The Apex Multifocal is a corneal GP developed by Precision for your presbyopic patients. It employs the unique back surface of the PC-IV design but with front add designed to deliver the add at the specific pupil diameter of your patient. Employing the comfort of the PC-IV back surface with the optimized distance, intermediate and near optics of the front surface, the Apex Multifocal offers your patients an exceptional solution for presbyopia
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. PTS carries numerous designs, so we can provide you and your patients with options depending on the specific case and visual demands.
Precision carries 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 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 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.
The PC-IV is a single vision corneal GP lens developed by Precision. It employs a proprietary and unique aspheric optical zone to better distribute its landing on the aspheric nature of the normal cornea. Coupled with a larger diameter, this design is easy to fit, forgiving and improves initial adaptation. The PC-IV should be your lens of first choice for corneal GP patients.
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 generally favours 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's 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 uses. 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’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.
KBA™ keratoconic Design
The Acronym “KBA” stands for “Keratoconus Bi-Aspheric” which is a corneal GP for the diseased, post surgical and irregular eye. This revolutionary lens employs a high aspheric back surface throughout the posterior side of the lens to best align with the high asphericities seen in the keratoconic and abnormal eye. Then the front surface includes a compensating asphere to neutralize the high eccentricity on the back and create sharp vision for patients. This larger, 10.2mm diameter, bi-ashperic design is lens of first choice for the challenging corneas that present to the practice.
Precision carries 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.
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.
The TriAdd Multi-focal GP is a multi-zonal, posterior sphere that works through a combination of simultaneous vision and translation. By utilizing zones of spherical radii rather than asphericity to achieve reading power, we are able to govern the power of each zone independently. Each zone is transitioned to the next utilizing an aspheric filet curve to achieve a truly progressive power effect.