Wavefront
Diagnostics Outcomes and New Technologies
What
is the current state of wavefront science and what role will it play in
clinical practice in the future? How might wavefront be employed to benefit
'unhappy' refractive patients? What are the remaining relevant clinical
issues for refractive surgeons in wavefront science? What technical advancements
now in the research and development stages are likely to further the field
of custom ablation?
An international panel of well known clinical investigators, chaired by
Douglas Koch, MD, addressed these and other related questions at Wavefront
Diagnostics, Outcomes and New Technologies Symposium.
The symposium took place during the annual ASCRS Symposium on Cataract,
IOL and Refractive Surgery, May 31st in Philadelphia, PA. The EyeWorld
CME event was sponsored by ASCRS. More than 700 people from 21 countries
attended the symposium.
The
Current state and future direction of wavefront science
"It is so extraordinary to think where we've come in this field from
seemingly a few years ago when we were just trying to understand what
an excimer laser was about, and where this field has come in terms of
not only our ability to treat patients, but our understanding of the cornea
and our understanding of the way the eye sees," noted Dr Koch in
his opening remarks.
Noting that aberrometry is still in its infancy, he said
that ophthalmic surgeons are only just beginning to understand how to
utilise the data aberrometry provides. It is currently proving itself
to be useful for preoperative screening, as a sort of automated refractor,
and as a postoperative assessment tool.
"But I think that really just scratches the surface of what we can
do with it. The knowledge base is only beginning to form. Aberrometry
is going to be used as a wavefront ablation driver, as a means of trying
to predict outcomes for patients, as a way of assessing accommodation,
and as a way of detecting pathology, even in areas such as cataracts,"
he commented.
The hardware and software continue to evolve. What are the criteria for
the ideal aberrometer? It should provide accurate and repeatable data.
The optimal tool should provide clinical correlations that inform the
patient and surgeon, rather than just a "bunch of strange numbers".
In addition, an ideal device needs to be flexible enough to incorporate
new technology as it becomes available.
Dr Koch reported a study conducted by his own group that looked at the
accuracy of the WaveScan compared to subjective manifest refraction. Dr
Koch's fellow at the time, Nan Wang MD, performed meticulous subjective
manifest refractions and WaveScan measurements on a series of 69 eyes
of 42 patients. The series included normal patients as well as postoperative
patients who had undergone an array of refractive procedures including
LASIK, PRK and Intacs implantation.
The spherical equivalent differed between the two modalities by 0.25 D
on average, with a standard deviation of 0.4D, and a range from -1.20
D to +1.05 D. Sphere and cylinder values differed by similar amounts.
Three consecutive measurements were also taken which revealed excellent
reproducibility of the WaveScan refraction, Koch added.
"I think one's initial impression is to say, "Well, that means
that the device is not accurate." But I think what we're learning
is we must remember that manifest refraction is not only measuring sphere
and cylinder, but is incorporating the effect of all these other aberrations
on our vision. We're beginning to learn and understand that, in fact,
the information we're getting from devices such as the WaveScan actually
is much richer and more meaningful," Koch noted.
The development of wavefront measurement tools is also promoting a reconsideration
of how refractive surgery outcomes are described. In addition to the established
standards of uncorrected and best-corrected visual acuity, the new technology
offers data on everything from point spread function and RMS values to
Zernike polynomials and scotopic acuity. Understanding the clinical correlations
of the new data has become a priority in the field of refractive surgery.
"Our refractive surgery results continue to improve. In the last
decade, 20/20 was the minority outcome for refractive surgery. Today,
20/20 is the majority outcome. I think we're quickly approaching a time
when 20/20 will be the minimum standard and only one element of the standard
in the sense that we'll be looking at things other than simply uncorrected
acuity," Koch noted.
Correlating
aberrations to quality of vision
Most LASIK surgeons have encountered patients who were unhappy despite
having good postoperative uncorrected visual acuity. Steven C. Schallhorn
MD discussed how wavefront technology can offer new insights into the
visual complaints that make these patients unhappy.
Dr Schallhorn described
research done at his own institution looking at the possible connections
between pre- and postoperative aberrations and quality of vision after
LASIK. One hundred consecutive patients underwent standard LASIK to correct
myopia and astigmatism. All patients had low to moderate myopia with or
without astigmatism. The surgeons performed bilateral non-wavefront guided
ablations using a 6.5 mm optical zone size with a transition zone.
Patients completed questionnaires preoperatively and one month postoperatively
to assess glare, haze and halo disability. The researchers compared the
subjective findings with preoperative and postoperative aberrations identified
using a Hartmann-Shack wavefront device.
