In intrim have found someone to fit me with Synergeyes hybid lens. Still in process of getting good fit but there is hope and this is the best I have done to date. A few optics questions. There is a "post surgical"lens in development with different geometry not to be released until 2007. Currently I am in Synergeyes A lens with some comfort issues. My doc is excellent and patient and I think will do well for me. My question is this. We are moving to steeper lenses for comfort. There will clearly be more tear layer trapped under lens. I know we are looking for centering, and and a steeper lens with out air bubbles. Will I get as acute a vision correction under these circumstances? I do note that when the lenses come out there is significant blurr I presume because of temporary changes in corneal shape. Will the post surgical design improve this? Is there anything short term to help this as I am non functional for hours after their removal. Also will the lenses be easier to remove if steeper or shallower? Removal is a problem still. Thank you. Doc A

One reason people get excited by SynergEyes is because it has a soft lens skirt, enabling it to center better and permitting the lens edge to tuck in behind the lids, making it more comfortable. The removal problems are most probably the combination of the steeper rigid center with a soft skirt that is too snug (although the lens has four skirt geometries available). The steepening of the central curve will reduce clarity somewhat. (A steep fit is when the curve vaults over the corneal center.)

From the specs I have seen, the post-RS SynergEyes lens provides six flatter central curves (9.1 to 9.6). However, the posterior optic zone diameter will also be widened from 7.8 mm to 8.4 mm, with the entire RGP center diameter going from 8.4 mm to 9.00 mm. Most patients and doctors believe a larger posterior optic zone diameter is necessary to solve night vision/large pupil problems. But, considering that the stated OPTICAL ablation zone of most LASIK patients is 6.0 mm and about 6.5 mm on newer systems (they usually measure smaller than this on topographies), the large posterior optic zone on the SynergEyes PS will be trying to cover a highly variable corneal terrain. For improved vision, the lens should follow the central curvature but this will be too flat for the area outside the optical ablation zone. Therefore, the back curve will be steepened, in an attempt to enhance comfort (which I believe is what your doctor is doing now). But this will mean a tighter fit centrally with the increased potential for irregular corneal molding, poor post-wear vision (spectacle blur) and additional removal frustrations. Large RGP optical zones can work reasonably on non-surgical corneas and do, in fact, improve the night vision/large pupil performance. But successful RGPs for surgically-altered corneas don't follow this simple design axiom, a fact that seems impossibly elusive to lens designers.

The SynergEyes lens, in both its A form and PS form, essentially carries a monocurve RGP lens center. As in all things, it will be an improvement for those who have had worse fitting RGP lenses, but the new geometry will be limited because the benefit of the flatter curves will be compromised by the larger posterior optical zone. (An analogy would be... the shoes you want are finally available in size 14 but only in extra wide, and you have a very narrow foot.)

I should point out that patients whose pre-op Rx was minimal have a little better chance of getting success with a large, posterior optical zone (and, therefore, SynergEyes). Because the difference between their ablation curvature and the untreated cornea is less, they are not as likely to receive an intolerably steep lens. The lens calculator for empirical fitting of the SynergEyes lens (available at the company's website) typically fits even non-surgical eyes about a diopter steep. IMO, this approach will reduce the long-term success rate.

This message has been edited. Last edited by: Dr. DavOD Hartzok,

Dr. Harzog, I will take some time to digest your kind reply and keep you posted as my fitting progresses. Perhaps you will have some suggestions to maximize my potential for sucess. Again thank you for listening and responding. DocA

Dr. Harzog, The problems you have mentioned seem to be quite so as fitting proceeds with Synergeyes. Lost visual acuity as lens became more steep. Removal is well, interesting. I believe you have made the point and I want to be sure I get it correct that perhaps properly designed plain rgps may obviate some of these problems. Am I correct? Comfort is definitely an issue even with Synergeyes. Would you recommend I ask my OD to consider plain (properly designed) rgp lenses if the Synergeyes fail? Would you be willing to share your experience with him if that were the case? Best wishes for this holiday season. DocA

There are several things that have to be considered:

First... What were your corneas like before LASIK? What RGPs would have provided an excellent fit before surgery? More precisely, what would have been an excellent fit before LASIK in a large, about 11.0 mm, RGP? Practically no one fits RGPs that large and, if they did, they would have to use a rather wide peripheral curve (1.0 mm) that is 1.5 to 2.0 diopters flatter than the central K readings. This part of the RGP lens is going to rest on the natural cornea, the part untouched by the ablation, so the fit has to be extrapolated from the pre-surgical data. IME, fitting the post-ablation cornea starts in the periphery. The peripheral fit should be well aligned with the cornea.

Second... Exactly how much ablation was performed? This seems straightforward enough since the numbers can be pulled directly from the surgery data. If four diopters of LASIK was performed at the corneal plane, then there should be four diopters change from the pre-op curvature. But, when the outcome is over or under-powered for the stated amount of ablation, this gets a little more complicated. Was the pre-op refraction accurate? Has the cornea bowed forward? Does the patient have a pre-existing binocularity problem that is no longer being compensated for post-operatively? Supposing the amount of stated ablation works out perfectly and the post-op refraction is PLANO, then the central curve of the RGP should be whatever curve provides for a PLANO lens power. (This is for nearsighted LASIK, not farsighted. Farsighted LASIK RGPS are different.) Similarly, if the post-op Rx is +1.25, then the lens curve is whatever requires a +1.25 lens power.

