By Dr. Tom Quinn
22 yo waitress interested in contact lenses
OD -1.00-3.00 X 180
OS -2.00-2.25 X 175
OD 41.00 @ 180; 44.00 @ 090
OS 43.00 @ 175; 45.00 @ 085
- Toric soft contact lenses
- Spherical GP lenses
- Toric GP lenses
Diagnostic Lens Applied OD:
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 DiameterBC/Cornea Relationship – HorizontalBC/Cornea Relationship – Vertical
|Small (8.0-8.6mm)||0.25 STK||0.50 FTK|
|Intermediate (8.7-9.3mm)||ON K||0.75 FTK|
|Large (9.4-10.2mm)||0.25 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
Ks: 41.00/ 44.00 @ 090
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
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: Custom Bitoric Design and Fitting
By Dr. Ed Bennett
History: 16-year-old spectacle wearer who has been wearing soft torics for sports.
OD: +0.75 -5.50 x 180 20/20
OS: +1.00 -5.50 x 180 20/20
OD: 41.50 @ 180; 47.00 @ 090
OS: 41.50 @ 180; 47.00 @ 090
Slit Lamp 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.
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?
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.