Fitting Dyna Intra Limbal For Pellucid Marginal Degeneration, Globus Keratoconus, Low and Superior Cones

Aim and Ideal Fit

• The principles used in fitting all these conditions are the same. The fluorescein fit, however, will appear different depending on the condition
• The ideal fit (Fig. 1) will have:
  • A fluorescein pattern as close to alignment as possible
  • A light feather touch at the apex of the steepened area
  • 0.5 to 1mm of movement

Figure 1

Trial Lens Selection

Manual keratometer fitting:

• The first trial lens has a base curve closest to 0.2mm flatter than the median K reading

Topography Fitting:

• Start with a trial lens that is close to the measurement at the temporal 4-5mm position

Fitting and Troubleshooting

Diameter selection:

• The standard DIL diameter is 11.2mm. The overall diameter needs to be at least 0.2mm smaller than the cornea

Edge Profile:

• The desired edge lift will show 0.2mm of clearance. The DIL system starts with a standard edge lift. Flatter or steeper edge lifts are available in a step system
• Ensure that you have a good central fit first and then consider the edge fit
  • If edge clearance is too low (Fig. 2) then order a lens with a step 2 flat edge profile
  • If edge clearance is too high then order a lens with a step 2 steep edge profile
  • Increase or decrease the number of steps in 2 step increments as needed to achieve the desired 0.2mm of edge clearance. Use the intermediate step increments for fine tuning if needed

Flat/Steep option

• This allows one edge quadrant to be made flatter or steeper than the others. This will help combat edge stand-off which is usually found at 270º due to inferior steepening
• Order one peripheral curve (PC) at 90º and another at 270º. Prism ballast to minimise rotation. i.e. standard P.C at 90º and 2 steps steep at 270º with 1.25D prism at 270º (Fig. 3 and 4)
• 3 & 9 o/c staining can be corrected by adding toric peripheral curves
• The appearance of a classic dumbbell pattern would indicate the need for a base toric or bi-toric addition

Pellucid Marginal Degeneration

• Most fits exhibit more pooling inferiorly due to the rapid corneal steepening at the base of the pellucid area. This may be ignored as long as good comfort and proper movement exist. Remember, steepening this area will negatively affect the rest of the edge area unless you use the flat/steep option

Figure 2

Figure 3

Figure 4

Fitting Dyna Intra Limbal For Post Penetrating Keratoplasty Patients

Aim and Ideal Fit

• It is important to vault the host-graft interface area
• Reverse geometry is often needed for sunken grafts
• The ideal fit will have:
  • Minimal vault over the donor cornea
  • Good alignment with the host cornea
  • In the case of a steepened graft, a feather touch at the apex of the steepened area is desirable
  • 0.5 to 1mm of movement

Trial Lens Selection

Manual Keratometer:

• Start with the middle base curve lens from the trial set. Go steeper or flatter with the base curve until you get good alignment

Topography Fitting:

• Start with a trial lens close to the measurement at the temporal 4-5mm position

Fitting and Troubleshooting

Diameter selection:

• The standard DIL is 11.2mm. The overall diameter needs to be at least 0.2mm smaller than the cornea

Edge Profile:

• The desired edge lift will show 0.2mm of clearance. The DIL system starts with a standard edge lift. Flatter or steeper edge lifts are available in a step system
• Ensure you achieve a good central fit first and then consider the edge fit
  • If edge clearance is too low then order a lens with a step 2 flat edge profile
  • If edge clearance is too high then order a lens with a step 2 steep edge profile
  • Increase or decrease the number of steps in 2 step increments as needed to achieve the desired 0.2mm of edge clearance. Use the intermediate step increments for fine tuning if needed

Flat/Steep Option:

• This allows one edge quadrant to be made flatter or steeper than the others. This will help combat edge stand-off which is usually found at 270º due to inferior steepening
• Order one peripheral curve at 90º and another at 270º. Prism ballast to minimise rotation. i.e. standard P.C at 90º and 2 steps steep at 270º with 1.25D prism at 270º (Fig. 5 and 6)
• If reverse geometry is needed please see the Fitting Guide for Post Refractive Surgery Patients on the next page

Figure 5

Figure 6

Post Refractive Surgery Patients

It is best to think of fitting post-refractive surgery corneas as fitting two distinct areas – the flatter ablated zone and the original peripheral cornea.

The ideal fit (Fig. 7) will have:

• As close to alignment as possible although in reality, this is difficult to achieve
• Minimal vaulting in the central region
• 0.5 to 1mm of movement
• No impingement of the limbus
• It is important that this lens is made in a material with good oxygen transmission and good wetting properties so metabolic wastes are washed away

Trial Lens Selection

• Because of the calculations made for reverse geometry lenses, it is useful to take Keratometry or Topography measurements in dioptres for this lens

Topography Fitting:

• Take the central Ks and a reading at the temporal area

Manual Keratometer Fitting:

• Take central Ks and then get temporal measurements or use pre-surgery K-readings
• The base curve of the DIL lens will be 1 dioptre steeper than the flat central K
• Reverse Curve:
  • Series A has 2.00D of reverse curve
  • Series B has 3.00D of reverse curve
  • Series C has 4.00D of reverse curve
  • Series D has 5.00D of reverse curve
  • Series E has 6.00D of reverse curve
• To determine the amount of reverse curve needed to calculate the difference between the base curve and the 4mm temporal K or sim K reading
  • Example:
    • Flat K = 40.00D
    • One dioptre steeper than flattest K of 40.00D = 41.00D
    • Base curve is 41.00D
    • Difference between base curve and temporal K of 44.00D = 3.00D
    • Try a series B Dyna Intra-Limbal that has a 3.00D reverse curve

Fitting and Troubleshooting

Diameter selection:

• Select the 11.2mm diameter unless you have a small cornea or a very large cornea
• Lenses are available 10.80 to 12.00mm
• If the mid-peripheral area is pinched off reduce the amount of reverse curve
• If the mid-peripheral area is showing pooling then increase the amount of reverse curve

Edge Profile:

• No one peripheral system will work on all corneas
• You can get the edge profile in standard or any degree flatter or steeper.
• DO NOT fit the edge too tight. You must have adequate tear exchange under the lens.

Fitting Set Parameters

Parameters