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Frequently Asked Questions

Corneal GP (PC-IV)

Does material matter in terms of corneal GP success?
Generally speaking, material matters very little in terms of the success of a corneal GP fit.  Of course, more oxygen is required for overnight wear such as orthokeratology.  In irregular corneal fits, lower oxygen and stiffer materials are helpful when trying to avoid lens flexure.  But considering the size of a corneal GP and its ability to exchange fluid, oxygen permeability is rarely an issue regardless of the material we choose.  Some lenses wet better on specific patients but essentially, its difficult to find big differences from one plastic to the next.  Precision and Cardinal generally favour material manufacturers that have both a proven product but back it up with educational support.  The more the material manufacturer does to support both the lab and practitioners, the more likely we are to use them.  Considering that materials are so similar, it comes down to educational efforts made.
What is new in GP lens design?
Scleral and orthok lenses have taught us bigger is better.  Increasing size, increases sagittal depth.  Increasing sagittal depth, decreases movement.  Decreasing movement, increases comfort.  10.5mm in corneal GP’s for single vision and multifocal lenses is the standard diameter that Precision and Cardinal use.  Additionally, GP’s fit on normal corneas that are disease and surgery free, have a high eccentricity surface.  In other words, the normal cornea is aspheric.  Our lenses should similarly follow this natural rate of flattening from the center to the periphery to create a glove fit.  The PC-IV back surface design that’s used in our single vision and presbyopic lenses employs a high eccentricity to best match the eye surface.  Coupled with the large diameter, the PC-IV gives the best chance of first fit success and the most optimal initial comfort.
What information is required to order GP lenses?
We can construct a lens from as little as the keratometry readings and Rx. But if you have the topography, we can build the lens with improved predictability and first fit success.  And if you have a Medmont topographer, we can construct the lens right in the contact lens software which is the most scientific approach, allowing us to build the lens in 3D space.  Beyond corneal shape, it is always helpful to have visible iris diameter as well.
When trouble shooting a lens fit, what does the consultant need to know to optimize the outcome?

The most important observation to make is a detailed assessment of the fluorescein pattern.  Does the lens clear the corneal apex?  Is the apical clearance adequate, excessive, inadequate?  Where does the lens land?  Where does the lens pool or vault?  What is the edge lift?  If the lens is decentering, manually position the lens centrally to assess what is wrong when it’s centered to the iris?  Position and movement before and after the blink is valuable and of course the over-refraction and visual acuity is necessary.  Start in the center (apical clearance) and make your observations going from the center to the periphery (landing, edge lift, movement).

Should we trial fit or empirically order our corneal GP’s?

Precision and Cardinal’s premier lens design is called the PC-IV.  This high aspheric lens with a 10.5mm diameter is much different from the older generation 9.5mm multicurve designs.  For a new patient, it may be best to empirically order today’s generation of GP, the PC-IV.  However, if you have a PC-IV fitting set, this can help us choose the right parameters of lens and accurately determine the final lens power.  Both trial and empirical orders have their advantages, so you can’t choose the wrong start.

Presbyopic Lenses (Apex Multifocal)

How successful are corneal GP Multifocals?

No company can claim near 100% success fitting the presbyopic eye.  Providing a good fit, comfort and vision at both near, far and in between is incredibly challenging.  However, GP lens optics typically provide patients with an incredibly crisp image when using single vision lenses.  Using gas permeable lenses with their stiffer plastic and polished surfaces gives us the best chance of success in the presbyopic eye.  Precision and Cardinal carry numerous designs, so we can provide you and your patients with options depending on the specific case and visual demands.

Precision and Cardinal carry numerous presbyopic options in corneal GP’s, which one should I use?

Our flagship design is the Apex Multifocal.  This corneal GP is designed based on the back surface platform of the PC-IV.  Using a large diameter and high asphericity, the Apex Multifocal can provide a forgiving fit, comfort and centration.  But the success of presbyopic fitting isn’t limited to the back-surface construction and lens diameter.  The second part of the story is we must provide the patient with the near, distance and intermediate within a specific pupil size.  If you provide us with the patient’s pupil diameter in normal illumination, we can construct the required power distribution within the specific pupil size.

How difficult are multifocal GP lenses to fit?