The average preoperative refraction was -4 D. By one month postoperatively,
more than 90% of patients had achieved 20/20 or better. However, the subjective
survey did reveal a variety of quality of vision complaints, including
glare, halo and reduced sharpness of vision.
A multiple regressions analysis found a significant correlation with postoperative
aberration and glare problems. Several higher-order aberrations were correlated
with postoperative quality of vision complaints. The analysis found no
correlation between preoperative secondary astigmatism and preoperative
glare complaints.
Halo symptoms increased significantly in the postoperative period. There
was a weak but statistically significant correlation between postoperative
halo complaints and pupil size.
Preoperative higher aberrations were also associated with subsequent halo
complaints. In many cases the non-wavefront guided LASIK appeared to increase
higher order aberrations postoperatively.
An analysis of higher order RMS values showed no relationship between
the values in glare or halos, but did reveal a correlation for best corrected
visual acuity. People with higher levels of higher order RMS had a reduction
of their best corrected visual acuity. The same was found for contrast
acuity.
"These findings go along with sort of what we've been thinking all
along, that higher order aberrations do play a factor in those kinds of
things," noted the former US Navy fighter pilot and TOPGUN instructor.
The
halos were also significantly correlated with de-focus. People with significant
levels of postoperative sphere tended to have more halo complaints. There
appeared to be no relationship with coma and trefoil. However, there was
a strong correlation with spherical aberration, glare and halos.
"We find a host of fourth and fifth order terms, especially astigmatism
terms, that are strongly correlated with these quality of vision indices.
Some of these higher order terms, fifth order and astigmatism in particular,
are correlated with a loss of best corrected visual acuity and a loss
of contrast acuity," he reported.
This data begins to show correlations between aberrations and visual complaints
after LASIK. The data suggest that if you can reduce the level of spherical
aberration after LASIK, perhaps with wavefront guidance, one may be able
to reduce the incidence of quality of vision complaints, he said.
"There is much we don't understand about higher order aberrations
and how they are related to vision, but we're getting a much better handle
on it now than we did say a year ago or even six months ago," Dr.
Schallhorn said.
Robert
K. Maloney MD, MA (Oxon) presented a selection of case studies illustrating
the variety of ways that decentration can occur. Dr Maloney is the director
of the Maloney-Seibel Vision Institute, Los Angeles, California, US.
Wavefront Ablation - long term results in low and moderate myopia Dr
Colman Kraff first reviewed the one-year follow-up data on the preliminary
feasibility study of the Visx WavePrint system. That study included a
cohort of 19 eyes with low to moderate myopia. The mean preoperative sphere
was -1.9D, with a mean cylinder of +0.3 D and an MRSE of -1.7 D. All
patients underwent preoperative WaveScan measurements. The surgeons then
used the WavePrint software to produce an ablation plan. The surgeons
then ablated a PreVue lens, a plastic lens placed in a trial frame that
allows the patient to preview the effects of wavefront corrections. The
patients have to read at least three letters on the 20/16 line with the
PreVue lens in order to qualify for the study. Finally, the surgeons performed
the WaveScan guided LASIK ablations. No nomograms were used. Uncorrected
visual acuity remained stable at six, nine and 12 months. All of the patients
achieved 20/20 or better, with 65% achieving at least 20/16. Nearly one
quarter of the patients reached 20/12 or better. At the one-year mark,
nearly half of patients had superior uncorrected vision than their best-corrected
preoperative vision. International
Wavefront Trials Some
158 eyes have undergone Visx WavePrint-guided ablations in international
trials. Patients were treated for up to -6 D of myopia, up to -3D of astigmatism
and up to -6D of spherical equivalence. The surgeons performed bilateral
LASIK targeting emmetropia, but without using nomograms. After obtaining
WavePrint data, the surgeons programmed variable spot scanning (VSS) pulses
to fit the waveprint contours. The treatment consisted of a 6 mm optical
zone which was blended to 8 mm. Wavefront
LASIK makes happy hyperopes Presbyopic
LASIK produces promising preliminary results Custom-ContoureD
ablation patterns - C-Cap takes off Applying
C-Cap to irregular astigmatism HELP
at last for post-LASIK night vision complaints "A
number of these patients were referred to us and are undergoing active
litigation with their original treating surgeon and so everyone had a
vested interest in trying to correct these patients before these cases
came to trial. This is a very difficult group. The patients are often
very defensive. They are very reluctant to sign what are basically IRB
approved consent forms. Patient
questionnaires conducted one month postoperatively provided encouraging
subjective data. All of the patients reported that their overall visual
sharpness and acuity were improved. A total of 90% of patients said that
driving in daylight conditions was better following the surgery.
