Centra SS Max
Large diameter lenses have been successfully prescribed for many years through various designs like full scleral and haptic lenses.
With the manufacture of large diameter blanks (17mm and 21mm) in materials like Acuity 200, Menicon Z and Boston XO, this has assisted the fitting of the advanced Keratoconus, Pellucid Margin Degeneration and Post Graft patients in what is commonly known as Semi or Mid Scleral lenses.
These lenses fit on the sclera therefore allowing the lens to applanate an area of eye which is more symmetrical rather than the distorted areas of the central cornea. The Centra SS Max is a well-known lens in New Zealand, Australia, Canada, and the USA.
Centra SS Max has been designed with the Practitioner in mind. Our goal is to create a lens which provides large diameter coverage of the cornea, thin profile, and the flexibility of design to allow for difficult corneas to be successfully fitted.
Corneal Lens wants to put the understanding of the design back into the hands of the Practitioner so they can alter and refine the fitting to meet the needs of the patient’s eye, to provide comfort, clarity of vision and no disruption to the surface of the eye.
PATIENT SELECTION
Centra SS MAX should be selected as a first lens of choice for patients who:
- Cannot adapt to smaller lenses due to lid interaction causing popping out issues
- Discomfort with smaller lenses
- Distorted cornea
- Keratoconus – micro lens intolerant
- Post Graft
- Poor VA with smaller lenses
- I regular astigmatism from trauma or scarring
MODIFICATIONS
- Spherical
- Eccentricity in optic
- Toric Surface Periphery
- Back Surface Toric
- Front Surface toric
- Bitoric
- Bisym
- Quadsym
- Std Increased Lift (0.6 flatter)
- Std Decreased Lift (1.2 steeper) Other lifts are possible
PARAMETERS
| Parameter | Option |
| MATERIAL | ANY |
| BASE CURVE | 5.3 – 8.8MM (IN 0.1 STEPS) |
| BCOR/BOZR | VARIABLE |
| DIAMETER | 12.00 -18.0 MM (IN 0.1 STEPS) |
| POWER | +30.00 |
FITTING
Undertake a normal examination including K readings, topography maps and Spectacle RX. Following a normal method of approach, utilise the K readings and select from the trial set a lens with a base curve which is close to or slightly steeper than the central cornea region.
Due to the large size of the lens, it is helpful to fill the back of the contact lens with a Preservative Free Drop or Saline. This will reduce the potential of air bubbles being introduced. Local anaesthetic may be used to reduce the initial sensation of a large lens.
Ask the patient to lean forward to allow the fluid filled lens to be placed on from directly below. Once the patient has returned to a normal head position and the lens has settled, apply Fluorescein to the eye so you can assess the physical fit of the lens.
Remember a filter is required as Boston XO is UV Blocked. Be aware that the lens will tighten post insertion. It is recommended to reassess the fit at least 40 minutes later. Centra SS Max patients need to be reviewed more regularly than standard RGP patients. Due to the lack of movement with semi scleral lenses, a thorough cleaning regime is recommended.
1. CENTRAL OPTIC ZONE
The trial lens should allow tear exchange under the lens. With fluorescein you can observe the exchange of tears and the action of the tear pump mechanism in conjunction with the lid blinking.
If the lens adheres peripherally and movement of fluorescein has stopped, then the lens is too tight. Flatten the base curve initially by 0.2mm to see whether the tear exchange is increased.
If there is not a significant improvement then you may wish to flatten it a further 0.2mm, provided you have not as a result now got an increased bearing zone on the apex of the cornea. If there is an increase bearing zone, you may wish to revert to the steeper curve and modify the peripheral curves.
OPTIMAL FIT CENTRALLY
Non Keratoconus: Central pooling 70-100nm deep
Keratoconus; No touch the central cone, just ensure base curve clears apex of the cone post setting.
Post Graft: 80-120nm of tear film with a graft..
Making a change to the central base radius will affect the sagittal height of the lens and a power adjustment will be required. As a general rue add -0.50 for every 0.1mm steeper or add +0.50 for every 0.1mm flatter. This rule applies for bases from 7.0-8.6, otherwise steeper than 7.0 add more minus power.
2. ASSES THE MID PERIPHERY
The mid periphery is made up of a series of flattening radii and each curve can be altered to either reduce or increase the alignment profile. To adjust this area, you will need to change the radii of some or all the documented radii. Another option to change the curves is to apply eccentricity to each or separate curves. This can be – or + eccentricity.
MID PERIPHERY ALIGNMENT
Spherical cornea: 2mm to 2.5mm of close alignment with spherical appearance.
Astigmatic cornea: Depending on the amount of astigmatic alignment in each meridian between 2 – 2.5mm is ideal. This can be corrected by changing the amount of buckle that is incorporated into the back surface of the lens.
Keratoconic cornea with central cone: 2mm to 2.5mm band of alignment but some may present with 12 and 6 o’clock positions appear excessive in their pooling and the horizontal meridian is acceptable then a TSP should be considered. A minimum of 1.0mm TSP should be applied to the back surface.
Keratoconic cornea with decentred cone: 2mm to 2.5mm band but if the horizontal meridian is not acceptable then address this first before attempting to correct the vertical meridian. Another presentation of the decentred cone is that the 6 o’clock position has excessive pooling then a Bisym should be applied. A minimum of 0.8mm should be considered.
Post Graft cornea: Depending on the size of the graft, selecting the appropriate optic size is important to achieve a vaulting effect.
3. ASSES THE EDGE LIFT
The edge profile is very important to the comfort of the Centra SS Max. Due to the size of the lens ensure the edge is not too tight or narrow on dispensing. The lens will slightly tighten over the next two weeks, so allow a 0.75 to 1.00 band of edge width. Ensure that the edge lift is not allowing bubbling or frothing. By altering the last two curves you can affect a change to either reduce or increase the edge lift. A 0.6mm alteration will assist tear exchange.
4. REFRACTION
Over- refract the RX and work out the required power and note that on your order. A cylinder correction can be incorporated into the parameters by utilising Back Surface Toric, Bi-Toric or Front Surface Toric designs.
PER CASE PLAN
To make use of the per case plan, CLC requires the use of a Centra SS Max trial set. These sets can be purchased or loaned. If the initial lens has been selected after used of a Centra SS Max fitting set and the final R lens is unsuccessful CLC will issue a 50% credit of the per lens price.
WARRANTY
Corneal Lens Corporation NZ Ltd guarantees all CLCNZ made lenses against all defect in materials and workmanship for 30 days from the original invoice.