RGP Lens Fit

Hi there-

I'm new to this forum - hoping to get some advice on my post-op condition.  Back in 2009, I had SBK surgery - performed by a clinic in Ottawa, ON.  My vision was pretty terrible to begin with (+4.75 Left, +5 Right, slight astigmatism and strabismus) - but I was an approved candidate and moved forward with the operation.  Immediate results were good - but, I always had night vision problems (starbursts, halos, double vision, ghosting...) 

My ophthalmologist prescribed me 4% pilocarpine gel, which was awful.  I tried Alphagan-P drops, but that didn't seem to make much of a difference.   Fast forward to today and my vision has regressed.  I have since tried soft contact lenses and glasses, which both helped to correct my vision - but, night vision was still poor.  For reference, here is my prescription for glasses, taken February 2018:

OD; Sphere = +2.25, Cyl = Sph

OB; Sphere = +2.25, Cyl = +1.00, Axis = 040

I am now trying RGP (Boston) lenses and they are definitely promising, but I'm hoping to get some advice on next steps.  I saw immediate results with the first set of lenses - vision was crisp, but we noticed they were slipping down my cornea at my 2-week follow up - causing double vision / ghosting, both during the day and at night.  Since then, we are trying a second set.  My Dr. has increased the optic zone (I believe from 7.7 to 8.3mm) and optic diameter (not sure about this measurement), as well as thinned out the edges - and it seems to have made an improvement when I first put the lenses in, but I'm still noticing double vision / ghosting once they settle in.  If I blink really hard it seems to correct the problem for a few seconds then reverts back.

All that said, I see the potential with GP lenses and I'm hopeful.  I would love to hear other people's thoughts / experience.  Does it get better with time?  Are there other options worth exploring?  Thank you!

Original Post

Your posted experiences point 100% to a problem with the fit. Fitting RGP lenses is becoming a lost art, particularly if the patient has had refractive surgery. If your fitter is unable to achieve a satisfactory fit, notify Barbara Berney here at VSRN to see if she has a fitter near you.

Thanks so much for the quick reply, Dr Hartzok. I will see how the next follow up / fitting goes and keep my fingers crossed.

In your experience - would you say that increasing the lens diameter makes a difference, or perhaps working with a different material than the traditional GP lenses?  Anything else that you might recommend as a consideration?  It seems that I’ve reached the max. optic zone so I suppose it’s really just keeping that area centered over my iris / pupil.

I know there is so much that goes into fitting a lens and every cornea is different - has there been a tried and true method for cases like mine? 

Thanks again. Appreciate your time! 

You mentioned having "reached the max. optic zone ..."

Most practitioners think in terms of large optic zones when, in fact, the optic zone should be sized closer to the effective diameter of the treated cornea - generally smaller than what most contact lens fitters prescribe. So, in general, most RGPs have too large a prescribed optic zone which means the central curve of the lens is improperly aligned with the area outside the treated refractive zone of the cornea. This creates mechanical fit problems and reduces that chance of the lens centering.

For practitioners to become effective post-refractive surgery fitters they need a paradigm shift in their approach, and it is this: The secondary curvature of the RGP lens is ALSO OPTICAL. Just like the surgically constructed refractive zone is not the only optical zone of your cornea, the "optic zone" of an RGP is not the only optic zone fo the contact lens. So, while larger "optic zones (central curve diameters)" are typically considered in normal contact lens fittings, SMALLER optic zones are needed on post-RS corneas. This is the antithesis of what optometrists have been taught about RGPs.

The material? Another paradigm shift: Keep the silicone content low. This improves the optics, the mechanical stability and the lens wetability.

Thanks again for the reply, Dr. Hartzok - really appreciate your input! 

Over the last few weeks I have been piggybacking over a soft lens, which has significantly improved the GP lens fit.  It’s relatively centered now - and because of that, I’m finally able to see at night without the starburts / halos.  The only side effect (aside from it being a short term solution) is that my vision is quite hazy - like I’m looking through a foggy window, which seems to increase with wear.

I am now waiting for lens #3, which will be increased to just over 10mm, with some adjustment to the edge lift / curvature.  We will give the new GP lens a try and if it is still falling / sitting low we will move to a Rose K.  I’m not too familiar with the benefits of this design over a standard GP, but willing to try anything at this point. 

The haziness/fogginess is potentially exacerbated by piggybacking an RGP over a soft lens. Re-designing the RGP is a better way to go. Most RGP fitters fit the lens too steeply (too much vault over the central cornea) with too much bearing (heavy touch) of the outer curvatures. Following refractive surgery, the relationship between the central corneal shape and the peripheral corneal shape is no longer "natural" and a significant consideration for this discrepancy is required in the fitting of RGPs.

Rose K is a lens design for patients with keratoconus where the central cornea is steeper (more sharply curved) than the periphery, similar to your post-surgery cornea. Theoretically a Rose K or similar keratoconus RGP may work (and probably better than what you have tried so far) provided Rose K design curves can be found that closely follow the shape of your post-surgery cornea.

Let me know how you get along.

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