The reason so many patients have reduced visual quality and aberrations in dim light is because lasers don't ablate tissue evenly. More tissue is ablated in the central cornea than in the periphery. The result is that the full correction is achieved centrally (which varies with varying levels of myopia) but the periphery of the cornea is left with uncorrected refractive error. The reason this happens is because lasers were designed to treat flat surfaces. The cornea is not flat, it's prolate, like the tip of a football standing up on its end. With the introduction of customized treatments and small spot lasers, more laser engery is being applied in the periphery to account for the loss of efficiency on the slope of the cornea.

http://www.crstoday.com/PDF%20Articles/ ... 06_06.html

Excerpts:

The latest algorithm, called myopic astigmatism, is wavefront guided (by definition), but it also places additional pulses in the periphery of the cornea to compensate for UV light reflection and decreased laser efficiency.

Also, the laser's Gaussian flying spot provides a smooth ablation with prolate optimization, which maintains the natural outer curvature of the corneal surface and thereby minimizes induced spherical aberration.

Of course, if you want to avoid NVDs it is essential not to have uncorrected or even undercorrected area in the periphery. However, ablating more tissue in the periphery, and the deeper peripheral ablations required to maintain a prolate shape while achieving the desired correction consumes more tissue and leaves the patient more susceptible to ectasia - and of course, damages more corneal nerves.

You just can't win with LASIK.

Your doctor may have ablated so much tissue in your first surgery that you may be stuck with 'induced spherical aberration' for life.

That describes my situation. I'm already down to ~300 microns RST now. There's no way I'll ever consent to having more tissue removed under my flaps, and MMC is too toxic for me to consider a surface treatment.

My doctor didn't just underablate in the periphery -- he didn't ablate at all beyond 6 mm. Not good with an 8 mm pupil. A so-called expert stated that I have aberrations even within the OZ. No kidding, genius! So does everyone with a medium or large pupil treated with a VISX cookie cutter S2 laser. The only time I DON'T have aberrations is in very bright light.

When I think about the radial compensation function, it seems hard to believe that the engineers that work for these laser companies that design the lasers didn't know that laser pulses applied on a slope would not ablate as efficiently as laser pulses applied at 90 degrees, but that's apparently the story. Geniuses. Even more bizzare, as so many patients complained of poor vision in dim light, certain laser companies, like VISX, denied it was related to pupil size (large pupils allow light to enter the eye through the peripheral cornea), yet they have now added wider optical zones with blend zones to smooth the transition and now even ablate deeper in the periphery to account for the radial compensation function (they call it wavefront custom, but that's just marketing hype -- they are still inducing more aberrations than they are correcting). These laser upgrades are simply an attempt to maintain the original prolate shape of the cornea. Yet some, like VISX, still claim it's not related to pupil size but the patients complain in dim light when their pupils are large, especially if the patient has naturally large pupils. And what do the surgeons do when large pupil patients complain? They give us glaucoma drugs that have a side effect of reducing the size of our pupils. These glaucoma drugs have some nasty side effects and the pupil reducing effect quickly fades with repeated use.

Pilocarpine and Alphagan both can cause excruciating pain the next day due ocular surface damage - these drugs are no friend to the dry eye patient. Since doctors know that LASIK both induces dry eye and causes visual disturbances for large pupil patients, how on earth could a conscientious surgeon perform LASIK on a large pupil patient and then hand them a bottle of drops that are by no means a cureall. The drops do give you a small taste, sometimes, of the good vision that your refractive surgeon stole from you.

Corneal refractive surgeons - quickly becoming the leading cause of vision loss in America!

EuroTimes
January 2006

Refractive Surgery - A ten year learning curve
Roibeard O’ hEineachain

Excerpt:

Another important development in laser technology for corneal refractive procedures over the last few years has been the implementation of a radial compensation function by virtually all laser manufacturers, Dr. Holladay noted. Initially the lasers did not apply enough energy onto the periphery because they were calibrated on flat surfaces.Therefore, as the beams progressed out from the centre it would hit the cornea increasingly obliquely, he explained.
“The effect of that is substantial and it’s the reason why we were originally making oblate corneas and inducing spherical aberration. Nowadays, a radial compensation function has been implemented into every single laser. There are variations among the companies in terms of how good they are and no-one today has a radial compensation function that is 100% effective.” Dr. Holladay noted that while wavefront and topography-guided systems appear to induce the least amount of spherical aberrations, standard LASIK with lasers with highly accurate radial compensation functions do nearly as well in that respect. Moreover, most of the wavefront and topography-guided treatments still induce spherical aberration as the amount of correction increases, if the radial compensation functions are not sufficient. “That means that they need the radial compensation function to be improved. If you reduce spherical aberration then it’s a combination of the improved ablation profiles and the radial compensation function that allows you to deliver what you wanted.”