Third... The posterior center curve of the lens should be no more than about 6.5 mm in diameter, even less, depending on the topographic profile and the laser data. Allowing for a 6.5 mm diameter center, a 1.0 mm peripheral curve and a 0.25 mm edge curve, leaves a 1.0 mm width for an intermediate curve.

Fourth... the intermediate curvature, IME, should be one-half the ablation total steeper than the central curve. So, if the patient had four diopters of ablation, the intermediate curve of the RGP would be two diopters steeper.

All of this is a theoretical model, a concept. Actual lens designs may vary since the pre- and post-op measured data may not all add up properly. I am not particularly confident in some of the pre-op refraction data I see. Refraction is not always cut and dried since our eyes and visual system are very dynamic. Correcting central vision while leaving the periphery uncorrected can create problems for some people more than others. How is one to know, in advance, what combination of factors for any one individual will prove highly unsuccessful while similar factors in others are of seemingly little consequence? The perpetual amazement to me is how vocal successful RS patients can be about their positive outcomes to the point of denying credibility to those who express unhappiness. Refractive surgery outcomes are not black and white issues. Refractive surgery is not all good or all bad but there can be little argument that when refractive surgery goes badly for the patient, restoring the patient to a functional visual and contented psychological level is challenging. Vision is only good when we are subjectively unaware of it.

DocA... if your doctor would like to ask me about this, have him email me. I use specially designed trial lenses to help this process but the theoretical design (and initial trial lens selection) is determined almost exclusively from pre- and post-op data provided by the patient. The trial lenses are necessary to fine tune the expected design.

This message has been edited. Last edited by: Dr. DavOD Hartzok,

Dr. Harzog, Again my thanks for your help and patience. I have contacted the department in North Dakota that did the original LASIK to obatin pre procedure scans as you suggest. I did have one further procedure in Omaha on my right eye. Is there any information to be gleaned from pre op scans there also or is the original one the most important. Also this is a little off topic but within this section on VSRN there is a note from a patient who had good experience with a wavefront lens (I think) designed to deal with hoa, perhaps an Accuvue model, I can go back and check. Do you have any opinions on a wavefront guided soft lens? Again my thanks as I collect the data you suggest. Doc A

It was the Definition AC lens.

This is a quote about Definition AC soft lenses:

"Definition AC, unlike other aspheric lenses in the market, incorporates the ideal aspheric curvature for each soft lens power and thickness and compensates for aberrations caused by flexture on the eye."

What is the "ideal" aspheric curvature would be relative to the lenses' power and possibly thickness BUT all of this won't begin to compensate for "aberrations caused by flexure on the eye." The Definition AC lens comes in only one base curve which is like selling t-shirts in size medium only. If someone has a very low degree of RS and can get by with a soft lens, then they are lucky. And, if this particular soft lens seems better than others they have tried, its fortunate that they found it. BUT, the asphericity designed into the lens surface does not correlate specifically to patients' RS-induced HOAs. One size does not fit all. When a patient discovers some advantage to a lens, they want to share their good result. The perception is that the solution is simply to find the right "brand" and that THIS brand is the solution to THIS problem. But, "THIS" problem (RS complication), is quite individualized. If a brand could fix it, we would just link VSRN to the company's website.

Wavefront measurements are essentially measuring in inches what can only be provided to the nearest mile. Soft lenses, particularly on the post-RS eye, are not stable to the point that wavefront would only be of some value when HOAs are averaged and applied to measured spherical aberrations, with control of pupil size - since pupil size will alter the HOAs.

Wavefront devices are the rage. So are cars with 500+ horsepower. Both items are sexy and desirable but, when it comes right down to it, neither is all that practical. And, like many things that are not practical, they are heavily promoted to get our attention.

This message has been edited. Last edited by: Dr. DavOD Hartzok,

OK maybe I am slowly "getting it". How about a compare and contrast if you would of macro lens vs. wave lens. It seems that all I can find leads to these possibilities assuming a proper "custom" fit can be obtained. Again my thanks, Doc A

A macro is an RGP, typically about 13 or 13.5 mm in diameter, about the same diameter as a standard soft lens. A Wave (ZWave) lens can be any diameter the fitter chooses.

A macro can have some of the benefits of a soft lens in that the lens is large and the edges can tuck in behind the eye lid margins. However, the lens rests on the conjunctiva - the mucous membrane that covers the white of the eye. The conjunctiva is very vascular, somewhat spongy, and subject to compression. A large RGP that extends onto the conjunctiva is subject to fitting too tightly by settling deeply into the conjunctiva (compression). Ideally, the lens should be free to move a little - at least 0.5 to 1.0 mm - to remain comfortable and be tolerated physiologically. Doctors who fit a lot of macros have to deal with this aspect of the lenses. It is essential to point out that macro usage tends to be limited to patients with RS problems or a naturally occurring corneal degenerative condition. The larger diameter of the macro lens adds this additional parameter or variable which can thwart the success.

