By Dr. Tom Quinn
PE was a 22 year old waitress interested in contact lenses.
Test Procedures, Fitting/Refitting, Design and Ordering
OD -1.00-3.00 X 180 20/20
OS -2.00-3.00 X 175 20/20 Ks:
OD 41.00@ 180; 44.00 @ 090
OS 43.00 @ 175; 45.50 @ 085
Spherical diagnostic lens applied OD:
Base Curve OAD/OZ Power ct
8.03mm (42.00D) 9.2/7.8 -2.00 .16
Spherical diagnostic lens on right eye demonstrates poor centration; therefore elected to pursue toric GP fit.
How would you proceed?
What I Did
Designed a Toric GP:
1. Diameter selection: Since upper lid covers upper limbus, attempt lid attachment, so bias diameter large. Patient has small aperture, so select intermediate diameter: 9.2 mm
2. Base curve selection: Fit horizontal meridian near alignment, vertical meridian slightly flat to promote vertical lens movement with blink (see table).
|Recommended Toric RGP Base Curve Selection with Varying Lens Diameter|
|Lens Diameter (mm)||Base Curve/ Cornea Relationship|
|Small (8.0 to 8.6)||0.25 D STK*||0.50 D FTK**|
|Intermediate (8.7 to 9.3)||On K||0.75 D FTK|
|Large (9.4 to 10.2)||0.25 D FTK||1.00 D FTK|
Base Curves Chosen:
OD 41.00 (8.23mm)/ 43.25 (7.80mm)
OS 43.00 (7.85mm)/ 44.75 (7.54mm)
3. Power Selection: Adjust spectacle power:
a. for vertex effects in any meridian with power greater than -4.00
b. to account for tear lens power by amount of tear lens power (see summary diagram for OD).
OD -1.00/ -3.25
OS -2.00/ -4.00
Lens Design Analysis:
If the difference in base curve power (Δ BC) between major meridians is equal to the difference in lens power (Δ BVP) between major meridians, then the lens is a Spherical Power Effect (SPE) Design and you do not need to be concerned about lens rotation.
OD Difference between BC (41.00 / 43.25) = 2.25 D
Difference between BVP (-1.00/-3.25) = 2.25 D
OS: Difference between BC (43.00 / 44.75) = 1.75D
Difference between BVP (-2.00/ -4.00) = 2.00D
Summary Diagram for Right Lens:
Follow-up Care/Final Outcome
Patient experienced excellent vision with a stable, well positioned lens (see photo below).
SPE Toric GP on right eye demonstration good centration and movement.
By Dr. Clarke Newman
Patient: JN, 34y/o, white male, professional musician
CC: c/o decreased VA through iso-spherical RGP lenses.
HPI: Symptoms noted for 6 mo., Symptoms are stable. RGP wearer, 15 yrs, care system: Boston Original
PMH: Unremarkable and Non-Contributory
OD: Plano DS 20/20
OS: +1.00 -1.00 X 156 20/20 -1
Δ K = 0, OU
OD: -4.75 -1.50 X 007 20/20 +1
OS: -2.00 -4.75 X 161 20/20
OD: 43.75 @ 008 / 45.00 @ 098
OS: 43.25 @ 165 / 46.25 @ 075
Calculated Residual Astigmatism
OD: None OS: 1.00 X 163
|Left Eye with Old Spherical Lens||Left Eye with New Bitoric Lens|
Acuity and Sphero-Cylinder Over-Refraction
OD: 20/20-1 +0.25 -0.50 X 130 20/20+1
OS: 20/25+2 -0.25 -0.25 X 170 20/20