Read the entire article at: http://www.escrs.com/Publications/Eurot ... urgery.pdf

EyeWorld Supplement
June, 2006

Comparing wavefront-optimized to wavefront-guided LASIK

"After undergoing LASIK patients' most frequent complaints usually focus on glare and halos at night. Symptoms such as these can be very debilitating and can ruin an otherwise optimal outcome. Such glare and halos are the result of increased post-spherical aberration. The fact is that there is a linear relationship between increasing asphericity and mounting spherical aberration. To ensure that we preserve the best quality of vision for our patients the solution seems obvious: We must keep the ideal corneal asphericity, or Q factor, in mind. We must try to maintain an optimum corneal profile. Practitioners must aim not only to correct refraction but to preserve the cornea's natural prolate shape, which is steeper in the middle and flatter in the periphery. With conventional treatments a similar amount of laser energy is used in the center and on the sides. The problem is that as a result of the corneas' curvature, as the angle of the laser beam striking the eye changes, the amount of tissue removal changes. The laser energy in the periphery is spread over a larger area and is less effective at removing tissue. These conventional treatments increase patients’ spherical aberrations by factors up to 10 when compared to pre-op measures. The wavefront-optimized aspheric ablation profile was developed to reduce the significant side effects of glare and halos that result from such spherical aberrations. The Allegretto Wave system (WaveLight AG, Erlangen, Germany) takes two factors into account. First, the angle of the beam relative to the corneal surface and compensates for this, making superior vision results possible. With the system the number of spots applied to the periphery is increased based upon a proprietary algorithm. Second, the amount of spherical aberration that would have been induced by a treatment with conventional ablation profiles. As a result of this mid-peripheral overcorrection, the WaveLight system is able to obtain a spherical or slight prolate cornea inside the optical zone. Patients with this more prolate cornea resulting from this wavefront-optimized ablation profile have far fewer problems with glare, halos, and low-light vision. Optical zones are another important factor in helping patients to attain the highest quality vision with LASIK. Functional optical zones created by conventional treatments (typical 3 -4 mm) tend to be significant smaller than those created with the wavefront-optimized approach (typical 6 - 7 mm). These larger optical zones are safer and result in fewer night-vision complaints. Because the treatment takes into account the cornea's aspheric shape, transition zones are optimized with the wavefront-optimized approach. The problem is that optical zones created using traditional ablation profiles show a refractive gradient towards the edges, which results in optical distortions. In contrast, this refractive gradient is practically zero after wavefront-optimized ablations (Fig. 1). This is one of the most important outcomes, indicating a nearly physiologic optics of the cornea inside the treated zone. As a result, patients treated with the wavefront-optimized approach report an excellent quality of vision and minimal halos."

Read the entire article at:
http://www.eyeworld.org/supplements/Wav ... 0print.pdf

From article above, quoting Dr. Holladay:



THIS MEANS THEY ARE STILL INDUCING ABERRATIONS IN VIRGIN CORNEAS AND NOT TELLING THE PATIENTS WHAT THEY ARE DOING IN CLEAR LANGUAGE, BEFORE SURGERY.

If your doctor said that you had 'normal' low pre-op corneal distortions but he was going to create some with his big fancy laser, where would you spend your money? Hint, likely not in a laser clinic.

Am J Ophthalmol. 2006 Aug;142(2):227-32.

Size of corneal topographic effective optical zone: comparison of standard and customized myopic laser in situ keratomileusis.Racine L, Wang L, Koch DD.

Baylor College of Medicine, Department of Ophthalmology, Houston, Texas.

PURPOSE: To investigate the corneal topographic effective optical zone (EOZ) in eyes after wavefront-guided myopic laser in situ keratomileusis (LASIK) and to compare them with the EOZ after standard LASIK.

DESIGN: Retrospective, case-control study.

METHODS: We evaluated the corneal topographic maps of 41 eyes of 25 consecutive patients who had CustomVue LASIK (CV LASIK) and 41 eyes of 23 patients who had standard LASIK with correction up to - 7 diopters using the VISX Star S4 laser (VISX Inc, Santa Clara, California, USA). On the refractive map of the Humphrey Topography System, we defined the EOZ as the area outlined by a change of corneal power of 0.5 diopters from the power at the center of the pupil. We analyzed the differences in EOZs of the two ablation patterns and the correlation between EOZ and magnitude of refractive correction.

RESULTS: The mean postoperative EOZs were 17.9 +/- 3.7 mm(2) and 11.4 +/- 3.4 mm(2) after CV and standard LASIK, representing 60% and 40% of the laser-programmed optical zones, respectively (both P < .0001). There was no correlation between the postoperative EOZs and the magnitude of refractive correction for both ablations (all P > .05). In eyes with spherical correction (cylinder </=0.25 diopters), CV LASIK increased the preoperative EOZ by 3.8 +/- 5.6 mm(2) (P = .018), whereas standard LASIK decreased EOZ by 4.5 +/- 5.2 mm(2) (P = .005).