The Next Generation of Tracking Technology
Wavefront assessment
in today's practice
John F. Doane MD is a WaveScan pioneer, having used the system for nearly
three years. He shared his experiences with some practical diagnostic applications
of Visx WaveScan technology.
"I use it
in every case in my practice. I'm not only looking at topography and standard
refraction. Every eye of every patient gets a WaveScan measurement prior
to surgery or during evaluation. It's used as a screening tool looking for
some cases that maybe shouldn't be done, or at least telling me what to
tell the patient," noted Dr Doane.
The WaveScan system can provide a wealth of information, providing an objective
mathematical calculation of refraction. In addition to regular sphere, cylinder
and axis, it produces an acuity map that provides all the lower and higher
order aberrations. It can also produce a Bille aberration map looking only
at the higher order aberrations. The system provides quantitative data on
root mean square errors. The user can also look at point spread function,
Zernicke coefficients, Hartmann-Shack images and difference maps.
The WaveScan system serves as a confirmation tool for sphere, cylinder and
axis or manifest refractions. It is also proving useful in the postoperative
setting, where it can be used to identify and describe specific higher order
aberrations that may be consistent with the patient's subjective complaint.
The WaveScan can also be a useful research tool. Dr Doane said he is conducting
an ongoing prospective study of patient outcomes. In particular, he is looking
at patients who have large pupils, greater than 7 mm, and treating them
with the Visx Star3 laser 6.5 mm ablation with an 8 mm blend. He then follows
this with postoperative visual analog scale surveys, subjective questionnaires
and pre- and postoperative WaveScan data. The goal is to look for the correlations
between the patient's subjective complaints and the objective findings.
Dr Doane presented several case studies demonstrating WaveScan in action.
One case involved a patient who presented with a mixed astigmatic refraction
and decreased best corrected vision of a couple of lines following refractive
surgery. The WaveScan revealed a well-centred ablation, but also an area
of inhomogeneous tissue removal.
"The WaveScan showed a typical coma-like pattern. We could tell that
the photons entering on to the macular arrived much sooner in the superior
temporal quadrant than they did in the inferior nasal quadrant, again giving
the person an abnormal macular receptive area," he explained.
Another case involved spherical aberration in a patient who had a myopic
laser procedure. The WaveScan showed that the cornea was oblate. Looking
at the point spread function showed that this was not "an ideal situation",
he noted.
The WaveScan system can provide very precise information in common clinical
situations. For example, in a case of a moderate myope with low cylinder,
retinoscopy showed 1D of astigmatism, manifest refraction showed 0.5D, and
topography showed a little bit more. But the WaveScan was much more precise,
working in a 0.01D range, rather than a 0.25 D range.
The Visx system is also useful for sorting out less common presentations.
Dr Doane presented a case of an odd refraction of a patient who has low
myopia and low astigmatism in both eyes. The right eye was very straightforward.
But in the left eye, the retinoscopy was significantly different from what
the patient was wearing habitually. The manifest refraction was close to
what the glasses were, but the retinoscopy was markedly different.
"When we went to WaveScan, it was almost identical to what we have
on manifest refraction, again confirming at least preoperatively what I
thought was a very odd evaluation on my part. We pulled the data straight
off the WaveScan. By using the WaveScan plus our manifest refraction we
were right on target with the postoperative result in this patient,"
he recounted.
How much does the WaveScan refraction drive the laser? At the moment, that
still depends on the patient's subjective approval. Dr Doane said that at
the moment, the WaveScan is his starting point in all cases and the final
point in a large percentage of cases.
He emphasised that subjective manifest refraction still has an essential
role to play. Wavefront provides useful information on the cornea, lens
and retina. But manifest refraction provides feedback from the visual cortex
and the patient's subjective experience. He predicted that the WaveScan
system would soon incorporate subjective data input.
"Ultimately, we will be able to assess not only regular sphere and
astigmatism, but all contributions to what we have previously lumped together
as irregular astigmatism. We'll have all the quantitative data we need to
correct the patient. The patient at that point will be able to provide us
the valuable subjective input that we need for treatments and happy postoperative
patients," he predicted.
Keeping track of trackers
Ablation decentration is a leading cause of suboptimal outcomes, unhappy
patients and re-treatments. Eric D. Donnenfeld MD noted that before decentration
can be prevented, it is necessary to understand how and why decentration
occurs.