That said, what becomes of the central part of the macro - the part that centers over the cornea? The shape of the cornea for RS or corneal degenerative conditions is quite variable and, as discussed before, an RGP must accommodate these various curvatures for comfort and optical quality. Essentially, the corneal part of the macro must still fit well - as well as the corneal design I detailed above. So, a macro may "carry" a well-designed center or it may carry a poorly-designed center. If the center is well-designed and the conjunctival portion of the lens is well-tolerated, then a macro is going to work well. Again, macros DO add an additional variable and complexity to the fitting process because of their large diameter.

A Wave or ZWave lens can be as large as a macro or may be a corneal lens, a lens that fits entirely within the bounds of the cornea. These lenses derive their central curvature design from data provided by a corneal topographer. Most corneal topographers are only capable of giving good data over the central 6 or 7 mm of the cornea. Therefore, the peripheral curves of the lens must be extrapolated from the topography data. An experienced fitter must be involved who understands how well or how badly those peripheral curves fit. In the case of RS, the central topography readings are POST surgery, so the computer software is particularly unable to determine the peripheral (natural) curves. Patients tend to think that fitting a lens strictly based on the corneal topography readings should provide a perfect fit. They don't understand the limits of topographical analysis and the fact that transitioning the posterior lens curvature from the center to the periphery is ill-defined by a topographer. A "glove-fit" RGP on a post-RS cornea does not transition well to the periphery. Topographical design will create, or attempt to create, unnecessarily steep secondary curves on the lens, causing the lens to vault centrally, reducing comfort and vision. A ZWave fitter who can look at the computer output and modify the lens design from the software presets, can get a ZWave to accommodate the patient's needs but that ability is not something found in the manual.

Dr. Harzog, My thanks again and acknowlegement that you clearly go beyond the extra mile to explain things in way I can understand. This obviously takes time and patience and bodes well for any patient you might take on regarding the arduous task of post op lens fitting. There are not too many questions left for me to ask but as I ramp down taking any more of your time and effort a few last questions. Since transition is important in lens design, do the pre op scans help the fitter? Also in your practice what lenses have worked best for your post op patients and when you do see a patient fail in his or her efforts (hopefully not often) what are the reasons, assuming proper lens fit and adequete vision recovery? Finally, in a perfect world of optics design, what would constitute a perfect lens (if money, lens material, dryness, etc,) were not issues? That is besides the "pre op" lens we all started with and wish we had back! Regards and thanks, DocA. I will probably frequent the board periodically but not with my current intensity after this exchange and I wish you the best and extend my sincerest thanks.

DocA,

BTW, I meant to say, above, the transition curve should be steeper than the central curve by a factor of one-half the total ablation. I just corrected it.

The pre-op scans don't tell me much, other than the optical integrity and normalcy of the cornea. Since topos typically don't give accurate peripheral curves, I can derive as much fitting information from keratometer readings (the peripheral info is extrapolated). The transition curve is mostly calculated. The central curve is based on the ablation data.

What lenses have worked best for me? I am not sure what you are asking. I have detailed how I fit lenses based on the pre-op and post-op data, the use of trial lenses combined with empirical data and follow-up. The easiest patients are those who have previously worn RGPs. Materials are not nearly so significant as most doctors think. Changing plastics does not solve fit problems but I prefer lower silicone values for improved wettability.

A perfect lens is a lens that allows a patient to forget they had refractive surgery. The optics are no more complicated than any other RGP. The fit mechanics are the chief issue. Some non-surgical patients are easy RGP fits; others retain some awareness and are not successful. After surgery, some patients are easier to fit and achieve RGP success relative to others and the reason is not always obvious. IME, most doctors suffer from "brand mentality" as much as their patients and that is certainly the case for post-surgical cases. Labs and companies have "brands". Marketing is about "brands". Selling is about "brands".

If a company COULD produce a perfect "brand", the directors would be back in the board room in less than a year trying to find a way to market the Perfect Brand Plus or the Perfect Brand Two. This mentality applies to every commodity. When the patient and the doctor are thinking brand, then the patient is stuck with generic specifications. Most RS patients do some kind of homework before having surgery and when they are happy with the outcome, they presume they made all the right choices. Most patients would have been happy with their RS even if they had made a dozen different combination of choices while others would have had a negative outcome regardless of their combination of laser and surgeon. RS is an imperfect science. Fitting RGPs on post-RS patients is an imperfect science. It is the paradigm that a good outcome depends on the patient and doctor making all the "correct" choices that is wrong. A deep look at the reality is that not all the variables are knowable before surgery and before RGP fitting. The advantage to the latter is that we can tinker with the RGP design without further damage to the cornea and can work on refining the fit. Unfortunately the "brand" mentality kicks in at the loss of any fitting "PROCESS". Without a process, without a necessary measure of customization, RGPs cannot approach perfect.