Fitting Tips for Quad Sym Designs
I. How To Call Out Quadrants.
The quadrants are referred to as Quad 1, Quad 2, Quad 3 and Quad 4. The Quads start at 4:30 to 1:30 and go around the clock, counter-clockwise just as we refer to degrees of 0 to 180. Quad 1 = 4:30 to 1:30, Quad 2 = 1:30 to 10:30, Quad 3 = 10:30 to 7:30 and Quad 4 = 7:30 to 4:30.
II. Quadrant Specific Designs Explained.
Quad Sym designs allow for 4 different base curves and 4 different edge lifts. One analogy to explain Quadrant Specific Technology is to a pie. Cut a pie into 4 quarters and one of those pieces represents one Quad Sym Base Curve. If we deal only with the crust on that piece of pie, it is a Quad Sym Peripheral Curve. And the practitioner can get both separate base curve treatments with different peripheral curve treatments.
III. Fitting Criteria.
LDI employs a modified topography / trial lens fitting methodology. Start with a trial lens of Dyna Cone Plus or Dyna Intra-Limbal. Try to get at least one quadrant aligned and make notes as to what is happening in the other 3 quadrants. (i.e. Pooling, touch, etc.) Perform over refraction. Get these details along with axial topography map to LDI. Files sent via the internet should be in PDF files or JPEG files to orderentry@lensdynamics.com
IV. Rotation Issues.
These designs tend to locate with the flat-to-flat and steep-to-steep areas. A half diopter of prism is standard, but up to 2 diopters can be incorporated to stop excessive rotation. Each lens has marks midway in Quads 1 and 3. Therefore, the marks should be at 3 and 9 o’clock on the eye. Always make note of where the rotation dots locate. The transition areas between Quads are mono-centric. No visual “jump” occurs with these designs. Each front radius matches the base curve radius to achieve a given power.
V. Case Histories.
Case One:
Note flat peripheral areas at 11:00 and 4:00 o’clock. Single base curve lenses were not adequate. The 7.67 BC Dyna Intra-Limbal (DIL) produced –4.25 power but vaulting in other quadrants.
FINAL LENS PARAMETERS:
DIL: -4.25, 11.2 /9.4
Quad Sym base curve= Q 1 = 8.44, Q 2 = 7.67, Q 3 = 8.44, Q 4 = 7.85. Quad Sym PCs = Q 1 = Standard, Q 2 = 4 steep, Q 3 = Standard, Q 4 = 4 steep
Case Two:
Note quadrant 4 covers the entire quadrant, but flattens out over the rest of the cornea. Nothing remarkable in periphery. Trial fit with DIL 6.82, 11.2 / 9.4 With a resultant power of –7.75. Excessive touch in other quadrants.
FINAL LENS PARAMETERS:
DIL: -7.75, 11.2 /9.4 Standard edge lift
Quad Sym base curve: Quad 1 and 3 = 7.67, Quad 2 = 7.85, Quad 4 = 6.82
Case Three:
OD:
Note large steep area in quadrant 4 with other quadrants fluctuating in radius. This is a prime example of why a trial fit is essential on these corneas. Looking at the OD cornea, one would surmise full base curve, Quad Sym design would be needed. A DIL trial lens of 7.20, -2.00, 11.2 / 9.4 was tried. The single radius base curve worked satisfactorily but edge lift was poor. Quad 1 edge was too tight, Quad 2 was tight but not as much as Quad 1, Quad 3 was OK, and Quad 4 was standing off.
OR = -1.00 -3.00 X 125
FINAL LENS PARAMETERS:
DIL: 7.20, -3.00 –3.00 x 125, 11.2 / 9.8
Quad Sym PCs: Quad 1 = 3 Flat, Quad 2 = 1 Flat, Quad 3 = Standard, Quad 4 = 5 Steep
OS:
Note steep Quadrant 4 and flat in Quadrants 2 and 3. This cornea presents looking like a full Quad Sym base curve cornea. The results from a single base curve trial lens showed acceptable fit but poor edge lifts. Quad 1 was Ok, Quad 2 and 3 were pinched off and Quad 4 was standing off.
FINAL LENS PARAMETERS:
DIL: 7.60, -0.25, 11.2 /9.4
Quad Sym PCs: Quad 1 = Standard, Quad 2 & 3 = 4 Flat, Quad 4 = 6 Steep.