Accurate centration is a matter of where the laser is pointed and if the
eye is fixating properly. Therefore, an effective photoablation system
requires both an accurate tracker and verified patient fixation, Dr Donnenfeld
stressed.
Beam placement
and beam shape are two key factors for proper centration. Beam placement
involves the angle of the beam relative to the corneal and iris planes.
The beam shape that reaches the corneal plane can differ from what leaves
the laser, which underscores the importance of tracking the Z axis, he
explained.
"Why does ablation de-centration occur? Very commonly it is because
tracking systems don't always track where they are intended. Tracking
systems were developed to increase ablation accuracy. The only thing worse
than a no tracking system, is a good tracking system that tracks the wrong
area," he noted.
Dr Donnenfeld said that systems such as the Visx Star3 have been shown
to produce good results without any eye tracking at all. The eye tracker
gives the surgeon an additional level of control. This can help maintain
centration and produce the intended ablation pattern.
But not all trackers are alike. Dr Donnenfeld compared the design and
function of two systems, the Visx Star3 ActiveTrak and the LADAR tracker.
The Visx Star3 excimer laser provides real-time tracking via its ActiveTrak
system. The entire pupil is tracked without dilation. The eye position
is directly measured which increases system accuracy.
The automated ActiveTrak system all but eliminates human error. The LADAR
system, in contrast, utilises indirect pupil tracking. This involves pre-imaging
of the eye rather than real-time tracking. This means there are several
steps in the process where human error can occur. It also means that such
systems ablate not where the pupil is, but where the laser thinks the
pupil is, he noted.
Decentration can result if the eye moves too far during the ablation.
The Visx Star3 ActiveTrak includes an innovative feature to anticipate
problems with cyclotorsion. In the event of cyclotorsion, the tracker
continues to function but the ablation process halts temporarily until
fixation is re-acquired.
Dr Donnenfeld
cited a study of the Autonomous tracking system ( SJ Coorpender, SD Klyce,
MB McDonald. "Corneal topography of small-beam tracking excimer laser
photorefractive keratectomy." Journal of Cataract and Refractive
Surgery, V25, May 1999) indicating that the ablated centre did not correlate
well with the preoperative centre. Indeed, 32.7% of the ablations in the
study were decentred more than 0.5 mm. Six percent of ablations were off
centre by more than 1.0 mm.
But even when a tracker is used, patient fixation is still the gold standard.
Dr Donnenfeld noted that fixation is a lot easier with the Visx Star3
system because the pupil is not dilated. He cited published data (Schwiegerling
J, Snyder RW. "Eye movement during laser in situ keratomileusis."
Journal of Cataract and Refractive Surgery, 2000 Mar;26(3):345-51) indicating
less than 0.1 mm of patient fixation decentration when using the Star3
ActiveTrak system. Recent studies from Minnesota researchers (Hardten
Dr, Wachter TM.
"LASIK Results with and without using the Visx STAR S3 ActiveTrak
Eyetracker." Journal of Cataract and Refractive Surgery, submitted)
indicated significantly improved UCVA and spherical equivalents when the
ActiveTrak was used.
Real world clinical experience shows that accurate eye tracking improves
surgical outcomes in diverse conditions including anxiety, obesity and
nystagmus. It is likely that accurate eye tracking will become increasingly
important for large field ablations, prolonged ablations, customised ablations
and hyperopia, he said.
He re-iterated that the use of eye tracking does not preclude the possibility
of a decentred ablation. He reported a case of a myope who was treated
with a tracking laser system, only to end up with more than 1.0 mm of
decentration.
"This patient was complaining bitterly, which is how they ended up
in my office.
How could it end up de-centred? I think this patient had a Bell's phenomenon.
The eye rolled upwards during the treatment so the ablation ended up on
the inferior half of the cornea. This underscores that if the patient
is eccentrically fixating you will end up with a decentred ablation even
if you are perfectly centred on the pupil. So it's critical that patients
be fixated," he emphasised.
He presented a second case study concerning a patient who presented with
complaints about the left eye. An examination showed that the right eye
was perfectly centered. However, the left eye had a significant temporal
decentration of the ablation in relation to the pupil.
In that case it appeared that the eye turned nasally and the ablation
ended up on the temporal cornea. The problem was probably simply that
the patient wasn't fixating properly.
"Decentration can happen with any laser. Both of these patients were
treated with the Autonomous laser. I think a dilated pupil makes decentration
more likely. The reason for that is that it is harder for the patient
to see the fixation light because the blur circle, defined by the dilated
pupil, is gigantic on the retina. They don't know where the fixation light
really is. And with the pupil widely dilated, it's harder to tell where
on the cornea the fixation light is falling. It's harder for the surgeon
to monitor fixation," Dr Maloney noted.
