GP Lens Design Fitting & Problem-Solving
Dr. Keith Ames
CASE REPORT
1. Patient N.V. 57 year old female. Never worn contact lenses
REFRACTION
OD) Pl - 2.00 x 15 20/20 Add +2.25
OS) PL - 1.50 x 160 20/20
KERATOMETRY
OD) 41.25/43.00 @100
OS) 41.50/42.75 @85
LID ANATOMY
Wide apertures with lower lids at limbus
I fit this patient empirically with prism ballasted alternating GP lenses. I believe this is possible when the patient's lid anatomy is such that the upper lid is high and will not interfere with the dynamics of the the lens and the lower lid is correctly positioned at the lower limbus. An added bonus is when the RX is a low minus or plus power so that the natural dynamics of the lens is to positon lower where I want it.
LENS PARAMETERS
OD) 8.10 BC 9.6 DIAM -.25/+2.00 1.5 prism seg 1.0mm below center
OS) 8.10 BC 9.6 DIAM PL/+2.00 1.5 prism seg 1.0mm below center
At one week and three weeks I was very pleased with the fit and vision and the patient was successfully wearing the lenses fulltime. However she commented that occasionally the lenses would displace off the eye and rarely blinked out. I ordered identical parameters except for a larger diameter ( 9.9 ) and this solved the displacement issue. I believe empirically fitting this patient was the correct approach. I do not think the small adjustment I made in final diameter would have been made by non-dispensing trial fitting and required several weeks of experience by the patient before deciding this was an appropriate change to make.
2. Patient PM. 43 year old female. Soft contact lens wearer
REFRACTION
OD) -8.50 20/20 Add +1.00
OS) -7.75 20/20
KERATOMETRY
OD) 44.75/44.75@90
OS) 44.75/45.00@90
LID ANATOMY
Moderately wide aperture with borderline upper lid coverage
I decided to fit this patient empirically with an aspheric design that works best thru lid attachment, the Essentials 2 design. I believe this lens can be successfully fit empirically when the lid anatomy is favourable for lid attachment and the RX is moderate to high minus so the natural tendecy of the lens is to position superiorly where I want it. It is also a very appropriate choice for the early presbyope.
LENS PARAMETERS
OD) 7.40 BC 9.6 DIAM -8.50
OS) 7.40 BC 9.6 DIAM -7.75
This patient was able to successfully wear these lenses fulltime. The fit and vision was acceptable but the lenses tended to decenter slightly laterally and the edge lift was borderline flat. After several weeks of wear, I decided to steepen the lenses .1mm each with a corresponding increase in minus power .50. Again I believe empirically fitting these lenses was the best approach and the fine -tuning adjustment I made was possible because the patient was able to adapt to the correction and I had confidence the lateral decentration was not an adaptational/excessive tearing issue but a true fitting concern that could be addressed.