The Apex Multifocal and all Precision/Cardinal presbyopic lenses start with a good back surface fit.  With a good fit, we are more likely to have good centration.  With good centration, we can deliver the powers the patient requires within their specific pupil diameter.  However, if the lens decenters or moves too much, its not worth assessing vision.  A successful Apex Multifocal starts with a good back surface fit and a centered lens.  Then the distance, intermediate and near vision can be assessed if optimization is necessary.

I have a presbyopic patient interested in trying multifocal contact lenses, but I’ve never fit one. How do I begin?

Treat the presbyopic patient the same as single vision patient.  Your Precision and Cardinal consultant requires the corneal shape data, refraction, add power and pupil size.  If you have topographer, send the axial maps of eye.  If you have a Medmont, send the export files (.mxf file).  The good news is we are there to support you through the fit.  Contact your consultant for assistance with the fit.  And you can have confidence knowing that if we are unsuccessful, you can return your multifocal lenses for full credit.

Keratoconus Corneal GP (KBA)

Precision and Cardinal carry numerous keratoconus lenses. Which product should I use on my irregular corneas when I need a corneal GP?

Although we carry a wide range of irregular cornea options, our flagship product is the KBA Lens designed by John Mountford in Brisbane, Australia.  The KBA uses a larger, 10.2mm standard diameter to decrease movement and increase comfort.  It also uses an exceptionally high eccentricity to match the high rate of flattening seen in most keratoconic corneas.  By matching the eccentricity of lens to the eccentricity of cornea, we create improved alignment, centration and comfort.  We would recommend starting with this product first as it’s the one most likely to achieve success.

Do I need a fitting set to fit the irregular cornea or can we empirically order?

It is always recommended to fit the irregular by fitting set rather than empirically order.  The complexity of the surface in the diseased or post surgical eye makes it very challenging to fit empirically.  Even for those with a Medmont topographer, where we can construct the lens from the contact lens module, its almost impossible to predict the final power necessary.  It is always more efficient to diagnostically fit the irregular cornea.  This way, you can find the diagnostic lens that achieves the best fit, comfort and centration.  From this lens the over-refraction provides an incredibly accurate final power required.  Empirical ordering for the irregular cornea can result in numerous office visits and become costly in chair time and lenses.

I only see one keratoconic or irregular cornea in a year, do I need to purchase a fitting set for such a small specialty contact lens practice?

Of course, its nice to have a diagnostic set when you need it so we would always encourage the purchase of the tools required to fit these abnormal eyes.  However, you have the option to loan the KBA Fitting Set.  Simply contact customer service and book the loaner for a week that’s convenient for you and the patient.

How different is fitting irregular cornea compared with the normal eye? Do I need to change fitting philosophy when seeing the regular or irregular eye?

Nothing changes in terms of fitting philosophy.  Analyze and record the fluorescein pattern from the center to the periphery.  Does the lens clear the central cornea?  Is the apical clearance adequate, inadequate or excessive?  Where does the lens land?  Where does the lens vault?  What is the edge lift?  Where does the lens position?  Where is the lens immediately before and after the blink?  Over-refraction?  Visual acuity?  Basically, all the rules are the same in terms of assessment.  We just expect to see an atypical pattern when fitting an irregular, asymmetric surface.

Orthok (Various Lenses)

What is required to begin orthokeratology practice?

There are two principle components required to begin orthok treatment in your office.  The first is you must complete the certification process to be approved to order lenses.  The second is you require a corneal topographer.  Our consultation or sales team can assist with both.

Which of the many Precision and Cardinal orthok designs should I choose to begin treatment?

There are many approaches to orthok treatment.  We can separate them into empirically ordered, trial set or inventory designs.  Our sales team can assist in determining which set is best suited to your needs.  For instance, if you would prefer to empirically order, then the BE Free may be the best design for your practice.  If you prefer a trial fitting method, then the BE Retainer maybe the best choice.  If you prefer to dispense from inventory, then the CRT may be best for your practice.

What diagnostic information do I need to collect to begin Orthok treatment?

The patient Rx, date of birth and the corneal topography are what we require to begin with any of the designs.  There is specific topographical information that the various designs require.  Some require only the k-readings while others require shape specifics to build the lenses.  Our consultation team can assist with this the required data based on the lens design you are using.

Precision and Cardinal recommend the Medmont E300 Corneal Topographer. Why is this the best choice for my practice?