These cases illustrate the two conditions that are required for accurate
laser centration. First of all, the surgeon has to centre the laser on
the entrance pupil. Second, and equally important, the patient also has
to be fixated properly, he stressed.
The early promise offered by wavefront technology to improve LASIK outcomes
is now starting to be confirmed in clinical trials. Conference attendees
heard data from several clinical studies indicating that wavefront guided
ablations can help low and moderate myopia patients achieve high quality
vision in a one-step surgical procedure.
The one-step procedure also appeared to be quite safe. At 12 months postoperatively,
one eye lost three letters, (not a line) of BSCVA. That patient went from
20/16, +3, to 20/16. Another eye developed an epithelial defect that eventually
resolved, he reported.
In terms of aberrometric data, eyes with a higher RMS pre-operatively
had the greater possibility for reduction in RMS post-operatively.
Dr Kraff also presented six-month results from an ongoing higher myopia,
higher astigmatism study. Patients in that trial had a mean sphere of
-5.1 D and a mean spherical equivalent of -5.3 D. All patients were treated
with the Visx WavePrint system using the same protocol as the feasibility
study.
At one month, 95% of the patients were seeing 20/20 or better uncorrected.
Some 70% of patients attained 20/16 or better, with 15% achieving 20/12
or better. Six months after surgery, 95% remain at 20/20 or better. Almost
60% are 20/16 or better, and 21% are 20/12 or better. At six months, 84%
of the eyes were within 0.5 D of ametropia. One-hundred percent were within
1 D.
One patient was undercorrected in both eyes. He has subsequently been
enhanced and his UCVA at one month since his enhancement using the WaveScan
guided ablation was 20/12.
"In this study 42% of the eyes have an uncorrected visual acuity
that is better than their preoperative best-corrected visual acuity. I
think that is quite impressive," noted Dr Kraff.
Patient satisfaction was also high. Patients reported being more satisfied
with their vision in a variety of conditions postoperatively, including
brightly lit conditions, normal working environment and at night with
glare.
"Another thing to consider is the reduced potential for human error
with this system. Because the WaveScan data is automatically transferred
to the laser via the disk, there is no risk for data entry error. There
is no risk for flipped axes, and less room for human error. I get calls
from a number of doctors around the country that have had problems with
flipped axis errors. I've acted as an expert witness in a medicolegal
case, on a patient that had bilateral wrong axes entered into the data.
This eliminates that. So it really increases the level of safety for these
patients," he emphasised.
US multicentre wavefront LASIK trial results
Terrence P. O'Brien MD presented data from an ongoing multicentre trial
that is designed to determine if one-step wavefront-guided LASIK ablations
can improve results for low to moderate myopic patients.
"We are already
performing customised ablation with conventional treatments based on the
patient's functional needs, both occupationally and recreationally. We're
performing anatomical customisation to a degree based on topographic features.
But with Wavefront sensing, we now can move towards a true optical customisation,
measuring and including the subtle aberrations in our treatment,"
said Dr O'Brien.
In the multicentre study, 176 eyes underwent bilateral wavefront-guided
LASIK treatment with the Visx Star S3 laser at five centres. Mean preoperative
manifest spherical equivalent (SE) was -3.1 D. The patient group included
moderate myopes with a mean sphere of -3.5 D, and moderate cylinder or
minimal cylinder of +0.5 D, with a range of 0 to +2.8. The mean spherical
equivalent was -3.2 D.
At the one month postoperative visit, 95% of eyes had achieved 20/20 uncorrected,
with 74% achieving 20/16. At six months, 47% of the eyes had better postoperative
uncorrected visual acuity compared to their preoperative best corrected
visual acuity. Some 94% of eyes were within 0.5 D of the intended correction
at the six month mark.
In terms of higher order aberrations, 70% of the eyes achieved either
a decrease in root mean square, or a minimal change of less than 0.1 microns
at six months, he reported.
"We obtained some interesting information from the patient questionnaires.
Perhaps not surprisingly in bright conditions there was little or no change
between the preoperative satisfaction and the post-treatment satisfaction.
However, there was a slightly higher increased percentage of patients
either very satisfied or satisfied in their night vision at six-months
postoperatively compared to the preoperative level. We also saw an increasing
trend postoperatively towards a greater percentage of patients being satisfied
with their night vision and glare, and a high percentage of patients who
reported no postoperative halo," Dr O'Brien reported.
The postoperative data on contrast sensitivity was also good. An analysis
disclosed that 81% of eyes maintained the same or better contrast sensitivity
in dim conditions with glare an important limitation of conventional LASIK.