CONCLUSION: CV LASIK created larger corneal topographic EOZs than standard ablation. In eyes with spherical correction, the preoperative EOZ was expanded by CV LASIK and reduced by standard LASIK.

http://www.ascrs.org/publications/jcrs/editjun02.html



Ref:
Patel S., Alió J.L., Pérez-Santonja J. A model to explain the difference between changes in refraction and central ocular surface power after laser in situ keratomileusis. J Refract Surg 2000; 16:330–335

Received 17 April 2006; revised 12 June 2006; accepted 14 June 2006
26 June 2006 / Vol. 14, No. 13 / OPTICS EXPRESS 6156

Experiments on PMMA models to predict the impact of corneal refractive surgery on corneal shape



Ref: M. Mrochen, T. Seiler, “Influence of corneal curvature on calculation of ablation patterns used in photorefractive laser surgery,” J. Refract. Surg. 17, 584-587 (2001).

Higher Order Aberrations and Relative Risk of Symptoms After LASIK

Journal of Refractive Surgery Vol. 23 No. 3 March 2007

Munish Sharma, MD; Brian S. Boxer Wachler, MD; Colin C.K. Chan, MD, FRANZCO



BE's comment: More evidence that wavefront is a hoax. The reason patients have less night vision disturbances with wavefront is not because the technology "measures and treats all the tiny visual imperfections", it's because the industry finally understood that the cornea is not flat, it's prolate, and the laser loses efficiency on the slope of the cornea; therefore newer technology now applies more laser energy in the periphery to reduce the induction of spherical aberrations.

Hi Broken Eyes,

This is Bluestar from Singapore, pretty far from where you guys are. I was scheduled for a lasik op tomorrow, using both wavefront and Intralase technologies. My short sightedness are about 500 degress in both eyes with some astig too. Just managed to chance upon this forum recently.

Prior to this op, I was not told of any major risks involved - only some dry eye issues which seems solvable and will go away after some time. The well known and reputable surgeon who was going to operate on me only shrugged when I asked if he had any problematic cases - "none so far... " , "yours should be ok too".

Some background info for u guys about my country
- costs for lasik have come down in a big way. for a consultant (non-senior), you only have to spend SGD $2,600 or USD $1,625 (USD 1 = SGD $1.60) for a simple lasik treatment (microkeratome).
- my treatment was going to cost me about USD $2,900 in a major hospital with a reputable surgeon. This involved both Intralase (said to be cutting edge) and wavefront technologies.
- many people are now impressed with Lasik ops in a big way and have gone on to introducing to their friends it after their operations.
- as you will see below, media coverage is controlled as Lasik is now beocoming a money churning industry - I have also not been able to find any (serious) negative reports or complaints against Lasik. Maybe we are in an early stage here?

PS - You can also see that the US FDA is quoted in this article for the ICl treatment.
http://health.asiaone.com.sg/mensmatter/20070112_001.html

In the media, are false hopes being communicated to the public? "Symptoms such as halos, glares and ghosting are common after Lasik treatments but they usually disappear after about three months. "
http://www.channelnewsasia.com/stories/health/view/276448/1/.html

I have since cancelled the op after going thru this forum. Not worth the risk, in my opinion.

Another smart patient!

Yes, LASIK is hype. If you only measure success by the reduction of the need for corrective lenses, then it's a success. If you measure it by visual quality and side-effects and complications and long-term adverse consequences that are hidden from the public, then it's a miserable failure. The LASIK industry is as deceptive as the tobacco industry.

Read www.thelasikreport.com

May, 1999

http://www.revophth.com/1999/may_articl ... 5lasik.htm

J Cataract Refract Surg. 2005 Feb;31(2):379-84.

Functional optical zone after myopic LASIK as a function of ablation diameter.

Nepomuceno RL, Boxer Wachler BS, Scruggs R.
Boxer Wachler Vision Institute, Beverly Hills, California 90210, USA.

PURPOSE: To analyze spherical aberrations in patients who had myopic laser in situ keratomileusis (LASIK) with different optical zones and varying degrees of attempted corrections.

SETTING: Laser Refractive Center, University of California, Los Angeles, USA.

METHODS: This retrospective analysis comprised 78 eyes of 56 consecutive patients who had LASIK for myopia with the Alcon LADARVision excimer laser. The preoperative and 3-month postoperative functional optical zones (FOZs), a measure of spherical aberrations, were assessed in each eye. The change in FOZs was analyzed by size of the primary optical zone and degree of attempted correction.

RESULTS: The mean preoperative FOZ was 6.1 mm +/- 0.6 (SD) and the mean 3-month FOZ, 5.2 +/- 1.0 mm. The mean decrease was 0.9 +/- 1.0 mm (P < .0001). The mean decreases were 0.005 +/- 0.7 mm, 0.7 +/- 0.9 mm, and 1.6 +/- 0.9 mm in the low, moderate, and high attempted correction groups, respectively (P < .05), and 1.3 +/- 0.9 mm, 1.2 +/- 1.0 mm, 0.5 +/- 1.3 mm, and 0.3 +/- 0.7 mm in optical zone groups of 6.0 to 6.5 mm, 6.6 to 7.0 mm, 7.1 to 7.5 mm, and 7.6 to 8.0 mm, respectively (P < .05).

CONCLUSIONS: Larger optical zones had fewer postoperative spherical aberrations. Higher attempted corrections had larger increases in spherical aberrations. Larger treatment diameters minimized postoperative spherical aberrations.