Allegretto Eye-q 400hz Optemized vs. VISX Customvue Custom

[pthein]

Hello all -

Just trying to decide which machine is going to be best for me. I am nearsighted with astigmatism in both eyes (Left is -1.25/-2.75 myopic/astig and the right is -.75/-1.25 mypoic/astig). Both corneal thickness are 570+ and natural dilated pupil is 5.7-5.9. I am able to correct down to 20/15 in both eyes. HOA's in both eyes of 0.17%

I am a pilot and need stable BCVA of 20/20 to fly.

One dr. says the VISX is a true custom wavefront technology which would be best for me given the need for best vision. Other dr. says Allegretto Eye-q is best for night vision. Allegretto is wavefront optemized which was explained as optemized but still the same for everyone where the VISX is wavefront customized which means everyone gets slightly different treatment???? Is this true???



Research I have done really says that either machine should do the job, but which is really best?


1. Which machine would you choose and why?
2. Whats the difference between Allegretto's wavefront optemized and VISX's wavefront customized??


Please help!!

Thanks

Phil

[LasikExpert]

Research I have done really says that either machine should do the job, but which is really best?

The one in the control of the best surgeon. At the risk of quoting myself (US News & World Report); "No amount of technology can compensate for an inferior surgeon."

1. Which machine would you choose and why?

Allegretto for your unique circumstances and if all issues regarding surgeon quality are equal. If you do not have a USAEyes Certified Lasik Surgeon in your area, use our 50 Tough Questions To Ask Your Lasik Doctor to help evaluate a potential surgeon.

2. Whats the difference between Allegretto's wavefront optemized and VISX's wavefront customized??

All the details about wavefront optimized v. customized wavefront are at our article about custom wavefront Lasik. This issue, in my opinion, is a red herring. There are other issues that are likely more important.

Astigmatism means that the cornea is not spherical like the top of a ball, but is elliptical like the back of a spoon. The "tip" of the spoon catches some light passing though the cornea and focuses it off center. This can present to the patient as blurred or doubled vision. In a very real sense, astigmatism is a bump on the cornea.

Astigmatic Lasik will attempt to reduce the size of the bump on the tip of the spoon. You will want to read about Lasik and astigmatism to learn the greater difficulties faced by astigmatism correction with a laser. This is where the difference between a Visx and an Allegretto may become important.

Pupil size. There is a lot of conflicting information about the importance (or lack thereof) of pupil size in regard to Lasik. We have a detailed article about Lasik pupil size issues that you should read so you understand the foundation of why I suggest the Allegretto may be a better choice for you.

True treatment zone. The optical treatment zone (OTZ) is the area of the cornea that is fully corrected. The blend zone (BZ) is the area that transcends from the OTZ out to the untreated surface of the cornea. You are going to be very interested in the OTZ for your correction because it is primarily astigmatism. The BZ is going to give you very limited benefit.

Visx users will be quick to note that in custom wavefront-guided mode the Visx has a OTZ of a bit over 6.0mm, but that is not true in your case. In order to remove the "bump" of the astigmatism, the OTZ is reduced in size on one side. In other words, instead of a 6.0mm round OTZ, you have an OTZ that is 6.0mm by 5.0mm (just a guesstimate. Your doctor can determine actual numbers in advance of surgery). This means that at one meridian the OTZ with a Visx will be close to or smaller than the size of your naturally dilated pupils. That brings you back to the pupil size issue. You will want to know if the true OTZ for the most narrow meridian is equal to or wider than your naturally dilated pupils for the minimum risk of low-light vision aberrations.

Flying spot v. adjustable beam. Allegretto is a flying spot laser. This means that laser energy is applied as a pulse in a small spot at one location on the cornea, then another spot, then another spot, all very swiftly until the entire treatment area has been ablated. Because the spot is small, a nuanced ablation like astigmatic Lasik - which is attempting to remove a bump - is somewhat easier to achieve. A Visx is a broadbeam laser with an adjustable iris that controls the width and location of the beam. In some cases a broadbeam laser has advantages, but not necessarily in your circumstances. I'm sure the Visx sales people and doctors who are fans of the Visx machine will point out that the Visx can correct astigmatism just fine, but you are asking for minutia to help direct your decision. Because the Allegretto is a flying spot laser, it is somewhat less affected by the elliptical narrowing of the OTZ (6.0mm x 5.0mm). Additionally, the OTZ and BZ of the Allegretto are larger than the Visx.