Moreover, 96% of eyes maintained the same or better level in bright conditions.
"I think we can see that this Visx platform allows successful treatments
in a single step with a non-nomogram adjusted optical customisation to
reduce errors of input and other human errors. These six-month results
allow us to project with a high confidence to our patients excellent outcomes
including nearly 100% of the patients being able to achieve uncorrected
visual acuity of 20/20 or better. We are clearly raising the bar compared
to what was experienced with conventional LASIK," Dr O'Brien said.
On the international front, clinical trials of wavefront-guided LASIK
are underway in the United Kingdom, Spain, Germany, Taiwan and Colombia.
"Each patient had three wavescan measurements taken and these measurements
had to be clustered within +/- 0.25 D for both sphere and cylinder. They
also had to have higher order RMS values within 0.06 microns. Only then
were they allowed to have a PreVue lens ablated. The WavePrint acuity
had to be better or equal to the best spectacle corrected visual acuity,"
he explained.
Overall, the international results with WavePrint ablations are similar
to those reported in US studies. Nearly 90% of eyes show uncorrected visual
acuity of 20/20 or better at the one month follow-up visit. Slightly more
than half of patients achieved 20/12.5 or better in the same period. The
majority of patients, 83%, were within 0.5 D of emmetropia.
The manifest refraction spherical equivalent improved from a preoperative
mean refraction of -3.3D to a value close to zero at the first week and
at the one month mark, he noted.
As in the American studies, the safety of the procedure was confirmed.
There were no sight-threatening complications.
"The data from the international trials is telling us that wavefront
ablations are effective and can be used to better personalise laser vision
correction treatment for patients," Dr Williams told the session.
In addition to Dr William's group, the clinical results come from trials
being supervised by José Alfonso Sánchez MD of Oviedo, Spain;
Michael Armbrust MD Lohr, Germany; Anthony Lin MD, Changhua,Taiwan; Luis
Ruiz MD and Gustavo Tamayo MD, both of Bogota, Columbia. The study will
now be expanded to include additional sites and other countries.
The treatment of hyperopia with LASIK has posed something of a challenge
to refractive surgeons. W. Bruce Jackson MD FRCSC reported some promising
early results using wavefront guided LASIK to treat hyperopic patients.
He recounted
his experience in treating 12 eyes of six patients in a prospective, non-randomised
study. The patients, who had an average age of 52 years, had up to +3.0
D of hyperopia with astigmatism. After WaveScan analysis, the planned
correction was verified using the PreVue lens. Dr Jackson then performed
variable spot scanning treatments using the Visx STAR S3 excimer laser
with ActiveTrak. Emmetropia was the goal in all cases.
"The optical zone in these cases was blended to 9 mm of a total ablation
area. The ablation target was created with the WaveScan wavefront map,
including up to sixth order aberrations. The variable spot scanning pulses
fit to the wavefront contour within one laser pulse or 0.25 micron,"
he explained.
Two-thirds of the patients were seeing 20/20 uncorrected by one week after
surgery. All of the patients achieved uncorrected visual acuity of 20/20
by the one month visit. Half of the patients were seeing 20/16 or better
after the first week. This declined slightly at one month, to 33%. A majority,
92%, was within 0.5D of the intended treatment goal at one month.
"These preliminary results support the safety and accuracy of treatment
of hyperopia by using WaveScan-guided LASIK. The patients demonstrate
excellent unaided visual acuity and appear stable at early time points.
I must say I've never dealt with a group of patients that were so pleased.
I first started treating hyperopes on the Visx laser back in 1995 and
we thought those results were great, but these patients are absolutely
ecstatic," Dr Jackson reported.
Successful treatment of presbyopia is one of the Holy Grails in refractive
surgery. While early attempts to treat presbyopia involved monovision
strategies or the use of concentric ablations, clinical investigators
are now trying a different, aspheric approach that utilises wavefront
guided customised ablations to correct both near and distance acuity.
Researchers began considering the idea of multifocal LASIK following the
appearance of anecdotal reports of the resolution of presbyopic symptoms
following hyperopic ablation in older patients. Extensive topographic
analysis of those patients provided enough data to design a clinical study.
Dr Naranjo-Tackman
conducted a feasibility study of the new approach in Mexico. He performed
four unilateral treatments with up to one year of follow-up. He observed
multifocal effects in these early cases, with no significant loss of best-corrected
distance visual acuity.
