Links to Case Studies:
Case 1
By: Dr. Tom Quinn
History: 22 yo waitress interested in contact lenses
Refraction:
OD -1.00-3.00 X 180
OS -2.00-2.25 X 175
K’s:
OD 41.00@ 180; 44.00 @ 090
OS 43.00 @ 175; 45.00 @ 085
Treatment options:
- Toric soft contact lenses
- Spherical GP lenses
- Toric GP lenses
Diagnostic lens applied OD:
Base Curve OAD/OZ Power ct
8.03mm (42.00D) 9.2/7.8 -2.00 .16
Spherical diagnostic lens demonstrates poor centration; therefore elected to pursue toric GP fit. Where to start?
Choosing Toric Base Curve Based on Lens Diameter
Lens Diameter
Small (8.0-8.6mm)
Intermediate (8.7-9.3mm)
Large (9.4-10.2mm) |
|
BC/Cornea Relationship |
Horizontal
0.25 STK
ON K
0.25 FTK |
Vertical
0.50 FTK
0.75 FTK
1.00 FTK |
|
All maintain a 0.75 difference in fitting relationship between horizontal and vertical meridians to mimic fitting the “ideal” cornea.
Rx: -1.00-3.00 X 180
K’s: 41.00/ 44.00 @ 090
Order:
BC: 41.00 (8.23mm)/ 43.25 (7.80mm)
BVP: -1.00/ -3.25
Difference in base curve (D): 2.25 D
Difference in lens powers: 2.25D
Conclusion: Spherical Power Effect (SPE) Design
- difference in base curve (D) is equal to the difference in lens power (in air)
- provides fit like a toric base lens with power effect of non-flexing sphere
- advantage: lens can rotate without compromising vision!
Diagnostic spherical lens OD
Toric lens on same eye
Case 2
By: Dr. Ed Bennett
Custom Bitoric Design and Fitting
History: 16 year old spectacle wearer who has been wearing soft torics for sports.
Refraction:
OD: +0.75 - 5.50 x 180 20/20
OS: +1.00 - 5.50 x 180 20/20
Keratometry:
OD: 41.50 @ 180; 47.00 @ 090
OS: 41.50 @ 180; 47.00 @ 090
Slit Lamo Evaluation:
Grade 2 papillary hypertrophy OU
Vascularization x 2mm inferiorally OU
What SPE diagnostic lenses to use?
Remember: Fit the lens 0.12 – 0.50D flatter than “K”
If 3D SPE diagnostic fitting set is the following:
BCR: 40.50/43.50 to 45/48 in 0.50D steps, all with powers of Pl/-3.00D, the following lens should be used OU.
41.00(8.23mm)/44.00(7.67mm) Pl/-3.00D
If OR = +1.25DS OD & +1.50DS OS
What are the powers to order?
Simply add the over-refraction to the diagnostic powers:
OD: +1.25/-1.75; OS: +1.50/-1.50D
What would be the fluorescein pattern?
Mild dumbbell pattern OU
What changes would you make in BCR
Steepen steeper curve & add minus; for example, change to
41D(8.23mm)/45(7.50mm) & add 1D to steeper meridian power
What would be the final lens powers?
OD: +1.25/-2.75; OS: +1.50/-2.50D
What peripheral curves would you order?
With this amount of base curve toricity, toric PCs are indicated. You can add 1mm and
3mm to each base curve radius.
Toric Peripheral Curves: 9.2/8.5; 11.2/10.5mm
What about center thickness?
This would equal the center thickness of a spherical lens having the power equal to the
most plus meridian of the bitoric lens (i.e., +1.25D or +1.50D)
What about lens material and diameter?
This should be no different than for a spherical lens.
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