The Medmont is regarded as the gold standard in corneal topography for specialty contact lenses.  It is accurate, easy to use, captures a large surface area and provide both the practitioner and lab consultant with the information required to build any contact lens.  The Medmont also allows map data to be shared with the consultant through a simple email export so our team can assist with your specialty contact lens fits.  The Medmont is simply the best choice for specialty contact lens practice.  Any other instrument may not provide us with the corneal coverage, accuracy and contact lens oriented analysis that assists us in building or consulting on your fits.

Following overnight wear, what do the consultants need to assist me in optimizing treatment?

The post treatment Rx and resultant acuity is always important.  But post treatment axial and tangential subtractive maps are necessary to understand how we altered the eye.  If you don’t have a Medmont topographer, then save the axial and tangential maps as image files (JPEG, BMP, etc.).  If you have a Medmont, highlight the pre and post topographies OU and then go to “file” and “export” and save them as a .mxf file and email them to your Precision/ Cardinal consultant.

Scleral (ICD FlexFit)

I have a patient that would probably benefit from a scleral lens, but I have never fit one. How do I begin?

There are numerous training videos on the ICD website (www.icdlens.com).  There are quick fit videos as well as hour long training sessions.  Additionally, there are short videos on the various specifics of the lens or problem-solving techniques.  Our consultants are here to support you through the process, and in some cases, we may be able to visit your practice and assist with the fit.

How difficult is it to fit scleral lenses like the ICD FlexFit?

Scleral lenses are much easier to fit than corneal GP’s.  Their size and lack of movement makes them immediately comfortable so even a poor fitting ICD FlexFit can provide little sensation to the patient.  The volume of fluid between lens and cornea makes them very forgiving and ICD FlexFit uses the symmetric nature of the sclera to work to our advantage.  We vault over the irregular cornea and land on the regular scleral shape.  Application and removal is certainly more challenging than in corneal GP’s but in general, sclerals can be considered much easier to fit.

Do I need a corneal topographer to fit the ICD FlexFit?

No, a topographer is not necessary.  In fact, keratometry readings are basically useless in fitting the ICD FlexFit.  You choose your lens based on the eye condition.  For instance, normal corneas fall within a specific range of sagittal depths so the ICD FlexFit nomogram will assist in choosing the correct initial lens.  If you have a keratoconic patient, the nomogram will suggest a slightly higher depth lens.  Transplant patients will require a lens even higher in depth.  So the ICD FlexFit really only requires an understanding of the condition and not the eye shape.  However, topography can be helpful in determining when a cornea has the greatest chance of success.  And the Medmont topographer can determine what actual sag to being with.  But generally speaking, a topographer is not required to fit the ICD FlexFit scleral.

The ICD FlexFit has two diameters. When do I used the smaller 14.8mm diameter and when do I use the larger 16.3mm diagnostic?

The first observation you should make prior to fitting is to measure the visible iris diameter.  The ICD FlexFit diameter should be approximately 3.5mm larger than the visible iris diameter.  If you have a smaller cornea (≤11.3mm), then choose the 14.8mm diagnostic.  If you have a larger cornea (≥11.4mm), then choose the 16.3mm.  If the patient has a small fissure and/or deep set eyes, you might be inclined to start with the smaller diameter.  Otherwise, its better to start with the 16.3mm because larger is generally more forgiving.  Another consideration is the more asymmetry, the larger the lens you may require.  In other words, the more bulging or irregular the cornea, the larger the “dome” you may need to place over the eye.  However, if the eye surface is less asymmetric, a smaller diameter may be able to achieve the vault necessary.

There are so many scleral lenses on the market, what makes the ICD FlexFit different?

The ICD FlexFit uses tangents or straight-line surfaces where the eye is more angular as opposed to curves.  The AS-OCT has taught us the peripheral cornea becomes tangent in shape from approximately 10mm to around 20mm.  Generally, inside 10mm, the eye is curved and outside 20mm, the eye is curved.  However, in the middle the eye generally straight lined or tangent in shape.  For this reason, the ICD uses multiple tangents in its construction which creates an incredibly comfortable and forgiving fit.

Do I need multiple fitting sets to fit a normal prolate cornea with ocular surface disease versus an oblate post refractive surgery patient?

The standard 14 lens ICD FlexFit fitting set has a wide range of sagittal depths and two diameters.  This should provide you with a diagnostic lens for >97% of patients regardless of whether they are a bulging, prolate eye or an extreme oblate, post surgical shape.  The use of tangents means the ICD FlexFit is very forgiving in fit.  But the design is robust in terms of modifications that can be made to each of the four principle zones to fine tune the fit even in the most extreme of eye shapes and conditions.