The promising results from the safety study led to the creation of an
expanded clinical trial. W. Bruce Jackson MD Director of the University
of Ottawa Eye Institute reviewed the preliminary results of that trial
using the Visx Star S3 WavePrint system for the treatment of presbyopia
using multifocal corneal ablation.
The study enrolled eight myopes and six hyperopes. The myopes, mean age
52 years, presented with mean MRSE of -3.30 D and a mean add requirement
of 2.31 D. The hyperopes, mean age 55 years, presented with a mean MRSE
of 2.26D and a mean add of 2.29 D. All patients received bilateral treatments
targeting improvements in both distance and near vision.
The new approach to presbyopia treatment attempts to steepen the central
area of the cornea to provide a myopic region for near vision, while also
targeting the peripheral optical zone targeted for emmetropia. The Visx
WavePrint system is used to create the multifocal ablation profile, explained
Dr Jackson.
At the three month follow-up, all of the eyes achieved 20/40 distance
uncorrected acuity, with 80% reaching 20/40 near acuity. The mean near
add requirement dropped in both groups. All patients achieved best-corrected
acuities of 20/20, with 70% seeing 20/16 or better, and 45% attaining
20/12.5. Mean MRSE improved to -0.16 in the myopic cohort and -0.67 in
the hyperopic group.
"These results confirm that the presbyopic ablation pattern does
not compromise accuracy of distance correction. We've demonstrated the
safety of this approach. Now we need to do some work to refine the ablation
profile to improve the effectiveness for near vision correction. A second
treatment group has been started and we'll continue to optimise this ablation
profile," reported Dr Jackson.
Roger F. Steinert MD reviewed the primary applications of C-CAP.
The Custom Contoured Ablation Pattern (C-CAP) method from Visx Inc. is
a software upgrade to the Visx Star 3 Excimer Laser System that allows
normalisation of corneal curvature through unique ablation patterns, following
sub-optimal laser vision correction surgery.
Dr Steinert
explained that the objective of C-CAP treatment is to reduce or eliminate
the visual complaints associated with decentration. These include reduced
visual acuity, debilitating glare and/or halos and monocular diplopia.
The new FDA approval limits the indications for C-CAP to treatment of
asymmetrical ablation patterns caused by decentration from prior laser
refractive surgery. In order to be considered for treatment, patients
are required to have at least six microns difference on the elevation
topography from the lowest to highest point either over a 6.5 mm diameter,
or over the patient's pupil diameter as measured by the Zeiss Humphrey
topographer, whichever is larger.
"First
of all, we're trying to enhance the overall quality of vision. From the
patient's point of view, in most cases there are visual aberrations as
well as potentially loss of best corrected visual acuity that we're trying
to reduce and hopefully, eliminate through making the corneal surface
more regular and thereby optimising best corrected visual acuity,"
he said.
The C-CAP combines the diagnostic capabilities of the Humphrey Topographer
with the Visx Star3 LASIK system. The surgeon uses the Humphrey "VisionPro"
Ablation Planning Software to to analyse decentred corneal irregularities
and identify appropriate treatment areas. The surgeon proposes a size,
location, and shape of an ablation. After test driving the proposed ablation
on the topographer, the surgeon programs the information into the laser
software. If the preview looks good, he then performs the ablation. If
not, the characteristics can be modified until the results improve.
"We know that we have problem patients out there and they need something
done. Right now C-CAP is the only effective treatment that's available
for eccentric, irregular patterns after LASIK. When you do this planning,
you don't want the patient under the laser ready to go. This is something
you need to do in advance and have time, without rushing and without pressure,
to go to your Humphrey planning software and simulate these treatments
and have time to methodically work through this to get the optimised treatment.
And if you do, I think you are going to see some markedly improved and
much happier patients, Dr Steinert predicted.
The C-CAP system is not approved for virgin eyes. Other contraindications
include abnormally thin corneas or signs of keratoconus. Patients who
are taking either isoretinoin (Accutane) or amiodarone hydrochloride (Cordarone)
are also not eligible for C-CAP.
Gustavo E. Tamayo MD reported his early experience with using the C-CAP
method for treating irregular astigmatism following refractive surgery.
Among the first
to use C-CAP, Dr Tamayo has treated 54 eyes with the system since 1999.
Patients were post-refractive surgery cases with various visual defects,
including reduced BCVA, debilitating glare, monocular diplopia and/or
debilitating halos.
"I want to remind those who are going to use the C-CAP method that
we are not doing this for getting rid of glasses, at least not in the
first attempt. What we are doing is trying to regularise the corneal contour
so the topography map should be better, and that's what we aim for in
order to get rid of symptoms," he noted.
