront refraction and higher order
aberrations. Visual symptoms were correlated to higher-order aberrations in
three different pupil sizes (5mm, 7mm and scotopic pupil size). Pearson’s
correlation coefficient and generalized estimating equations (GEE) were used
for statistical analysis.
Results: In post-LASIK eyes, wavefront refraction components were
poorly correlated to manifest and cycloplegic components. The comparison
between manifest, cycloplegic and wavefront refraction with total amount of
higher order aberrations showed no strong correlation. The comparison between
topography and manifest, cycloplegic and wavefront refraction did not show
strong correlation. Visual symptoms analysis showed: correlation of double
vision with total coma (p=0.008, p=0.014) and with horizontal coma (p=o.014,
p=0.024) for the 5mm and 7mm pupil size, respectively; correlation between
starburst and total coma for the 7mm pupil size (p=0.038); and correlation of
double vision with horizontal coma (p=0.033), glare with spherical aberrations
(p=0.010) and with total aberrations (p=0.041), and starburst with spherical
aberrations (p=0.014) for the scotopic pupil size. Scotopic pupil size had
positive association with starburst (p=0.001) and negative association with
double vision (p=0.011).
Conclusions: The LADARWave wavefront measurement device is a
valuable diagnostic tool in measuring refractive error with ocular aberrations
in post-LASIK eyes. A strong correlation between visual symptoms and ocular
aberrations, such as monocular diplopia with coma and starburst and glare with
spherical aberration, suggest this device is valuable in diagnosing symptomatic
LASIK induced aberrations. Horizontal coma was correlated with double vision,
while vertical coma was not.
Surface Ablation With Topical Mitomycin for High Myopia
Correction
A.Laurenzi, M.R. Chalita, R.R. Krueger. Refractive Surgery,
Cleveland Clinic Foundation, Cole Eye Institute, Cleveland, OH.
Purpose:Evaluate refractive outcome and haze incidence of surface
ablation procedures (Laser Epithelial Keratomileusis-LASEK, and Photorefractive
Keratectomy-PRK) with the use of topical mitomycin 0.02% intraoperatively for
high myopia correction.
Methods: Retrospective noncomparative single surgeon case series.
Twenty-two eyes were evaluated (10 eyes had PRK and 12 eyes had LASEK). The
surgical technique used in LASEK cases was an 8.0-mm circular ring filled with
20% ethanol solution and applied on the cornea for 30 seconds. Laser ablation
was performed using the Summit Autonomous LADARVision Excimer Laser. After
laser ablation, a 8.0-mm round sponge soaked with mitomycin 0.02% solution was
applied on the stromal bed for 2 minutes and then removed. PRK procedures were
done by removing the epithelium after applying 20% ethanol solution on the
cornea for 30 seconds and laser ablation was performed using the same laser as
for LASEK. Postoperatively, all patients received Fluorometholone 0.1% for 1
month. Corneal haze, BCVA, UCVA and manifest refraction were the parameters
evaluated. Corneal haze was graded based on Fantes classification.
Results: Of all primary treated eyes, the greatest haze grade
found was 0.5 at the three-month follow-up. Eyes that were previously treated
and had haze, when retreated with combined use of mitomycin, showed significant
improvement in haze grade and best corrected visual acuity. No complications
due to mitomycin use were reported and no re-epithelization delay was noted.
Conclusions: Surface laser correction, in spite of being safe and
predictable, can lead to corneal haze, myopic regression, discomfort and
delayed recovery. Topical mitomycin is a safe adjunct in eyes with high
correction, preventing haze occurrence and consequent regression, and making
surface treatments much more reliable.
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