Lasik or PRK. You didn't ask this, but you are going to hear about my bias toward surface ablation techniques like PRK, LASEK, and Epi-Lasik. The first step in Lasik is to create a flap of corneal tissue, which is moved aside and the laser energy is applied on the exposed area. After the tissue is ablated, the Lasik flap is replaced over the treated area. By applying the laser energy deeper into the cornea the wound response is muted. This is why Lasik commonly has no pain and very quick vision recovery. PRK applies the laser energy to the surface of the cornea.

There are several issues about the Lasik flap that should be important to you. One is complications. The probability of a Lasik flap complication during surgery or at any time in your life (remember that once you have had Lasik you have always had Lasik) is quite low, but if you don't have a Lasik flap you have no possibility of a Lasik flap complication. In nearly all cases, no possibility is better than a low probability.

Today's lasers are able to create very nuanced ablation profiles, yet the flap is then placed over this nuanced ablation. It's like putting a comforter over wrinkled sheets. The effect of the wrinkles is lost. That may be fine on a bed, but is the exact opposite of what you want for your vision correction surgery.

You are very likely going to need enhancement surgery. It is possible that all the astigmatism will be resolved with one treatment, but past experience indicates that to get everything precise with your high astigmatism, you will likely need more than one surgery. That means either the Lasik flap will be lifted - leading to an increased risk of epithelial ingrowth and other flap related complications - or the second surgery will be PRK on top of the Lasik flap. Here again, the relative advantages of ablation on the surface of the cornea rather than under a flap are evidenced.

The vision recovery for PRK is much longer and with much more discomfort than Lasik. I tell people that they will wish they had Lasik during the first six weeks, and be glad they had PRK for every day thereafter.

Important concerns. As a pilot, your low light vision is very important. Take all the issues about OTZ and BZ very seriously. The changes after astigmatic laser correction may not be as easily corrected with specticals as what you have now. It is likely that correcting residual astigmatism with glasses will be easier after laser vision correction surgery, but nothing is guaranteed in surgery. There is always some element of risk that you need to consider carefully.

Your Higher Order Aberrations (HOA) are relatively low. Actually, quite low. As a general rule, HOA are elevated by laser vision correction surgery. Not always, and they can go down, but yours are so low that it seems more likely they will be elevated. The elevation may bring you up to only "normal" vision, but normal vision would be a reduction in your current vision clarity. You have excellent vision optics with your corrective lense and this is reflected in your ability to be refracted to 20/15 vision (better than normal). This may not be achieved after vision surgery. You may only get 20/20. This may seem like a non-issue, but I recommend you have your doctor undercorrect you so that you have glasses that bring you only to 20/20 and you may even leave in about 0.25 diopter of astigmatism. This would give you an idea of what vision after surgery - but without glasses - would be like.

For most people having 20/20 uncorrected vision is the goal. For you, it may be a let down. Considering your profession, you may want to consider if the convenience of a reduced need for corrective lenses is worth the risk of "normal" vision.

One other issue that caught my attention is that you said you need to have stable best corrected vision acuity (BCVA) of 20/20 to fly. There are two yellow flags here. One is that it appears 20/25 would threaten your job. It is possible that you would achieve only 20/25 BCVA after vision correction surgery. The other is the stability statement. Is your visual acuaity currently fluctuating? If so, how much?

[pthein]

Can I get some further information on why the Allegretto would be a better choice than the VISX all other factors being equal - ie surgeons skil and experience etc. ????? Why wouldnt VISX fully custom be better than Allegretto optemized??

Whats the difference between a flying spot laser and a variable spot laser?

Is astigmatism of -2.5 - -2.75 D considered high astigmatism?

My vision is stable and has been so for years. The stability statement was associated with post op certification required by the faa.

[LasikExpert]

Why wouldnt VISX fully custom be better than Allegretto optemized??

The majority of your refractive error is astigmatism, which is effectively a topography problem. The relative advantage of custom wavefront does not seem to be fully realized in high astigmatism cases. Different tools work better in different circumstances. You can get from point A to point B in a Ferrari or a Hummer, but if you are going over rough terrain the Hummer is the choice most likely to get you there with the least amount of trouble.

Whats the difference between a flying spot laser and a variable spot laser?

A flying spot laser is a laser the emits a small spot of energy, usually under 1.0mm. A variable spot is a laser that emits a large area of energy, usually over 6.5mm, that is made smaller by an adjustable iris between the laser source and the patient.

Is astigmatism of -2.5 - -2.75 D considered high astigmatism?

Yes, very high.

My vision is stable and has been so for years. The stability statement was associated with post op certification required by the faa.

Thanks for the clarification.