The 54 eyes in his series all had undergone refractive surgery of different
types including incisional surgery and LASIK. Before undergoing C-CAP
treatment, 80% of patients had uncorrected vision of 20/200 or worse.
Following C-CAP, 58% of eyes achieved 20/30 or better, compared to none
before the surgery. More than two-thirds of the eyes achieved at least
20/50 uncorrected vision. No patient saw 20/20 before C-CAP. Afterwards,
36% of patients had 20/20 best-corrected visual acuity.
No patients lost lines of corrected acuity, with 18% gaining two lines
and 42% gaining one line, he reported.
The range of astigmatism was reduced following C-CAP, with significant
decreases in the K cylinder and in the refractive cylinder. Perhaps more
importantly, visual complaints were reduced or eliminated in all patients
following C-CAP. Some 75% of patients reported that they were very satisfied
with the result, he added.
"Based on our experience, we believe C-CAP is a safe and very effective
in treatment of irregular astigmatism seen after different types of refractive
surgery. The approval of the C-CAP method is a step forward in the treatment
of all those poor patients with visual complaints following refractive
surgery."
Night vision complaints are one of the more annoying adverse effects of
refractive surgery for both patients and surgeons. Follow-up treatment
with wavefront guided ablations appears promising as a way of resolving
many of these issues, reported Julian Stevens FRCS, Moorfields Eye Hospital,
London, England, UK.
This is going to be one of the key areas of being able to have a safety
net to bail ourselves out of difficulty. I think this is one of the most
exciting areas of refractive surgery because if we can advise our patients
when they come into refractive surgery that should they have a difficulty,
we can bail them out, then it just makes everybody feel more comfortable,"
Dr Stevens commented.
Dr Stevens and colleagues are conducting a prospective study of wavefront-guided
LASIK to treat 100 eyes of 100 patients who have had reduced quality night
vision.
The rigorous protocol includes a full eye exam and objective testing of
night vision complaints, including Oculus mesometer evaluations. Patients
also undergo preoperative topography and wavefront scanning using the
Visx WaveScan system. After confirming the treatment outcome with the
PreVue lens, patients undergo wavefront-guided LASIK.
He presented the results of the first 18 eyes treated in the protocol.
Objectively, the treatments produced significant improvements in Pelli-Robson
contrast-sensitivity scores and mesometer scores.
Nearly two-thirds of the patients reported that night vision symptoms
were somewhat or much improved. Another 27% noted no improvement, and
9% reported some worsening of symptoms. When asked specifically about
driving at night with oncoming headlights, no patient reported excellent
vision, but 55% reported good or very good vision under those circumstances.
No patients reported excellent vision in dim light. Some 45% reported
good or very good vision in dim light conditions, with 54% reporting fair
or poor vision.
Overall, patients seemed satisfied with the outcomes. Some 45% of patients
reported an excellent level of satisfaction with the wavefront experience.
Another 45% reported a good or very good level of satisfaction.
"In our experience, wavefront ablation to attempt to correct night
vision problems in post-LASIK eyes has been very successful. We also have
other studies that are in progress at Moorefield's looking at wavefront
guided LASIK after previous PRK and LASIK after radial keratotomy. We've
seen similar improvements in those groups. It appears that the wavefront
technology has a therapeutic role to play in correcting these difficult
patients," Dr Stevens asserted.
In a presentation immediately after the RSS symposium, Carol Harner, PhD,
vice president of research and development at Visx, discussed a new iris
registration technology that is designed to further enhance the accuracy
of wavefront-guided ablation procedures.
While current systems are helpful for tracking linear motion in the X,
Y and Z-axes, the new Visx Torsional Iris Registration Method uses automatic
iris registration to track cyclotorsion, the rotational movement of the
eye around the Z-axis. Registration is tracked from the diagnostic unit
to the laser, and during, or intraoperatively, under the laser.
Many clinicians currently use a manual system of marking the sclera preoperatively
to track cyclotorsion. This approach is very prone to human error. It
is also very time sensitive, since the inks fade. The new fully automatic
iris image registration system, in contrast, is not prone to human error.
Moreover, the iris images can be stored for later use, she noted
The system registers an iris image from the WaveScan and from the laser
preoperatively. The system registers a unique iris pattern for each eye,
based on samples of prominent iris features. After selecting reference
points on those iris images, matching reference points are identified.
Those reference points are then used to calculate the torsional angle.
This provides data that can be used during the ablation.
"If we're able to do this, one anticipates a much tighter alignment
of laser ablation to the eye rotation, and potentially better clinical
results, which is really the name of the game," emphasized Dr. Harner.